12 weeks pregnant

How big is your baby at 12 weeks?

About the size of a plum — 5.4 cm (2.1 in) long from head to bottom, according to the NHS.

A note on the numbers: in the first trimester babies are measured crown to rump — head to bottom, not head to heel, because the legs are curled. Weight is not reliably estimated this early, so any site quoting grams or ounces before about 14 weeks is guessing.

What's developing this week

The internal organs and muscles have grown substantially, and the heartbeat can now be picked up on an ultrasound scan. The skeleton, which has been cartilage and tissue, is hardening into bone. The sex organs have formed, though most scans cannot determine sex until later. There is a good chance the placenta is now feeding the baby, having taken over from the yolk sac — and once that handover completes hormone levels settle, which is a large part of why so many people feel better from around now.

The 12-week scan

You will be offered your dating scan any time now — the NHS window is around 10 to 14 weeks. It confirms how many weeks pregnant you are and gives an estimated due date, checks whether there is more than one baby, checks the pregnancy is developing in the right place, and looks at the baby's development, including conditions such as spina bifida. If you have agreed to Down's syndrome screening, the combined test is usually done at the same appointment. Your due date may move: the scan measurement is more accurate than a date calculated from your last period.

What you might feel

Many people turn a corner around week 12. Sickness subsides, appetite returns, exhaustion lifts — though not for everyone, and not on a schedule. Symptoms the NHS still lists include an aching stomach, nausea, mood swings, a metallic taste, sore breasts, indigestion, headaches, dizziness, a heightened sense of smell, discharge, cramping, darkened patches on the face, greasier skin and bloating.

On weight: the NHS says most people gain between 10 kg and 12.5 kg (22 lb to 26 lb) across the pregnancy, usually after week 20, and some gain nothing at first. You do not need extra calories until week 28. Folic acid is advised through the first 12 weeks; after that it is no longer required unless your doctor says otherwise.

Is 12 weeks pregnant 3 months?

Week 12 is in month 3. You are essentially three months pregnant — and in the NHS week-by-week guide, week 12 is the last week filed under the first trimester.

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 — "11 weeks and 3 days" — because a few days change what is offered.

Trimester boundaries vary. The NHS guide places weeks 1 to 12 in the first trimester and starts the second at week 13; many clinicians run the first trimester to the end of week 13. Neither changes your care.

Miscarriage risk at 12 weeks

Week 12 is the point most people have been counting towards, and the evidence supports it. Tommy's states that a lot of research shows the risk of miscarriage goes down dramatically after 12 weeks, that most miscarriages happen in the first 12 weeks, and that early miscarriage is estimated at 10 to 20 in every 100 pregnancies. Second-trimester loss — across the whole span from 12 to 24 weeks — is estimated at 3 to 4 in every 100.

You will find week-by-week miscarriage percentage tables all over the internet. Tommy's, which funds the UK's national miscarriage research centre, says openly that beyond the well-evidenced drop after 12 weeks, reliable week-by-week risk research does not really exist. We give you what is evidenced instead.

If you are waiting on a scan this week, the wait is the hard part, and there is nothing you can do in the meantime that changes the outcome. That is worth saying plainly, because a great deal of the anxiety of week 12 is spent looking for something to do.

The most common cause of early miscarriage is a chromosomal problem that happens by chance. Not lifting something, not a glass of wine before you knew, not stress or exercise. Tommy's states it directly: miscarriages very rarely happen because of something you did or did not do.

Is it safe to fly at 12 weeks pregnant?

Yes, in a straightforward pregnancy. 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 no evidence that flying causes miscarriage, early labour or your waters to break.

Week 12 is where flying becomes straightforward for most people: sickness is often easing and the steepest part of the miscarriage curve is behind you. The one thing to protect is your scan — the NHS window is 10 to 14 weeks and the combined screening test must happen inside it. Book around the scan, not over it.

The risk that is real: blood clots

Pregnancy raises deep vein thrombosis (DVT) risk from the earliest weeks. ACOG puts it plainly: any travel of four hours or more — car, train, bus or plane — 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

• No airline restricts travel this early — cut-offs sit around 36 to 37 weeks for one baby, 32 for twins.
• Check what maternity and emergency care exists at your destination.
• Tell your insurer you are pregnant; cover should include pregnancy-related care.
• Some travel vaccines and anti-malarial tablets are unsuitable in pregnancy; travel to Zika areas is not recommended.

The NHS names mid-pregnancy as the easiest time to travel; ACOG names 14 to 28 weeks.

When to call your midwife or doctor

Early pregnancy is full of sensations that turn out to be nothing. These are the ones worth a phone call.

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 bleeding with any of the following, which the NHS lists as needing immediate assessment:

• Severe abdominal pain you cannot concentrate through
• Pain in the tip of your shoulder
• Feeling sick, faint or dizzy, or losing consciousness
• Heavy bleeding that soaks through a pad quickly

Sudden sharp abdominal pain with dizziness, faintness or looking very pale can indicate a ruptured ectopic pregnancy, needing same-day surgery. Around 1 in every 90 UK pregnancies is ectopic, and the NHS notes symptoms usually appear between weeks 4 and 12 — where you are now.

Call your midwife, early pregnancy unit or health line today

• Light bleeding or spotting, with mild or no pain
• One-sided pain low in your abdomen or pelvis
• Brown, watery discharge that is new for you
• Pain when you pee or open your bowels
• You cannot keep food or fluid down for 24 hours, your urine is very dark or absent for 8 hours, you feel severely weak or faint, or you are vomiting blood or losing weight — the NHS triggers for pregnancy-sickness help, which is treatable

You do not need a booking appointment first, and you do not need to be certain something is wrong.