How many months is 21 weeks pregnant?

21 weeks pregnant puts you in month 5 of pregnancy. Month 5 covers weeks 18 to 22. Providers count in weeks; months are approximate.

How big is the baby at 21 weeks?

At 21 weeks, the baby is about the size of a carrot, roughly 26.7 cm long and around 360 g. That is an average; healthy babies vary.

Is my baby fully formed at 21 weeks?

The organs, limbs, bones and muscles have all been there since about 12 weeks, but many are still maturing. The lungs have the furthest to go. They keep developing for many more weeks, and even at around 24 to 26 weeks they are not ready to work well outside the womb. From about 23 weeks, the baby also starts to store fat, which fills out the wrinkled skin. So the weeks ahead are mostly about growth and maturing organs rather than new parts.

Is it rare to miscarry at 21 weeks?

Yes. By 21 weeks, the chance of losing the pregnancy is low. US doctors call a loss from 20 weeks onward a stillbirth, and it affects roughly 1 birth in 175. In the UK the dividing line is 24 weeks, so British sites may still use the word miscarriage at this stage. Warning signs that need a same-day call include vaginal bleeding, a trickle or gush of fluid, period-like pains that keep coming back, or your baby moving less than usual.

Are there symptoms of a boy at 21 weeks pregnant?

No symptom tells you the sex. Carrying high or low, skin breakouts, cravings and a fast or slow heart rate are all linked to boys or girls in old tales, but none of them is reliable. By 21 weeks, many people have already had the anatomy scan, and it often shows the sex to parents who want to know. If it wasn't clear at your scan, that is common: it depends on how the baby was lying at the time.

Is cramping normal at 21 weeks pregnant?

Some aching is common as the uterus grows and the ligaments around it stretch. Constipation and gas can also cause crampy pain. Other signs need a call straight away: regular tightenings, period-type pains, backache that is not usual for you, or a gush or trickle of fluid from the vagina. Before 37 weeks, these can be signs of early labour. Contact your provider or maternity unit rather than waiting to see if they pass.

21 Weeks Pregnant

At 21 weeks pregnant, your baby measures about 26.7 cm from head to heel, around the length of a carrot. It now weighs more than the placenta. Fine, soft hair called lanugo covers the skin, and the baby can hear noises and voices from outside the womb. Arm and leg movements are getting smoother and more frequent. The baby is also settling into its own pattern of sleeping and waking. This page covers what a 21-week ultrasound can show and how your bump is measured from now on. It also explains why you may feel less steady on your feet, and answers the questions people ask most this week, from miscarriage risk to how fully formed the baby is.

What trimester is 21 weeks?

Week 21 is in the second trimester, which runs from week 13 to week 27 (NHS). It is week 9 of 15 in this trimester, and the third trimester starts at week 28.

Week 21 — second trimester, month 5; 19 weeks to go until your due date.
Baby's size — about a carrot, ~26.7 cm.

Not sure it's 21 weeks? Try our due date calculator.

How big is your baby at 21 weeks?

Size of a

carrot

Length, head to heel

~26.7 cm

Weight

~360 g

Up from a banana last week to a carrot now.

Baby development at week 21

The fetus is now drinking amniotic fluid daily, which helps the digestive system practise and contributes to taste development — flavours from your diet pass into the fluid. Bone marrow is starting to make blood cells, and arm and leg movements are becoming smoother and more frequent. About the size of a carrot.

What an ultrasound shows at 21 weeks

If you haven't had your anatomy scan yet, 21 weeks is still inside the usual window of 18 to 22 weeks. In England, most are done by the end of week 21, with a second try before 23 weeks if the pictures aren't clear. Many people had theirs a week or two ago, so for them this is a week without a scan.

A 21-week scan shows a baby whose kicks and arm movements are now better coordinated. By around this time the baby can swallow amniotic fluid. The scan still checks the spine, heart and limbs, and measures how the baby is growing.

In England, routine care includes at least two scans: one at 11 to 14 weeks and one at 18 to 21 weeks. After that, growth is usually tracked by measuring your bump at checkups rather than by scans. You may be offered extra scans if the placenta was lying low (often rechecked at around 32 weeks), if you're carrying twins, or if you have certain health conditions.

Your body at 21 weeks

Stronger kicks and rolls
Stretch marks may appear on the belly, breasts, or thighs
Oily skin or breakouts
Increased appetite

Your belly at 21 weeks

From about 20 weeks, many providers measure your bump with a tape, starting at your pubic bone and ending at the top of your uterus. This is called fundal height. At 21 weeks it is usually about 21 cm, give or take 2 cm. A number outside that range can have simple causes, such as twins, fibroids, the way the baby is lying, your build, or the amount of fluid around the baby. Ask your provider what your number means for you.

As your bump grows, your centre of gravity shifts and your joints get looser, so you may feel less steady and be more likely to trip or fall. Take care on stairs and wet floors, and wear comfortable, flat shoes. Stretch marks may also appear now on your belly, breasts, bottom or thighs.

Tips for week 21

Moisturise skin, though stretch marks are partly down to genetics
Invite your partner to feel the baby move
Keep meals balanced as appetite grows

21 Weeks Pregnant: your questions

What trimester is 21 weeks?: Week 21 is in the second trimester, which runs from week 13 to week 27 (NHS). It is week 9 of 15 in this trimester, and the third trimester starts at week 28.
How many months is 21 weeks pregnant?: 21 weeks pregnant puts you in month 5 of pregnancy. Month 5 covers weeks 18 to 22. Providers count in weeks; months are approximate.
How big is the baby at 21 weeks?: At 21 weeks, the baby is about the size of a carrot, roughly 26.7 cm long and around 360 g. That is an average; healthy babies vary.
Is my baby fully formed at 21 weeks?: The organs, limbs, bones and muscles have all been there since about 12 weeks, but many are still maturing. The lungs have the furthest to go. They keep developing for many more weeks, and even at around 24 to 26 weeks they are not ready to work well outside the womb. From about 23 weeks, the baby also starts to store fat, which fills out the wrinkled skin. So the weeks ahead are mostly about growth and maturing organs rather than new parts.
Is it rare to miscarry at 21 weeks?: Yes. By 21 weeks, the chance of losing the pregnancy is low. US doctors call a loss from 20 weeks onward a stillbirth, and it affects roughly 1 birth in 175. In the UK the dividing line is 24 weeks, so British sites may still use the word miscarriage at this stage. Warning signs that need a same-day call include vaginal bleeding, a trickle or gush of fluid, period-like pains that keep coming back, or your baby moving less than usual.
Are there symptoms of a boy at 21 weeks pregnant?: No symptom tells you the sex. Carrying high or low, skin breakouts, cravings and a fast or slow heart rate are all linked to boys or girls in old tales, but none of them is reliable. By 21 weeks, many people have already had the anatomy scan, and it often shows the sex to parents who want to know. If it wasn't clear at your scan, that is common: it depends on how the baby was lying at the time.
Is cramping normal at 21 weeks pregnant?: Some aching is common as the uterus grows and the ligaments around it stretch. Constipation and gas can also cause crampy pain. Other signs need a call straight away: regular tightenings, period-type pains, backache that is not usual for you, or a gush or trickle of fluid from the vagina. Before 37 weeks, these can be signs of early labour. Contact your provider or maternity unit rather than waiting to see if they pass.

Useful at week 21

Fetal viability — what viability means, and why every extra week counts
Pregnancy weeks to months — 21 weeks is still month 5 — the full chart
Pregnancy weight gain calculator — track your gain as your appetite grows
Swimming in pregnancy — low-impact exercise as your balance changes
Baby gender predictor — a just-for-fun guess if the scan didn't show it

← 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.