20 weeks pregnant

How big is your baby at 20 weeks?

About the size of a banana — around 25.6 cm (10.1 in) long head to heel, according to the NHS, weighing roughly 330 g (11.6 oz).

Halfway. Twenty weeks behind you and, if your dates hold, twenty ahead.

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 now covered in vernix, a white greasy layer thought to stop the skin drying out in the amniotic fluid. It has a second job later: the slipperiness helps babies down the birth canal.

Activity increases daily — kicking, punching, turning, often thumb-sucking, which develops the sucking reflex needed to feed. You may start to feel a bubbling or fluttering; you may also not, and at 20 weeks with a first baby that remains ordinary.

What you might feel

The scan overshadows everything else this week. The other common arrival is leg cramp: sharp pains in the calves that wake you at night. The NHS advice is to rub the muscle hard or pull your toes up towards your ankle, and that more daytime exercise may help.

Twenty weeks is also the point from which pre-eclampsia becomes what your antenatal checks are really looking for. Its early signs — raised blood pressure and protein in your urine — are ones you cannot feel. That is what the cuff and the urine pot are for.

Is 20 weeks pregnant 4 months or 5 months?

Week 20 is in month 5, its third week — and the midpoint of a 40-week pregnancy.

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

This is the big one — the 20-week screening scan, the anomaly scan, the mid-pregnancy scan, the morphology scan or the level 2 ultrasound, depending where you live.

What it checks

The NHS is specific: it looks for signs of 11 conditions and checks your baby's growth, your placenta and the blood flow in your uterus. The 11 are anencephaly, open spina bifida, cleft lip and palate, diaphragmatic hernia, gastroschisis, exomphalos, serious cardiac abnormalities, bilateral renal agenesis, severe skeletal dysplasia, Edwards' syndrome (trisomy 18) and Patau's syndrome (trisomy 13). Some show more clearly than others, and the NHS says plainly it may not find everything. This is screening, not a guarantee.

When it happens

Usually between 18 and 21 weeks; NICE specifies 18+0 to 20+6, and in some cases up to 23 weeks. If you are between 18 and 23 weeks and have not had it, tell your midwife or GP. In the US, ACOG puts the standard ultrasound at 18 to 22 weeks.

On the day

Around 30 minutes in a dimly lit room. Wear loose clothing, take out a belly piercing, bring your maternity notes, and check beforehand about a full bladder, the cost of pictures, and whether children are allowed — most hospitals do not permit them. The sonographer presses the probe over your bump, sometimes firmly, and is often silent while working through the checklist. If your baby is lying badly you may be asked to walk about and come back.

Results, the sex, and your right to decline

You are told at the end, and most people are told their baby has no signs of any of the conditions. If something is found you may be offered further tests such as amniocentesis, and specialist referral. You may be asked whether you want to know the sex; say beforehand if you would rather not. The scan is offered, not imposed, and carries no known risk.

Also this week: the whooping cough vaccine is usually offered around now, and the MAT B1 certificate needed to claim UK maternity pay can be issued from 20 weeks.

Is it safe to fly at 20 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.

One point specific to week 20: have the anomaly scan before you travel. It tells your team where your placenta is lying and whether your baby needs closer monitoring.

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.