During the course of your pregnancy, your baby goes through various stages of development. Understandably, each baby develops at their own pace, but it’s possible to pinpoint the average stages of development on a week by week basis. Here’s our guide to what’s going on so you can understand how your baby is likely to be developing during each week of your pregnancy.

 

 

Although it’s very early on, during weeks one to three, all the key events are occurring. Your pregnancy due date is calculated from the first day of your last natural period, so this means that during your first week of pregnancy you’ll be having a period. Ovulation happens at the end of week two, when an egg is released and fertilised by sperm.

 

By week three, the fertilised egg divides into a cluster of cells and, five to seven days after ovulation, it implants into the wall of the womb. It will begin to produce ‘roots’ that help it cling to the uterus and these will eventually become the placenta.

 

 

By the end of week four, the cluster of cells will be fully implanted into the lining of the womb. They’re still tiny, but are now known as an embryo. During the fourth week, the amniotic fluid, which will play an important role in supporting and cushioning your baby during pregnancy, will be forming in a sac around the embryo.

 

 

Now is the time when the embryo starts to grow and the major parts of the body start to develop. By the end of the week, your baby’s brain and central nervous system will have formed and their heart will start to beat.

 

 

By the end of week 6, the embryo will have grown to the size of a small bean. Their brain is slowly growing, the heart will have begun pumping blood around the body and the areas where the arms and legs will grow will be changing.

 

 

Your baby’s arms and legs will be growing this week and the eyes, ears, nose and many organs will be starting to develop too.

 

By the end of week 8, more growth will have occurred and your baby may now be about 2cm long. The arms and legs will slowly be growing longer.

 

By week nine, your baby will now be called a foetus rather than an embryo. Your baby will be starting to move around within the amniotic fluid and may begin to respond to sounds, but you won’t be able to feel any movement. Their facial features will be developing.

 

 

The key organs in the body, such as the liver, lungs and kidney now exist and begin to grow bigger. A functioning liver means the baby will be producing red blood cells.

 

 

Your baby’s fingers and toes will now be fully grown and they’ll be able to separate them for the first time. The nails are not yet properly formed, but the layer of skin where they will grow now exists. Bones throughout the body will have formed and will be starting to get harder.

 

 

All the major organs and limbs are now formed properly and fingernails will have developed. Your baby will be moving around, clenching their fist and kicking, but as he is still only the length of a thumb, you won’t be able to feel any movement.

 

 

The face of your baby is constantly developing and becoming more recognisable. The first signs of eyelashes and eyebrows are appearing. Their brain is rapidly developing too.

 

 

You’re now officially in the second trimester of pregnancy and your bump may be starting to show a bit – or to you, at least! Your baby’s sex organs will be continuing to develop and his fingers will be finished off now with tiny fingerprints. 

 

 

A thin layer of soft hair will begin to grow over your baby’s body and their very thin skin. This hair, called lanugo, usually disappears before birth, but can be present on premature babies.

 

 

This is the first week when you may actually be able to feel your baby moving around. From now on, your baby will be more sensitive to light and will respond if your stomach is pressed.

 

 

By this stage in development, your baby will now have a functioning urinary system. This means that in addition to taking in fluids through the umbilical cord, your baby will be able to drink some of the amniotic fluid that helps him keep afloat. Any urine produced will then go back into the amniotic fluid.

 

By the end of this week, your baby should be able to make breathing movements. There’s no air for him to breath in yet, but he will be breathing in amniotic fluid instead of oxygen.

Your baby has been through immense development already, but by this their sense of hearing, touch and taste will be beginning to develop.

This week marks the halfway point during your pregnancy. For your baby, it means a white coating called vernix will be forming over their body. This greasy substance helps protect their skin, as it’s still so thin, and will help ease of movement when your baby is born.

 

As your baby’s digestive system continues to develop, he’ll now be able to absorb some nutrients from the amniotic fluid that surrounds him. The main source of food will still come via you, through the placenta.

 

 

Your baby will have now grown to about 20cm long and, for the first time, will start to look like a tiny newborn baby and less like a tiny blob.

 

 

By the end of this week, your baby may be able to hear noises from outside the womb. One of the first things he hears is likely to be your voice. It’s believed that noises heard when in the womb can be recognised after the birth, which makes it a great reason to talk to your bump.

 

 

Lots more development is going on inside your baby’s body. A substance named surfactant will start to be produced and this will coat the delicate tube lining the lungs and stop them from sticking together.

 

 

Fat will start to form under your baby’s skin, helping him to fill out a bit more. He’ll probably weigh at least one pound now.

 

 

Your baby’s eyelids begin to open and they’ll be able to blink. If light is shone through to the womb, they’re able to respond to it. 

 

 

Although most of the key bodily systems are now fully formed, the lungs and liver are still progressing. The immune system will also be developing now too.

 

 

More layers of fat are forming under your baby’s skin. Minute changes are taking places, such as the formation of tiny teeth under the gums and eyelashes on the eyelids.

 

By the end of this week, your baby is looking much more like a newborn baby. The body, head and limbs will have grown and he’ll be looking much more in proportion than he did before.

 

By this week you’re likely to be aware of plenty of movement and action in your womb, as your baby explores moving around. They’ll be experiencing lots of brain development and learning new skills, such as how to suck. They’ll now be about 24cm long.

 

 

Your baby will now start to put on a lot more weight and fill out more. By the end of this week, he will weigh about three pounds and five ounces.

 

 

Your baby will be developing muscles, which will add to the weight they’re putting on. He’ll also have discovered how to move his head from side to side.

 

 

As your baby draws in amniotic fluid, he may experience what’s known as foetal hiccups. You may be able to feel this hiccups when they occur – they’ll feel like little bumps on your stomach.

 

 

Your baby’s nervous system and brain are now developed fully and their bones will be starting to go harder. If you’re having a boy, his testicles will start to descend down into the scrotum.

 

 

Your baby may now be aware of more sound and light coming into the womb. This will affect their sleeping and active times and may well impact on you, affecting your own rest times.

 

 

At about this time, your baby will probably settle down into the cephalic position. This means they have their head down, ready for birth. If they have their feet first, then this is called a breech position.

 

 

Your baby will be preparing itself for the impending birth now and will turn towards the light. If you’re pregnant with twins, they may be born anytime now.

 

 

By this week, the amniotic fluid that your back has been breathing in turns into a waste product – what’s known as meconium – and remains in their intestines. This is what will form their first bowel movement. There’s a lot less room in your uterus now, so your baby may not move around so much.

 

 

Your baby’s lungs are now in the final stage of maturation and the downy hair that was covering him will now be nearly gone.

 

Congratulations, your baby is now fully developed and ready to be born. That doesn’t mean to say he’ll necessarily arrive this week, as pregnancies can go on for a couple more weeks, but you can be sure the birth is not far off.

Rachel Newcombe