How many months is 18 weeks pregnant?

18 weeks pregnant puts you in month 5 of pregnancy. Week 18 is the first week of that month, which runs to week 22. Providers count in weeks; months are approximate.

How big is the baby at 18 weeks?

At 18 weeks, the baby is about the size of a bell pepper, roughly 14.2 cm long and around 190 g. That is an average; healthy babies vary.

How should I lie down at 18 weeks pregnant?

Whatever is comfortable is usually fine at 18 weeks. In later pregnancy, the NHS advises not lying flat on your back for more than a few minutes, because the weight of the bump can press on a major blood vessel and make you feel faint. Sleeping on your front is fine early in pregnancy, and it usually just gets uncomfortable as the bump grows. From 28 weeks, go to sleep on your side, either left or right. A pillow under your bump or between your knees can help.

What should I avoid at 18 weeks pregnant?

Keep avoiding alcohol and smoking, and keep caffeine under 200 mg a day. With exercise, skip sports where you could fall or be hit in the tummy, like hockey, rugby or mountain biking, and avoid scuba diving. Don't lie flat on your back for long periods. Ask a pharmacist or your provider whether a medicine is OK before you take it. Most everyday activity, such as walking, is fine and good for you.

Will the 18-week scan show a boy or girl?

Often, yes, if your anatomy scan falls this week and the baby gives a clear view. The sonographer may ask whether you want to know. It isn't always possible, because the baby may be lying in a way that hides the genitals. Signs like morning sickness, bump shape or a fast heartbeat can't tell you either way. If you had cell-free DNA screening earlier, it may already have reported the sex chromosomes.

Is cramping normal at 18 weeks pregnant?

Brief, pulling pains on the sides of the bump are common at 18 weeks and are usually round ligament pain. Constipation can also cause crampy aches. But cramps or tightenings that come in a regular pattern, or that come with lower back pain, bleeding, fluid leaking or unusual discharge, need a call to your maternity team or provider straight away. So does pain when you pee or cloudy pee, which can be a sign of a urine infection.

What are good signs at 18 weeks pregnant?

Feeling the first flutters of movement is one. But many people don't feel them until 20 weeks or later, which is common in a first pregnancy. A heartbeat heard at your checkup is also a good sign, and so is an anatomy scan that shows normal growth. Tell your provider if you still haven't felt any movement by 24 weeks. Later, once you know your baby's usual pattern, call your provider right away if you feel less movement or the pattern changes.

18 Weeks Pregnant

At 18 weeks pregnant, your baby measures about 14.2 cm from head to bottom, similar in size to a bell pepper. Hearing, feeling, swallowing and sucking reflexes are developing, and the baby wriggles and moves its arms and legs a lot. This may be the week you feel those movements for the first time, as a soft flutter or bubbling. It's also when the detailed anatomy scan window opens. Your breasts may be getting bigger, and your blood pressure may be a little lower than before. Some people feel dizzy at times. This page covers the 18-week scan, your bump, how to lie down, and what to avoid.

What trimester is 18 weeks?

Week 18 is in the second trimester, which runs from week 13 to week 27 (NHS). It is week 6 of 15 in this trimester, and the third trimester starts at week 28.

Week 18 — second trimester, month 5; 22 weeks to go until your due date.
Baby's size — about a bell pepper, ~14.2 cm.

Not sure it's 18 weeks? Try our due date calculator.

How big is your baby at 18 weeks?

Size of a

bell pepper

Length, head to bottom

~14.2 cm

Weight

~190 g

Up from a pomegranate last week to a bell pepper now.

Baby development at week 18

The ears are now in their final position and the fetus may start to hear muffled sounds, including your heartbeat and voice. A protective coating called myelin begins forming around the nerves. In female fetuses, the uterus and fallopian tubes are forming; in males, the genitals are now distinct. About the size of a bell pepper.

What an ultrasound shows at 18 weeks

You may have the detailed mid-pregnancy scan this week or soon after. In the UK it's usually done between 18 and 21 weeks, and US guidance gives an ideal window of 18 to 22 weeks. It's the same scan whenever it happens in that window. It takes around 30 minutes. It won't hurt you or the baby, though it can feel a bit uncomfortable.

In the UK, the scan looks for 11 specific conditions. These include open spina bifida, cleft lip, serious heart problems, both kidneys missing, and the chromosome conditions Edwards' syndrome and Patau's syndrome. It also checks the baby's growth, the placenta and blood flow in the uterus. It cannot find every condition.

If the baby is lying in an awkward position, you may be asked to go for a short walk or have something to eat, then try again. If the pictures still aren't clear, you'll be offered another appointment, usually before 23 weeks. You may also be asked whether you want to know the sex. It can often be seen, but not always.

Your body at 18 weeks

Noticeable baby movements for many
Backache and round-ligament pain
Leg cramps, especially at night
Increased appetite

Your belly at 18 weeks

At 18 weeks, the top of your uterus is a short way below your belly button, and it usually reaches it at around 20 weeks. Many people have a clear bump by now, though in a first pregnancy it can still be small. As your shape changes, you might feel a little clumsier than usual.

A dark vertical line may appear down the middle of your belly. This is called the linea nigra, and it usually fades a few months after the birth. Soon, your provider may start measuring your bump with a tape measure at checkups. From about 20 weeks, that bump measurement in centimetres roughly equals your number of weeks.

Tips for week 18

The mid-pregnancy anatomy scan often happens around weeks 18–22
Talking or playing music to your bump is a lovely habit to start
Stretch before bed to reduce leg cramps

18 Weeks Pregnant: your questions

What trimester is 18 weeks?: Week 18 is in the second trimester, which runs from week 13 to week 27 (NHS). It is week 6 of 15 in this trimester, and the third trimester starts at week 28.
How many months is 18 weeks pregnant?: 18 weeks pregnant puts you in month 5 of pregnancy. Week 18 is the first week of that month, which runs to week 22. Providers count in weeks; months are approximate.
How big is the baby at 18 weeks?: At 18 weeks, the baby is about the size of a bell pepper, roughly 14.2 cm long and around 190 g. That is an average; healthy babies vary.
How should I lie down at 18 weeks pregnant?: Whatever is comfortable is usually fine at 18 weeks. In later pregnancy, the NHS advises not lying flat on your back for more than a few minutes, because the weight of the bump can press on a major blood vessel and make you feel faint. Sleeping on your front is fine early in pregnancy, and it usually just gets uncomfortable as the bump grows. From 28 weeks, go to sleep on your side, either left or right. A pillow under your bump or between your knees can help.
What should I avoid at 18 weeks pregnant?: Keep avoiding alcohol and smoking, and keep caffeine under 200 mg a day. With exercise, skip sports where you could fall or be hit in the tummy, like hockey, rugby or mountain biking, and avoid scuba diving. Don't lie flat on your back for long periods. Ask a pharmacist or your provider whether a medicine is OK before you take it. Most everyday activity, such as walking, is fine and good for you.
Will the 18-week scan show a boy or girl?: Often, yes, if your anatomy scan falls this week and the baby gives a clear view. The sonographer may ask whether you want to know. It isn't always possible, because the baby may be lying in a way that hides the genitals. Signs like morning sickness, bump shape or a fast heartbeat can't tell you either way. If you had cell-free DNA screening earlier, it may already have reported the sex chromosomes.
Is cramping normal at 18 weeks pregnant?: Brief, pulling pains on the sides of the bump are common at 18 weeks and are usually round ligament pain. Constipation can also cause crampy aches. But cramps or tightenings that come in a regular pattern, or that come with lower back pain, bleeding, fluid leaking or unusual discharge, need a call to your maternity team or provider straight away. So does pain when you pee or cloudy pee, which can be a sign of a urine infection.
What are good signs at 18 weeks pregnant?: Feeling the first flutters of movement is one. But many people don't feel them until 20 weeks or later, which is common in a first pregnancy. A heartbeat heard at your checkup is also a good sign, and so is an anatomy scan that shows normal growth. Tell your provider if you still haven't felt any movement by 24 weeks. Later, once you know your baby's usual pattern, call your provider right away if you feel less movement or the pattern changes.

Useful at week 18

Pregnancy weeks to months — 18 weeks starts month 5 — the full chart
Exercise in pregnancy — which activities are fine and which to skip
Hot tubs in pregnancy — why they're on the avoid list
Roller coasters in pregnancy — why jolting rides are best skipped
Chinese gender chart — a folklore guess to compare with your scan

← All weeks: the full pregnancy week-by-week guide

Sources

Checked against the following public guidance on October 2, 2026. Advice can differ between countries; your doctor, nurse or midwife can apply it to you.