13 weeks pregnant: baby's development, constipation and healthy eating

Welcome to the second trimester of pregnancy, a trimester of growth where your bump will get bigger and you’ll start to feel your baby moving.

Your baby’s development this week

Your baby is growing fast – and you may be too!

Your baby’s arms have developed rapidly by this point. Elbows, wrists and hands with fingers are now clearly visible on a 3D ultrasound.

The ovaries or testes have fully formed inside the body. And the external genitalia are developing from a small swelling between the legs into a recognisable penis or clitoris.  You may be able to find out whether you are having a boy or girl at your 20-week screening scan (although you don’t have to).

Get weekly updates on your baby's development from our expert midwives straight to your inbox.

Your pregnancy symptoms in week 13


Not all everyone has cravings during pregnancy. But if you do, it’s totally normal. Cravings can be triggered by hormonal changes in your body affecting taste and smell.

Take a look at our diet and nutrition guides on food swaps for a healthy pregnancy and how to have a balanced diet in pregnancy.

Feeling constipated or bloated

The hormonal changes in your body may cause you to become constipated very early on in your pregnancy. Try eating foods that are high in fibre, such as fruit and vegetables and drink plenty of water.

Here’s our guide to 10 common pregnancy complaints (and how to avoid them).

Painful urination

If it burns when you wee, this can be a sign of a urinary tract infections (UTIs), which can be common in pregnancy. This is not an emergency, but it is important that the infection is treated as soon as possible before it reaches the kidneys. Find out more about UTI symptoms and treatment.

What to do in week 13

How can I find antenatal classes near me?

Antenatal classes are a great way to prepare for the birth of your baby. And they’re sometimes a good way to meet other expectant families in your area.

Ask your midwife, health visitor or GP about local classes (NHS classes are free). Some of these may be offered online. The National Children’s Charity (NCT) also offers antenatal classes for a fee.

Healthy eating

Having a balanced diet in pregnancy is important for you and your baby. Good nutrition will keep you healthy and help your baby grow and develop.

If you were struggling with sickness in your first trimester and this has now stopped, you may be feeling hungrier. It’s a common assumption, but you don't need to eat for two!

You only need to increase your calorie intake in the third trimester, and even then you only need an extra 200 calories a day. This will help you manage your weight, which can help you stay healthy in pregnancy. 

Follow the storage instructions for your food

There are some foods you should avoid in pregnancy.

It’s also important to:

  • use foods by their use-by date
  • follow the storage instructions on the label and use opened foods within 2 days (unless instructions on the packaging say otherwise)
  • eat ready-to-eat food (food that you don’t need to cook or reheat before eating, such as salads or sandwiches) within 4 hours of being taken out of the fridge.

This can help you avoid an infection called listeriosis, which can cause problems in pregnancy. Find out more about how to avoid infections in pregnancy.

Staying active will give you energy

You may have felt a bit like sleeping more over the last couple of months, but hopefully you’ll find it a bit easier to stay active now. It doesn’t have to be an organised exercise class. Using the stairs, or walking to work, school or the shops really helps.

Being sedentary (sitting down a lot) in pregnancy increases your risks of complications so try to avoid this.

If you were active before pregnancy, you can continue doing whatever you did before at a level that feels comfortable for you. Research shows that exercise is safe and healthy in pregnancy. Here’s our guide to staying active in pregnancy.

Toning your pelvic floor muscles

If you haven’t already, this is a good time to start thinking about toning up your pelvic floor muscles.

Pregnancy and giving birth put a big strain on your pelvic floor. The more you can strengthen your muscles now, the better for the birth and after. Working these muscles will also help prevent you leaking wee when you laugh, sneeze or cough. It can make sex better too. 

You could do a set of pelvic floor exercises every time you brush your teeth, wait for a bus or put the kettle on.

Should I still take folic acid?

You don’t need to take folic acid after 12 weeks of pregnancy. But it isn’t harmful, so you can carry on if you’re taking pregnancy multivitamin tablets that contain it.

All pregnant people are recommended to take a 10 microgram (or 400 IU) supplement of vitamin D each day. This will give your baby enough vitamin D for the first few months of their life. 

Vitamin D may be included in your pregnancy multivitamin tablets, if you are taking them.

You can get vitamin supplements containing vitamin D free of charge if you're pregnant or breastfeeding and qualify for the Healthy Start scheme.

1. Regan, Lesley (2019) Your pregnancy week by week: what to expect from conception to birth. Penguin Random House, London

2. NHS. Common health problems in pregnancy. https://www.nhs.uk/pregnancy/related-conditions/common-symptoms/common-health-problems/ (Page last reviewed: 8 March 2021. Next review due: 8 March 2024)

3. NHS. Urinary tract infections (UTIs) https://www.nhs.uk/conditions/urinary-tract-infections-utis/ (Page last reviewed: 18 November 2020. Next review due: 18 November 2023)

4. NICE (2010). Weight management before, during and after pregnancy https://www.nice.org.uk/guidance/ph27

5. Food Standard Agency. Listeria. https://www.food.gov.uk/safety-hygiene/listeria

6. Badon, Sylvia E et al. (2018) Maternal sedentary behavior during pre-pregnancy and early pregnancy and mean offspring birth size: a cohort study. BMC pregnancy and childbirth vol. 18,1 267. 27 Jun. 2018, doi:10.1186/s12884-018-1902-2

7. NHS. Exercise in pregnancy. https://www.nhs.uk/pregnancy/keeping-well/exercise/ (Page last reviewed: 20 January 2020. Next review due: 20 January 2023) 

8. NHS. What are pelvic floor exercises? https://www.nhs.uk/common-health-questions/womens-health/what-are-pelvic-floor-exercises/ (Page last reviewed: 14 April 2020. Next review due: 14 April 2023) 

9. NHS. Vitamins, supplements and nutrition in pregnancy. https://www.nhs.uk/pregnancy/keeping-well/vitamins-supplements-and-nutrition// (Page last reviewed: 14 February 2020. Next review due: 14 February 2023) 

Review dates
Reviewed: 11 July 2022
Next review: 11 July 2025