🤰 Second trimester
18 weeks pregnant
Your baby is about the size of a sweet potato
By Emma Whitfield · Pregnancy & Baby Writer
Your baby at 18 weeks
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.
Your body at 18 weeks
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.
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.
Focus this week
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.
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
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.
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. Reviewed July 2026.