At 21 weeks pregnant you are about 5 months along, in the second trimester, with about 19 weeks to go until your estimated due date.
At 21 weeks pregnant you are just past the halfway mark. Many people feel flutters or kicks, the anatomy ultrasound is now or just behind you, and backaches and night leg cramps can show up.
Every clinical detail below was read in October 2026 on the primary sources named in the text. Where they disagree, we print both.
Key Takeaways
21 weeks pregnant is about 5 months, or 19 weeks after conception (Mayo Clinic), with about 19 weeks to go.
Mayo Clinic lists about 6 1/3 inches crown to rump at week 20 and about 7 1/2 inches and 1 pound at week 22.
UPMC says most people start feeling movement around 20 weeks, though some feel it as early as 16.
The anatomy ultrasound is done around 18 to 22 weeks (Cleveland Clinic), and glucose screening follows at 24 to 28 weeks (UPMC).
Sleep on your side, and call right away for bleeding, leaking fluid, severe belly pain, regular contractions or less movement.
Table of Contents
21 Weeks Pregnant at a Glance
Quick Answer
At 21 weeks pregnant you are about 5 months along, in the second trimester, with about 19 weeks to go. Mayo Clinic gives no week 21 size, but lists about 6 1/3 inches crown to rump at week 20 and about 7 1/2 inches at week 22. The anatomy scan window is 18 to 22 weeks (Cleveland Clinic).
21 weeks pregnant
What to know
Trimester
Second, on both definitions we checked: ACOG via UPMC (14 weeks 0 days through 27 weeks 6 days) and Cleveland Clinic (around week 13 through week 27).
Month
About month 5, near its end, counting 4 weeks and a few days per month. Months are a convention, not a medical unit.
Weeks to go
About 19 (40 minus 21, counted from the first day of your last menstrual period).
Baby’s size
No week 21 figure found. Mayo Clinic: about 6 1/3 inches and 11 ounces at week 20; about 7 1/2 inches and 1 pound at week 22 (crown to rump).
Common symptoms
Backache, leg cramps, heartburn, stretch marks and itchy skin, varicose or spider veins.
This week’s care focus
Finishing the anatomy ultrasound (18 to 22 weeks) and noticing your baby’s movements.
21 weeks pregnant: quick facts with sources.
How the weeks are counted. Cleveland Clinic explains that pregnancy is counted from the first day of your last menstrual period (LMP), about two weeks ahead of when conception actually occurs. That is why Mayo Clinic describes week 21 as “19 weeks after conception.” Cleveland Clinic also notes that an ultrasound can change your due date, usually by a few days; if yours was adjusted, go by the new dates.
21 weeks pregnant in months. Twenty-one weeks is a little under five calendar months. Cleveland Clinic’s guide counts four-week months (month 6 is weeks 21 through 24), so you may also see week 21 called month 6. Providers count in weeks for this reason.
Your Baby’s Development at 21 Weeks
These are typical changes, not a description of your own baby.
Source and timing
What it says is happening
Mayo Clinic, week 21 (19 weeks after conception)
Your baby is completely covered with lanugo, a fine, downy hair. The sucking reflex is developing, so your baby may be able to suck a thumb.
Cleveland Clinic, week 21
Limb movements are coordinated and frequent. The fetus has bone marrow that helps it produce blood cells.
Mayo Clinic, week 20
Your baby is regularly sleeping and waking and might be woken by noises or by your movements.
Mayo Clinic, week 22 (coming up)
Eyebrows and hair are visible. In boys, the testes have begun to move down into the scrotum.
Fetal development around week 21, by source.
Lanugo and vernix. Mayo Clinic describes lanugo covering the body by week 21 and vernix starting to cover the skin at week 19. Our vernix guide explains this coating.
Boy or girl? Cleveland Clinic says the sex can often be seen on the anatomy ultrasound, depending on position, and you can ask not to be told.
How Big Is Your Baby at 21 Weeks?
We found no week 21 measurement on the primary sources we read, so here are the nearest weeks exactly as reported.
Source
Week
Length
Weight
Mayo Clinic
20
About 6 1/3 inches (160 mm), crown to rump
About 11 ounces (320 g)
Mayo Clinic
22
About 7 1/2 inches (190 mm), crown to rump
About 1 pound (460 g)
Cleveland Clinic
End of month 5 (week 20)
About 9 to 10 inches
About 1 pound
Cleveland Clinic
End of month 6 (week 24)
About 12 inches
About 2 pounds
Baby size near 21 weeks. Sources differ, so each is printed as reported.
Why the numbers look so different. Mayo Clinic measures crown to rump (head to tailbone, legs left out). Cleveland Clinic does not say how it measures, and we have not converted either set.
Is there a fruit comparison for 21 weeks? Not on the primary sources we checked, so we have not printed one.
21 Weeks Pregnant Symptoms
These are the 21 weeks pregnant symptoms primary sources tie to this stage.
Symptom
What the sources say
What may help
Backache
Mayo Clinic says hormonal changes and a growing uterus can cause your back to ache. UPMC lists sore hips and back.
Low-heeled shoes with good support, and resting one foot on a stool if you must stand for a while (Mayo Clinic).
Leg cramps
Mayo Clinic says leg cramps are common as pregnancy goes on and often happen at night.
Stretch your calves before bed, stay active and drink fluids. (Mayo Clinic).
Heartburn
UPMC lists heartburn among second trimester symptoms.
Ask your provider before taking anything for it.
Stretch marks and itchy skin
Cleveland Clinic and UPMC list both. Mayo Clinic says you cannot prevent stretch marks but they mostly fade after birth.
Use sunscreen outdoors if you notice darker patches on your face (Mayo Clinic).
Varicose or spider veins
Cleveland Clinic lists varicose veins in the second trimester. Mayo Clinic describes tiny veins that can show up under the skin of the face and legs.
Mention painful or swollen veins at your next visit.
Braxton Hicks
Mayo Clinic describes a slight tightness in the belly that comes and goes, more likely in the afternoon or evening.
Drink plenty of fluids and empty your bladder often (Mayo Clinic).
Common symptoms at 21 weeks pregnant.
Other changes the sources list. Cleveland Clinic adds bleeding gums, nosebleeds or a stuffy nose, hemorrhoids, round ligament pain, and some swelling in the hands, feet and ankles. Mayo Clinic adds dizziness.
Discharge and urinary symptoms. Mayo Clinic says a clear or white discharge is typical, but to call if it smells strong, changes color or comes with pain or itching, and to call for painful or urgent urination or cloudy urine.
Tightening or contractions? Mayo Clinic says to contact your care team if contractions become regular and keep getting stronger, because that could be a sign of preterm labor.
Baby on the way? Get ahead on sleep.
Our free two-minute quiz builds a gentle, personalized sleep plan you can use from the first weeks at home.
The 21 weeks pregnant belly. Mayo Clinic says your belly grows as your uterus gets bigger to make room for the baby. Cleveland Clinic says not having a visible bump right away is normal: it takes time. Our pregnant belly by month guide shows the usual range.
Feeling your baby move. UPMC says most people start to feel fetal movement around 20 weeks, though you might feel it as early as 16 weeks. Cleveland Clinic says you will start to feel movement by 18 to 20 weeks and that movements usually become more consistent and predictable around 28 weeks. If you have not felt anything yet, mention it at your next appointment.
Breasts: Mayo Clinic says they keep growing and suggests a supportive bra with wide straps.
Appetite: UPMC says you need about 340 more calories a day in the second trimester.
Mood: Mayo Clinic says depression and anxiety are common in pregnancy and encourages you to get help.
Prenatal Care, Tests and Appointments Around Week 21
UPMC and Cleveland Clinic say second trimester visits are usually every four weeks.
Test or visit
Window
What it is
Source
Anatomy ultrasound (the 20 week scan)
Around 18 to 22 weeks
Checks the baby’s organs and body parts, the placenta and amniotic fluid. Plan for around 45 minutes.
Cleveland Clinic
Quad screen
Between 15 and 22 weeks
A blood test for the chance of certain conditions. Optional.
UPMC
Glucose screening
Between weeks 24 and 28 (coming up)
An oral glucose screening test for gestational diabetes.
UPMC
Other second trimester screening
During the second trimester
Rh factor, a complete blood count for anemia, and repeat syphilis screening.
Cleveland Clinic
Flu and COVID-19 vaccines
During respiratory virus season
Your provider will offer them, per UPMC.
UPMC
Tests, scans and vaccines around week 21, with the window each source gives.
The 21 weeks pregnant ultrasound. Week 21 sits inside the anatomy scan window. Cleveland Clinic says the scan does not diagnose conditions; if your provider has a concern, they will order more tests. If your scan has not been booked, call now, because week 22 is the end of the window Cleveland Clinic gives.
Vaccines change. The vaccine row reflects the pages we read as of October 2026; confirm with your provider.
What to Do This Week: A Simple Checklist
Confirm your anatomy scan: it happens between about 18 and 22 weeks (Cleveland Clinic).
Put glucose screening on your calendar: it comes between weeks 24 and 28 (UPMC).
Keep moving: Cleveland Clinic suggests about 20 minutes a day, such as walking or swimming, and avoiding contact sports and fall risks.
Review what to avoid: Cleveland Clinic lists undercooked meat, unpasteurized dairy, deli meats, high mercury fish, hot tubs, the litter box, smoking, alcohol and drugs.
Start the planning list: Mayo Clinic suggests looking into childbirth classes, breastfeeding information, choosing a pediatric provider, child care, and your employer’s parental leave policy.
Sleep at 21 Weeks Pregnant
Sleep at 21 weeks pregnant can be disrupted by this stage’s symptoms. Mayo Clinic says leg cramps often happen at night and Braxton Hicks tightenings are more likely in the evening.
Sleep position. Cleveland Clinic’s second trimester guidance is to sleep on your side instead of your back at night, because this is best for your circulation, and to avoid lying on your back for long periods.
Seek medical care immediately. The CDC’s Hear Her campaign says these urgent maternal warning signs can be a sign of a life-threatening condition, and to seek medical care immediately if you have any of them:
A headache that won’t go away or gets worse over time.
Dizziness or fainting.
Changes in your vision.
A fever of 100.4 F or higher.
Extreme swelling of your hands or face.
Thoughts about harming yourself or your baby.
Trouble breathing, chest pain or a fast-beating heart.
Severe nausea and throwing up.
Severe belly pain that doesn’t go away.
Your baby’s movement stopping or slowing during pregnancy.
Vaginal bleeding or fluid leaking during pregnancy.
Severe swelling, redness or pain of your leg or arm.
Overwhelming tiredness.
Also call your provider for these, which Cleveland Clinic, UPMC and Mayo Clinic list for the second trimester:
Unusual or severe cramping or abdominal pain (Cleveland Clinic).
Regular contractions, more than four in an hour, or any fluid leaking from the vagina, which could signal labor (Cleveland Clinic).
Swelling, redness and warmth in one leg (UPMC).
Pain when you urinate or a fever above 100.4 F (UPMC).
If you are unsure whether something is serious, the CDC says to talk to your health care provider. If you cannot reach your provider quickly, go to labor and delivery or the emergency room. For heavy bleeding, chest pain, severe trouble breathing, fainting or a seizure, call 911. This article is general education, not medical advice.
Frequently Asked Questions
How many months is 21 weeks pregnant?
About 5 months. Twenty-one weeks is a little under five calendar months counted from the first day of your last period, so you are near the end of month 5. Guides that use four-week months, like Cleveland Clinic’s, place week 21 at the start of month 6.
How big is my baby at 21 weeks pregnant?
We did not find a week 21 measurement on the primary sources we read. Mayo Clinic lists about 6 1/3 inches crown to rump and 11 ounces at week 20, and about 7 1/2 inches and 1 pound at week 22. Cleveland Clinic lists about 9 to 10 inches and about 1 pound at week 20, without saying how it measures.
Can you feel the baby kick at 21 weeks?
Many people can. UPMC says most people start to feel movement around 20 weeks, and some as early as 16. Cleveland Clinic says movements usually become more consistent and predictable around 28 weeks. If you have not felt anything yet, mention it to your provider.
Is 21 weeks too late for the anatomy scan?
No. Cleveland Clinic says the anatomy ultrasound, often called the 20 week scan, is done around 18 to 22 weeks of pregnancy. It checks the baby’s organs and body parts, the placenta and amniotic fluid, and takes around 45 minutes. If yours is not booked yet, call your provider soon.
What are normal pains at 21 weeks pregnant?
Mayo Clinic says backache from hormones and a growing uterus and leg cramps at night are common, and Cleveland Clinic lists round ligament pain. Mild Braxton Hicks tightenings can come and go. Severe belly pain that does not go away, or contractions that become regular and stronger, need a call right away.
How should I sleep at 21 weeks pregnant?
Cleveland Clinic advises sleeping on your side instead of your back at night in the second trimester, because it is best for your circulation, and avoiding lying on your back for long periods. Ask your provider before using any sleep aid.
Calmer days, better nights.
Betteroo builds a personalized sleep plan for your baby. Take the free two-minute quiz and have it ready before the newborn weeks.
