First trimester maternal serum inhibin A concentrations in smokers

Abstract

Screening for trisomy 21 in pregnancy is commonly carried out in the first trimester at 10-13 completed gestational weeks, or in the second trimester at 14-20 weeks. Such gestational age windows have been chosen to profit from the most favourable discrimination in marker levels between affected and unaffected pregnancies. The performance of each maternal serum screening marker does not, however, switch on and off at a particular gestational week or day, rather it improves and declines gradually. Pregnancy associated plasma protein A (PAPP-A) is most discriminatory at 9 weeks, and then from weeks 10 to 14, its performance begins to decrease. The performance of free hCGb increases from week 10 onwards and into the second trimester, and hence is included in both the first trimester combined test and the second trimester quad test. The performance of dimeric inhibin A, a quad test maker with second trimester levels more than twice as high in trisomy 21 compared with unaffected pregnancies, also improves with gestational age. Various studies have reported that inhibin A is significantly elevated by the late first trimester in trisomy 21 pregnancies.1-3 The addition of inhibin A to the combined test has the potential to increase the detection rate of Trisomy 21 by 3% 4 or reduce the false positive rate by 1.9% 5 over the 10-13 gestational week period. In addition, inhibin A is a potential marker for pre-eclampsia in both the first and second trimesters. 6Maternal smoking status is one of several factors known to affect many maternal serum screening markers, perhaps because of anatomical changes in the placenta induced by smoking. 7 In the second trimester, maternal smoking results in an almost 50% increase in inhibin A levels, 8 pushing them upwards towards trisomy 21 levels, and the increased levels seen in pre-eclampsia. For this reason, it is essential that maternal smoking status is recorded accurately and corrected for in screening algorithms. To our knowledge, there is no published data on the impact of smoking on inhibin A levels in the first trimester of pregnancy, and this study aims to investigate this. We searched our first trimester prenatal screening database for pregnancies screened between April 2010 and January 2011 and randomly selected 710 women who had identified themselves as smokers and 549 who had identified themselves as nonsmokers. Samples were retrieved from À20 C frozen storage, and inhibin A concentrations were determined by a Beckman Coulter Access2 immunoassay, used by our laboratory for routine second trimester screening. In 692 of the selfassigned smokers and 443 of the self-assigned nonsmokers, there was sufficient sample volume to also determine serum cotinine concentration by a manual enzyme linked immunosorbant assay (Concateno formally known as Cozart, Abbington, UK). The self-assigned nonsmoker/smoker groups were 74.7%/ 88.0% Caucasian, 11.7%/3.4% Asian, 0.8.6%/5.4% Afro-Caribbean, and 5.0%/3.2% Oriental or 'other', and the mean maternal age was 28 years 2 months in the self-assigne...

Effect of smoking status on inhibin‐A in second‐trimester prenatal screening for Down syndrome

“…They recommended that a simple adjustment could be used to ensure that the screening performance of the quadruple test was similar among smokers and non‐smokers. Cowans and Spencer reported that the level of inhibin‐A in the first trimester of pregnancy was only around 10% higher among women who smoked compared with women who did not, which suggests that the difference increases with gestation and a single adjustment in the second trimester maybe too simplistic. Further, it has recently (personal communication) been suggested that the increase among women who smoke was not as high as 60%.…”