A Study of Smoking and Pregnancy with Special Reference to Fetal Growth

A prospective study of the influence of smoking on pregnancy and its outcome was made of 5272 women in an urban community during 1974/75. Approximately 90 % of the pregnant women in the population took part in the programme. Ultrasonic measurements of the fetal biparietal diameter (BPD) were made from the 18-20th week (early in the study the first BPD measurements were obtained at 28 weeks). Growth curves of BPD were constructed for each week, separately for the smoking groups (49 %) and the non-smoking group (51 %) by compiling 5714 BPD measurements, only women subsequently delivered between 266 and 294 days after the last menstrual period were included to avoid erroneously skewed growth profiles. The BPD increased faster during gestation in the non-smoking group, the difference from the smoking group being significantly apparent from the 28th week onwards and positively correlated to the average number of cigarettes smoked. There was a preponderance within the non-smoking group for marriage, and preeclampsia; and within the smoking group for abruptio placentae, pre-term delivery, low birth-weight, short birth-length, small head circumference, and small-for-gestational-age. The low birth-weights were independent of maternal prepregnant weight and weight gain. Compared with data obtained in a similar study in the same community, 1963/64, the prevalence of smoking among pregnant women had increased from 44 % to 49 %. The present study demonstrates the early onset of intrauterine growth retardation in pregnancies of smoking mothers. The results suggest that the fetal growth retardation is a direct pharmacological effect on the fetus rather than an influence resulting from nutritional deprivation and points to appearent inefficiency of the programme deterring women from smoking.