Brand JS, et al. - Data from 8,621 European liveborn singletons in two population-based pregnancy cohorts (the Generation R Study, the Netherlands 2002–2006 [n = 4,682]) and the Born in Bradford study, United Kingdom 2007–2010 [n = 3,939]) with fetal ultrasound and birth anthropometric measures, parental smoking during pregnancy, and maternal genetic data was investigated in order to examine the relationships of maternal quitting, decreasing, and continuing smoking during pregnancy with longitudinal fetal growth by triangulating evidence from three analytical approaches to establish causal inference. From the early second trimester onwards, a linear dose-dependent organization of maternal smoking with fetal growth was noted whilst no major growth deficiency was seen in females who left smoking at the beginning of pregnancy except for a smaller femur length throughout late gestation. Outcomes strengthen the significance of smoking discontinuance advice in preconception and antenatal care and designate that decreases in smoking could reduce the risk of impaired fetal growth in women who strive to quit.