501 Two blood markers moderately accurate in screening for Down syndrome

December 24, 2016

written by Brian R McAvoy

Clinical question

How accurate are first-trimester serum markers for the detection of Down syndrome in the antenatal period?

Bottom line

Tests involving 2 markers in combination with maternal age – specifically PAPP-A (pregnancy-associated plasma protein A), free beta-hCG (beta-human chorionic gonadotropin) and maternal age – were significantly better than those involving single markers, with and without age. They detected 7 out of 10 Down-affected pregnancies (3 in 10 were missed), and a fixed 5% of all tested women got a false-positive result. The addition of further markers (triple tests) was not shown to be statistically superior; the studies included were small, with limited power to detect a difference. The screening blood tests themselves had no adverse effects for the woman, over and above the risks of a routine blood test.

Caveat

Some women who have a “high risk” screening test result, and are given amniocentesis or chorionic villus sampling, have a risk of miscarriage of a baby unaffected by Down syndrome. Parents need to weigh up this risk when deciding whether or not to have amniocentesis or chorionic villus sampling following a “high risk” screening result.

Context

Down syndrome is the most common congenital cause of mental disability, and it also leads to numerous metabolic and structural problems. Non-invasive screening based on biochemical analysis of maternal serum or urine, or foetal ultrasound measurements, allows estimates of the risk of a pregnancy being affected, and provides information to guide decisions about definitive testing.

Cochrane Systematic

Review Alldred SK et al. First trimester serum tests for Down’s syndrome screening. Cochrane Reviews, 2015, Issue 11. Art. No.: CD011975.DOI: 10.1002/14651858. CD011975. This review contains 56 studies involving 204,759 participants (including 2113 with Down syndrome).

Pearls are an independent product of the Cochrane primary care group and are meant for educational use and not to guide clinical care.