20 weeks pregnant: halfway, the anomaly scan and baby size
20 weeks pregnant is the halfway point, the NHS and the Office on Women’s Health say, and the NHS gives the baby as around 25.6 cm long, about the size of a banana (NHS, 2026). This page sets out what the NHS, ACOG and the Office on Women’s Health say about week 20, including why the NHS figure jumps at this week.
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Seek help now if you have any of these symptoms
Bleeding and cramping are common in early pregnancy and often do not mean miscarriage. The symptoms below, however, need to be assessed straight away.
- Soaking two or more sanitary pads per hour, or passing large clots
- Severe lower abdominal pain, especially on one side
- Pain at the tip of the shoulder
- Dizziness, fainting, or collapse
- Signs of shock — pale, clammy, rapid heartbeat, breathlessness
- Pain on opening bowels, or bladder or bowel changes
- Feeling very unwell, or feverish
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How the sources describe development around 20 weeks
- Size and shape, NHS
- The NHS week 20 page in its week-by-week guide (NHS, 2026) gives the baby as around 25.6 cm long and compares it to a banana. It says measurements are now taken from head to heel, whereas in earlier weeks babies are measured from head to bottom because the legs are curled up.
- Skin and movement, NHS
- The NHS says the baby is now covered in a white, greasy layer called vernix, which is thought to protect the skin from drying out in the amniotic fluid, and that the baby will be getting more active each day, kicking, punching and turning around, and perhaps sucking a thumb (NHS, 2026).
- Size and development, Office on Women’s Health
- The Office on Women’s Health page on the stages of pregnancy (2025) says that at 20 weeks the baby is more active, is covered by fine downy hair called lanugo and a waxy coating called vernix, and has formed eyebrows, eyelashes, fingernails and toenails. It says the baby can hear and swallow and is about 6 inches long and weighs about 9 ounces. It does not say which measurement it uses, so its figure and the NHS’s are not directly comparable.
- Development, ACOG
- ACOG’s list for weeks 17 to 20 includes the digestive system working and soft downy hair called lanugo starting to form and cover the body (ACOG, How Your Fetus Grows During Pregnancy, 2024).
Weeks are counted from the first day of the last menstrual period, so about two weeks of the count come before conception (ACOG, How Your Fetus Grows During Pregnancy, 2024). This page covers 20 weeks 0 days to 20 weeks 6 days.
A normal pregnancy lasts about 40 weeks from the first day of the last menstrual period, so at 20 weeks about 20 weeks remain to the estimated due date (ACOG, How Your Fetus Grows During Pregnancy, 2024). Your own due date depends on your last period or a scan, not on the week alone.
Halfway
The NHS says you are now halfway through your pregnancy, and the Office on Women’s Health says the same at 20 weeks (NHS, 2026; Office on Women’s Health, 2025). A pregnancy lasts about 40 weeks counted from the first day of the last menstrual period (ACOG, 2024).
The scan and other checks
The NHS says you may have your anomaly scan this week, in which the sonographer checks your baby’s development and examines your placenta (NHS, 2026). NICE guideline NG201 recommends the scan be offered between 18 weeks 0 days and 20 weeks 6 days (NICE, 2021). The NHS says you might be woken at night by sudden sharp pains in the calves, which it says is probably cramp and is common in pregnancy (NHS, 2026).
Whooping cough vaccination
The NHS says the whooping cough vaccination is usually offered around week 20, and can be had from week 16 to week 32, and that the immunity is passed to the baby through the placenta and protects until the routine vaccine that most babies have at 8 weeks old (NHS, 2026). The CDC recommends the Tdap vaccine during the 27th through 36th week of each pregnancy (CDC, Tdap Vaccination for Pregnant Women, 2025).
Work out which week you are in
The Pregnancy week calculator takes your last period, conception date, scan or IVF transfer and shows how many weeks and days pregnant you are today.
Sources
- NHS Best Start in Life. Week 20 of pregnancy (week-by-week guide to pregnancy). nhs.uk, 2026.
- National Institute for Health and Care Excellence. Antenatal care (NG201). NICE, 2021.
- American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy (FAQ156). ACOG, 2024.
- Office on Women's Health, US Department of Health and Human Services. Stages of pregnancy. womenshealth.gov, 2025.
- Centers for Disease Control and Prevention. Tdap Vaccination for Pregnant Women. CDC, 2025.
Frequently asked questions
How big is the baby at 20 weeks pregnant?
The NHS says around 25.6 cm, about the size of a banana, measured from head to heel (NHS, 2026). The Office on Women’s Health says about 6 inches and about 9 ounces (Office on Women’s Health, 2025). The NHS measures head to heel from week 20 and head to bottom before, so the NHS figure rises sharply at this week.
Is 20 weeks halfway through pregnancy?
The NHS and the Office on Women’s Health both say so (NHS, 2026; Office on Women’s Health, 2025). ACOG says a normal pregnancy lasts about 40 weeks from the first day of the last menstrual period (ACOG, 2024).