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First trimester

13 weeks pregnant

At 13 weeks, you are in the final week of the first trimester, which ends at 13 weeks 6 days. Vocal cords are forming, the head is starting to look more in proportion, and movements are becoming more deliberate, though you will not feel them yet.

This page covers 13 weeks 0 days to 13 weeks 6 days (13+0 to 13+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 13.

Botanical illustration of a lemon

About the size of a lemon

Typical crown-rump length 7.0 cm to 8.3 cm (2.7 in to 3.3 in) across this week, from the Robinson equation.1

A reference value, not a measurement of your baby.

How your baby is developing

  • Vocal cords are forming, and the head, which has been very large for the body, is starting to grow more in proportion.2
  • The fetus is moving around. Movements start out jerky and random, then begin to look more deliberate.3
  • Some babies suck their thumb in the uterus, which helps develop the sucking reflex they will need for feeding.3
  • The ovaries or testes are fully developed inside, and the external genitals are still developing.3
  • Nails are on the fingers and toes, the liver is making red blood cells, and tooth buds for the baby teeth are in place. The eyelids are closed and will stay that way until around 28 weeks.4

Changes you may notice

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

  • A small bump may start to show as your uterus grows upward and outward. If you have needed to pee more often, this may ease as the uterus moves up away from your bladder.3
  • More blood is flowing around your pelvis. Some people notice a higher sex drive or feel more thirsty. Sex is safe in pregnancy unless your midwife or doctor has advised otherwise.3
  • Swollen, painful or bleeding gums are common in pregnancy. A soft toothbrush and gentle brushing can help, and if you vomit, rinse your mouth with water to protect your teeth.3
  • You may notice pains on the sides of your belly as the uterus stretches (round ligament pain), as well as nosebleeds, headaches or constipation. Some earlier symptoms, such as nausea or mood swings, may continue.3

Care around this week

  • In the US, the window for first-trimester screening closes at 13 weeks 6 days, and an ultrasound up to that point is the most accurate way to date a pregnancy. If you have not yet discussed screening or dating, this week is a good time to ask. Cell-free DNA screening can be done from 10 weeks.5,6
  • UK note: the dating scan can be done up to 14 weeks 1 day, and the combined test for Down's, Edwards' and Patau's syndromes is offered between 10 and 14 weeks. If your scan happens after 14 weeks, you will be offered the quadruple blood test between 14 and 20 weeks instead.7,8,9
  • Infection precautions are worth discussing: avoid contact with anyone who has chickenpox or rubella, ask someone else to empty a cat litter tray, and avoid undercooked or cured meats and unpasteurized goat's milk and cheese because of toxoplasmosis.3

Questions to ask your provider

  • Is there still time for first-trimester screening, or which options remain for me now?
  • Is my due date now confirmed by ultrasound?
  • What should I do if I am exposed to chickenpox or another infection?
  • Are my gum symptoms something a dentist should check during 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.11,12,13,14

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.13,15
  • 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.13,14,16,17
  • 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.13,18
  • 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.11,13,14
  • Sudden swelling of your face, hands or feet, or swelling, redness or pain in a leg.11,13,14
  • Belly pain that is severe or does not go away after resting, or pain just below the ribs.11,13,19
  • Regular tightenings or contractions, period-type pains, or backache that is unusual for you before 37 weeks, which can be signs of preterm labor.17,19
  • A fever of 100.4°F (38°C) or higher, or feeling hot, cold or shivery.13,14,17
  • Shortness of breath that comes on suddenly or happens when you lie flat, chest pain, a racing or pounding heart, or dizziness or fainting.13,14
  • Very itchy skin, especially on the palms of your hands or soles of your feet, or itching that is worse at night.20
  • 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.13,21
  • Thoughts of harming yourself or your baby. Get help right away, and call 911 or 999 if you think you might act on them.13,22

Questions about 13 weeks

Is 13 weeks the second trimester?

Not by the ACOG definition, which counts the first trimester through 13 weeks 6 days and starts the second at 14 weeks 0 days. Some sources, including the NHS week-by-week guide, group week 13 with the second trimester.3,10

Is it too late for first-trimester screening at 13 weeks?

Not yet. In the US, first-trimester screening runs until 13 weeks 6 days, and cell-free DNA screening can be done from 10 weeks. In England, the combined test is offered up to 14 weeks, and the quadruple test is offered from 14 to 20 weeks.5,8

When will I feel the baby move?

Usually not for a while yet. The NHS says you may not feel any movement until around 17 weeks, and Cleveland Clinic notes that most people feel the fetus moving by the end of the fifth month.2,3

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 13 – 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. Antenatal care (NG201)National Institute for Health and Care Excellence, 2021
  8. Screening for Down's syndrome, Edwards' syndrome and Patau's syndromeNHS (England)
  9. 12-week scanNHS (England)
  10. How Your Fetus Grows During PregnancyAmerican College of Obstetricians and Gynecologists
  11. Pre-eclampsiaNHS (England)
  12. Epilepsy and pregnancyNHS (England)
  13. Urgent Maternal Warning Signs and Symptoms (Hear Her campaign)US Centers for Disease Control and Prevention
  14. Pregnancy symptoms you need to get help forNHS (England)
  15. Vaginal bleeding in pregnancyNHS (England)
  16. Signs of going into labourNHS Best Start in Life
  17. Premature labour and birthNHS (England)
  18. Your baby's movementsNHS (England)
  19. Stomach pain in pregnancyNHS (England)
  20. Itching in pregnancyNHS (England)
  21. Severe vomiting in pregnancyNHS (England)
  22. 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