Free family guide · Pregnancy week by week · First trimester

5 weeks pregnant

Week 5 is in the first 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; NICHD; FoodSafety.gov; MedlinePlus; NIMH; HRSA; CDC

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 embryo is around 2 mm long.[3]
  • The NHS says the nervous system is developing, with the brain and spinal cord taking shape.[3]
  • OWH says to call a doctor after a positive home test.[4]

Which trimester is week 5?

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 5 in the first trimester.[1][2][5]

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.[5]

Your body this week

The NHS says many people realize they are pregnant around now.[3]

The NHS lists these symptoms around week 5:[3]

  • extreme tiredness;[3]
  • nausea;[3]
  • mood swings;[3]
  • light spotting, which can be implantation bleeding.[3]

The NHS says to tell your midwife about unusual cravings, such as for dirt, which is called pica and is linked to a lack of iron.[3]

Your baby this week

The NHS says the embryo is around 2 mm long.[3]

The NHS says the nervous system is developing, with the brain and spinal cord taking shape.[3] It says the heart is starting to form and will beat for the first time around now.[3] It says the face is taking shape, and the eyes stay closed until about 28 weeks.[3]

Visits and tests around week 5

For a healthy pregnancy, NICHD describes visits once a month until 28 weeks.[6]

Things to do this week

  • OWH says to call a doctor after a positive home test.[4]
  • The NHS advises 400 micrograms of folic acid a day until at least week 12.[7]
  • FoodSafety.gov says to avoid hot dogs and deli meats unless they are reheated until steaming (165°F).[8]
  • MedlinePlus says to keep caffeine under 200 mg a day, about 1 to 2 small cups of coffee or tea.[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]

The NHS says around 1 in 5 mothers feel anxious or stressed during pregnancy.[3]

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

CDC lists urgent warning signs to watch for during pregnancy and in the year after birth, including:[12]

  • a headache that will not go away or gets worse;[12]
  • dizziness or fainting;[12]
  • a fever of 100.4°F (38°C) or higher;[12]
  • severe nausea and vomiting;[12]
  • severe belly pain that does not go away;[12]
  • vaginal bleeding or leaking fluid;[12]
  • thoughts of harming yourself or the baby.[12]

MedlinePlus says some people spot in early pregnancy and do not miscarry, but any bleeding should prompt a call to a provider.[13]

Questions families ask

Which trimester is week 5?

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

How big is the baby at 5 weeks?

The NHS says the embryo is around 2 mm long.[3]

Is spotting at 5 weeks normal?

The NHS lists light spotting around week 5, and says it can be implantation bleeding.[3] MedlinePlus says any bleeding in pregnancy should prompt a call to a provider.[13]

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). 5 weeks pregnant guide. Checked October 24, 2026.
  4. Office on Women's Health (HHS). Knowing if you are pregnant. Checked October 24, 2026.
  5. American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy. Checked October 24, 2026.
  6. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NIH). What happens during prenatal visits?. Checked October 24, 2026.
  7. NHS (United Kingdom). 4 weeks pregnant guide. Checked October 24, 2026.
  8. FoodSafety.gov (HHS, USDA, FDA). People at Risk: Pregnant Women. Checked October 24, 2026.
  9. MedlinePlus (National Library of Medicine). Caffeine in the diet. 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. Centers for Disease Control and Prevention (HEAR HER campaign). Urgent Maternal Warning Signs and Symptoms. Checked October 24, 2026.
  13. MedlinePlus (National Library of Medicine). Miscarriage. Checked October 24, 2026.