Maternal smoking could affect a child's ocular health even into adulthood. Photo: Getty Images.

Because a developing fetus is entirely dependent on the health and physiology of the mother, the lifestyle choices she makes are often fraught with additional layers of responsibility. Smoking while pregnant is known to negatively affect a child’s ocular health and increase the risk of refractive errors, strabismus and retinal or optic nerve abnormalities. A thinner retinal nerve fiber layer (RNFL) has also been observed in children with in utero exposure to cigarette smoke. In addition, alcohol consumption during pregnancy has been linked to a number of ocular issues. A team of researchers recently found that in utero exposure to smoke, but possibly not to alcohol, may continue to adversely affect the RNFL into young adulthood.

The researchers gathered participant data from the Raine Study in Western Australia, which had been following a cohort since the prenatal period (n=1,287). Between 1989 and 1991, pregnant women completed questionnaires at 18- and 34-weeks pregnant about their current smoking and drinking habits, which they completed again at one- and 13-year follow-ups after the birth of their child. At the 20-year follow-up, participants underwent a comprehensive eye examination, including spectral domain optical coherence tomography imaging of the RNFL.

Of the participants, aged 19 to 22 at the time of examination, 77% had no in utero exposure to cigarette smoke and 21% had continual exposure. The researchers corrected for potential confounders, including in utero alcohol exposure and childhood passive smoking, and found that participants who had continued in utero exposure to cigarette smoke had a thinner RNFL.

“Participants who had continued in utero exposure to >10 cigarettes/day and ≤10 cigarettes/day had thinner RNFLs by 6.6µm and 3.7µm, respectively, than those with no exposure,” the researchers wrote in their paper. “The repercussions of in utero exposure to smoking on fetal health may be largely attributed to the reduction in blood flow to the placenta induced by constituents of cigarette smoke such as nicotine and carbon monoxide, resulting in fetal hypoxia.”

Interestingly, childhood passive smoking was not found to affect RNFL thickness after accounting for in utero exposure to smoking.

No association was detected between RNFL thickness and in utero alcohol exposure, even though half of the mothers reported drinking more than once during their pregnancy. This finding came as a shock to the researchers, considering optic nerve hypoplasia is a common ocular manifestation of fetal alcohol syndrome; however, the researchers attribute this partly to the small proportion of heavy drinkers in the sample. Even in the group of mothers who consumed more than one drink per week, 75% consumed less than nine per week.

“It is likely that, for many of these mothers, alcohol consumption was spread out in small amounts over a period of time rather than due to binge-like drinking behavior, which is known to be more detrimental to fetal health,” the researchers suspect.

The study did confirm that maternal smoking leads to negative outcomes on a child’s ocular health. “In utero exposure to cigarette smoke is associated with a thinner RNFL in young adulthood, independent of other early-life environmental factors,” the investigators concluded. They plan to continue following the same cohort to determine if negative effects are sustained through older adulthood.

Lee SSY, Mackey DA, Sanfilippo PG, et al. In utero exposure to smoking and alcohol, and passive smoking during childhood: effect on the retinal nerve fiber layer in young adulthood. Ophthalmic Epidemiol. September 5, 2021. [Epub ahead of print].