What pregnancy week 18 means
Anatomy scan window opens. “18 weeks pregnant” means 18 weeks have passed since the first day of the last menstrual period — the standard way pregnancy is dated. Conception usually happened about two weeks after that date, so the baby’s own age (fetal age) is roughly 16 weeks. Week 18 runs from 18 weeks 0 days to 18 weeks 6 days; on the following day the pregnancy is 19 weeks.
Your baby at 18 weeks
The ears have moved into their final position, and the baby may begin to hear sounds such as your heartbeat. A protective coating of myelin is beginning to form around nerves.
A common way to picture it: the baby is now about the size of a bell pepper — roughly about 14 cm and about 190 g. These are averages; babies grow at different rates, and ultrasound measurements vary.
Your body at 18 weeks
Blood pressure is often slightly lower in the second trimester, so standing up quickly can make you dizzy. Getting up slowly and drinking enough fluids may help.
Care and appointments around week 18
The detailed anatomy (anomaly) scan is commonly offered between about 18 and 22 weeks. It checks the baby’s growth and organs and the position of the placenta.
The timing of tests and appointments differs between countries and care providers. If anything worries you — such as bleeding, severe pain, fluid leaking, fever — contact your midwife, doctor or maternity unit straight away rather than waiting for your next appointment.
Week 18 in your pregnancy timeline
Week 18 is in the second trimester (weeks 14–27) and in pregnancy month 5, which covers roughly weeks 18–22. The third trimester begins in 10 weeks.
| Pregnancy start (first day of last period) | |
|---|---|
| Estimated conception | |
| Third trimester begins (28 weeks) | |
| Full term (39 weeks) | |
| Estimated due date (40 weeks) |
Dates assume you are exactly 18 weeks 0 days today. For dates based on your own last period, use the calculator above or the main Pregnancy Calculator.
18 weeks pregnant in days and months
18 weeks is 126 days of pregnancy — 45% of a 40-week pregnancy. Counted in calendar months, 18 weeks is about 4.1 months, which is usually described as month 5 of pregnancy. Months are only a rough grouping; healthcare professionals almost always talk in weeks and days because they are more precise. See Pregnancy Month Calculator for how weeks map to months.