OB Wheel

13 weeks pregnant: baby size, symptoms and what to expect

At 13 weeks pregnant you’re at the end of the first trimester by the common 0–13 week convention (some services, including the NHS, count the first trimester as ending at 12 weeks). For many people, early symptoms start to ease from about now.

TrimesterFirst
Month of pregnancyMonth 3
Baby is about the size ofa plum — about 73 g
Weeks to go (to 40)27 weeks

Your baby at 13 weeks

  • The baby is about 7 cm long from crown to rump — roughly the size of a plum or a peach — and weighs around 73 g.
  • The ovaries or testes are fully formed inside, and the external genitals are still developing.
  • Movements are becoming smoother and more deliberate. Some babies suck their thumb, practising the sucking reflex they’ll need for feeding.
  • You probably won’t feel movements for a few more weeks yet.

See how your baby grows week to week on the baby size by week chart.

Your body at 13 weeks

  • A small bump may start to show as the womb rises out of the pelvis.
  • Needing to pee often may ease as the womb moves up and away from the bladder.
  • Increased blood flow can bring nosebleeds, bleeding gums, feeling hot and thirstier than usual.
  • Round ligament pain (twinges on the sides of the bump), headaches, constipation and indigestion are common.

Appointments and things to do

  • If you haven’t had your dating scan, it’s usually done by 14 weeks.
  • This is a common time to tell your employer or others, now that the first scan has been done.
  • Keep active — the usual advice is about 150 minutes of moderate activity a week, if your pregnancy is uncomplicated.
  • Start thinking about antenatal classes.
When to get help. Contact your doctor or midwife straight away if you have vaginal bleeding, severe tummy pain, a high temperature or a burning feeling when peeing that doesn’t settle.

Working out your dates

“13 weeks pregnant” is counted from the first day of your last period, not from conception, which is about two weeks later. If you’re not sure exactly how far along you are, the gestational age calculator gives the exact weeks and days, and the OB wheel shows your due date and every milestone. For which trimester and month you’re in, see the trimester calculator and the weeks to months converter.

Frequently asked questions

How many months is 13 weeks pregnant?

13 weeks pregnant is in month 3 of pregnancy, at the end of the first trimester. Month 4 starts at around 13½ weeks.

Is 13 weeks the end of the first trimester?

By the common convention the first trimester runs to 13 weeks 6 days, so yes. Some services, including the NHS, say it ends at 12 weeks.

How big is the baby at 13 weeks?

About 7 cm from crown to rump and around 73 g — roughly the size of a plum or a peach.

When will I feel the baby move?

Usually between 16 and 24 weeks. In a first pregnancy, many people don’t notice movements until after 20 weeks.

Sources

  1. NHS — Pregnancy week by week
  2. ACOG — Methods for Estimating the Due Date (Committee Opinion 700)
  3. NHS — Your baby’s movements
  4. Robinson HP, Fleming JE. A critical evaluation of sonar “crown-rump length” measurements. 1975
  5. Hadlock FP et al. In utero analysis of fetal growth: a sonographic weight standard. Radiology 1991

Last meaningfully updated: 2026-10-20.