Maternal smoking during pregnancy and fetal growth. Effects in preterm infants of gestational age less than 33 weeks.

Objective: To evaluate the effects of maternal smoking during pregnancy on foetal growth in preterm infants with gestational age (GA) <33 weeks.

Population And Methods: Prospective observational cross-sectional study from two French perinatal networks cohort of preterm infants. Cases were 358 very preterm infants (GA 24-32 weeks) divided into two groups as maternal smokers (129) and non-smokers (229). 361 term infants (GA 37-41 weeks) also divided into two groups as maternal smokers (129) and non-smokers (232) served as comparison group (controls). We studied the influence of maternal smoking on foetal anthropometric growth parameters (BW, BL and head circumference defined according to AUDIPOG curves) in groups and compared cases and controls. Other causes of foetal growth restriction were excluded.

Results: Maternal characteristics (age, height, pre-pregnancy body weight, parity, foetus sex) were similar in both groups and sub-groups. Mothers who smoked were younger (P <0.001), more likely to be unemployed (P <0.001) and to have undergone less school education (P <0.001). Smoking did not alter foetal growth in preterm infants: maternal smokers versus non-smokers BW (P = 0.52), BL (P = 0.44) and HC (P = 0.81). Growth restriction was marked in term infants with BW (P <0.001), BL (P <0.001) and HC (P <0.01). In multivariate analysis, after adjustment for other confounding factors, foetal growth appeared to be significantly altered by maternal smoking during pregnancy only in term infants.

Conclusion: Our study suggests that effects of maternal smoking during pregnancy on foetal growth are gestational age-dependent.