Triple screen (second-trimester maternal serum screening): AFP, Unconjugated estriol (uE3), human chorionic gonadotropin (HCG+β)

About the tests

Depending on how many tests are performed, the tests may be known by different names. For example, the triple test combines the results of three tests (AFP, hCG, and uE3). 

The screening tests involve measuring different proteins and hormones found in the mother’s blood. In addition, the mother is asked to provide additional information about herself that is used to improve the accuracy of the screening test, such as her age, weight, ethnicity, smoking status, and whether she has diabetes. The following blood tests may be performed as part of second-trimester screening:

• Alpha fetoprotein (AFP) is a protein produced by the developing baby. AFP moves from the baby across the placenta and amniotic membranes into the mother and appears in the maternal blood. Levels in the mother’s blood tend to rise throughout the first half of pregnancy.

• Human chorionic gonadotrophin (HCG+β) are hormones produced by the placenta. Levels in the mother’s blood rise early in pregnancy and then fall later.

• Unconjugated oestriol (uE3) is a hormone produced by the baby and the placenta. Levels gradually increase through the first and second trimesters of pregnancy.

Purpose of the test

In most centers, women will be offered second-trimester tests, usually between 14 and 20 weeks of pregnancy. A blood sample is taken from a vein in the arm. The results from the laboratory may be combined with the results from an ultrasound scan to improve the overall effectiveness of the screening test.

These tests assess the risk of a fetus having certain chromosomal abnormalities, such as Down syndrome (trisomy 21) or Edward’s syndrome (trisomy 18).