Week 31 of pregnancy
Updated 25 Oct 2026
Your baby this week
About the size of a pineapple
Source: Vinmec – Bảng cân nặng và chiều dài thai nhi theo tiêu chuẩn của WHO
Your baby's development
Your baby weighs about 1.5 kg and is about 41 cm long, the size of a coconut. The fine body hair (lanugo) is gradually shed and replaced by hair. Your baby's eyes are gradually sensing light, though not clearly yet.
The connections between your baby's brain cells are developing very quickly, forming billions of nerve cells (neurons). Your baby can now receive and process information from all 5 senses, and the first smell your baby can sense is your smell – baby's favourite smell later on.
Your baby is now a big fan of sleep, sometimes sleeping for several hours. Your baby is now breathing, hiccuping, kicking and even sucking their fingers. Interestingly, some babies are born with a slightly callused thumb because they sucked it so hard and so often while still in the womb.
Your body
At week 31 varicose veins and leg swelling may get worse. This is caused by rising pregnancy hormones and the uterus pressing on the vena cava, putting pressure on the peripheral veins. You may also feel short of breath because the growing uterus pushes your organs upwards and presses on your diaphragm. In addition, as your bump grows your body gets heavier and you may have back pain. Sometimes there are occasional headaches and mild sleep problems.
You will need to wee more often. Your memory may get clumsier too; this is because brain cell volume shrinks slightly in the third trimester, but it returns to normal a few months after birth. Don't worry. It's actually rather endearing anyway – like a superhero saving the world who forgot to brush her teeth in the morning.
Advice for you
Lying on your left side while resting eases breathlessness. Practising deep breathing can also help you sleep better, so practise deep breathing regularly with Doti. If your legs swell a lot, you need to see a doctor because this is one of the symptoms of pre-eclampsia.
Doing yoga and drinking plenty of water bring many benefits for both you and your baby. You can still talk to your baby during this time as a way to feel better and forget about those symptoms. Or think about what colour your baby's first outfit will be.
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Signs that need a doctor now
If you notice any of the signs below, please go to the nearest health facility to be checked by a doctor.
Vaginal bleeding in pregnancy
This sign needs to be checked by a doctor. Please go to the nearest health facility now. If the bleeding is heavy or comes with severe pain or faintness, call the emergency number 115.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Convulsions (fits)
A convulsion in pregnancy is an emergency. Family members should call 115 at once, lay the mother on her side in a safe place and get her to the nearest hospital.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Fever in pregnancy
A temperature above 38°C counts as a fever. Please go to a health facility so a doctor can find the cause and advise on safe ways to bring it down; do not take medicine on your own.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Leaking fluid or waters breaking
Fluid leaking from the vagina may mean the waters are leaking or have broken and needs to be checked by a doctor. Please go to a health facility soon, lying with your head low while travelling.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Severe headache, blurred vision, sudden swelling
Headache with blurred vision, or sudden swelling of the face, hands or eyelids, can be a sign of high blood pressure in pregnancy or pre-eclampsia. This sign needs to be checked by a doctor. Please go to the nearest health facility now.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Reduced or no fetal movement
A clear drop in the baby's movements, or no movement, needs to be checked by a doctor. Please go to the nearest health facility now rather than waiting until tomorrow.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Severe or worsening abdominal pain
Abdominal pain that keeps getting worse, does not ease, or is severe needs to be checked by a doctor. Please go to the nearest health facility now. If the pain is severe with sweating, faintness or bleeding, call 115.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Sources
Content advised by our doctors.
- Vinmec (accessed 22 Oct 2026)
- ACOG (accessed 22 Oct 2026)
- NHS (accessed 22 Oct 2026)
- Source for fetal size: Vinmec – Bảng cân nặng và chiều dài thai nhi theo tiêu chuẩn của WHO
- Source for the signs that need a doctor: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
This article helps you understand and prepare. It does not replace a check-up. For an answer about your own situation, please ask the doctor who is caring for you.

