Free family guide · Prenatal tests

The anatomy scan

ACOG says at least one standard ultrasound exam is done in pregnancy, usually at 18 to 22 weeks.[1]

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Sources on this page: ACOG; OWH; MedlinePlus; NHS; WHO

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.

When it is done

Sources differ

Sources give different weeks:[2][3][1][4][5][6]

  • OWH lists a standard ultrasound, often at weeks 18 to 20.[2]
  • MedlinePlus lists an anatomy ultrasound around week 20.[3]
  • ACOG says usually at 18 to 22 weeks.[1]
  • The NHS week 18 page says around 18 to 20 weeks.[4]
  • The NHS week 9 page says around 18 to 21 weeks.[5]
  • The World Health Organization (WHO) recommends one ultrasound before 24 weeks.[6]

What it checks

ACOG says the standard exam can check:[1]

  • the baby's development, and screen for major problems;[1]
  • how far along the pregnancy is;[1]
  • the baby's position, movement, heart rate, size and weight;[1]
  • the amount of fluid and where the placenta is;[1]
  • the number of babies.[1]

The NHS says the scan finds a range of conditions, but not all of them.[4] It says the scan also checks the placenta.[7]

ACOG says the baby's sex can be seen if the position allows.[1] The NHS says the sex may or may not be revealed.[4]

Getting ready and safety

ACOG says an ultrasound through the belly may need a full bladder, from several glasses of water in the 2 hours before, while an ultrasound through the vagina needs an empty bladder.[1]

ACOG says there is no evidence that ultrasound harms a developing baby, and that it should be used only for medical reasons, by qualified professionals.[1]

If there is unexpected news

The NHS says to talk to your midwife if the scan brings unexpected news.[8]

MedlinePlus says a screening test estimates risk, and an abnormal result means more information is needed, while a diagnostic test confirms whether a condition is present.[9]

Questions families ask

What week is the anatomy scan?

ACOG says usually at 18 to 22 weeks.[1] OWH lists it often at weeks 18 to 20.[2]

Is ultrasound safe for the baby?

ACOG says there is no evidence that ultrasound harms a developing baby.[1]

Do I need a full bladder?

ACOG says an ultrasound through the belly may need a full bladder, and one through the vagina needs an empty bladder.[1]

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. American College of Obstetricians and Gynecologists. Ultrasound Exams. Checked October 24, 2026.
  2. Office on Women's Health (HHS). Prenatal care and tests. Checked October 24, 2026.
  3. MedlinePlus (National Library of Medicine). Prenatal care in your second trimester. Checked October 24, 2026.
  4. NHS (United Kingdom). 18 weeks pregnant guide. Checked October 24, 2026.
  5. NHS (United Kingdom). 9 weeks pregnant guide. Checked October 24, 2026.
  6. World Health Organization. New guidelines on antenatal care for a positive pregnancy experience (news release, Nov 7, 2016). Checked October 24, 2026.
  7. NHS (United Kingdom). 20 weeks pregnant guide. Checked October 24, 2026.
  8. NHS (United Kingdom). 21 weeks pregnant guide. Checked October 24, 2026.
  9. MedlinePlus (National Library of Medicine). Prenatal Testing. Checked October 24, 2026.