Pregnancy Week 13: Welcome to the Second Trimester

Quick answer: Week 13 begins the second trimester, and your baby is now about the size of a peach, roughly 73mm from crown to rump. Fingerprints are forming, the intestines have moved into the abdomen, and the placenta is taking over hormone production, which is one reason nausea often eases. Energy often improves and your bump may start to show.

What parents need to know

Congratulations — you've made it to the second trimester! Week 13 marks the beginning of what many women describe as the most comfortable and enjoyable phase of pregnancy. First trimester symptoms often start to ease, energy returns, and the bump begins to show. There's still a great deal happening for your growing baby too.

How big is your baby at 13 weeks?

Your baby is now about the size of a peach — roughly 73mm from crown to rump. Growth is accelerating, and over the next few weeks your baby's body will start to catch up with the size of their head.

What's happening with your baby?

Your baby's fingerprints are beginning to form this week — completely unique ridges and whorls that will remain for life. The intestines, which were temporarily housed in the umbilical cord during early development, have now moved into their permanent position in the abdomen. Your baby's bones continue to harden, and the vocal cords are developing (though it will be many months before you hear them used). Your baby can now make a wide range of facial expressions, though these are reflex movements rather than conscious actions. The placenta is now taking over hormone production from the corpus luteum in the ovary, which is one reason why nausea often eases around this time.

What's happening in your body?

The second trimester brings welcome relief for many women. Nausea typically eases (though it doesn't disappear for everyone), and energy levels often improve. Your bump may be starting to become visible, particularly if this is not your first pregnancy. As the uterus rises out of the pelvis and into the abdomen, you may notice a more pronounced, firm roundness low in your belly.

Your skin may start to change in visible ways. The linea nigra — a dark line running from the navel to the pubic bone — may begin to appear due to increased melanin production. This is harmless and fades after birth. Some women develop chloasma, or ‘the mask of pregnancy’ — patches of darker skin on the face. Using sun protection helps prevent this from worsening.

Your libido may return during the second trimester as nausea fades and energy improves. Sex is completely safe during a straightforward pregnancy unless your midwife or doctor has specifically advised otherwise.

Antenatal care in the second trimester

Now that you're in the second trimester, your antenatal appointments will continue at regular intervals. If this is your first pregnancy (a primigravida), the NHS schedule typically includes appointments at around 16, 25, 28, 31, 34, 36, 38, 40, and 41 weeks (if you haven't given birth by then). If this is a subsequent pregnancy, appointments may be less frequent. Your 20-week anomaly scan will be offered between 18 and 21 weeks and is a significant milestone — more on that when you get there.

Exercise in pregnancy

Unless you have been advised otherwise by your midwife or GP, regular exercise during pregnancy is beneficial for you and your baby. The NHS recommends aiming for at least 150 minutes of moderate-intensity activity per week. Walking, swimming, pregnancy yoga, and pilates are all excellent choices. Exercise helps manage weight gain, reduces the risk of gestational diabetes and pre-eclampsia, improves mood and sleep, and can even help with labour.

Avoid activities that carry a risk of falling or abdominal impact, contact sports, scuba diving, and exercising at high altitude. If you were not exercising regularly before pregnancy, start gradually and build up slowly.

Your week 13 checklist

This week:

• Celebrate reaching the second trimester.
• Book your 16-week midwife appointment if you haven't already.
• Start gentle exercise if you haven't been active.
• Look out for your linea nigra and use SPF on your face if chloasma is a concern.
• Enjoy this often more comfortable phase of pregnancy.