13 weeks pregnant

How big is your baby at 13 weeks?

About the size of a peach — around 7.4 cm (2.9 in) long, according to the NHS. Roughly 37 times the length it was at 4 weeks.

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 ovaries or testes are fully developed inside, and the final external details are being finished.

Movement changes character this week. It has been jerky and random; now it starts to look deliberate. Some babies suck their thumb at this stage, which is not decorative — it develops the sucking reflex they will need to feed. You will probably not feel any movement until around week 17, and often later in a first pregnancy.

What you might feel

If you have had morning sickness, the NHS says you will probably start to feel better around 13 or 14 weeks. Needing to pee constantly often eases too, as the womb moves up and away from your bladder. A small bump may become visible as the womb grows upwards and outwards.

Newer second-trimester symptoms appear on the NHS list from now: sensitive or bleeding gums, nosebleeds, round ligament pain (a sharp pull low down when you move suddenly), constipation, heartburn, bloating, and swelling in the hands and feet. There is also more blood flowing through the pelvic area, and some people find that increases their sex drive.

Two practical things this week: tell your employer if you have not, which triggers your maternity rights, the right to attend antenatal appointments in paid working time, and a workplace risk assessment. And start pelvic floor exercises.

Is 13 weeks pregnant 3 months or 4 months?

Week 13 is the last week of month 3. Month 4 begins at week 14.

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.

Week 13 is also where sources disagree about trimesters. The NHS week-by-week guide files week 13 under the second trimester, so by that reckoning the first trimester is behind you; many clinicians count the first trimester as running to the end of week 13. Nothing about your care changes either way — but it explains why one app congratulates you this week and another waits until next.

Miscarriage risk at 13 weeks

The steep part of the curve is behind you. Tommy's is clear that 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. From here the relevant figure is second-trimester loss, also called late miscarriage, estimated at 3 to 4 in every 100 pregnancies — and that number covers the whole span from 12 to 24 weeks, not this week.

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.

The NHS defines miscarriage as the loss of a pregnancy before 24 weeks. The most common symptom is vaginal bleeding, and the NHS is explicit that any bleeding in pregnancy should be checked.

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.

Many people choose this week to tell family and friends. There is no medically correct time to do that and no obligation to wait — some tell early precisely so they would have support if something went wrong. Either choice is reasonable.

Is it safe to fly at 13 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 13 is effectively the start of the window everyone recommends. ACOG names 14 to 28 weeks as the best time to travel — energy back, morning sickness improved or gone, still able to get around easily. The NHS says much the same, naming mid-pregnancy, roughly 4 to 6 months.

Check your dating scan has happened before you go: the NHS window is 10 to 14 weeks and the combined screening test cannot be done outside it. You may be advised not to fly if you have severe anaemia, sickle cell disease with a recent crisis, recent significant vaginal bleeding, a serious heart or lung condition, or an increased chance of preterm labour.

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.

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.