Foetal growth: Conception to birth

You're pregnant. Congratulations! You are curious to know how big your developing baby is, what it looks like as it grows inside you, and when you'll feel it move, aren’t you?  Take a peek inside the womb to see how a foetus develops from month to month.

Conception

If a sperm cell meets and penetrates an egg, it will fertilise it. This is known as conception. At this moment, the genetic make-up is complete, including the sex of the infant. Within about three days after conception, the fertilised egg, which is dividing rapidly into many cells, passes through the fallopian tube into the uterus where it attaches to the uterine wall. The placenta, which will nourish the baby, also begins to form.

Foetal development at four weeks

At this point of development the structures that eventually form the face and neck are becoming evident. The heart and blood vessels continue to develop. A home pregnancy test is now positive.

Foetal development at eight weeks

The baby is now about the size of a small grape - around 1.5cm in size. Eyelids and ears are forming and even the tip of the nose is visible. The arms and legs are well formed. The fingers and toes grow longer and more distinct.

Foetal development at 12 weeks

The foetus measures about 6cm and starts to make its own movements. You may start to see and feel the top of the uterus above the pelvic bone. Your doctor may hear the baby's heartbeat with special instruments. The sex organs of the baby should start to become clear.

Foetal development at 16 weeks

The foetus now measures about 10 to 12cm long and weighs about 80 - 100 grams. The top of your uterus should be easily felt below your belly button. The heart and blood vessels are fully formed. The baby’s urinary system is fully functional.

Foetal development at 20 weeks

The baby weighs about 300 grams and is about 26 cm long (crown to heel). The uterus should be at the level of the belly button. The baby can suck a thumb, yawn, stretch and make faces. Soon -- if you haven't already -- you'll feel your baby move, which is called "quickening."

For more BootsWebMD pictures of foetal development, click “Next”

Time for an ultrasound

An ultrasound is generally performed for all pregnant women at between weeks 10 and 14, and again at around 20 weeks of gestation. During this ultrasound, the doctor will confirm that the placenta is healthy and attached normally and that your baby is growing properly in the uterus. The baby's heartbeat and movement of its body, arms, and legs can also be seen on the ultrasound. The gender of the baby can usually be determined at 20 weeks.

Shown here is a 2D ultrasound (inset) contrasted with a 4D ultrasound, both at 20 weeks.

Foetal development at 24 weeks

The foetus weighs about 600 grams now. It responds to sounds by moving or increasing its pulse. You may notice jerking motions if it hiccups. With the inner ear fully developed, it may be able to sense being upside down in the womb.

Foetal development at 28 weeks

The foetus weighs about 1kg (2lbs 6oz). It changes position frequently at this point in pregnancy. There's now a good chance of survival if your baby is born prematurely. Ask your doctor or midwife about preterm labour warning signs. Register for antenatal classes. Antenatal classes prepare you for many aspects of childbirth, including labour and delivery and parenting the newborn.   

Foetal development at 32 weeks

Often on the move, the foetus weighs almost 1.8kg (4lbs). The baby's skin has fewer wrinkles as a layer of fat starts to form under the skin. It will gain up to half its birth weight between now and delivery. Ask your doctor or midwife how to do a foetal movement chart. Think about breastfeeding. Soon you may start leaking colostrum from your breasts, a yellowish fluid that precedes milk production.

Foetal development at 36 weeks

Babies differ in size, depending on many factors (such as gender, the number of babies being carried and size of the parents), so your baby's overall rate of growth is as important as the actual size. On average, it's about 47cm and weighs around 2.6kg. The brain has been developing rapidly. Lungs are nearly fully developed. The head is usually positioned down into the pelvis by now. A pregnancy is considered 'at term' once 37 weeks has been completed; baby is ready!

Birth!

A mother's due date marks the end of her 40th week. A pregnancy begins with implantation and the delivery date can be calculated using the first day of the last period. Based on this, pregnancy can last between 38 and 42 weeks with a 'full term' delivery occurring around 40 weeks. Some post-term pregnancies - those lasting more than 42 weeks - are not truly post-term. A common ‘cause’ is an incorrect due date. For safety reasons, most babies are delivered by 42 weeks, inducing labour if necessary.

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