Inhibin-A is a useful marker in antenatal screening for Down syndrome and forms part of the quadruple test (alphafetoprotein, unconjugated oestriol, human chorionic gonadotrophin and inhibin-A) and the integrated test (nuchal translucency and pregnancy associated plasma protein-A in the first trimester of pregnancy and the quadruple test in the second trimester). Rudnicka et al. reported that the level of inhibin-A among women who smoke at the time of their screening test is about 60% higher than that seen in women who do not smoke. 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 Spencer2 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%.
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