This paper looks at the relationships between genes, smoking, and birth weight. It finds that each additional daily cigarette smoked during pregnancy reduces birthweight by between 20 and 40 grams, regardless of the childs’s genetic predisposition.
The researchers used information from a sample of 5000 mother-baby pairs in the Avon Longitudinal Study of Parents and Children (ALSPAC), for whom it was possible to assess the mothers’ smoking through urine samples. They then checked the results using data from the UK Biobank, which contains self-reported information on a much bigger sample of 250,000 people.
They were able to compare the ALSPAC smoking information with data on the women’s genetic propensity for smoking to affect their child’s weight – scientists have identified one of the most important genetic variants through which this effect takes place. They also produced a score to measure the child’s genetic tendency to be born with a larger weight.
The research confirmed earlier findings that both genes and smoking could significantly affect birth weight. But they found no evidence that the child’s genetic inheritance could cushion the damage from smoking: babies genetically predisposed for higher birth weight still suffered the same effect.
This suggests that both nature and nurture affect birth weight, but there are no meaningful interactions between the two. The authors say the work represents the most comprehensive analysis so far on the interplay between smoking, genes and birth weight, and can serve as a template for future studies.