Objective: To analyse the effects of smoking on first trimester parameters used in prenatal screening for Down's Syndrome.
Design: A chart study.
Setting: Primary care centres and maternity clinics of the participating universities' and central hospitals.
Population: Three thousand and one hundred fifteen women screened by nuchal translucency measurement and 4436 women screened by maternal serum samples. Only normal singleton pregnancies were included.
Methods: The mean multiples of median of pregnancy associated plasma protein A (PAPP-A), free beta human chorionic gonadotrophin (beta-hCG) and nuchal translucency were compared by independent samples t test after logarithmic transformation of the data between smokers and non-smokers.
Main outcome measures: PAPP-A and free beta-hCG concentrations and nuchal translucency measurements.
Results: PAPP-A was significantly reduced and nuchal translucency increased if the mother smoked. The smokers were more frequently considered as being at high risk for Down's Syndrome.
Conclusions: Correcting PAPP-A median for smokers down by 20% might improve the accuracy of the risk evaluations given to individual women. If the association between increased nuchal translucency and smoking can be confirmed, it poses interesting questions as to the reasons for increased nuchal translucency among normal pregnancies.