Your baby at 13 weeks
Your baby weighs around 25g.
Your baby's ovaries or testes are fully developed inside their body, and the genitals are forming outside their body.
Where there was a swelling between the legs, there will now be a penis or clitoris growing, although you will not usually be able to find out the sex of your baby at an ultrasound scan at this stage.
You at 13 weeks
If you've been feeling sick and tired with morning sickness, you'll probably start to feel better when you're around 13 or 14 weeks pregnant.
You may start to experience an increased sex drive around this time, possibly as a result of pregnancy hormones or increased blood flow to the pelvic area. It is perfectly normal if you do not.
Read more about sex in pregnancy.
You'll notice a small bump developing as your womb grows and moves upwards. If you've been feeling the urge to pee more often over the last few months, it's because your womb was pressing on your bladder. This should ease off now.
See your doctor if you notice any pain when you pee. Urinary tract infections (UTIs) can happen in pregnancy, and it's important to treat them quickly to reduce the risk of kidney infection.
Things to think about
Find out about the pregnancy care you can expect if you're having twins.
You may be able to get help to buy food and milk through the Healthy Start scheme, if you're pregnant or have children under the age of 4 and if you receive certain benefits, or you're pregnant and under 18.
For more information, visit the Healthy Start scheme website.
Start4Life has more about you and your baby at 13 weeks of pregnancy
You can sign up for Start4Life's weekly emails for expert advice, videos and tips on pregnancy, birth and beyond.