Second trimester
18 weeks pregnant
Your baby is about the size of a sweet potato
- First trimester1st trimester weeks 1–12
- Second trimester2nd trimester weeks 13–26
- Third trimester3rd trimester weeks 27–40+
By Clever Mum Parenting · Parenting guides
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How big is the baby at 18 weeks pregnant?
At 18 weeks pregnant, your baby is about the size of a sweet potato, roughly 14.2cm and around 190g. The baby can hear now — your heartbeat, tummy rumbles and muffled voices from outside. They may startle at sudden loud noises. Nerve cells are forming connections rapidly. These are typical averages — your midwife's measurements are the ones that matter for your pregnancy.
What might you feel at 18 weeks?
Most people at 18 weeks notice some mix of the symptoms below — and plenty notice none of them. You may feel more movement as the weeks go on. Some experience leg cramps, especially at night, and a bigger appetite. Backache can start as posture changes. None of this is a diagnosis; contact your midwife if something worries you.
Common symptoms this week
- Movements becoming noticeable
- Leg cramps at night
- Backache beginning
- Bigger appetite
Symptom lists are typical, never exhaustive — and having none of them is normal too.
What should you do at 18 weeks pregnant?
The useful job this week is practical, not medical. Your anomaly scan (18–21 weeks) is coming up — a detailed check of the baby's development and, if you want, a chance to find out the sex. Pair it with the NHS week-by-week guide if you want a second description of the same stage.
Week 18 checklist
- Confirm your anomaly scan appointment (18–21 weeks)
- Decide in advance whether you want to find out the sex — tell the sonographer either way at the start
What antenatal care is due around 18 weeks?
These appointments, vaccines and deadlines fall around this stage. Your maternity team will confirm your own dates.
- Quadruple test if you missed combined screening. If you are past 14 weeks, the NHS may offer the quadruple blood test between 14 and 20 weeks. It checks for Down's syndrome but is not as accurate as the combined test. NHS: screening in pregnancy
- Whooping cough vaccine (from 16 weeks). Offered in every pregnancy from 16 weeks, usually around 20 weeks. Antibodies pass to your baby before they can have their own vaccines at 8 weeks. Pregnancy and baby vaccines
- 20-week scan (usually 18 to 21 weeks). The mid-pregnancy scan screens for 11 physical conditions and takes around 30 minutes. It cannot find every condition, and it is your choice whether to have it. What the 20-week scan checks
What else is useful at 18 weeks?
Use the week page for size and symptoms; use the guides below for the decisions that actually sit in this window — pay, packing, car seats, labour signs.
18 weeks pregnant: common questions
Can I find out the sex at the 20-week scan?
Usually yes — most hospitals will tell you if you ask, and the sonographer can often see at the anomaly scan (18–21 weeks), though no unit guarantees it since it depends on the baby's position. Some trusts have a policy of not telling; ask your midwife what yours does.
How big is my baby at 18 weeks pregnant?
At 18 weeks, your baby is approximately the size of a sweet potato, about 14.2cm and around 190g. These are approximate averages — every baby grows at its own pace.
What's happening at 18 weeks pregnant?
The baby can hear now — your heartbeat, tummy rumbles and muffled voices from outside. They may startle at sudden loud noises. Nerve cells are forming connections rapidly. For you: you may feel more movement as the weeks go on. some experience leg cramps, especially at night, and a bigger appetite. backache can start as posture changes.
What appointments or vaccines are due at 18 weeks pregnant?
Around 18 weeks: quadruple test if you missed combined screening; whooping cough vaccine; 20-week scan. Your maternity team will confirm the dates that apply to you.
Which trimester is 18 weeks?
18 weeks pregnant is in the second trimester. The first trimester runs to the end of week 12, the second from weeks 13 to 26, and the third from week 27 to birth.
Sources & further reading
This is general information, not medical advice — every pregnancy is different. For anything that worries you, and for all your antenatal care, speak to your midwife or GP. If your baby's movements ever slow down or change, contact your maternity unit immediately, day or night.