Smoking in pregnancy, maternal blood pressure, pregnancy outcome, baby weight and growth, and other related factors. A prospective study.

Abstract

A prospective survey was conducted among 200 women attending the 2 primary maternity units in Sheffield in an attempt to establish what factors are primarily responsible for the smaller size of the infants born to smokers. Fetal size and growth was related to the maternal smoking pattern and to various associated matters. The mothers were classified according to their smoking habits into 5 groups - nonsmokers occasional smokers regular smokers of about 10 cigarettes daily and smokers of 20 or more cigarettes daily. When maternal blood pressure and smoking were compared highly significant differences were seen. The lowest blood pressure group contained relatively more smokers and the highest blood pressure group relatively fewer. When pregnancy outcome was related to blood pressure levels and maternal smoking a significant difference was found implicating smoking as an additional hazard. The frequency of maternal smoking was compared with a number of factors - social class of consort maternal age parity maternal height social class of womans father educational level age of consort maternal attitude to the pregnancy work in pregnancy and sex of offspring - factors which might themselves be responsible for smaller fetal weight. A number of these factors were linked with maternal smoking but when mean fetal weights were compared for smoking and each of the other factors in turn it was clear that the smoking effect was clearly independent of each of the other factors regardless of whether the factor was linked with smoking and whether it was itself linked to smaller infants. The results fail to support the idea that smaller infants born to smokers are smaller because of associated factors. Smoking per se is implicated without any reasonable doubt.