According to a study published in the journal PLoS One, maternal smoking reduces birth weight, supporting current research. Researchers from Lund University tested the effect of maternal smoking using sibling analysis.
More than 677,000 singleton births were included in the study. Births took place from 2002-2008. When the births were narrowed to include only sibling pairs researchers were able to isolate about 63,000 pairs born to just more than 28,000 mothers who admitted smoking during pregnancy.
Researchers found a connection between smoking habits and low birth weight. Light smokers gave birth to infants weighing up to 162 grams less than counterparts born to non-smoking mothers. Heavy smoking affected birth weight even more with infants weighing up to 226 grams less than counterparts. Quitting smoking during pregnancy reduced the impact, but if women started smoking again the relapse reduced infant weight by up to 83 grams – more than the 29 gram increase associated with quitting while pregnant.
Source: Juárez SP, Merlo J. Revisiting the Effect of Maternal Smoking during Pregnancy on Offspring Birthweight: A Quasi-Experimental Sibling Analysis in Sweden. PLoS One. 2013 Apr 17;8(4):e61734. doi: 10.1371/journal.pone.0061734. Print 2013.