Fetal Development Week by Week: Your Complete Pregnancy Timeline

Pregnancy is a remarkable journey of transformation, both for the mother and the developing baby. From the moment of conception to the anticipation of birth, each week brings significant changes and milestones.

Understanding these developmental stages can be both fascinating and reassuring. This guide provides a detailed look at fetal development week-by-week, offering insight into the incredible process of life unfolding within the womb.

Join us as we explore the intricate details of each stage, from the very beginning to the threshold of birth.

Weekly Fetal Development:

Week 1: The Beginning of the Journey

While you’re not technically pregnant yet, week one marks the start of the gestational clock. This week is defined by your menstrual period, the shedding of the uterine lining, and the preparation for potential ovulation.
Your menstrual period begins this week. You’re not technically pregnant yet, as conception hasn’t occurred.
Your body is shedding the previous month’s uterine lining while simultaneously preparing for potential ovulation.
Pregnancy dating traditionally begins from the first day of your last menstrual period, even though conception hasn’t occurred yet.
Your body is preparing a new egg for potential fertilization, and hormone levels of estrogen and progesterone are at their lowest during this time.
Hormonal changes trigger menstruation.

Week 2: The Fertile Window

Week two is crucial, as it’s when ovulation typically occurs. This is the time when a mature egg is released, making fertilization possible.

Ovulation typically occurs during this week. Your body releases a mature egg from one of your ovaries, which begins its journey through the fallopian tube where it can be fertilized by sperm.
Your uterine lining continues to thicken in preparation for a potential pregnancy.
This is your fertile window, the time when pregnancy is possible. The egg survives for only 12-24 hours after release.
Cervical mucus becomes thin and stretchy to help sperm navigate to the egg, and basal body temperature typically rises slightly after ovulation.

Week 3: Fertilization and Blastocyst Formation

If fertilization occurs, rapid cell division begins, forming the blastocyst. This is the very beginning of your baby’s development.

If fertilization occurred (typically in the fallopian tube), cell division begins immediately. The fertilized egg (zygote) divides repeatedly as it travels toward the uterus, forming a tiny ball of cells called a blastocyst.
By the end of this week, the blastocyst has around 200-300 cells organized into an outer layer (which will become the placenta) and an inner cell mass (which will become your baby).
The blastocyst contains all the genetic information for your future baby, and cell specialization begins, with cells starting to take on specific roles.
This is when identical twins may form if the inner cell mass splits. You’re still not likely to feel any pregnancy symptoms.

Week 4: Implantation and Embryo Development

The blastocyst implants into the uterine lining, officially becoming an embryo. This week marks the beginning of the placenta and amniotic sac formation.

The blastocyst implants into your uterine lining, usually 6-12 days after fertilization. Once implanted, it’s officially called an embryo.
The placenta begins to form, creating the vital connection between mother and baby. The amniotic sac also starts developing to protect the embryo.
Three primary cell layers form that will develop into all of your baby’s organs and tissues.
Implantation may cause light spotting, known as implantation bleeding, for some women. The hormone hCG begins to be produced, which is what pregnancy tests detect.
The primitive placenta begins secreting hormones that maintain the pregnancy, and the neural tube, which will become the brain and spinal cord, begins to form.

Week 5: Early Organ Development

This week marks significant development as the baby’s heart, brain, and spinal cord begin to form.

This marks the beginning of the embryonic period proper. Your baby’s heart, brain, and spinal cord begin rapid development. The neural tube forms and begins to close.
Blood cells form and circulation begins. The foundations for all major organs are being established. Tiny buds that will develop into arms and legs start to appear.
The heart begins as a tube-like structure that starts to pulse. The neural tube closes this week; adequate folic acid is crucial during this time.
The placenta continues developing but isn’t fully functioning yet. First missed period typically occurs, often prompting a pregnancy test.
Early pregnancy symptoms may begin, including fatigue, nausea, and breast tenderness.

Week 6: Facial Features and Heartbeat

Baby’s facial features begin to take shape, and the heartbeat can be detected.

Your baby’s face is taking shape, with dark spots for eyes, and openings for the mouth, nose, and ears becoming visible.
Brain development accelerates with the formation of brain hemispheres. The beginnings of the digestive and respiratory systems appear.
The heart rate can now be detected with specialized ultrasound. Arm and leg buds are more defined.
The umbilical cord is forming, connecting the embryo to the developing placenta. Tiny blood vessels form a primitive circulatory system.
Morning sickness may intensify around this time.

Week 7: Hands, Feet, and Brain Growth

Baby’s hands and feet start developing, and brain cells multiply rapidly.

Baby’s hands and feet are developing as paddle-like buds with subtle ridges that will become fingers and toes.
Brain cells are multiplying rapidly, with about 100 new brain cells forming every minute.
The intestines begin to form, and the appendix and pancreas are developing. Eye lenses start to form, and nostrils become visible on the face.
The head is much larger than the rest of the body due to rapid brain growth. Kidneys are in place and begin to form urine.
The liver begins producing red blood cells. The embryo makes spontaneous, reflex-like movements, though you can’t feel them yet.

Week 8: Organ System Formation

All major organs and body systems are forming, and the heart is fully formed and beating.

All major organs and body systems are forming! The embryo’s heart is fully formed and beating at 150-170 beats per minute.
Fingers and toes are becoming more defined but may still be webbed. Breathing tubes extend from the throat to the developing lungs.
The digestive tract continues developing, and the neural pathways in the brain are forming.
Facial features become more distinct with the lips and nose taking shape. Tiny movements become more coordinated as muscles develop.
Bones begin to replace cartilage. The embryo floats in the amniotic fluid, which provides protection.
External genitalia begin to develop but are not yet distinguishable, and the tail-like structure (caudal end) is disappearing.

Week 9: Fetus Formation and Limb Development

The embryo is now officially a fetus, with distinct fingers and toes and developing organs.

The embryo is now officially called a fetus! Your baby has distinct fingers and toes that are no longer webbed.
Nipples and hair follicles begin to form. The arms grow and elbows develop, allowing for more movement.
Essential organs like the liver, spleen, and gallbladder continue to develop and begin functioning.
The external ears are forming, and the eyes are becoming more obvious but remain closed. The heartbeat can be heard with a Doppler ultrasound device.
The placenta is now fully formed and functioning.
The fetus can make tiny movements.
Reproductive organs are developing but not yet visible on ultrasound. The diaphragm is forming, and the fetus may have hiccup-like movements.

Week 10: Vital Organ Function and Limb Movement

All vital organs are formed and beginning to function, and the fetus can bend its elbows.

Your baby can bend their elbows and has a more human-like appearance with a prominent forehead.
All vital organs are now formed and beginning to function. The brain continues rapid development and can now control muscles.
The intestines rotate into their proper position. The hands and feet have individual fingers and toes with tiny nail beds forming.
Tooth buds for baby teeth are developing. The risk of miscarriage decreases significantly after this week.
Your baby can swallow amniotic fluid and produce urine. The skeleton is forming, though it’s still mostly cartilage.
External genitalia are developing but may not yet be visible on ultrasound. The neck becomes more defined, separating the head from the shoulders.
The eyelids are fused shut and will remain so until about week 27.

Week 11: Hand Movements and Yawning

The baby can now open and close their hands and even yawn.

Your baby can now open and close their hands and yawn! The body is growing faster than the head, beginning to create more proportional features.
The diaphragm is forming, and your baby may start to hiccup, though you won’t feel it yet. Tiny tooth buds are developing beneath the gums.
The liver is now producing red blood cells, a job that was previously handled by the yolk sac, which is now shrinking.
Genitals are developing, but it’s still difficult to determine the sex via ultrasound. The facial bones are forming, and the ears are moving into their proper position on the sides of the head.
Your baby is becoming more active, stretching and kicking, and even practicing breathing movements.

Week 12: Reflexes and Organ Function

Baby now has reflexes and can move all joints. The kidneys begin to produce urine.

Baby now has reflexes and can move all joints. The kidneys begin to produce urine, which becomes part of the amniotic fluid.
The digestive system is beginning to practice contractions, and the bone marrow is forming.
Your baby’s face is looking more human, with the eyes moving closer together and the ears finding their final position.
The fingernails and toenails are beginning to develop. The pituitary gland at the base of the brain has formed and starts producing hormones.
The brain continues rapid development, with nerve cells multiplying and forming connections. The intestines, which had been developing in the umbilical cord, are now moving into the abdomen.
By the end of this week, all critical systems and structures have formed.

Week 13: Fingerprints and Fine Hair

Fingerprints are forming, and the baby is growing fine, downy hair.

Fingerprints are forming! Your baby can make facial expressions and is growing fine, downy hair (lanugo) all over their body.
This soft hair helps regulate body temperature and will typically shed before birth. The vocal cords are developing in the larynx.
Your baby’s liver and spleen are producing bile and red blood cells. The pancreas is developing and beginning to produce insulin.
The intestines continue to develop and begin to contract in preparation for digestion. Bone marrow starts forming in the larger bones.
The thyroid gland is now functioning and producing hormones.
If your baby is female, her ovaries now contain more than two million eggs—this is the maximum number of eggs she will ever have, though this number will decrease to about one million by birth.

Week 14: Facial Expressions and Breathing Practice

Baby practices breathing, sucking, and swallowing, and can make various facial expressions.

Baby practices breathing, sucking, and swallowing. They can make various facial expressions like squinting and frowning as facial muscles develop further.
Your baby’s eyes are becoming sensitive to light, even though the eyelids remain fused shut. The roof of the mouth (palate) is completed this week.
The thymus gland is developing behind the breastbone and will play a crucial role in immune system development.
Meconium, your baby’s first stool, begins to form in the intestines. The prostate gland begins to develop in male fetuses, while female fetuses are developing the milk-producing glands in the breasts.
Hair patterns are forming on the head. Your baby’s posture is becoming more upright, and movements are becoming more coordinated.

Week 15: Hearing and Bone Development

Baby’s ears are reaching their final position, and bones are getting stronger.

Baby’s ears are reaching their final position and can detect loud sounds. Bones are getting stronger as calcium builds up within them.
Hair is growing on the head, and eyebrows are forming. The skin is still thin and translucent, but it’s becoming less transparent as fat begins to accumulate beneath it.
Taste buds are developing on the tongue. Blood vessels are clearly visible beneath the skin.
The legs are growing longer than the arms now, and all joints and limbs can move. Your baby may respond to loud noises by moving or increasing their heart rate.
The scalp hair pattern is forming. In male fetuses, the testes are beginning to descend from the abdomen, though they haven’t reached the scrotum yet—this process can take several months.

Week 16: Coordinated Movements and Hearing

Baby can make facial expressions and may suck their thumb. The ears are nearly in their final position, making it easier for your baby to hear.

Baby can make facial expressions and may suck their thumb. The head is more proportionate to the body. Eyebrows and eyelashes are becoming more defined.
The ears are nearly in their final position, making it easier for your baby to hear your voice and heartbeat.
The nervous system is forming connections that will allow your baby to make more coordinated movements.
The heart is now pumping about 25 quarts of blood each day. Blood vessels continue to develop throughout the body.
The skeletal system continues to harden from cartilage to bone. In female fetuses, the vagina is formed and the ovaries have descended from the abdomen.
The skin is becoming less transparent as fat deposits increase. Your baby’s movements may be strong enough for you to feel them for the first time—this is called quickening.

Week 17: Fat Development and Movement

Baby is putting on fat, growing stronger, and developing sweat glands. They are moving frequently!

Baby is putting on fat, growing stronger, and developing sweat glands. They are moving frequently!
The umbilical cord is growing thicker and stronger. The placenta continues to grow and develop, now processing about 1 pint of blood per minute.
Your baby is practicing sucking and swallowing movements, preparing for feeding after birth.
The heart is now regulated by the brain, becoming more efficient. The body is forming adipose (fat) tissue, which will help regulate body temperature after birth.
The skeleton continues to ossify or harden. The toenails are now fully formed.
The body is becoming more proportional as the legs grow longer. The skin is still wrinkled because there isn’t enough fat underneath yet, but this will change in the coming weeks.

Week 18: Hearing and Sleep-Wake Cycles

Baby’s ears are more prominent. They can hear your voice and may yawn or hiccup.

Baby’s ears are more prominent. They can hear your voice and may yawn or hiccup.
Your baby is developing a sleep-wake cycle and may be awakened by loud noises or your movements. The digestive system is practicing contractions through the intestines.
Myelin, a protective covering, is beginning to form around the nerves. This coating is essential for proper nervous system functioning.
The retinas have become sensitive to light, even though the eyes remain closed. The bones of the inner ear are hardening, allowing your baby to hear more clearly.
If your baby is female, her uterus and fallopian tubes are formed and in position.
Your baby may develop a regular schedule of movement and rest. Reflexes are becoming more refined, and your baby might respond to stimuli like sound or pressure.

Week 19: Protective Skin Coating and Brain Growth

Baby develops a protective coating on their skin (vernix caseosa) and has regular sleep cycles. Kicks are stronger!

Baby develops a protective coating on their skin (vernix caseosa) and has regular sleep cycles. Kicks are stronger!
This white, cheese-like coating protects the skin from the constant exposure to amniotic fluid and will be particularly thick at birth.
Brown fat, a special type of fat that helps generate body heat, is developing.
Your baby’s brain continues its impressive growth and is developing specialized areas dedicated to taste, smell, hearing, vision, and touch.
Hair on the head is growing and taking on color, though this may change after birth.
The fetus is swallowing more amniotic fluid, which helps the digestive system mature. The kidneys continue to produce urine.
The lungs are developing surfactant, a substance that will allow the air sacs to inflate after birth—this is crucial for breathing outside the womb.
Movements are becoming stronger and more coordinated.

Week 20: Halfway Point and Sensory Development

Halfway there! Baby’s face is fully formed. Taste buds are developing, and they can taste what you eat.

Halfway there! Baby’s face is fully formed. Taste buds are developing, and they can taste what you eat through changes in the amniotic fluid.
Your baby now has unique fingerprints and footprints. Nails have grown to the tips of the fingers and toes.
The liver, pancreas, and spleen are all functioning. The brain continues its rapid development, with nerve cells forming connections that will help with everything from breathing to sensing to thinking.
The skin is less transparent as fat continues to be deposited.
A female baby’s vagina is fully formed, and in male babies, the testes continue their descent. The fetus is producing meconium in the intestinal tract.
Limb movements are coordinated and purposeful. Your baby can now hear sounds outside your body and may startle at loud noises.
The heartbeat is now loud enough to be heard through a stethoscope placed on your abdomen.

Week 21: Increased Activity and Immune Development

Baby’s movements are becoming stronger and more coordinated. Eyebrows and eyelids are fully formed.

Baby’s movements are becoming stronger and more coordinated. Eyebrows and eyelids are fully formed, giving your baby’s face a more complete appearance.
Your baby is now more active than ever, with rhythmic movements of limbs that you can distinctly feel.
The digestive system continues to develop, and the intestines are accumulating a substance called meconium, which will become the baby’s first bowel movement after birth.
Bone marrow is now the main site of blood cell production.
The arms and legs have reached their relative proportions, though your baby still needs to put on more weight. Brown fat, which helps regulate body temperature after birth, is beginning to form.
The immune system is developing as antibodies are passed from you to your baby through the placenta.

Week 22: Sensory Development and Balance

Baby’s senses are developing rapidly—they can hear your voice clearly and react to light and sound! The brain is developing rapidly.

Baby’s senses are developing rapidly—they can hear your voice clearly and react to light and sound! The brain is developing rapidly with nerve cell branching that allows for complex connections.
Your baby’s inner ear is now fully developed, giving them a sense of balance. The liver and pancreas are producing essential enzymes and hormones.
The lungs are developing further, though they’re not ready for breathing air. The skin is less translucent as fat accumulates underneath.
Fingernails have grown to the tips of the fingers. Hair is becoming visible on the head, though the color and texture may change after birth.
The reproductive system continues to develop—in females, the vagina is formed and the uterus continues to develop; in males, the testes are descending from the abdomen.
Your baby now has a distinct sleep-wake cycle and may be more active at certain times of the day.

Week 23: Miniature Newborn Appearance and Lung Development

Baby looks like a miniature newborn! They are gaining weight and have tiny fingernails and nipples.

Baby looks like a miniature newborn! They are gaining weight and have tiny fingernails and nipples.
The lungs are developing branches of the respiratory tree and cells that produce surfactant, a substance that will help the air sacs inflate after birth.
Blood vessels in the lungs are developing to prepare for breathing. Your baby’s skin is still wrinkled and translucent but becoming more opaque as fat deposits increase.
The pancreas is developing, producing essential hormones including insulin. The bone marrow is completely taking over the production of blood cells.
The sense of hearing continues to develop as your baby responds to sounds like your voice, heartbeat, and digestive sounds.
The brain is rapidly developing, creating billions of motor neurons that help your baby control movements voluntarily.

Week 24: Lung Development and Viability

Baby’s face is fully formed with eyelashes, eyebrows, and hair. Lungs are developing rapidly, creating more air sacs (alveoli) in preparation for breathing.

Baby’s face is fully formed with eyelashes, eyebrows, and hair. Lungs are developing rapidly, creating more air sacs (alveoli) in preparation for breathing.
Your baby’s skin is still thin and translucent but increasingly covered with vernix caseosa, a protective waxy coating.
The central nervous system is developed enough to control some body functions, and the brain waves are similar to those of a newborn.
The inner ear is fully developed, giving your baby a sense of balance and the ability to tell which way is up.
Taste buds are fully formed, and your baby can taste the amniotic fluid, which is flavored by what you eat. Footprints and fingerprints are now deeply etched into the skin.
If born at this stage, your baby would have about a 60-70% chance of survival with intensive medical care, as this is considered the age of viability.

Week 25: Response to Voice and Touch

Baby responds to your voice and touch! They are developing a strong grip and regular sleep patterns.

Baby responds to your voice and touch! They are developing a strong grip and regular sleep patterns.
Your baby’s hands are fully developed, and they can strongly grasp objects like the umbilical cord.
The respiratory system continues to develop as more cells produce surfactant, the substance that will keep the air sacs in the lungs from sticking together after birth.
Blood vessels in the lungs are also developing to prepare for breathing air. Your baby’s nostrils, which have been plugged until now, begin to open.
Fat continues to accumulate under the skin, making your baby look more like a newborn.
The brain’s cortex is developing rapidly, adding layers that allow more complex brain functions.
Your baby can now distinctly hear sounds from outside

Week 26: Eyes Open and Brain Responses

Baby’s eyes can open! Brain waves show responses to touch and sound. Lungs are developing surfactant.

Baby’s eyes can open! Brain waves show responses to touch and sound. Lungs are developing surfactant, the substance needed to keep the lungs inflated after birth.
Your baby is growing more hair on their head, and the hair is developing pigment which may indicate its eventual color, though this often changes after birth.
The sucking reflex is developing, and your baby may suck their thumb or fingers. The immune system continues to strengthen as antibodies are passed from you to your baby.
The spine is becoming stronger and more flexible. Your baby’s skin is still wrinkled but becoming smoother as fat continues to be deposited.
The nervous system is developing rapidly, improving coordination and responses.
The lungs, though still immature, would be potentially functional if your baby was born prematurely, especially with medical intervention.
Your baby has established regular patterns of sleeping and waking.

Week 27: Third Trimester Begins and Dreaming

Last week of the second trimester! Baby sleeps and wakes regularly and can taste sweet flavors. Brain activity suggests dreaming.

Last week of the second trimester! Baby sleeps and wakes regularly and can taste sweet flavors.
Brain activity is increasing dramatically, with rapid eye movement during sleep suggesting your baby may be dreaming.
The retinas in the eyes are now fully developed, and your baby can open and close their eyelids and detect light.
Your baby’s hearing is continuing to develop, and they can recognize your voice, which they’ll remember after birth.
Lungs are continuing their rapid development, though they’re not completely mature yet. The brain is growing rapidly, with billions of neurons making connections.
Bones are fully developed but still soft and flexible for delivery.
Your baby has developed their own unique sleep patterns and may be more active at specific times of day that you’ll start to recognize.
They can hiccup regularly now, which you might feel as rhythmic movements.

Week 28: Third Trimester and Light Response

Welcome to the third trimester! Baby can blink, may dream, and responds to sound and light.

Welcome to the third trimester! Baby can blink, may dream, and responds to sound and light.
Your baby’s eyes can focus now, and they will blink in response to bright light. Brain wave activity shows distinct sleep cycles, including REM (rapid eye movement) sleep when dreams may occur.
The digestive system is developed though not yet functional. Your baby practices breathing by inhaling and exhaling amniotic fluid, preparing the lungs for air.
The central nervous system can now control rhythmic breathing movements and body temperature.
If born now, your baby would have about an 80-90% chance of survival with intensive care, as the lungs and other systems are more developed.
The brain continues its rapid growth and complexity, forming the grooves and folds characteristic of a human brain.
Your baby is more sensitive to sound, light, and touch, and you may notice they respond to stimuli from the outside world like loud noises or music.

Week 29: Brain Development and Temperature Regulation

Baby’s brain is developing rapidly! They can regulate body temperature and have stronger bones.

Baby’s brain is developing rapidly! They can regulate body temperature and have stronger bones.
The brain is forming billions of neurons and connections that will determine your baby’s personality, intelligence, and coordination.
Most of the wrinkles and folds in the brain have developed. Your baby is gaining significant weight from fat being deposited all over the body, making the skin appear smoother.
The bone marrow is now completely responsible for producing red blood cells. Muscles and lungs are continuing to mature.
The head-to-body ratio is becoming more proportionate as the body catches up to the size of the head. Your baby can now regulate their own body temperature.
The immune system is continuing to develop, and your baby is receiving your antibodies that will protect them for the first few months of life.
The eyes can track light, and your baby may turn toward bright sources of light.

Week 30: Brain Wrinkles and Light Sensitivity

Baby’s brain wrinkles are developing rapidly! Eyes can follow light, and the pupils dilate and constrict.

Baby’s brain wrinkles are developing rapidly! Eyes can follow light, and the pupils dilate and constrict.
The brain’s surface is developing many grooves and convolutions, increasing the brain’s surface area and capacity for neurons.
Lungs and digestive tract are nearly mature. Your baby is now sensitive to temperature, touch, and sound.
Hair on the head is growing thicker, and lanugo (the fine body hair) may be starting to disappear.
The bone marrow is completely in charge of red blood cell production. Fingernails and toenails are fully formed and may need trimming at birth.
If born now, your baby would have about a 95% chance of survival with modern medical care.
Your baby is practicing breathing motions regularly, though they’re still getting oxygen through the placenta.
The nervous system is developed enough to control some body functions, and your baby can now regulate their own temperature and partially control breathing and cardiac function.
The pupils in your baby’s eyes can now constrict and dilate in response to light, preparing for the outside world.

Week 31: Rapid Weight Gain and Lung Maturation

Baby is gaining weight rapidly! The brain is controlling breathing and body temperature more efficiently.

Baby is gaining weight rapidly! The brain is controlling breathing and body temperature more efficiently.
The brain continues its remarkable development with billions of neurons making connections that will determine everything from personality to motor skills.
Your baby’s lungs are maturing, and they’re practicing breathing movements more consistently.
The digestive system is nearly fully developed, and your baby is swallowing amniotic fluid regularly.
The retinas are becoming increasingly sensitive to light, and your baby may turn toward bright sources of light from outside your abdomen.
The amount of body fat is increasing significantly, helping your baby to better regulate their body temperature after birth.
Your baby’s immune system continues to strengthen as it receives antibodies from you that will protect them in early life.
The bone marrow is completely responsible for red blood cell production. The skin is smoother and pink-colored as blood vessels develop close to the surface.

Week 32: Five Senses and Coordinated Reflexes

Baby practices breathing, sucking, and swallowing. All five senses are working! Your baby is developing coordinated reflexes.

Baby practices breathing, sucking, and swallowing. All five senses are working! Your baby is developing coordinated reflexes and can now move their eyes in different directions, tracking movements and light sources.
The lungs are producing surfactant, the substance that prevents the air sacs from sticking together when your baby begins to breathe air.
Taste buds are fully developed, and your baby can taste the different flavors that come through in the amniotic fluid from your diet.
The fingernails have reached the fingertips, and toenails are growing too. Your baby’s movements may feel different now as there is less room to move around, but you should still feel regular activity.
The layer of fat under the skin continues to grow, filling out your baby’s body and limbs. Your baby’s skin is becoming less red and wrinkled as fat accumulates.
The skeleton continues to harden, though the skull remains soft and flexible for birth.

Week 33: Bone Development and Immune Strengthening

Baby’s bones are fully developed, except for the soft skull. The immune system is strengthening rapidly.

Baby’s bones are fully developed, except for the soft skull. The immune system is strengthening rapidly as antibodies from your body continue to pass through the placenta.
Your baby’s brain continues its remarkable development, with connections forming that will allow for conscious thought, reasoning, and memory.
The lungs are continuing to mature, with increasing amounts of surfactant being produced to prepare for breathing air.
Your baby is now able to coordinate sucking and swallowing with breathing, an important skill needed for feeding after birth.
The pupils in your baby’s eyes can now detect light and constrict or dilate in response.
The amniotic fluid is beginning to decrease as your baby takes up more space in the uterus.
The digestive system is fully formed, though still inactive as nutrition continues to come through the umbilical cord.
The nervous system is sophisticated enough now that your baby may be startled by sudden loud noises.

Week 34: Central Nervous System Maturation and Testicle Descent

Baby’s central nervous system is maturing! Fingernails reach the fingertips. In boys, the testicles descend.

Baby’s central nervous system is maturing! Fingernails reach the fingertips. In boys, the testicles descend from the abdominal cavity into the scrotum; in girls, the labia are now completely developed.
Your baby’s skin is becoming smoother as more fat accumulates under the skin surface.
The lungs continue their development with increased production of surfactant for breathing air.
Your baby’s immune system is continuing to strengthen, receiving antibodies from you that will protect them for several months after birth.
The brain is developing at an extraordinary rate, with billions of neurons forming connections.
Your baby has definite sleep and wake cycles, and you may notice patterns in their activity.
The bones of the skull remain soft and flexible to allow the baby to pass through the birth canal.
Most babies are now positioned with their heads down toward the birth canal, though some may still turn in the coming weeks.

Week 35: Kidney Development and Organ Readiness

Baby’s kidneys are fully developed! Most organs are ready for the outside world, except the lungs, which continue to mature.

Baby’s kidneys are fully developed! Most organs are ready for the outside world, except the lungs, which continue to mature.
Your baby is gaining about half a pound per week, primarily in the form of body fat that will help regulate body temperature after birth.
The hearing is fully developed, and your baby will recognize familiar voices, particularly yours, after birth.
The skin is becoming less red and more pink or ivory in color as fat deposits increase.
Your baby’s movements may feel different—less kicking and more squirming—as space in the uterus becomes limited.
Brain development continues at a rapid pace as neurons form connections that will support learning and memory.
The liver is processing some waste products, and the kidneys are fully functioning.
The lungs are still maturing but would function adequately if birth occurred now.

Week 36: Lung Surfactant and Facial Fullness

Baby’s lungs are producing surfactant for breathing. Your baby’s face appears smooth and full as fat continues to be deposited.

Baby’s lungs are producing surfactant for breathing. Your baby’s face appears smooth and full as fat continues to be deposited, particularly in the cheeks.
The sucking muscles are strong and well-coordinated in preparation for feeding.
The lungs are nearly mature, with increasing amounts of surfactant to keep air sacs from collapsing after birth.
Your baby’s immune system continues to receive antibodies from your body that will protect them through the first few months of life.
The lanugo (fine body hair) is disappearing, though some may remain on the shoulders and back at birth.
The vernix caseosa (protective waxy coating) is becoming thinner but still covers the skin.
The digestive system contains meconium, which will be the baby’s first bowel movement after birth.
Your baby’s brain continues its remarkable development, with connections forming that will support consciousness, thinking, and feeling.

Week 37: Early Term and Lung Readiness

Baby is early term! Lungs are ready for air breathing. They are still gaining weight and shedding vernix.

Baby is early term! Lungs are ready for air breathing. They are still gaining weight and shedding vernix.
Your baby is considered early term now, meaning they would be ready for life outside the womb if born at this point.
The lungs are mature enough for breathing air, though some babies born now may need a little help at first.
Your baby continues to gain weight, primarily in the form of fat.
The brain continues its rapid development with connections forming between neurons that will support learning after birth.
The vernix caseosa is thinning but may still be present in skin creases at birth.
Your baby’s movements may feel different as they have less room to maneuver in the uterus.
The immune system has received many antibodies from you that will protect your baby from infections in early life.
Some babies born at this stage may need a little extra help with feeding and temperature regulation, but most do very well.

Week 38: Full Term and Brain Development

Baby is full term! The brain is still developing rapidly. They are ready for birth with mature organs.

Baby is full term! The brain is still developing rapidly. They are ready for birth with mature organs. Your baby is now considered full term and could be born any day.
The lungs are fully mature and ready to take that first breath of air.
Your baby continues to gain about half a pound per week, with fat accumulating under the skin for insulation and energy storage.
The brain continues its remarkable development, forming connections that will be used for learning and development after birth.
The bones of the skull remain soft and separated to allow for passage through the birth canal.
Most of the lanugo (fine body hair) is gone, though some may remain on the shoulders.
The vernix caseosa (waxy coating) continues to thin but may still be present in skin creases.
Your baby’s immune system has received antibodies from you that will provide protection for several months after birth.

Week 39: Final Brain Development and Preparation for Birth

Baby’s brain is still developing rapidly. There is very little vernix left on the skin. They are ready for birth.

Your baby continues to gain weight, with fat accumulating throughout the body.
The brain continues to develop rapidly—a process that will continue for years after birth.
The lungs are fully mature and prepared for breathing air. Your baby’s movements may feel different due to the tight quarters, but you should still feel regular activity.
The vernix caseosa (waxy coating) is mostly gone, leaving your baby’s skin smooth. The lanugo (fine body hair) has largely disappeared.
Your baby’s nails may extend beyond the fingertips and may need trimming after birth.
The immune system has received antibodies from you that will provide protection from infections for the first months of life.
Your baby is fully prepared for life outside the womb, with all essential organs and systems functional.

Week 40: Full Term and Ready for Labor

Baby is full term and fully developed! They are ready to meet you whenever labor begins.

All organs and body systems are fully developed and functioning.
Your baby’s brain continues its remarkable development, with connections forming that will support consciousness and learning.
The lungs are completely prepared for breathing air. Your baby has accumulated enough fat to help regulate body temperature after birth.
The immune system has received maternal antibodies that will provide protection from infections for several months.
Your baby’s skin is smooth, with very little vernix caseosa remaining. The bones of the skull remain separated and flexible to allow for passage through the birth canal.
Your baby has developed reflexes that will help them find the breast or bottle, suck, and swallow.
Your baby is in the optimal position for birth, usually head-down with their chin tucked to their chest.

Week 41: Late Term and Continued Growth

Baby is fully developed and waiting for birth. They continue to gain weight and shed the vernix coating.

Your baby is now considered late-term but continues to develop. The brain continues its remarkable growth and maturation.
Your baby continues to gain weight, primarily in the form of fat, at a rate of about half a pound per week.
The skin is smooth and may be peeling in places as the remaining vernix disappears.
The placenta continues to provide oxygen and nutrients but may begin to function less efficiently now.
Your healthcare provider will monitor your baby closely for any signs of distress.
The amniotic fluid is decreasing, giving your baby even less room to move around.
The fingernails and toenails continue to grow and may be quite long at birth. Your baby’s skull bones remain separated and flexible for birth.
Your baby’s movements may feel different but should still be regular; any significant decrease in movement should be reported to your healthcare provider immediately.

Week 42: Post-Term and Close Monitoring

Baby is post-term. Doctors closely monitor your health and placenta function. Baby is fully ready for birth.

Two weeks past your due date, your baby is considered post-term.
Your healthcare provider will monitor you and your baby closely, as the placenta may begin to function less efficiently at this stage.
The amniotic fluid continues to decrease, which can make it more difficult for your baby to move.
Your baby’s skin may appear dry and peeling at birth due to the complete loss of vernix caseosa.
The fingernails and toenails may be quite long. Your baby continues to pass meconium into the intestines, and there is a small risk that they might pass some into the amniotic fluid.
Your healthcare provider will conduct tests to ensure your baby’s continued wellbeing, including monitoring heart rate patterns and amniotic fluid levels.

Conclusion

The journey of fetal development is a testament to the incredible complexity and wonder of life. From the microscopic blastocyst to the fully formed baby ready for birth, each week brings significant changes and milestones.

By understanding these stages, expectant parents can gain a deeper appreciation for the miracle unfolding within. As you progress through your pregnancy, remember that each week brings you closer to the joyous moment of meeting your baby.

Disclaimer: This information is for general knowledge only and is not medical advice. Consult your healthcare provider for personalized guidance.