Smoking and the correlation between birth weight and placental weight. Evidence of interaction with maternal haptoglobin phenotype

ObjectiveThe negative effects of cigarette smoking on human reproduction are well known. In a previous paper we have reported that negative effects of smoking on fertility are observed in women carrying the Haptoglobin (Hp) 2 phenotype only. In the present note we have examined the effect of smoking on the correlation between birth weight (BW) and placental weight (PW) and the interaction with maternal Hp phenotype.Study designWe have studied 584 consecutive newborns and their healthy mothers from the White population of the central area of Italy. Written informed consent was obtained by mothers to participate to this investigation that was approved by the Department of Pediatrics. Maternal Hp phenotype was determined by the method of Smithies as previously described. Differences between correlation coefficients were evaluated according to Snedecor and Cochran and according to Soper. Difference between means was calculated by Student's-t test using commercial software (SPSS).ResultsA strong decrease of correlation is seen in smoking mothers with Hp 2 phenotype only (p < 0.0001). No statistically significant effect of smoking is present in mothers with Hp1 or Hp2-1 phenotype. A statistically significant decrease of BW in smoking mothers is observed in both Hp 2 mothers and in mothers carrying the Hp*1 allele. On the contrary a decrease of PW is observed only in mothers carrying Hp*1 allele but not in Hp 2 mothers. This indicates a concordant effect of smoking on BW and PW in mothers carrying Hp*1 allele but a discordant effect of BW and PW in Hp 2 mothers. This could explain the lack of correlation between BW and PW in smoking mothers carrying the Hp 2 phenotype.ConclusionThe combined phenotype smoking-Hp 2 shows different effects on BW and PW. Hp 2 has no effect on the decrease of BW determined by smoking but shows important effect in neutralizing the decrease of PW due to smoking: Hp polymorphism may be a factor with protective effects prevalent on placental growth as compared to fetal growth.