Free family guide · Pregnancy week by week · First trimester

12 weeks pregnant

Week 12 is the last week of 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; MedlinePlus; ACOG; NICHD; WHO; USPSTF; CDC; FoodSafety.gov; FDA; EEOC; 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

  • By week 12, OWH says the baby is about 3 inches long and can make a fist.[1]
  • OWH lists the first trimester screen at weeks 11 to 14 and chorionic villus sampling (CVS) at weeks 10 to 13.[3]
  • MedlinePlus says prenatal testing is optional and is your decision, made with your provider.[4]

Which trimester is week 12?

OWH counts the first trimester as weeks 1 to 12 and the second as weeks 13 to 28.[1] The NHS guide counts the first trimester as weeks 4 to 12 and the second as weeks 13 to 27.[2] Both place week 13 at the start of the second trimester.[1][2]

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] The NHS also dates pregnancy from the first day of your last period.[6]

ACOG counts the first trimester to 13 weeks 6 days, so week 12 is still in the first trimester in its system too.[5]

Your body this week

OWH lists these common changes in the first trimester:[1]

  • tiredness;[1]
  • tender breasts;[1]
  • nausea, with or without vomiting.[1]

Sources differ

Sources describe how long morning sickness lasts in different ways:[7][8]

  • ACOG says it usually starts before 9 weeks, and for most women it goes away by 14 weeks.[7] It says for some it lasts several weeks or months, and for a few the whole pregnancy.[7]
  • The NHS says it usually clears up by weeks 16 to 20.[8]

The NHS week 12 page says sickness may ease around now.[9]

MedlinePlus says to call a provider for any of these signs of severe nausea and vomiting:[10]

  • signs of dehydration;[10]
  • not keeping fluids down for more than 12 hours;[10]
  • dizziness;[10]
  • blood in vomit;[10]
  • belly pain;[10]
  • losing more than 5 pounds.[10]

Your baby this week

  • In the first trimester, OWH says the brain and spinal cord begin to form.[1]
  • OWH says the heart beats steadily by about week 8.[1]
  • The NHS week 12 page says the heartbeat can be picked up on an ultrasound, the skeleton is hardening into bone, and the sex organs have formed.[9]

Sources differ

Sources give the baby's size at week 12 in their own units:[1][9]

  • OWH says that by week 12 the baby is about 3 inches long and can make a fist.[1]
  • The NHS says the baby is 5.4 cm long from head to bottom.[9]

Visits and tests around week 12

NICHD says the first visit usually happens after about week 8, and it is one of the longest visits.[11] The World Health Organization (WHO) recommends a first contact within the first 12 weeks.[12]

Tests OWH lists around this week:[3]

TestWhen OWH lists it
Chorionic villus sampling (CVS)Weeks 10 to 13
First trimester screenWeeks 11 to 14
Amniocentesis (coming up)Weeks 14 to 20
Maternal serum screen (coming up)Weeks 15 to 20

Sources differ

Sources give slightly different weeks for first-trimester screening:[3][13]

  • OWH lists the first trimester screen at weeks 11 to 14.[3]
  • ACOG says the blood test and nuchal translucency ultrasound are usually done together between 10 and 13 weeks.[13]

The NHS says its dating scan is done at 8 to 14 weeks.[6]

MedlinePlus says a screening test estimates risk, and an abnormal result means more information is needed.[4] It says a diagnostic test confirms whether a condition is present.[4]

For a healthy pregnancy, NICHD describes visits once a month until 28 weeks, every 2 weeks from 28 to 36 weeks, then every week until birth.[11]

Things to do this week

  • The US Preventive Services Task Force advises a daily folic acid supplement through the first 2 to 3 months of pregnancy.[14]
  • MedlinePlus says to use prenatal vitamins rather than regular ones.[15]
  • CDC says to talk to your providers before you start or stop any medicine.[16]
  • FoodSafety.gov says to avoid hot dogs and deli meats unless they are reheated until steaming (165°F).[17]
  • The FDA advises 2 to 3 servings a week (4 ounces each) of fish from its Best Choices list, such as salmon, sardines, shrimp, cod, tilapia and canned light tuna.[18]
  • The FDA says to avoid king mackerel, marlin, orange roughy, shark, swordfish, bigeye tuna and tilefish from the Gulf of Mexico.[18]
  • MedlinePlus says to keep caffeine under 200 mg a day, about 1 to 2 small cups of coffee or tea.[19]
  • MedlinePlus says most people need about 340 extra calories a day in the second trimester.[20]
  • CDC says to avoid lying flat on your back during exercise after the first trimester.[21]
  • The EEOC says the Pregnant Workers Fairness Act covers employers with 15 or more employees.[22]

Feelings check-in

According to the National Institute of Mental Health (NIMH):[23]

  • Perinatal depression includes depression during pregnancy, not only after birth.[23]
  • Signs last at least 2 weeks, and can include sadness or emptiness, loss of interest, guilt, and changes in sleep and appetite.[23]
  • Thoughts of harming yourself or the baby are also a sign.[23]

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

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:[25]

  • a headache that will not go away or gets worse;[25]
  • dizziness or fainting;[25]
  • changes in vision;[25]
  • a fever of 100.4°F (38°C) or higher;[25]
  • trouble breathing, chest pain or a fast heartbeat;[25]
  • severe nausea and vomiting;[25]
  • severe belly pain that does not go away;[25]
  • vaginal bleeding or leaking fluid;[25]
  • thoughts of harming yourself or the baby.[25]

MedlinePlus says some people spot in early pregnancy and do not miscarry, but any bleeding should prompt a call to a provider.[26]

Questions families ask

Is 12 weeks the end of the first trimester?

OWH counts the first trimester as weeks 1 to 12, and the NHS guide counts it as weeks 4 to 12.[1][2] Both start the second trimester at week 13.[1][2]

How big is the baby at 12 weeks?

OWH says that by week 12 the baby is about 3 inches long and can make a fist.[1] The NHS says the baby is 5.4 cm long from head to bottom.[9]

What tests are usually offered around 12 weeks?

OWH lists the first trimester screen at weeks 11 to 14 and CVS at weeks 10 to 13.[3] NICHD says the first visit can include blood tests, a pelvic exam, possibly an ultrasound, and an offer of genetic screening.[11]

Do I have to have genetic screening?

MedlinePlus says prenatal testing is optional and is your decision, made with your provider.[4]

Is it still normal to feel sick at 12 weeks?

OWH lists nausea, with or without vomiting, as a common first-trimester change.[1] MedlinePlus says to call a provider if you cannot keep fluids down for more than 12 hours, feel dizzy, see blood in vomit, have belly pain or lose more than 5 pounds.[10]

How long does morning sickness last?

ACOG says for most women it goes away by 14 weeks.[7] The NHS says it usually clears up by weeks 16 to 20.[8]

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. Office on Women's Health (HHS). Prenatal care and tests. Checked October 24, 2026.
  4. MedlinePlus (National Library of Medicine). Prenatal Testing. Checked October 24, 2026.
  5. American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy. Checked October 24, 2026.
  6. NHS (United Kingdom). 4 weeks pregnant guide. Checked October 24, 2026.
  7. American College of Obstetricians and Gynecologists. Morning Sickness: Nausea and Vomiting of Pregnancy. Checked October 24, 2026.
  8. NHS (United Kingdom). Vomiting and morning sickness. Checked October 24, 2026.
  9. NHS (United Kingdom). 12 weeks pregnant guide. Checked October 24, 2026.
  10. MedlinePlus (National Library of Medicine). Hyperemesis gravidarum. 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. World Health Organization. New guidelines on antenatal care for a positive pregnancy experience (news release, Nov 7, 2016). Checked October 24, 2026.
  13. American College of Obstetricians and Gynecologists. Prenatal Genetic Screening Tests. Checked October 24, 2026.
  14. US Preventive Services Task Force. Folic Acid Supplementation to Prevent Neural Tube Defects: Preventive Medication. Checked October 24, 2026.
  15. MedlinePlus (National Library of Medicine). Pregnancy and Medicines. Checked October 24, 2026.
  16. Centers for Disease Control and Prevention. Medicine and Pregnancy: An Overview. Checked October 24, 2026.
  17. FoodSafety.gov (HHS, USDA, FDA). People at Risk: Pregnant Women. Checked October 24, 2026.
  18. US Food and Drug Administration. Advice about Eating Fish. Checked October 24, 2026.
  19. MedlinePlus (National Library of Medicine). Caffeine in the diet. Checked October 24, 2026.
  20. MedlinePlus (National Library of Medicine). Pregnancy and Nutrition. Checked October 24, 2026.
  21. Centers for Disease Control and Prevention. Pregnant & Postpartum Activity: An Overview. Checked October 24, 2026.
  22. US Equal Employment Opportunity Commission. What You Should Know About the Pregnant Workers Fairness Act. Checked October 24, 2026.
  23. National Institute of Mental Health (NIH). Perinatal Depression. Checked October 24, 2026.
  24. Health Resources and Services Administration (HRSA). National Maternal Mental Health Hotline. Checked October 24, 2026.
  25. Centers for Disease Control and Prevention (HEAR HER campaign). Urgent Maternal Warning Signs and Symptoms. Checked October 24, 2026.
  26. MedlinePlus (National Library of Medicine). Miscarriage. Checked October 24, 2026.

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