Comprehensive Fetal Growth Charts: Weekly Development, Weight and Length

Weekly foetal development overview 

1. Fetal Development in the First Trimester

Fetal Development in Weeks 1-3 of Pregnancy

• Your pregnancy "starts" on the last day of your menstrual period.
• Ovulation takes place at about the midpoint of your cycle.
• The sperm meets the egg and fertilization takes place.
• The placenta begins to form, and will help nourish your baby until birth.

Fetal Development in Pregnancy - Week 4

• The fertilised egg implants in the uterus and begins to develop into an embryo. 
• The umbilical cord begins to form from the placenta. 
• Your little one is about the size of a poppy seed. 

Fetal Development in Pregnancy - Week 5

• Big steps are underway as the neural tube (which eventually forms the brain, backbone and spinal cord) develops. 
• The lungs and heart begin to form, and the heart may start to beat. You might get to hear it via ultrasound sometime between weeks 6 and 12. 
• The amniotic sac has formed and is filled with amniotic fluid, which will help protect your baby throughout your pregnancy. 
• This might be when you suspect you’re pregnant — time to take a home pregnancy test and schedule a visit with your healthcare provider. 
• The embryo is about the size of an orange seed. 

Fetal Development in Pregnancy - Week 6

• The embryo is now huddled up in a curved C-shape. 
• Little buds are appearing that will become arms and legs. 
• The embryo is about the size of a pomegranate seed. 

Fetal Development in Pregnancy - Week 7

• • The brain and face are growing. 
  • Eyelids and bones start to form. 
  • Nostrils and retinas begin to develop. 
  • The embryo is about the size of a blueberry. 

Fetal Development in Pregnancy - Week 8

• All major organs have formed and are growing — the building blocks are in place. 
• Tubes connect the throat with the lungs to allow for future breathing. 
• By the end of this week, your little one is no longer an embryo and is instead called a fetus, medically speaking, that is. 
• The fetus is now about the size of a raspberry. 

Fetal Development in Pregnancy - Week 9

• Little facial features form, including a more prominent nose. 
• The head is large in proportion to the body, but your little one now has more of a mini-baby shape. 
• The fetus is about the size of a cherry. 

Fetal Development in Pregnancy - Week 10

• The head is rounding out. 
• Eyelids and ears continue to develop — someone’s getting ready to see and hear you. 
• Your little one is about the size of a strawberry. 

Fetal Development in Pregnancy - Week 11

• Muscle formation begins. 
• The backbone is still soft and flexible, but other bones begin to harden. 
• Red blood cell production begins in the liver. 
• The head still makes up half of your baby’s body length. 
• The fetus is about the size of a Brussels sprout. 

Fetal Development in Pregnancy - Week 12

• Your little one is moving, but you won’t feel it quite yet. 
• Hands and arms are more developed than the lower limbs. 
• Facial features are becoming more defined. Your little one might just be growing into your nose or your partner’s chin. 
• If you have a Doppler exam this week, you might hear a heartbeat. 
• The fetus is about as big as a passion fruit. 

Fetal Development in Pregnancy - Week 13

• The sex hormones, testosterone and oestrogen, are being produced. 
• Your little one can now produce urine after swallowing amniotic fluid. 
• All organs are fully formed and growing steadily. 
• The average fetus is the size of a large plum. 

Fetal Development in the Second Trimester

Fetal Development in Pregnancy - Week 14

• Your little one can now move hands to mouth. 
• The senses of taste and smell are starting to develop. 
• The skin is beginning to thicken. 
• The neck and lower limbs are becoming more defined. 
• The fetus is now about the size of a nectarine. 

Fetal Development in Pregnancy - Week 15

• The fetus can now roll and flip. 
• That tiny heart pumps up to 100 pints of blood every day. 
• Hair follicles have started to develop. 
• The fetus is now about the size of a small grapefruit. 

Fetal Development in Pregnancy - Week 16

• The digestive system starts working. 
• The fetus can now hear some sounds, so keep talking and singing. 
• Your little one could be the size of an apple. 

Fetal Development in Pregnancy - Week 17

• The glands may start to produce vernix, a greasy substance that protects the skin in the womb. 
• The eyes are now able to move slowly. 
• Toenails are starting to grow. 
• The fetus is now roughly the size of a pear. 

Fetal Development in Pregnancy - Week 18

• Fine hair known as lanugo begins to cover that little body. 
• The fetus may wake from sleep in response to your movements. 
• Your little one is about the size of a sweet potato. 

Fetal Development in Pregnancy - Week 19

• Kicks and movements may be getting stronger. 
• Ovaries have developed in girls and testes have formed in boys. 
• The fetus may be able to (adorably) suck a thumb. 
• Your little one is about the size of a mango. 

Fetal Development in Pregnancy - Week 20

• Some facial features and external genitals may be visible via ultrasound. 
• Your baby is producing meconium, which is the waste that will become his first poop after birth. 
• His fingernails are growing. 
• The average baby is about the size of a bell pepper. 

Fetal Development in Pregnancy - Week 21

• Fingers and toes have completed their development, ready to be counted at birth.
• The rhythmic movements you feel may be the baby hiccupping.
• She may have a favorite sleeping position.
• Your baby is about the size of a banana.

Fetal Development in Pregnancy - Week 22

• The eyes have been able to move for a few weeks, but eyelids are still fused shut.
• Your baby’s hearing becomes more acute; he may move suddenly when he hears loud noises.
• His eyebrows are growing.
• Your baby is now about the size of a papaya.

Fetal Development in Pregnancy - Week 23

• Your baby might now respond to the sound of your voice by moving.
• She spends much of her time in the rapid eye movement (REM) phase of sleep.
• Your baby is approximately the size of an eggplant.

Fetal Development in Pregnancy - Week 24

• Fetal lung development is under way. The lungs have formed but are not functional just yet.
• The skin is thin and wrinkled, and blood vessels are visible.
• The average baby is as big as an ear of corn.

Fetal Development in Pregnancy - Week 25

• Your baby’s nervous system is developing quickly.
• She's gaining weight and adding fat, filling out those chubby cheeks you’ll soon get to squeeze.
• Your baby could be about the size of an acorn squash this week.

Fetal Development in Pregnancy - Week 26

• Your baby starts to produce melanin, the pigment that gives skin its color.
• Fetal lung development continues as the lungs start producing surfactant to help them inflate properly.
• Your little one is about the size of a zucchini.

Fetal Development in Pregnancy - Week 27

• Your little one can now make grasping motions.
• Hearing your voice is calming for her; her heart rate may decrease when you talk or sing to her.
• Your baby may kick and stretch more often.
• Your baby is now about the size of a head of cauliflower.

3. Fetal Development in the Third Trimester

Fetal Development in Pregnancy - Week 28

• His eyes can now open and close.
• Breathing is becoming more rhythmic.
• He may start to grow eyelashes this week.
• The average baby is the size of a head of lettuce.

Fetal Development in Pregnancy - Week 29

• Kicks and movements may be more noticeable.
• Your baby might be as big as a butternut squash.

Fetal Development in Pregnancy - Week 30

• Fine body hair called lanugo may begin to shed.
• Your baby may have hair on his head.
• Bone marrow starts to produce red blood cells, which help transport oxygen.
• Your baby is now about the size of a head of cabbage.

Fetal Development in Pregnancy - Week 31

• Your baby is now able to regulate her own body temperature.
• Bones begin to harden.
• The skull is still soft and pliable, and won’t harden completely until your baby is around 2 years old.
• Your baby is now about the size of a coconut.

Fetal Development in Pregnancy - Week 32

• Toenails may be visible this week — it might be time for a little pedicure shortly after birth.
• Your baby is adding fat, and his skin is now less transparent.
• He’s approximately the size of a Napa cabbage.

Fetal Development in Pregnancy - Week 33

• Your baby will likely gain about a half a pound each week from now until birth.
• Brain development continues, and all five senses are working.
• Your baby is now about the size of a pineapple.

Fetal Development in Pregnancy - Week 34

• Your baby might shift to a head-down position as he prepares for birth.
• Fingernails continue to grow.
• Your baby continues to plump up, adding fat.
• He’s now about the size of a cantaloupe.

Fetal Development in Pregnancy - Week 35

• Fetal brain development continues; other parts of the nervous system and the lungs are also still developing.
• As your baby puts on fat, her skin becomes more pinkish, and less transparent.
• The musculoskeletal system has fully developed to enable movement after birth.
• Your baby could be as big as a honeydew melon.

Fetal Development in Pregnancy - Week 36

• He’s taking up more space in the amniotic sac.
• Fetal kicks, rolls, and other movements continue.
• Your little one is about the size of a head of romaine lettuce.

Fetal Development in Pregnancy - Week 37

• Your baby is still growing and is considered to be early term.
• Body hair called lanugo has almost been entirely shed.
• Your baby has added nearly enough fat to keep her warm after birth.
• The average baby is as big as a bunch of Swiss chard.

Fetal Development in Pregnancy - Week 38

• Liver and lung development are nearly complete.
• The head and abdomen may have about the same circumference.
• He may start to drop further into your pelvis.
• Your baby is about the size of a bunch of rhubarb.

Fetal Development in Pregnancy - Week 39

• Your baby is now officially full term.
• Fetal brain development continues, and her brain will keep growing well into early childhood.
• Your baby is about the size of a watermelon.

Fetal Development in Pregnancy - Week 40

• In terms of development, your baby is ready to be born.
• His length will likely be between 18 and 20 inches.
• The average newborn weighs between six and nine pounds, about as big as a pumpkin.

Foetal length and weight growth chart  

Conclusion