A systematic review of associations between maternal exposures during pregnancy other than smoking and antenatal fetal measurements

Background
Reduced birth weight is associated with many maternal environmental exposures during pregnancy, but the gestational age at onset of this association is unknown. We have previously reported associations between maternal smoking and fetal size.

Objective
To report on our systematic review of the literature describing associations between antenatal size and growth and maternal exposures during pregnancy.

Data sources
Electronic databases (OVID and EMBASE) and web sites for cohort studies were searched. Study eligibility. Studies were eligible if they examined associations between maternal environmental exposures (including ambient air exposure, diet and alcohol) and antenatal fetal ultrasound measurements. Study appraisal. The Navigation Guide was used to assess the strength of evidence.

Results
There were 451 abstracts identified and 36 papers were included of which maternal diet was the exposure of interest in 15, maternal ambient air exposure in 10, maternal alcohol in 3 and other exposures in 8. The first paper was published in 2006. Associations were present between exposures in 18% of comparisons with second trimester measurements and in 46% of comparisons with third trimester measurements. In the third trimester, when an association was present, reduced head size was most commonly (58%) associated with current or previous maternal exposure, with reduced length being least commonly (32%) associated and reduced weight being intermediate (52%). In the third trimester, increased maternal nitrogen dioxide exposure was associated with reduced head size was associated with in all seven studies identified and reduced fetal weight in five out of six studies.

Conclusion
There is sufficient evidence of toxicity in the context of maternal exposure to nitrogen dioxide and reduced third trimester fetal head size. There is insufficient evidence of toxicity with regard to maternal exposures to dietary factors, alcohol and environmental chemicals and reduced fetal size.