Your unborn baby week by week: First trimester development

Looking down at your tummy and wondering what's really going on inside that teeny-tiny bump?

Here's how your unborn baby is developing from conception to the end of the first trimester at 12 weeks. Prepare to be amazed, there's a lot going on in there even though you may not be showing yet.

Your growing baby: First trimester

Week two
 Ovulation usually happens around the end of week two or at the start of week three, and then... conception! Sperm meets egg and a zygote is formed. It heads off towards the uterus down the fallopian tube.
Week three
 The cells multiply on the journey. Once they settle into the wall of the uterus the embyonic stage has begun. The embryo is still very tiny. It would fit on a pin head! The placenta now starts to grow.
Week four
 Amazingly, the body's main organs have already started to grow. The heart is forming into chambers and beginning to beat, although it doesn't have a regular rhythm yet. If you could have a peek inside your womb, you'd maybe be able to spot the embryo; it is a few milimetres long.
Week five
 A number of blood vessels have formed and the nervous system and brain start to develop around this time too. The embryo doesn't look anything like a baby so far, it resembles a tadpole with a big head instead!
Week six
 By the end of week six the embryo should be a bit bigger than a grain of rice. Tiny lumps originate where the arms and legs will appear. The face starts to develop its shape with bumps, dents and holes where different features will eventually be.
Week seven
 It's still busy in there! The beginnings of teeth appear and fingers and toes start to develop. Those fingers and toes will be webbed for a few weeks. Movement can often be seen on an ultrasound by the end of week seven.
Week eight
 About the size of a bean, the embryo's tail is now disappearing and the body starts to look more straightened out. All the internal organs are present and they all start to do their jobs! Bones are developing as the limbs grow longer.
Week nine
 Muscles have become strong enough to move the arms and legs of the embryo around this time. Skin starts to develop into two layers. The placenta is cleaning away waste, and is making food for your future child along with hormones.
Week ten
 By the end of this week your embryo turns into a foetus. Finger nails start to grow, as well as taste buds in the tongue. Blood is being made and pumped around the body. Downy hair starts to grow from new hair follicles.
Week eleven
 The foetus can move more of its body. It can form a fist and arch its back. Eyelids are fully developed by now and the eyes will stay shut until much later in the pregnancy.
Week twelve
 You won't be able to feel any movement yet even though the embryo can respond to your touch at this stage. It might even get hiccups! By the end of the first trimester the foetus is pretty much fully formed. Now it just has to grow!
Week one
 The first week of pregnancy is actually classed as the week after your last period. You haven't even ovulated yet! The baby-to-be really is still just a twinkle in your partner's eye at this stage.