Free family guide · Pregnancy week by week · Third trimester

33 weeks pregnant

Week 33 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]

Last reviewed: Next review: No outside ads and no affiliate links.

Sources on this page: OWH; NHS; ACOG; MedlinePlus; NICHD; NHTSA; 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 43.7 cm long.[3]
  • The NHS says the brain and nervous system are fully developed.[3]
  • The NHS suggests packing your hospital bag now.[3]

Which trimester is week 33?

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]

All three place week 33 in the third trimester.[1][2][4]

Your body this week

The NHS says pelvic heaviness may mean the baby is head down.[3]

Sources differ

Sources give different numbers for group B strep:[3][5]

  • The NHS says up to 2 in 5 people carry it.[3]
  • ACOG says about 1 in 4 pregnant women carry it.[5]

Your baby this week

The NHS says the baby is around 43.7 cm long.[3]

The NHS says the brain and nervous system are fully developed.[3] It says the skull bones stay soft and separate until about 12 to 18 months after birth.[3]

Visits and tests around week 33

Sources differ

Sources give different weeks for the group B strep test:[6][5][7]

  • OWH lists the group B strep test at weeks 36 to 37.[6]
  • ACOG says the swab is done at 36 to 38 weeks.[5]
  • MedlinePlus says the swab is done a few weeks before the due date.[7]

NICHD describes visits every 2 weeks from 28 to 36 weeks.[8]

Things to do this week

  • The NHS suggests packing your hospital bag now.[3]
  • The NHS suggests a list of phone numbers, including your midwife or hospital, your birth partner and someone to drive you, because it is not safe to drive yourself.[3]
  • The NHS says to get a car seat for the trip home.[3]
  • NHTSA says babies under 1 should always ride rear-facing.[9]

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.[10]

HRSA says the National Maternal Mental Health Hotline, 1-833-852-6262, takes calls and texts 24/7 in English and Spanish.[11]

When to call your provider or get help

MedlinePlus says to call your provider in the third trimester for:[7]

  • bleeding, or discharge that smells bad;[7]
  • fever, chills, or pain when you urinate;[7]
  • headaches or changes in vision;[7]
  • the water breaking, or regular painful contractions;[7]
  • the baby moving less;[7]
  • a lot of swelling, chest pain or trouble breathing.[7]

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.[12]

Questions families ask

Which trimester is week 33?

OWH places week 33 in the third trimester.[1] The NHS guide places it in the third trimester.[2] ACOG places it in the third trimester.[4]

How big is the baby at 33 weeks?

The NHS says the baby is around 43.7 cm long.[3]

How many babies are born on their due date?

The NHS says only 1 in 20 babies arrive on their due date.[3] ACOG also says only about 1 in 20 women give birth on their due date.[4]

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). 33 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. American College of Obstetricians and Gynecologists. Group B Strep and Pregnancy. Checked October 24, 2026.
  6. Office on Women's Health (HHS). Prenatal care and tests. Checked October 24, 2026.
  7. MedlinePlus (National Library of Medicine). Prenatal care in your third trimester. Checked October 24, 2026.
  8. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NIH). What happens during prenatal visits?. Checked October 24, 2026.
  9. National Highway Traffic Safety Administration. Car Seats and Booster Seats. Checked October 24, 2026.
  10. National Institute of Mental Health (NIH). Perinatal Depression. Checked October 24, 2026.
  11. Health Resources and Services Administration (HRSA). National Maternal Mental Health Hotline. Checked October 24, 2026.
  12. NHS (United Kingdom). 32 weeks pregnant guide. Checked October 24, 2026.