18 weeks pregnant

How big is your baby at 18 weeks?

About the size of a bell pepper — around 14.2 cm (5.6 in) long head to bottom, according to the NHS, weighing roughly 222 g (7.8 oz).

Month 5 starts this week, and so does the window for the most significant scan of the pregnancy.

A note on the numbers: up to week 19 the NHS measures crown to rump — head to bottom, because the legs are curled. At week 20 it switches to head to heel, which is why the length appears to leap 10 cm in a week. Weights here are the median from the WHO fetal growth charts, which begin at 14 weeks; half of babies weigh more, half less.

What's developing this week

Hearing, feeling, swallowing and sucking reflexes are all developing this week, and your baby is doing a great deal of wriggling, with plenty of arm and leg movement.

Those things are connected. The reflexes being rehearsed now — swallow, suck, startle — are the ones needed to feed and breathe after birth, months before they will be used. The digestive system is working, and ACOG notes that by this stage the ears, nose and lips are recognisable on an ultrasound — which is exactly why the anomaly scan happens in the next three weeks rather than earlier.

What you might feel

You may be starting to feel clumsier as your belly grows, and your breasts may have gone up a size, particularly in a first pregnancy.

Your blood pressure is probably a little lower than it was, which is normal in mid-pregnancy. The NHS gives the practical consequence: do not leap up from the sofa, because it can make you dizzy.

You may notice a dark line down the middle of your stomach, the linea nigra. It is ordinary skin pigmentation and usually fades a few months after birth.

And you may start to feel movement — a bubbling or fluttering rather than anything you would call a kick. The NHS says movements are first felt between 16 and 24 weeks, and after 20 weeks with a first baby. Feeling nothing at 18 weeks is entirely ordinary.

Is 18 weeks pregnant 4 months or 5 months?

Week 18 is the first week of month 5.

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 week the anomaly scan becomes possible. NICE says it should take place between 18 weeks and 0 days and 20 weeks and 6 days; the NHS describes it as usually done between 18 and 21 weeks, and up to 23 weeks in some cases.

Also called the 20-week screening scan, the mid-pregnancy scan or the morphology scan, it looks at your baby in detail for anything unusual about their development. It checks for 11 specific conditions, and also checks growth, where your placenta is lying and the blood flow in your womb. The NHS is straightforward that it can pick up a range of conditions but not all of them.

It will not hurt you or your baby, though it can feel uncomfortable, because the sonographer may need to press firmly for a clear view. There is no known risk to either of you. In the US, ACOG describes the same examination as the standard ultrasound, usually performed at 18 to 22 weeks.

Finding out the sex

The sonographer may be able to tell you, but not everyone wants to know and it is not always hospital policy to say. If you do not want to know, say so at the start of the appointment.

Free prescriptions and dental care

NHS prescriptions and dental treatment are free during pregnancy and for a year afterwards. You need a Maternity Exemption Certificate; ask your midwife, GP or health visitor for form FW8. People forget this one and pay for a year of prescriptions they did not owe.

Is it safe to fly at 18 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.

Eighteen weeks is about as comfortable as flying in pregnancy gets. The only complication is the scan: if a trip would push it past 21 weeks, move the trip.

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
• If movements have started and they slow, weaken or change, call immediately — not in the morning. Having felt nothing yet at 18 weeks is ordinary.

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