21 weeks pregnant

How big is your baby at 21 weeks?

About the size of a carrot — around 26.7 cm (10.5 in) long head to heel, according to the NHS, weighing roughly 398 g (14 oz).

This is the week your baby overtakes the placenta in weight. Until now the organ feeding them has been the heavier of the two.

A note on the numbers: from week 20 the NHS measures head to heel, not head to bottom. That is why the length jumps from 15.3 cm at 19 weeks to 25.6 cm at 20 — no baby grew 10 cm in a week, the tape measure moved. Weights here are the WHO fetal growth chart median; half of babies weigh more, half less.

What's developing this week

Your baby is developing lanugo, a fine downy hair whose purpose is probably temperature regulation. It usually disappears before birth. Head hair and eyebrows are growing too.

Hearing is now functional enough to pick up noises and voices from outside the womb. The NHS puts it nicely: if you sing to your bump, no matter how badly, they will be your biggest fan.

Sleep patterns are establishing — genuine cycles that will not necessarily match yours. ACOG describes weeks 21 to 24 as when kicks get stronger, fat starts forming under the skin, and the ridges that become fingerprints and footprints form.

What you might feel

You may feel unsteady. Your centre of gravity has shifted and your joints are looser — a genuine change in your balance rather than clumsiness. The NHS gives the reassurance and the instruction together: if you have a fall, try not to panic because your baby is well protected, but tell your midwife as soon as possible.

Sleep gets harder from here, partly because your baby may be wide awake exactly when you want to be asleep. Naps are a strategy, not a failure.

Piles appear on the NHS list this week — swellings around the bottom causing itching, soreness or pain when passing a stool. They are common and treatable, as is the backache that also starts now.

Is 21 weeks pregnant 4 months or 5 months?

Week 21 is in month 5, its fourth week.

There is no official weeks-to-months map. A calendar month averages about 4.3 weeks, not 4, so 40 weeks is a little over nine months — and two apps can disagree about which month you are in. The most widely used mapping:

• Month 1 — weeks 1 to 4
• Month 2 — weeks 5 to 8
• Month 3 — weeks 9 to 13
• Month 4 — weeks 14 to 17
• Month 5 — weeks 18 to 22
• Month 6 — weeks 23 to 27
• Month 7 — weeks 28 to 31
• Month 8 — weeks 32 to 35
• Month 9 — weeks 36 to 40

Your maternity team will not use months. Everything is booked by week and day — "19 weeks and 3 days" — because a few days change what is offered. The anomaly scan window is 18+0 to 20+6 weeks, not "about five months".

What's happening at your appointments around now

In the UK there is usually a long, quiet gap here. If the anomaly scan is done, the next routine appointment for a first baby is at 25 weeks; if you have given birth before, the next is at 28 weeks.

Two loose ends. If your anomaly scan has not happened, or a repeat was needed, the backstop is 23 weeks. And if you have not had the whooping cough vaccine, it can be given any time from 16 to 32 weeks.

A quiet gap is not a rule about when you may make contact. Reduced movements, bleeding and blood pressure worries are all reasons to ring between appointments.

Getting to know your baby's movements

By 21 weeks most people have felt something, though not everyone, and a first pregnancy often runs later. The NHS range is 16 to 24 weeks, after 20 weeks with a first baby.

What matters now is not whether you have felt movement but what you do once you have. There is no set number and no need to count kicks — both the NHS and Tommy's are explicit. What you are learning is your own baby's pattern, day to day.

Two things make movements harder to feel, and neither means anything is wrong: an anterior placenta cushions the kicks, and you notice far less when busy and upright than lying still.

If movements reduce, weaken or change from what has become usual, call your maternity unit immediately, not in the morning. Tommy's is direct about why: reduced movements do not cause stillbirth, but they are one of the signs something may be wrong, and in around half of stillbirths the mother had noticed movements had lessened.

Is it safe to fly at 21 weeks pregnant?

Yes, in a straightforward pregnancy — and you are inside the window everyone recommends. The RCOG is unambiguous: occasional air travel is not harmful in an uncomplicated pregnancy. There is no evidence that cabin pressure or humidity harm you or the baby, and none that flying causes miscarriage, early labour or your waters to break. ACOG names 14 to 28 weeks as the best time to travel; the NHS names mid-pregnancy.

Nothing about week 21 changes the advice. If your anomaly scan has been done and was normal, this is as straightforward as flying in pregnancy gets.

The risk that is real: blood clots

Pregnancy raises deep vein thrombosis (DVT) risk, and that does not ease in the second trimester. ACOG puts it plainly: any travel of four hours or more doubles DVT risk, and pregnancy adds to that. Under four hours the RCOG says you are unlikely to need special measures. Over four hours:

• Loose clothing, comfortable shoes, an aisle seat, regular walks about the cabin
• In-seat exercises roughly every 30 minutes
• Water steadily; cut down on caffeine
• Graduated compression stockings — not ordinary flight socks, and sized for you by a midwife or doctor

With other clot risk factors you may be advised to have heparin injections around the flight.

Practical points

• Airline cut-offs are usually 37 weeks for one baby, 32 for twins, so nothing restricts you yet — but from 28 weeks most airlines want a letter from your midwife or doctor, which the NHS warns can cost money and take weeks.
• Check what maternity and emergency care exists at your destination, and tell your insurer you are pregnant so that cover includes pregnancy-related care.
• Some travel vaccines and anti-malarial tablets are unsuitable in pregnancy; travel to Zika areas is not recommended.

When to call your midwife or doctor

The second trimester is the quietest stretch of pregnancy for most people, which is exactly why it is worth knowing what is not ordinary. Maternity units are staffed around the clock.

Get emergency help now

Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand) or go to an emergency department if you have:

• Heavy vaginal bleeding, or any bleeding with severe abdominal pain
• Abdominal pain you cannot concentrate through
• Fainting or collapse, chest pain, or sudden breathlessness
• A severe headache painkillers do not touch, blurred vision or flashing lights, pain below your ribs, or sudden swelling of your face, hands or feet — the NHS lists these as pre-eclampsia symptoms, most likely from 20 weeks, needing immediate assessment

Call your midwife or maternity unit today, whatever the hour

• Any vaginal bleeding, however light
• A gush or a steady trickle of fluid from your vagina
• Regular tightenings, or persistent low backache and pelvic pressure
• Discharge that changes colour or texture, smells strongly, or brings itching or soreness
• Itching without a rash, especially at night or on your palms and soles — the NHS asks for this to be checked, because it can be intrahepatic cholestasis of pregnancy
• A temperature, feeling generally unwell, or burning when you pee
• Any reduction, weakening or change in your baby's usual pattern of movements — the NHS says call immediately, even at night, and not to use a home doppler, because hearing a heartbeat does not mean your baby is well
• If you have felt no movement at all by 24 weeks, tell your midwife

You do not need to be certain something is wrong. That is what the number is for.