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21 Weeks Pregnant: Lanugo Forms and Baby May Suck a Thumb

Medically reviewed by

Sarah Riffle, RN Jul 30, 2026

Line illustration of a carrot: at 21 weeks pregnant your baby is about the size of a carrot, roughly 16 to 19cm crown to rump

Line drawing of a 21-week foetus sucking its thumb, the sucking reflex developing

Line drawing of a woman's torso at 21 weeks pregnant, showing the uterus risen past the navel

Your baby is the size of a

Carrot

Between ~320 grams and 460 grams

~16–19 cm / ~6.3–7.5 in

Key Takeaways

At 21 weeks pregnant, Mayo Clinic says your baby is completely covered with fine, downy lanugo hair, which helps hold the vernix caseosa on the skin. The sucking reflex is developing too, so your baby may be able to suck a thumb.

Mayo Clinic gives no single length or weight for week 21. Between its week-20 and week-22 figures, your baby sits roughly between 160mm and 190mm from crown to rump, and between about 320 grams and 460 grams.

Movement is becoming more regular. The Society of Obstetricians and Gynaecologists of Canada (SOGC) says by 24 weeks almost all women feel their baby's movements in a predictable way, and calls this one of the strongest indicators of wellbeing.

Your Baby at 21 Weeks: Development & Growth

At 21 weeks pregnant, your baby is "completely covered with a fine, downy hair called lanugo," according to Mayo Clinic, and the sucking reflex is developing so your baby "may be able to suck a thumb." Mayo Clinic does not publish a length or weight for week 21; based on its neighbouring weeks, your baby is roughly 160 to 190 millimetres crown to rump and about 320 to 460 grams.

The skin gets its covering this week. Mayo Clinic explains that at 21 weeks "your baby is completely covered with a fine, downy hair called lanugo," and that "the lanugo helps hold the vernix caseosa on the skin." That vernix is the greasy, cheeselike coating that protects your baby's skin in the amniotic fluid.

Your baby is also learning to suck. Mayo Clinic notes that at 21 weeks "the sucking reflex also is developing, so your baby may be able to suck a thumb." It is early practice for one of the first things a newborn needs to do well.

On size, it is worth being straight with you. Mayo Clinic gives no length or weight at week 21, so any single number you see elsewhere is a guess. What Mayo Clinic does give is the weeks on either side.

At week 20, Mayo Clinic puts your baby at "about 6 1/3 inches (160 millimeters) long from crown to rump" weighing "about 11 ounces (320 grams)." By week 22, that becomes "about 7 1/2 inches (190 millimeters) long from crown to rump" and "about 1 pound (460 grams)." So this week sits somewhere between — around 160 to 190 millimetres, and 320 to 460 grams.

Length is still measured crown to rump at this stage, because your baby's legs stay curled. The full head-to-heel measurement comes later.

Your Body at 21 Weeks: Symptoms & Changes

At 21 weeks pregnant, many mothers are in the more comfortable middle stretch of the second trimester, though the ordinary discomforts of pregnancy can still come and go. SOGC lists tender breasts, constipation, backaches, headaches, mood swings and leg cramps among them. This is also a week when movement often becomes more of a pattern. Every pregnancy is different.

Movement is the theme of these weeks. SOGC explains that "some women feel movement as early as 13-16 weeks from the start of their last period," while "first-time" mothers "may not feel movement until 18-20 weeks." If you are only now feeling clear movement, or it is settling into a rhythm, that is on time.

What you feel is meaningful. SOGC states plainly that "your perception of your baby's movements is one of the strongest indicators of your baby's wellbeing." SOGC adds that "after a while, you will be able to feel a pattern in the movements" — and that pattern is worth getting to know.

Everyday symptoms can still visit. SOGC lists tender or swollen breasts, "constipation, gas or bloating," backaches and headaches, mood swings, and leg cramps among the common discomforts of pregnancy. Any of these can be part of your week, and SOGC reminds readers that "every pregnant woman is different."

Your body is carrying more than a baby. SOGC explains that weight gain "isn't just the baby" — "your placenta, increased blood volume, larger breasts, and fat stores to support breastfeeding, also contribute." A rounder middle is your body doing exactly what it should.

One note on mood. SOGC says most mood swings "are not usually severe," but also that "depression or disruptive mood swings are not normal and it is important to seek help for these more serious concerns." That line is worth remembering, for you or someone near you.

What to Do at 21 Weeks Pregnant

NUTRITION AT 21 WEEKS PREGNANT

Keep the second-trimester increase modest. SOGC states: "In the second trimester you need about 340 extra calories per day," and notes this "generally equates to 2 or 3 additionally servings from any of Canada’s Food Guide’s food groups" — for example "1 piece of toast and a cup of milk." Quality matters more than quantity.
Stay on top of iron. SOGC advises increasing "your daily iron intake to 27mg daily during the final six+ months of pregnancy to support an increase in red blood cells and fetal tissues," adding that "like most women, you may need a good supplement to meet this need."
Include omega-3s for your baby’s development. SOGC notes omega-3 fatty acids are "needed for fetal development, particularly eye and brain development," that food sources are recommended over supplements, and that DHA from fish is "the best source" — "Aim for 1.4g daily."

WHAT SUPPLEMENTS TO TAKE AT 21 WEEKS PREGNANT

Keep taking 400mcg of folic acid daily. The Public Health Agency of Canada states that "a daily multivitamin with 400 mcg (0.4 mg) of folic acid is recommended for anyone who could become pregnant," and advises: "Continue taking folic acid throughout your pregnancy and while breastfeeding."
Don’t raise your folic acid dose on your own. The Public Health Agency of Canada advises: "You should not increase your dose of folic acid beyond 1 mg per day without talking to your health care provider." A higher dose is a conversation, not a decision for the supplement aisle.
Check that your prenatal covers iron and choline. SOGC notes that, like most women, "you may need a good supplement" to reach 27mg of iron a day, and that "choline intake above 450mg a day is linked to improved fetal stress responses and a reduced risk of neural tube defects" — a nutrient it says "may not be found in your prenatal daily vitamin."

LIFESTYLE TIPS AT 21 WEEKS PREGNANT

Keep moving — aim for at least 150 minutes a week. SOGC advises that "pregnant women should accumulate at least 150 minutes of moderate intensity physical activity each week," spread across "at least 3 days a week, and up to 7 days a week." Walking, swimming and stationary cycling are all good options.
Build in pelvic floor exercises. SOGC notes that "pelvic floor muscle training (e.g., Kegel exercises) can be performed every day to reduce the risk of urinary incontinence." Easy to fold into a daily routine.
Keep caffeine to 300mg a day. Health Canada lists a recommended maximum daily caffeine intake of "300 mg" for "people who are pregnant." For reference, Health Canada puts one 8 oz (237 ml) cup of brewed coffee at "135 mg" — so roughly two cups is the ceiling, and that total includes tea, cola and chocolate.
Start noticing your baby’s pattern. SOGC says "after a while, you will be able to feel a pattern in the movements," and that your perception of movement "is one of the strongest indicators of your baby’s wellbeing." Getting to know that rhythm now makes it easier to notice a change later.

When to Contact Your Doctor or Midwife

Most of week 21 is steady growth, not alarms. But some symptoms should always be checked. Contact your doctor, midwife or other health care provider if you experience:

Any vaginal bleeding. SOGC advises: "It's important for you to take any vaginal bleeding seriously. Contact your health care provider as soon as you notice any bleeding." SOGC notes that about one-third of pregnancies have some bleeding before the 20th week, and about half of these continue without further issues — but it should always be assessed.
Signs of infection, or heavy bleeding. SOGC advises that if you have "signs of infection like fever or heavy bleeding, you should see your care provider right away." If bleeding is heavy or you feel very unwell, seek emergency medical care immediately.
Any change or concern about your baby's movements. SOGC advises that "if you ever have concerns regarding your baby's movement pattern, you should have the baby assessed as soon as possible," and that mothers should always trust their intuition. If you think your baby is moving less, SOGC says you can do a kick count at any time — count movements for two hours, and if you don't feel 6 movements in 2 hours, contact your health care provider as soon as possible.
Persistent low mood or disruptive mood swings. SOGC advises that "depression or disruptive mood swings are not normal and it is important to seek help for these more serious concerns."
Severe abdominal pain, a severe or persistent headache, or any symptom that frightens you. Sudden, severe pain warrants urgent assessment — seek emergency medical care immediately if it is intense or you feel faint. For anything that simply worries you, your health care provider is there for exactly that.

Frequently Asked Questions

How big is my baby at 21 weeks pregnant?

Mayo Clinic does not publish a length or weight for week 21, so any single figure is an estimate. Based on Mayo Clinic’s neighbouring weeks, your baby is roughly 160 to 190 millimetres from crown to rump and about 320 to 460 grams. Mayo Clinic gives week 20 as "about 6 1/3 inches (160 millimeters)" and "about 11 ounces (320 grams)," and week 22 as "about 7 1/2 inches (190 millimeters)" and "about 1 pound (460 grams)." Length is measured crown to rump because the legs are still curled.

What is lanugo, and why is my baby covered in it?

Lanugo is fine, downy body hair. Mayo Clinic explains that at 21 weeks "your baby is completely covered with a fine, downy hair called lanugo," and that "the lanugo helps hold the vernix caseosa on the skin." The vernix is the waxy coating that protects your baby’s delicate skin in the amniotic fluid. Most of the lanugo sheds before or shortly after birth.

Can my baby suck a thumb at 21 weeks?

Possibly. Mayo Clinic notes that at 21 weeks "the sucking reflex also is developing, so your baby may be able to suck a thumb." It is early practice for the sucking your baby will rely on to feed after birth.

Should I feel my baby move at 21 weeks pregnant?

Often, yes — and it is becoming more regular. SOGC notes that "some women feel movement as early as 13-16 weeks," while those in a first pregnancy "may not feel movement until 18-20 weeks," and that "by 24 weeks, almost all women will feel their baby’s movements in a predictable way." If you ever have concerns about your baby’s movement pattern, SOGC advises having the baby assessed as soon as possible.

How much caffeine is safe at 21 weeks pregnant?

Health Canada lists a recommended maximum daily caffeine intake of "300 mg" for "people who are pregnant." Health Canada puts one 8 oz (237 ml) cup of brewed coffee at "135 mg," so roughly two cups a day is the ceiling — and that total should include tea, cola and chocolate, which also contain caffeine.

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Sources & References

Public Health Agency of Canada — Folic acid, healthy pregnancy and neural tube defect prevention
Health Canada — Caffeine in Foods (recommended maximum daily intake)
SOGC — Fetal movement and kick counts
SOGC — Healthy eating
SOGC — Exercise during pregnancy
SOGC — Symptoms of pregnancy
SOGC — Weight gain during pregnancy
SOGC — Pregnancy Loss
Mayo Clinic — Fetal development: The 2nd trimester (Week 20, Week 21, Week 22, Week 23)

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