How does smoking reduce the risk of preeclampsia?

Abstract

Although smoking during pregnancy may lead to many adverse effects, such as fetal growth restriction, placental abruption, stillbirth, and preterm labor, smoking is the only environmental exposure known to consistently reduce the risk of preeclampsia and gestational hypertension.1 The article by Wikstrom et al2 is a major step forward in understanding this protective effect. Using data from the Swedish Medical Birth Register in a large epidemiological study of >600 000 Nordic women, the authors conclude that use of Swedish snuff, a smokeless tobacco, did not reduce the risk of preeclampsia and gestational hypertension but that tobacco, when smoked, did. They infer that combustion products of tobacco, such as carbon monoxide (CO), protect against preeclampsia but that constituents of tobacco, such as nicotine, do not. The data strengthen and extend results of a previous smaller study using the Swedish Medical Birth Register, which had reported a similar association.3 Although snuff use did not reduce the risk of mild or severe preeclampsia, preeclampsia that began before or after 37 weeks of gestation, or preeclampsia with or without delivery of a small for gestational age (SGA) infant or stillbirth, smoking reduced the risk of all categories of preeclampsia except for preeclampsia with an SGA infant or stillbirth. Of considerable interest, using data from women who changed their tobacco habits at gestational weeks 30 to 32 from those reported at the first antenatal visit (usually before 15 weeks of gestation), Wikstrom et al2 found that women who had reported smoking at the first antenatal visit but no use of tobacco at 30 to …