# 18 Weeks Pregnant: Baby Size, Symptoms & What to Expect | Clever Mum > 18 weeks pregnant — your baby is the size of a sweet potato. What's developing, what you might feel, and what to focus on this week. * [ Home ](/) * › [ Pregnancy ](/pregnancy/) * › [ Week by week ](/pregnancy/week/) * › Week 18 Second trimester # 18 weeks pregnant Your baby is about the size of a sweet potato [ CP ](/authors/parenting-desk/) By [ Clever Mum Parenting ](/authors/parenting-desk/) · Parenting guides Published 11 July 2026 Quick answer — What happens 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. Who should skip this Skip this page if you need personal medical advice — it is general NHS-aligned information, not a substitute for your midwife. If your baby's movements slow or change, call your maternity unit, not a website. ## 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 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. * [Due date calculator](/tools/due-date-calculator/) * [Trimester to-do list](/pregnancy/pregnancy-to-do-list-by-trimester/) * [Maternity leave and pay](/pregnancy/maternity-leave-and-pay-uk/) ## 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 * [ You and your baby at 4 to 40 weeks pregnant ](https://www.nhs.uk/pregnancy/week-by-week/) — NHS * [ Your baby's movements ](https://www.nhs.uk/pregnancy/keeping-well/your-babys-movements/) — NHS [← 17 weeks](/pregnancy/week/17/) [All weeks](/pregnancy/week/) [19 weeks →](/pregnancy/week/19/) 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 August 2026. ## Week 18 at a glance Trimester Second trimester Baby size sweet potato Approx length ~14.2cm Approx weight ~190g Weeks to go 22 (to 40) Work out your dates Not sure how many weeks you are? Our [due date calculator](/tools/due-date-calculator/) maps your weeks and trimester dates from your last period.