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20 weeks pregnant

Your baby is now about 17-18 cm long and weighs around 280g.

Foetus at 20 weeks pregnant

Between 18 weeks and 20 weeks plus 6 days, your baby will have a 20 week scan, medically called a fetal anomaly scan. This means that the scan is not to see if she's sucking her thumb or waving cutely, but to make sure there's nothing wrong.

You may realise this and be anxious. The likelihood is overwhelmingly that your baby will be fine. But even if she is fine, you can sometimes be freaked by an offhand comment about her size, the amount of fluid you've got (a typical one) or something that is difficult to see on the scan.

Make sure you take someone with you and be clear that you want to ask questions if there is anything you do not understand.

The scan will specifically look for the following problems:

  • Spina bifida - a condition in which there is an opening in your baby's spine because it has not fused shut.
  • Cleft palate - the roof of the mouth and the lips do not join together properly. This is very upsetting but fixable.
  • Diaphragmatic hernia - the muscle between your baby's lungs and stomach does not form properly.
  • Gastroschisis - a hole in the baby's abdominal wall, which means her bowel escapes and develops outside of the baby's abdomen.
  • Heart problems - the ultrasonographer will check the four chambers of the heart are working.
  • Your baby's kidneys and brain and skull will also be checked.
  • Your baby will be measured to make sure she is developing in line with her dates - her abdominal and head circumferences, length of her thigh bone and the distance between the sides of your baby's head (the biparietal diameter) will all be measured.
  • You will have your amniotic fluid measured and the position of your placenta noted. It may still be lying low and yet be OK, as placentas often move up when the uterus expands upwards.

Your baby at 20 weeks

Your baby's skin is thickening and developing layers. Skin has an outer layer, the dermis, an inner epidermis, which is the thickest, and the subcutaneous bit, which is made mostly of fat. We like her growing thicker skin as she is still a bit see-through.

At the scan you may, if you ask, be told the sex of your baby (or you may choose to keep the only surprise in life).

Your body at 20 weeks pregnant

You are nominally halfway through your pregnancy, so how are you doing?

  • You will definitely feel your baby move between now and 22 weeks.
  • You will gain weight - how could you not? And it will be about 0.5kg to 1kg a week in your second trimester. About 3-4kg is from your baby, the placenta and the amniotic fluid. Some is from your growing breasts and uterus, and about 2.5kg is from fat that's laid down for you to use up in breastfeeding. We hate to say it, but you need to watch your weight in pregnancy as if you put on too much weight you're at risk of gestational diabetes and having a hefty baby.
  • Swelling - you may start getting mild swelling of your ankles and feet, so wear more comfy shoes. If you have other symptoms such as sudden swelling of your hands and face, a severe headache, blurred vision or flashing lights, vomiting and feeling scarily unwell, you may have pre-eclampsia, which is rare before 20 weeks but can occur from now (although it is most common in the third trimester). Pre-eclampsia can reduce the blood supply to your baby and make her smaller than she should be for her dates. If you have these symptoms, see your doctor pretty much straight away.
  • Your belly button will pop out at any time now. It will return to how it was before after your pregnancy.
  • People will start commenting on how big you are. It is officially open season. Some will comment on how small you are, making you panic that your baby is not growing properly, others that you are enormous and are you sure you've only got one baby in there? (ho, ho, ho) "It's going to be a whopper," is not uncommon. You can either give them a pained look or smile, depending on how much hatred you feel for them. Do not shout abuse at them.



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

Disclaimer: The information in the Mumsnet 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: 4 months ago