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First trimester

12 weeks pregnant

At 12 weeks, the organs, limbs, bones and muscles are all present and keep maturing. The placenta has likely taken over from the yolk sac, and many people notice early symptoms starting to settle, although this varies.

This page covers 12 weeks 0 days to 12 weeks 6 days (12+0 to 12+6), counted from the first day of the last period. Check how far along you are

Enter it to see the calendar dates of your week 12.

Botanical illustration of a lime

About the size of a lime

Typical crown-rump length 5.6 cm to 6.8 cm (2.2 in to 2.7 in) across this week, from the Robinson equation.1

A reference value, not a measurement of your baby.

How your baby is developing

  • All the organs, limbs, bones and muscles are present and will keep developing until they are fully working. The skeleton is gradually hardening from softer tissue into bone.2,3
  • The circulatory, digestive and urinary systems are working. Around this stage the fetus starts swallowing amniotic fluid and passing it back out as urine.2
  • The heartbeat can be picked up on an ultrasound scan, and the internal organs and muscles have grown.3
  • The sex organs have formed, but most scans will not be able to show the baby's sex until later in pregnancy.2,3
  • The fetus can make a fist, the face is well formed and the eyelids are closed. They will stay closed until around 28 weeks.4

Changes you may notice

Everyone’s experience is different. You may notice some of these, or none.

  • Once the placenta takes over feeding the baby from the yolk sac, hormones tend to calm down a bit, and some people start to feel better.3
  • Your waist may be thickening and your breasts getting bigger. As nausea eases, you may feel hungrier, but you do not need to eat for two.3
  • How big your bump looks depends on many things, including your hormones, your weight before pregnancy, how many babies you have had, and the strength of your muscles.3
  • Nausea, indigestion, an aching stomach, headaches, dizziness and mood swings can still happen. Contact your doctor or midwife about any bleeding.3

Care around this week

  • In the US, first-trimester screening is done between 10 weeks 0 days and 13 weeks 6 days, and cell-free DNA screening can be done from 10 weeks. An ultrasound up to 13 weeks 6 days gives the most accurate due date.5,6
  • UK note: the dating scan is offered between 11 and 14 weeks (NICE gives 11 weeks 2 days to 14 weeks 1 day). If you have chosen screening, the combined test is usually done at the same time. If the scan happens after 14 weeks, a different blood test, the quadruple test, is offered between 14 and 20 weeks instead.7,8,9,10
  • UK note: the NHS advises taking 400 micrograms of folic acid daily until at least week 12. Once you tell your employer you are pregnant, you have maternity rights, including paid time off for antenatal appointments.3

Questions to ask your provider

  • Did my scan change my due date, and which date should I use now?
  • When will I get my screening results, and how will you contact me?
  • Should I keep taking folic acid or switch to a different supplement after 12 weeks?
  • What weight gain is right for me in this pregnancy?
When to contact your provider straight away

Call 911 (US) or 999 (UK) in an emergency, such as heavy bleeding or bleeding with severe pain, a seizure, chest pain, or severe trouble breathing.13,14,15,16

These symptoms are not always serious, but each one needs prompt advice from your provider, midwife or maternity unit (or NHS 111 in the UK if you cannot reach them) rather than waiting for your next appointment, and it helps to tell them you are pregnant.

  • Vaginal bleeding or spotting at any stage of pregnancy. Call 911 or 999 if the bleeding is heavy or comes with severe belly pain, shoulder pain, or feeling faint or dizzy.15,17
  • Fluid leaking or gushing from your vagina, or discharge that is unusual for you. Get checked straight away if the fluid is greenish, colored or smells bad.15,16,18,19
  • Your baby moving less than usual, not moving, or a change in their usual pattern of movements. Call immediately, even in the middle of the night, and do not use a home Doppler to check yourself.15,20
  • A severe headache that does not go away with simple painkillers or gets worse, or sudden changes in your vision such as blurring or seeing flashing lights.13,15,16
  • Sudden swelling of your face, hands or feet, or swelling, redness or pain in a leg.13,15,16
  • Belly pain that is severe or does not go away after resting, or pain just below the ribs.13,15,21
  • Regular tightenings or contractions, period-type pains, or backache that is unusual for you before 37 weeks, which can be signs of preterm labor.19,21
  • A fever of 100.4°F (38°C) or higher, or feeling hot, cold or shivery.15,16,19
  • Shortness of breath that comes on suddenly or happens when you lie flat, chest pain, a racing or pounding heart, or dizziness or fainting.15,16
  • Very itchy skin, especially on the palms of your hands or soles of your feet, or itching that is worse at night.22
  • Being sick so often that you cannot keep food or drink down, or signs of dehydration such as dark urine, peeing very little, or feeling dizzy.15,23
  • Thoughts of harming yourself or your baby. Get help right away, and call 911 or 999 if you think you might act on them.15,24

Questions about 12 weeks

Is it safe to announce my pregnancy at 12 weeks?

There is no right time, and it is a personal choice. The chance of miscarriage falls as pregnancy goes on: MedlinePlus says most miscarriages happen in the first 7 weeks and the rate drops once the heartbeat is detected. The NHS notes that many people tell their employer after 12 weeks, once the risk of miscarriage has reduced and they have had their first scan.3,11

What does the 12-week scan check?

In England, the dating scan checks how many weeks pregnant you are and works out your due date. It also checks whether there is more than one baby, that the pregnancy is in the right place, and your baby's development. If you have agreed to it, screening for Down's syndrome can happen at the same scan.9

Is 12 weeks the end of the first trimester?

Not quite. Using the ACOG definition, the first trimester runs through 13 weeks 6 days, and the second trimester begins at 14 weeks 0 days.12

Sources

  1. A critical evaluation of sonar “crown-rump length” measurementsBritish Journal of Obstetrics and Gynaecology 82(9):702–710, 1975
  2. Fetal development: stages of growthCleveland Clinic
  3. Week 12 – week-by-week guide to pregnancyNHS Best Start in Life
  4. Fetal developmentUS National Library of Medicine
  5. Practice Bulletin No. 226: Screening for Fetal Chromosomal AbnormalitiesAmerican College of Obstetricians and Gynecologists, 2020
  6. Committee Opinion No. 700: Methods for Estimating the Due DateAmerican College of Obstetricians and Gynecologists, with AIUM and SMFM, 2017
  7. Your antenatal appointmentsNHS (England)
  8. Antenatal care (NG201)National Institute for Health and Care Excellence, 2021
  9. 12-week scanNHS (England)
  10. Screening for Down's syndrome, Edwards' syndrome and Patau's syndromeNHS (England)
  11. MiscarriageUS National Library of Medicine
  12. How Your Fetus Grows During PregnancyAmerican College of Obstetricians and Gynecologists
  13. Pre-eclampsiaNHS (England)
  14. Epilepsy and pregnancyNHS (England)
  15. Urgent Maternal Warning Signs and Symptoms (Hear Her campaign)US Centers for Disease Control and Prevention
  16. Pregnancy symptoms you need to get help forNHS (England)
  17. Vaginal bleeding in pregnancyNHS (England)
  18. Signs of going into labourNHS Best Start in Life
  19. Premature labour and birthNHS (England)
  20. Your baby's movementsNHS (England)
  21. Stomach pain in pregnancyNHS (England)
  22. Itching in pregnancyNHS (England)
  23. Severe vomiting in pregnancyNHS (England)
  24. Depression in pregnancyNHS (England)

Links checked November 12, 2026. Citing a source does not mean it endorses this site.

Written from the sources above and checked against them on 2026-11-12. Not reviewed by a clinician. Our editorial policy