Brand JS, Gaillard R, West J, et al. - Data from 8,621 European liveborn singletons in two population-based pregnancy cohorts (n = 4,682 and n = 3,939, respectively) with fetal ultrasound and birth anthropometric measures, parental smoking during pregnancy, and maternal genetic data was analyzed in order to examine the relationships of maternal stopping, decreasing, and continuing smoking during pregnancy with longitudinal fetal growth by triangulating evidence from three analytical approaches to establish causal reasoning. From the early second trimester onwards, a constant linear dose-dependent relationship of maternal smoking with fetal growth was noted, whilst in women who quit smoking early in pregnancy, no significant growth deficiency was discovered except for a shorter FL during late gestation. These findings strengthen the significance of smoking cessation advice in preconception and antenatal care and designate that in women who struggle to quit, smoking decreases could reduce the risk of impaired fetal growth.