Passively inhaled tobacco smoke - pregnancy and neonatal outcomes in correlation with placental histopathology

Introduction: We aimed to investigate the effect of maternal passive smoking (MPS) during pregnancy-on placental pathology and pregnancy outcomes. Methods: A prospective case-control study. We recruited low-risk laboring women at 37+0–41 + 0 weeks between 9/2019–7/2020. MPS was defined as exposure to in-house spouse tobacco smoking of >20 cigarettes/day in the absence of maternal active-smoking. In attempt to “purify” the effect of MPS on placental pathology-we excluded cases with preeclampsia, diabetes, suspected fetal growth restriction (FGR), preterm labor, and illicit drug use. Maternal characteristics, pregnancy outcomes, and placental pathology were compared between the MPS group and a control group matched for gestational age, maternal age, and delivery date. Placental lesions were classified according to the “Amsterdam” criteria. The study was powered to detect a 33% difference in placental malperfusion lesions. Multivariable regression was performed to identify independent associations with placental malperfusion lesions. Results: In labor, the MPS group (n = 115) had higher rates of meconium stained amniotic fluid (MSAF, p < 0.001) and non-reassuring fetal heart-rate (NRFHR,p = 0.006), compared to controls (n = 115). Neonates in the MPS group had higher rates of undiagnosed FGR (p = 0.01) and NICU admissions (p = 0.004). The MPS group had higher rates of placental-hypoplasia (p = 0.02) and fetal vascular malperfusion (FVM) lesions (p = 0.04). In regression analysis MPS was associated with FVM lesions independent of background confounders (aOR = 1.24 95% CI 1.10–2.65). Discussion: In otherwise low-risk pregnancies, MPS was associated with higher rates of MSAF, NRFHR, undiagnosed FGR, and NICU admissions, probably mediated via placental FVM. These worrisome findings mandate patient counseling and further investigation in larger population-based studies.