[The effect of cigarette smoking during pregnancy on fetal growth].

The association between maternal smoking and poor pregnancy outcome, which is well established in medical literature, has been confirmed during the study conducted in one of Belgrade hospitals. The study comprised 1011 women who gave birth to a live born baby between June 1992 and March 1993 (infants with malformations were excluded). The women were interviewed by one person during the first three days after delivery. Data were collected on smoking habits during the first, second and third trimester of pregnancy, and on potential confounders including age, education, marital status, obstetric history, height, weight before pregnancy, weight gain during pregnancy, history about diseases before and during pregnancy, housekeeping and occupational activities, data about delivery and data about alcohol consumption. By the use of factor analysis infants characteristics, taken from medical histories, were classified in two groups: I group-birth weight, birth length, head circumference and chest circumference; II group-apgar score after one and after five minutes. The rough relation of smoking to the outcome was examined first. Adjustment was made for the potential confounders by the use of multiple regression analysis. Variables associated with both smoking and birth weight or apgar score after one minute (i.e. maternal height and weight) were considered as potential confounders. Infant sex, gestational age and parity were also included as possible confounders due to their strong link with birth weight and apgar. In the sample 42% of women were smokers, and 98% of them smoked filter cigarettes. In the group of smokers 312 smoked throughout pregnancy and 111 were inconsistent smokers (those who smoked during one or two trimesters only). According to smoking habits, mothers were divided into three groups: nonsmokers, those who smoked 1-9 cigarettes per day and those who smoked 10 or more cigarettes per day (Table 1). There was a strong relationship with significant linear trend between smoking and all observed birth outcomes except apgar score (Table 2). Significant reductions in birth weight (by 205 g), birth length (by 1.28 cm), head circumference (by 0.38 cm) and chest circumference (by 0.66 cm) were found to be associated with an average daily smoking of 10 or more cigarettes after adjustment was made for potential confounders. Even a smaller number of cigarettes affected foetal growth. Infants born by mothers who throughout pregnancy smoked 1-9 cigarettes per day (mean 4.07, range 1-8) weighted significantly less (by 89 g) and had head circumference significantly smaller (by 0.23 cm) in comparison with infants born by mothers nonsmokers. Inconsistent smoking during pregnancy had no significant effect on foetal growth with the exception of smaller birth length (by 2.30 cm; p = 0.002) in infants born by mothers who smoked during the second and third trimester. It is possible that the relatively small number of women inconsistent smokers had a bearing on the results. According to the results obtained it seems that either there is no threshold for the effect of smoking on foetal growth, or it is very low. Nevertheless, since the effect of smoking is weaker if the number of cigarettes smoked is smaller it is reasonable to assume that the reduction in the number of cigarettes smoked in pregnancy would serve as prevention irrespective whether the threshold existed or not.