Free family guide · Pregnancy week by week · Second trimester

13 weeks pregnant

Week 13 is in the second trimester in both the US Office on Women's Health (OWH) system and the UK's NHS week-by-week guide.[1][2]

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Sources on this page: OWH; NHS; ACOG; MedlinePlus; NICHD; CDC; NIMH; HRSA

This page shares what health organizations say. It is not medical advice. It is general information. Talk to your doctor, midwife or pediatrician about your own situation.

In an emergency, call 911.

At a glance

  • The NHS says the baby is around 7.4 cm long.[3]
  • The NHS says the ovaries or testes are fully developed inside the body.[3]
  • The NHS says to let someone else empty the cat litter, because of the risk of toxoplasmosis.[3]

Which trimester is week 13?

OWH counts the trimesters as weeks 1 to 12, 13 to 28 and 29 to 40.[1] The NHS guide counts them as weeks 4 to 12, 13 to 27 and 28 to 41.[2] ACOG counts the first trimester to 13 weeks 6 days, the second from 14 weeks to 27 weeks 6 days, and the third from 28 weeks to 40 weeks 6 days.[4]

Sources differ

Sources place week 13 differently:[1][2][4]

  • OWH places week 13 in the second trimester.[1]
  • The NHS guide places week 13 in the second trimester.[2]
  • ACOG places week 13 in the first trimester.[4]

ACOG says pregnancy is counted from the first day of the last menstrual period, so 2 weeks are counted at the beginning when you are not yet pregnant.[4]

Your body this week

The NHS says a small bump may show, and you may pee less often as the womb rises.[3]

The NHS lists these common second-trimester symptoms:[3]

  • bleeding gums;[3]
  • pain in the ligaments around your belly;[3]
  • nosebleeds;[3]
  • constipation and heartburn;[3]
  • leg cramps;[3]
  • swollen hands and feet;[3]
  • urine and vaginal infections.[3]

Your baby this week

The NHS says the baby is around 7.4 cm long.[3]

The NHS says the ovaries or testes are fully developed inside the body.[3] It says movements become more deliberate, and some babies suck their thumb.[3]

Visits and tests around week 13

OWH lists chorionic villus sampling (CVS) at weeks 10 to 13.[5] ACOG also says CVS is done between 10 and 13 weeks.[6]

Sources differ

Sources give different weeks for first-trimester screening:[5][7]

  • OWH lists the first trimester screen at weeks 11 to 14.[5]
  • ACOG says the blood test and nuchal translucency ultrasound are usually done together between 10 and 13 weeks.[7]

ACOG says cell-free DNA screening can be done from 10 weeks, with results in about 1 week.[7]

The NHS says its dating scan is done at 8 to 14 weeks.[8]

Sources differ

Sources give different weeks for amniocentesis:[5][9][6]

  • OWH lists amniocentesis at weeks 14 to 20.[5]
  • MedlinePlus lists it between weeks 14 and 20.[9]
  • ACOG says it is usually done at 15 to 20 weeks.[6]

Sources differ

Sources give different weeks for the maternal serum (quad) screen:[5][9][7]

  • OWH lists the maternal serum screen at weeks 15 to 20.[5]
  • MedlinePlus lists the quad screen between weeks 15 and 22, most accurate at weeks 16 to 18.[9]
  • ACOG says the quad screen is done at 15 to 22 weeks.[7]

MedlinePlus says prenatal testing is optional and is your decision, made with your provider.[10]

For a healthy pregnancy, NICHD describes visits once a month until 28 weeks.[11]

Things to do this week

  • The NHS says to let someone else empty the cat litter, because of the risk of toxoplasmosis.[3]
  • The NHS says to avoid undercooked or cured meat and unpasteurized goats' milk or cheese.[3]
  • The NHS suggests starting pelvic floor exercises and looking into antenatal classes.[3]
  • CDC says to avoid lying flat on your back during exercise after the first trimester.[12]

Feelings check-in

The National Institute of Mental Health (NIMH) says perinatal depression includes depression during pregnancy, and its signs last at least 2 weeks.[13]

HRSA says the National Maternal Mental Health Hotline, 1-833-852-6262, takes calls and texts 24/7 in English and Spanish.[14]

When to call your provider or get help

CDC lists urgent warning signs to watch for during pregnancy and in the year after birth, including:[15]

  • a headache that will not go away or gets worse;[15]
  • dizziness or fainting;[15]
  • a fever of 100.4°F (38°C) or higher;[15]
  • severe belly pain that does not go away;[15]
  • vaginal bleeding or leaking fluid;[15]
  • thoughts of harming yourself or the baby.[15]

Questions families ask

Which trimester is week 13?

OWH places week 13 in the second trimester.[1] The NHS guide places it in the second trimester.[2] ACOG places it in the first trimester.[4]

How big is the baby at 13 weeks?

The NHS says the baby is around 7.4 cm long.[3]

Is it normal for gums to bleed at 13 weeks?

The NHS says swollen or bleeding gums are common, and suggests a soft toothbrush.[3] MedlinePlus lists nosebleeds and bleeding gums among common symptoms of pregnancy.[16]

Free from UpOnly Learning. Written for families of every faith. No outside ads and no affiliate links. Every fact on this page comes from the sources listed below. How we source and review these pages

Updated 2026-10-24: first published.

Sources

All sources were opened and checked on the date shown.

  1. Office on Women's Health (HHS). Stages of pregnancy. Checked October 24, 2026.
  2. NHS (United Kingdom). Week-by-week guide to pregnancy. Checked October 24, 2026.
  3. NHS (United Kingdom). 13 weeks pregnant guide. Checked October 24, 2026.
  4. American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy. Checked October 24, 2026.
  5. Office on Women's Health (HHS). Prenatal care and tests. Checked October 24, 2026.
  6. American College of Obstetricians and Gynecologists. Prenatal Genetic Diagnostic Tests. Checked October 24, 2026.
  7. American College of Obstetricians and Gynecologists. Prenatal Genetic Screening Tests. Checked October 24, 2026.
  8. NHS (United Kingdom). 4 weeks pregnant guide. Checked October 24, 2026.
  9. MedlinePlus (National Library of Medicine). Prenatal care in your second trimester. Checked October 24, 2026.
  10. MedlinePlus (National Library of Medicine). Prenatal Testing. Checked October 24, 2026.
  11. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NIH). What happens during prenatal visits?. Checked October 24, 2026.
  12. Centers for Disease Control and Prevention. Pregnant & Postpartum Activity: An Overview. Checked October 24, 2026.
  13. National Institute of Mental Health (NIH). Perinatal Depression. Checked October 24, 2026.
  14. Health Resources and Services Administration (HRSA). National Maternal Mental Health Hotline. Checked October 24, 2026.
  15. Centers for Disease Control and Prevention (HEAR HER campaign). Urgent Maternal Warning Signs and Symptoms. Checked October 24, 2026.
  16. MedlinePlus (National Library of Medicine). Common symptoms during pregnancy. Checked October 24, 2026.

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