20 weeks pregnant: halfway there
Twenty weeks down, about twenty to go. A big scan, a useful form and a vaccine that protects your baby from birth.
Updated October 13, 2026 · sources checked October 13, 2026
In short
At 20 weeks you are halfway. Your baby now measures about 25.6cm from head to heel, is covered in protective vernix and is getting more active every day. This is often the week of the detailed scan. This week, ask about the whooping cough vaccine and, in the UK, request your MATB1 maternity certificate from your midwife or doctor.
Where you are at 20 weeks
Halfway. Cleveland Clinic counts weeks 17 to 20 as month five, so this week closes it. If you want to see the second half laid out, the due date calculator gives your date and the pregnancy week calculator your exact week and day.
Your baby this week
From now on the NHS measures your baby from head to heel rather than head to bottom, because the legs are no longer curled out of sight. That is why the number jumps: around 25.6cm, which the NHS compares to a banana. Cleveland Clinic gives about 9 to 10 inches and about 1 pound at the end of month five.
- Vernix. Your baby is covered in a white, greasy layer thought to protect the skin in the amniotic fluid and to help on the way down the birth canal (NHS).
- More active. Kicking, punching, turning and possibly thumb sucking, which trains the sucking reflex for feeding (NHS).
- Senses. Cleveland Clinic says nails are reaching the ends of the fingers and the area of the brain for the five senses is developing.
Your body and common symptoms
Leg cramps at night. Sudden sharp pain in the calf is probably cramp, which is common now. The NHS suggests rubbing the muscle hard or pulling your toes up towards your ankle, and being more active during the day.
Flutters. You may notice bubbling or fluttering. The NHS movements page says you should feel movement by 24 weeks; tell your midwife if you have not.
Telling work. You do not have to yet, but GOV.UK says you must tell your employer at least 15 weeks before your due date, which is around week 25. Once you do, the NHS notes you can attend antenatal appointments in paid work time and ask for a workplace risk assessment.
Is this normal? When to call
Calf cramps at night, a growing bump and a baby who is active at odd hours are all normal at 20 weeks.
The NHS says pre-eclampsia can happen in the second half of pregnancy, and ACOG says it usually develops after 20 weeks. Call your midwife, maternity unit or OB-GYN straight away for a severe headache, blurred vision or flashing lights, pain just below the ribs, sudden swelling of your face, hands or feet, vaginal bleeding, fluid leaking, or a temperature of 38C (100.4F) or above. A calf that stays swollen, red or painful also needs checking the same day. In the UK, call NHS 111 if you cannot reach your maternity unit, and 999 in an emergency. In the US, call 911 in an emergency.
Appointments and tests around 20 weeks
The scan. In England the 20-week screening scan looks for signs of 11 conditions and checks growth, the placenta and blood flow; it is usually done at 18 to 21 weeks, sometimes up to 23. In the US, ACOG says the standard ultrasound is usually at 18 to 22 weeks. Neither can find everything. If something unexpected comes up, you will be given time and support to talk it through.
Whooping cough vaccine.
- UK: offered around 20 weeks, often at the same visit as the scan, and possible any time from 16 to 32 weeks. The NHS says you and your baby get the most protection if you have it before 32 weeks, and it is recommended in every pregnancy. A study of England's programme (Amirthalingam 2014) found the vaccine was 91% effective at protecting babies under 3 months.
- US: CDC recommends Tdap during weeks 27 to 36 of each pregnancy, earlier in that window being preferred. So your US provider will likely offer it later than a UK midwife would. Same vaccine aim, different timing.
Your checklist for week 20
For your partner
If you come to the scan, you might get to see your baby's profile. Afterwards, take a moment together to talk about how you each feel before sharing the news with others.
Previous and next week
Week 19: looser joints and better sleep · Week 21: balance and a rapid growth phase
Read the full second trimester guide or see all pregnancy weeks.
Questions parents ask
How many months is 20 weeks pregnant?
Cleveland Clinic groups weeks 17 to 20 as month five, so 20 weeks is the end of the fifth month. It describes the fetus at that point as about 9 to 10 inches long and about 1 pound.
Can stress cause a miscarriage at 20 weeks?
ACOG says that miscarriage is usually a random event and is not caused by working, exercising, stress or arguments. Ongoing stress still deserves care for your own sake, so talk to your midwife or doctor. Call straight away for bleeding, fluid leaking or strong tummy pain.
When can I get my MATB1 form?
GOV.UK says doctors and midwives give the MATB1 certificate no more than 20 weeks before your due date, so from around 20 weeks. You need it to claim Statutory Maternity Pay or Maternity Allowance.
When should I have the whooping cough vaccine?
In the UK the NHS offers it from 16 to 32 weeks, usually around the 20-week scan. In the US, CDC recommends Tdap during weeks 27 to 36 of each pregnancy, earlier in that window being preferred.
Sources
- NHS — Week-by-week guide to pregnancy, week 20 checked October 13, 2026
- NHS — 20-week screening scan checked October 13, 2026
- NHS — Whooping cough vaccine checked October 13, 2026
- GOV.UK — Maternity pay and leave, how to claim checked October 13, 2026
- CDC — Vaccine recommendations before, during and after pregnancy checked October 13, 2026
- ACOG — Early Pregnancy Loss checked October 13, 2026
- Cleveland Clinic — Fetal Development, week-by-week stages checked October 13, 2026
- Amirthalingam G et al. (2014), Effectiveness of maternal pertussis vaccination in England, The Lancet (PMID 25037990) checked October 13, 2026
- NHS — Pregnancy symptoms you need to get help for checked October 13, 2026
- ACOG — Preeclampsia and High Blood Pressure During Pregnancy checked October 13, 2026
- U.S. Department of Labor — Family and Medical Leave Act checked October 13, 2026
Mamavela explains; it does not replace your midwife, doctor or pediatrician, who know your situation. If something worries you, call them. In an emergency, call 911 (US), 999 (UK) or 112.