Impact of rising ambient temperatures on fetal development

Are the slowly rising temperatures across the United States and the world leading to fetal development issues, particularly fetal growth? A new study published in Environmental Health Perspectives indicates that higher temperatures may lead to lower fetal growth.

Researchers looked at 29,597,735 live births of a single newborn between 1989 and 2002 from 403 counties across the United States. They estimated the county-level average temperatures using a spatially refined gridded climate set. The study adjusted for a variety of variables including smoking or drinking during pregnancy, chronic hypertension, parity, year and month of conception, the mother’s demographics, and chronic hypertension.

The data indicate that exposure to a high ambient temperature (>90th percentile) throughout the entire pregnancy was linked to a higher risk of the baby being small for gestational age (SGA) and having a lower birth weight when born at term. Exposure to a low ambient temperature (≤10th percentile) for the entire pregnancy had no link to a newborn being SGA, but there was an association with a small decrease in birth weight at term. The researchers found that the risk of term SGA and lower birth weight was strongly linked with areas in the Northeast, areas with cold or very cold climates, and the temperature averaged across the second and third trimesters.

The researchers did emphasize that the study had limitations, including being unable to track the mobility of every pregnancy and an inability to correlate infants born to the same mother because of data deidentification; and that the use of county-wide temperatures could have led to a measurement error when compared with the temperature actually experience by the mother. They also emphasized caution in extrapolating the results to future impact on fetal development because adaptation to the increasing temperature may be possible.