Free family guide · Pregnancy week by week · Third trimester

39 weeks pregnant

Week 39 is in the third 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 50.7 cm long.[3]
  • The NHS says babies have an Apgar check within a minute of birth and again at 5 minutes.[3]
  • The NHS says the safest position to go to sleep is on your side, left or right.[4]

Which trimester is week 39?

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.[5]

All three place week 39 in the third trimester.[1][2][5]

Your body this week

The NHS says pregnancy normally lasts around 40 weeks, and most women go into labor within a week either side of the due date.[3]

Your baby this week

The NHS says the baby is around 50.7 cm long.[3]

The NHS says babies have an Apgar check within a minute of birth and again at 5 minutes.[3] It says blue hands and feet are normal at first, and gaps between breaths of up to 5 seconds are normal.[3]

Visits and tests around week 39

Sources differ

Sources give different weeks for the group B strep test:[6][7][8]

  • OWH lists the group B strep test at weeks 36 to 37.[6]
  • ACOG says the swab is done at 36 to 38 weeks.[7]
  • MedlinePlus says the swab is done a few weeks before the due date.[8]

NICHD describes visits every week from 36 weeks until birth.[9]

Things to do this week

  • The NHS says the safest position to go to sleep is on your side, left or right.[4]
  • CDC says to avoid lying flat on your back during exercise after the first trimester.[10]

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.[11]

HRSA says the National Maternal Mental Health Hotline, 1-833-852-6262, takes calls and texts 24/7 in English and Spanish.[12]

When to call your provider or get help

MedlinePlus says to call your provider in the third trimester for:[8]

  • bleeding, or discharge that smells bad;[8]
  • fever, chills, or pain when you urinate;[8]
  • headaches or changes in vision;[8]
  • the water breaking, or regular painful contractions;[8]
  • the baby moving less;[8]
  • a lot of swelling, chest pain or trouble breathing.[8]

The NHS says you should still feel the baby move at the same rate until you give birth, and to contact your midwife or hospital as soon as possible if the pattern changes or the baby stops moving.[13]

The NHS lists these signs to call your midwife or doctor about:[3]

  • vaginal bleeding;[3]
  • brown or pink discharge;[3]
  • severe itching, especially at night;[3]
  • a terrible headache that will not go away;[3]
  • vision problems such as blurring or flashing lights;[3]
  • pain just below the ribs;[3]
  • extreme swelling of the feet, ankles, hands or face;[3]
  • stomach pain that does not go away;[3]
  • a temperature above 37.5 °C with no cold or flu symptoms.[3]

Sources differ

Sources describe when to call in labor in different ways:[3][14]

  • The NHS says to call when contractions last at least 60 seconds and come every 5 minutes, or any time you are worried.[3]
  • MedlinePlus says to contact your provider for regular, painful contractions every 5 to 10 minutes for 60 minutes, and to follow your provider's instructions.[14]

Questions families ask

Which trimester is week 39?

OWH places week 39 in the third trimester.[1] The NHS guide places it in the third trimester.[2] ACOG places it in the third trimester.[5]

How big is the baby at 39 weeks?

The NHS says the baby is around 50.7 cm long.[3]

Can my waters break as a trickle?

The NHS says waters breaking can be a trickle, and to call your midwife, because induction may be needed due to the risk of infection.[3]

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). 39 weeks pregnant guide. Checked October 24, 2026.
  4. NHS (United Kingdom). Tiredness and sleep problems in pregnancy. Checked October 24, 2026.
  5. American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy. Checked October 24, 2026.
  6. Office on Women's Health (HHS). Prenatal care and tests. Checked October 24, 2026.
  7. American College of Obstetricians and Gynecologists. Group B Strep and Pregnancy. Checked October 24, 2026.
  8. MedlinePlus (National Library of Medicine). Prenatal care in your third trimester. Checked October 24, 2026.
  9. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NIH). What happens during prenatal visits?. Checked October 24, 2026.
  10. Centers for Disease Control and Prevention. Pregnant & Postpartum Activity: An Overview. Checked October 24, 2026.
  11. National Institute of Mental Health (NIH). Perinatal Depression. Checked October 24, 2026.
  12. Health Resources and Services Administration (HRSA). National Maternal Mental Health Hotline. Checked October 24, 2026.
  13. NHS (United Kingdom). 32 weeks pregnant guide. Checked October 24, 2026.
  14. MedlinePlus (National Library of Medicine). Am I in labor?. Checked October 24, 2026.