Screening for Down’s Syndrome, Edwards’ syndrome, and Patau’s syndrome with a Vanished Twin (349)

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The definition of a vanished twin is when one fetus in a twin pregnancy is non-viable. It may be partially or completely reabsorbed.

An ultrasound scan for the combined or quadruple test* may show either:

  • An empty second pregnancy sac
  • A second pregnancy sac containing a nonviable fetus

Empty second pregnancy sac and the combined test

When there is an empty second pregnancy sac, the combined test can be used to calculate the chance result

Second pregnancy sac containing a non-viable fetus and the combined test

When there is a second pregnancy sac containing a non-viable fetus, the combined test should not be used to calculate the chance result.

The quadruple test can be offered.

The quadruple test

The quadruple test can be offered to a woman with a vanished twin pregnancy

 

*The combined test assesses the chance of the baby having trisomy 21 (T21), trisomy 18 (T18) and trisomy 13 (T13) by using;

  • Maternal age
  • Biochemical markers free beta human chorionic gonadotrophin (bhCG) and pregnancy associated plasma protein-A (PAPP-A)
  • Ultrasound measurements- nuchal translucency (NT) and crown rump length (CRL)

The quadruple test screens for T21 only

The quadruple test uses maternal age and the following 4 biochemical markers measured from 14+2 to 20+0 weeks:

  • Alpha-fetoprotein (AFP)
  • Human chorionic gonadotrophin (hCG)
  • Inhibin-A
  • Unconjugated oestriol (uE3)

Editorial Information

Last reviewed: 23/10/2024

Next review date: 24/10/2027

Author(s): Dawn Kernaghan .

Version: 3

Approved By: Maternity Clinical Governance Group

Document Id: 349