The influence of smoking on maternal serum PAPP-A and free beta hCG levels in the first trimester of pregnancy.

In an analysis of 3111 singleton pregnancies routinely screened in the first trimester with nuchal translucency, free beta hCG and pregnancy associated plasma protein A (PAPP-A) smoking has been found to occur in 20.8 per cent of pregnant women. When the individual marker levels were assessed in smokers and non-smokers, levels of PAPP-A were reduced in smokers by some 15 per cent. Despite free beta hCG levels being reduced by 10-14 per cent in the second trimester of smoking women, in the first trimester period this is not evident. Simulation studies would suggest that in smokers the detection of trisomy 21 using free beta hCG, PAPP-A and maternal age will be reduced by some 5 to 6 per cent compared with that of the general population.