Correction of first trimester biochemical aneuploidy screening markers for smoking status: influence of gestational age, maternal ethnicity and cigarette dosage.

Objective: To examine the gestational age, maternal ethnicity and cigarette dosage effects of the reduction of maternal serum pregnancy-associated plasma protein A (PAPP-A) and free-β human chorionic gonadotrophin (free hCGβ) in smokers.

Methods: Maternal serum PAPP-A and free hCGβ corrected for confounders, excluding smoking, in first trimester smokers and nonsmokers were compared by gestational age, maternal ethnicity and cigarette dosage. A small set of second trimester smokers and nonsmoker controls were analysed for PAPP-A along with free hCGβ and assessed for gestational age effects of smoking.

Results: Pregnancy-associated plasma protein A reduction by smoking in the first trimester was not influenced by gestational age, however free hCGβ levels were only significantly reduced in weeks 12 and 13 in smokers. Ethnicity and cigarette dosage were also found to influence the reduction of both makers in smokers in the first trimester. In second trimester smokers, PAPP-A was found to be reduced by less and free hCGβ reduced by more than in the first trimester, although no second trimester gestational age effect on smoking was found.

Conclusions: Current methods of correcting for smoking status may be an oversimplification of a more complex subject.