Dose-Response Relationship between Maternal Involuntary Tobacco Smoking and Various Birth Outcomes

The main goal of this study was to assess the dose-response relationship between involuntary tobacco smoking of pregnant mothers and birth outcomes. The study covered a total of 285 healthy, non-smoking pregnant women aged 18-35 years and recruited from outpatient prenatal dispensaries being in the first and second trimester of pregnancy. The subjects were grouped into environmental tobacco smoke (ETS) exposure categories according to weighted number of cigarettes that were daily smoked by others at home during the last two trimesters of pregnancy. In respect to birthweight and head circumference the effect was only seen in the newborns of longer gestational age (LGA = 40 weeks and more), however, a reduction in natal body length could also be confirmed in the term babies with shorter gestational age (SGA = 39 weeks and less). In total, there was a higher proportion of variability of length at birth explained by ETS (4.7%) than of birthweight (1.9%) and head circumference (1.2%). With each 10 cigarettes of passive daily smoking the average reduction in birthweight was 97.15 g, while in the LGA group 155.4 g and in the SGA newborns 41.3 g. The average reduction in length at birth was 1.0 cm, and the effect was of about the same magnitude in the LGA group and in the SGA newborns. The mean reduction of head circumference per 10 cigarettes of passive smoking was 0.26 cm, while in the LGA group, the reduction in cranial parameter was 0.46 cm, the impact of ETS was not considerable in the SGA group. The results of the study may suggest that the body length at birth is a measure of fetal growth more vulnerable to adverse influences of external environment than the birthweight and head circumference.

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