Daily snuff use during pregnancy, gestational length and birth weight; register-based study

Snuff is a smokeless source of nicotine that is common in Scandinavia and increasingly used by women of fertile age. Persistent use of snuff during pregnancy has been associated with adverse pregnancy outcomes. Emerging data from the Medical Birth Registry of Norway distinguishes between occasional use and daily use. We provide preliminary estimates of associations between frequency of snuff and gestational length and birth weight.

Data on snuff use during pregnancies delivered in 2020 and 2021 were available for the west and central regions of Norway. Associations of snuff use with gestational length and birth weight at term (39-41 weeks) were estimated using quantile regression at the 25th, the 50th and the 75th percentiles, with adjustments for mother's age, pre-pregnancy weight, and parity. We compared associations with the pregnancy outcomes according to maternal snuff and cigarette use.

12.4% of 18 042 non-smoking women reported daily use of snuff before pregnancy, and 4.6% reported continuing use during pregnancy, with 1.2% still reporting daily use in the last trimester. Women with daily use through the last trimester delivered babies with a median gestational length reduced by 3.4 days (95% CI: -5.0 to -1.7 days) compared with women who never used snuff. The reduction was even stronger at the 25th percentile of gestational age. The median term birth weight was reduced by 44 g (95% CI: -134 to 46 g). These associations were much weaker for women who quit snuff at some point during pregnancy or used snuff only occasionally. Mothers who smoked daily through the last trimester had a median gestational length reduced by 2.1 days (95% CI: -2.7 to -1.4) and a median term birth weight reduced by 294 g (95% CI: -325 to -262) compared with never-smokers.

Daily snuff use through the last trimester reduced the median gestational length by more than three days. Snuff reduced birth weight, but not as much as smoking, suggesting that the predominant effect of smoking on fetal growth is not through nicotine but through the additional toxic chemicals in cigarettes or by reduced oxygen supply to the fetus.