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12 weeks pregnant

Your baby at 12 weeks

Foetus at 12 weeks pregnant

If you have a dating scan and get to see your baby this week, the chances are you'll be amazed. First, that there really is a baby in there and, second, at how brilliant she is.

You will see her heart, her skull and spine and limbs. And if you haven't been scanned before, you never know, it could be twins.

At 12 weeks, her movements are more purposeful and she can move her legs and arms individually. This is because she is developing the sorts of muscles we use to walk and run with. Under the microscope these look stripy.

Her head is still large but she manages to support it better with the neck she's growing and she is developing facial characteristics that are all her own (and her parents' of course). Her forehead is still high but she has a more defined nose, jaw and chin.

She's the size of a small plum. But much more interesting.

  • Her ears and eyes are moving towards where they should be - her eyes are still a bit far apart but are moving together. Her ears are almost done, including the inner and middle parts.
  • She has a fine layer of downy hair called lanugo, which covers most of her body and will only be shed towards the end of the pregnancy. This helps her stay warm.
  • Her bones are developing, with the middle bits of the cartilage scaffold she has been putting up now laying down calcium and becoming hard. Bones continue this ossification process until adolescence.
  • Her chest muscles are sufficiently strong for her to start practising breathing movements - this is a long-term limbering-up project.
  • She is growing finger and toe nails. Awww.
  • The intestines that she parked in the umbilical cord for a while have returned back inside her abdominal wall, where they will remain.
  • Her liver and kidneys are working and she has a bladder to store the urine she's made when she starts swallowing amniotic fluid.
  • Her liver is producing red blood cells - later on her long bones will do this for her. Her liver is also making bile, which will help her digest fats.
  • Your placenta is nearly or already complete. It will grow larger and is an amazing life support machine for your baby that provides her with food, breathes for her and gets rid of her waste.
  • Her heart is more fully formed and will start slowing down, maybe to 110-160 beats a minute as she gets more mature.

Your first antenatal appointment

If you have your first antenatal booking appointment this week you will be given lots of information, your urine and blood will be tested (the people who take blood are usually so brilliant you hardly notice). 

NICE recommends that you should be given a screening test for Down's syndrome. It's called a combined test because you have a blood test that measures specific proteins in your blood and a scan to measure the amount of fluid in the back of your baby's neck. This is called the nuchal translucency scan.

There are other methods of screening and you should discuss them with your antenatal team.

The combined test will detect 85% of babies with Down's syndrome. You will get the results sent to you as a risk, eg 1 in 500. The test is not perfect - it is a screening test not a diagnostic test - so will miss some babies with Down's syndrome.

Either an amniocentesis, in which a small needle collects and analyses a sample of amniotic fluid through your abdomen, or chorionic villus sampling (CVS), which takes some placental cells, will give you an almost 100% definitive diagnosis. New methods may be available and you should ask your antenatal team.

Both tests have risks. Most of the amnio and CVS tests will come back saying your baby does not have Down's syndrome. 

Your body at 12 weeks pregnant

  • Your growing uterus Your uterus is now the size of a grapefruit and starting to come out of the pelvis. This means you'll be able to feel it. It also means you'll get twinges of discomfort as it strains for freedom from the ligaments that are holding it to your abdominal wall. The ligaments will win but you may feel the pain. Avoid sudden movements.
  • Telling people You may be surprised at people's reactions. Some will immediately say "Congratulations" but you may hear "I can't see you as a mum" or "Was it planned?" and other unhelpful responses. It can be hard to tell someone whom you know will be upset. You need to decide when to tell your employer.
  • Weight gain It may not be much - the baby, placenta and fluid is just about 2lb. You need to wait until the last trimester to pack on a pound a week. But your body may no longer feel like it used to. If you've already had a baby your abdomen will go "I've done this before" and spring out like an inflated balloon. Unless you have done serious abdominal workouts since your last pregnancy, you're doomed to look close to term by the end of 12 weeks or, at best, find you can't fit into your jeans any more. It can be depressing (illogically, of course) but that's the problem with pregnancy, you know you're having a baby but you still feel fat.



Pregnancy Encyclopedia book coverIllustrations taken from The Pregnancy Encyclopedia, £25, published by DK.

Disclaimer: The information in the pregnancy calendar is for general information and is not intended as a substitute for the medical advice of your own doctor or antenatal team. Not all babies develop at the same time and in the same way, so this week-by-week guide may not always match your own experience. If you have any worries, consult your antenatal team or GP.

Last updated: 3 months ago