Blood proteins AFP and PAPP-A 

2 September 2004

Professor Gordon Smith from the University of Cambridge's Department of Obstetrics and his team have found that abnormal levels of certain proteins in a mother’s blood in early pregnancy predicted both pre-term delivery and low birth weight, as well as an increased risk of SIDS.

These abnormal protein levels probably indicate that the placenta isn’t functioning as well as it could, and more research is needed to see whether finding these abnormalities in early pregnancy might help doctors prevent later problems.

One study (1) examined the relationship between the level of alpha-fetoprotein (AFP) in maternal blood in the second trimester of pregnancy and the risk of SIDS in a large sample of Scottish women. AFP is a protein normally present in fetal blood; small amounts cross into the maternal circulation.

In another study (2) Professor Smith found that raised levels of AFP in a mother's blood was positively associated with the risk of preterm delivery in first pregnancies.

A third study (3) confirmed the finding that high levels of AFP during pregnancy predicted both low birth weight and preterm delivery, and also that low levels of another maternal blood protein called pregnancy-associated plasma protein A (PAPP-A) was an independent predictor of the same outcome.

If both risk factors were present (high AFP and low PAPP-A), the risk of both preterm delivery and low birth weight were increased almost 10-fold.


This research is published in:
(1) Smith GCS et al, Second trimester maternal serum levels of alpha-fetoprotein and the subsequent risk of sudden infant death syndrome. New England Journal of Medicine 351: 16-24.

(2) Smith GC, Shah I, White IR, Pell JP, Crossley JA, Dobbie R. Maternal and biochemical predictors of spontaneous preterm birth among nulliparous women: a systematic analysis in relation to the degree of prematurity. Int J Epidemiol 2006.

(3) Smith GC, Shah I, Crossley JA, Aitken DA, Pell JP, Nelson SM, et al. Pregnancy-associated plasma protein A and alpha-fetoprotein and prediction of adverse perinatal outcome. Obstet Gynecol 2006; 107(1):161-6.