Evaluation of smoking as a risk factor for activated protein C resistance during pregnancy

The effect of smoking on the activated protein C (APC) ratio in normal gestation was systematically investigated. The frequency of acquired APC resistance (APCR) in the smoking and non-smoking subjects with normal follow-up of pregnancy and the outcome observed in these two groups were documented.

A total of 180 normal pregnant women (non-smokers 138, smokers 42) in different trimesters of gestation admitted to the hospital were enrolled into a cross-sectional study. APC ratio, factor V, factor VIII, protein S and protein C were quantitated. Factor V Leiden mutation analyses were performed by real-time PCR.

This cross-sectional study tries to detail the effect of smoking on APCR together with the changes in some components of the protein C/protein S system which may contribute to alterations in the APC ratio in normal gestation. A decreased APC ratio observed in pregnancy was statistically significant in the smokers (p = 0.03). When the trimesters were taken into consideration, APC ratios were significantly lower in the third trimester in the smokers compared with the non-smokers in the same trimesters (p = 0.001). The difference in the APC ratio between the groups in early pregnancy was not significant.

These studies have demonstrated that the modified test abolishes the pregnancy-related effect on the APCRs in normal pregnant non-smoking women presumably by normalization of coagulation factors (except factor V). Our result for the non-smoking group is consistent with data provided in previous studies. However, we noted a very significant decrease in the APC ratio in smoking pregnant women in the third trimester, most likely secondary to decreased factor V levels.