What to expect from your baby’s month-by-month development in utero

Discover some interesting facts about your baby's month-by-month development.

Week 1 to 4

Seven days after you have ovulated, the fertilised egg will gradually implant itself in your uterus. The embryo will appear by the 10th day after the egg has been implanted. The inner cells of the embryo will form two layers at first and then later, the third layer will be formed. The first layer of the embryo will grow into your baby’s skin, eyes, ears, brain and nerve centre. The second layer will grow into the digestive organs and lungs, while the third layer will form your growing baby’s blood, muscles, heart and bones.

Baby's development in utero week 1 to 4 By the end of week 4, your baby’s average crown length will be 4mm and he will weigh approximately 0.4g.



Week 5 to 8

Your baby’s heartbeat is now visible on an ultrasound scan and the larger organs begin to take shape. Your developing baby’s facial features, brain and limb joints become visible at this stage of your pregnancy, and his fingers have started to develop. Even though you won’t be able to feel it at this stage, your little one may begin to move in week 8.

week 5 - 8Your baby’s crown length is about 28-30mm by the end of week 8 and he weighs about 2g.




Weeks 9 to 24 are known as the ‘foetal phase’ and this is when the placenta develops. Smoking, viral infections and a larger use of medicines may have more negative effects on your unborn baby, as your little one’s organs are busy developing at this stage.

ALSO SEE: Treating illnesses during pregnancy

Week 9 to 12

The growing embryo is now known as a foetus and the gender of your baby can be determined at this stage. Your little one’s ears, nose and mouth start forming. The eyes are covered with skin, which will become the eyelids. The
early stages of your little one’s arms and legs are visible and his nails begin to grow.

Week 9 - 12By the end of week 12, your baby’s crown length is about 8cm and he weighs about 19g.




Week 13 to 16

Your baby’s large organs are now fully formed and he can now also stretch his arms and legs and open his mouth. He already has 20 little milk teeth in place. Your little one’s face becomes more defined. His head-hair pattern begins to develop and his eyes can now face forward and can move slowly.

Week 13 - 16Your baby’s crown length is about 16cm and he weighs about 100g by the end of week 16.




Week 17 to 20

Your baby’s eyes are still shut, even though little eyelashes appear. His hair begins to grow and his fingerprints are formed. You may occasionally start feeling fluttering or stirring in your stomach as your baby moves around.

Week 17 to 20By the end of week 20, your baby’s crown length is about 19cm and he weighs about 300g.



ALSO SEE: When should my baby start kicking?

Your baby is fully developed at 24 weeks old, and all that is left is for him to go through the maturing phase. All babies are about the same length and weight up until the 24th week. After that, a baby will develop according to his genetic destination.

Week 21 to 24

Your baby’s muscle- and nerve connections are beginning to form. Maturation begins at this stage and along with it, early breathing practices and the experience of touch. Your little one can hear music and people talking as well.

Week 21 - 24Your baby’s crown length is 23cm and he weighs about 600g by the end of week 24.




From 25 weeks old, your baby is ready to survive outside the womb. The younger a baby is when born, however, the bigger the risk of complications.

ALSO SEE: Caring for your premature baby

Week 25 to 28

Your baby’s lungs begin inhaling and exhaling amniotic fluid. His eyes slowly start opening and you will be able to see them. His cycle of sleeping and waking will also start and you can hear his heartbeat with a stethoscope.

Week 25 - 28By the end of week 28, your baby’s crown length is about 27cm and he weighs about 1.1kg.



The weight your baby reaches by the end of week 32 can nearly be doubled to determine his birth weight. Your baby is also positioning himself for birth at this stage, and the chances of him changing his position before delivery are very slim.

Week 29 to 32

Your little one’s hair on his head grows longer each week now. His eyebrows and eyelashes become fully developed and he can begin to focus his vision. The fine hairs (lanugo) disappear from his face and his skin becomes a little less wrinkled.

Week 29 to 32Your baby’s crown length is about 30cm and he weighs about 1.8kg by the end of week 32.

Week 33 to 36

His eyes can blink and focus and they are also light-sensitive now. All your little one’s organ systems are now working and his fingernails are fully developed. Your baby’s movements will also become limited now, as he is getting bigger.

Week 33 - 36By the end of week 36, your baby’s crown length is 34cm and he weighs about 2.2kg.




A baby can be born now. From week 37 the chances that he won’t be able to live outside his mother’s womb are very slim.

Week 37 to 40

Half of your baby’s full-term weight will be reached during the last two months of your pregnancy. His head is the largest of all his body parts and the vernix (the creamy substance that your baby has been covered in all this time)
starts to disappear from his skin.

Week 37 to 40At birth, your baby’s crown length will be about 36cm and he will weigh approximately 3.2kg.




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