Fetal Anomaly Screening
All pregnant women should be offered two scans in their pregnancy.
First scan
The first trimester scan accurately establishes the gestational age, assesses viability and fetal number.
If the offer of Down’s syndrome screening has been accepted, nuchal translucency (NT) is also measured between 11 weeks and 13 weeks + 6 days gestation.
See Down’s Syndrome Screening on these pages.
Second scan
The second scan is carried out between 18 weeks and 21 weeks + 6 days gestation.
The purpose is to detect significant structural fetal abnormalities. Consent should be obtained.
The woman should be made aware that the ultrasound scan does not detect every abnormality.
Abnormality detection rates
The main abnormalities screened for and their detection rates are:
- Spina bifida 90%
- Anencephaly 99%
- Hydrocephaly 60%
- Major structural cardiac problems 25%
- Exompholus/gastroschisis 90%
- Diaphragmatic hernia 60%
- Major renal abnormalities 85%
- Missing limb/limb problems 90%
If an abnormality is detected, the woman is counselled regarding management, be it treatment during the antenatal period, or treatment after delivery, if these are available.
Alternatively, if this is relevant, she may also be given information to enable her to make an informed choice about whether to continue with the pregnancy.
NHS Fetal Anomaly Screening Programme
