Researchers from the Mount Sinai Institute for Exposomic Research found that exposure to heat and air pollution was associated with lower birth weight, an indicator for lifetime development
Maayan Yitshak-Sade, PhD, Assistant Professor, Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai.
“What was your baby’s birthweight?” is one of the first questions parents are asked by friends and family when they welcome a new baby to their home. This question has scientific roots: normal birth weight is a marker for development, with potential health consequences for later childhood and adulthood. Birth weight is mostly determined by the genome, but it is also shaped by the exposome, which incorporates maternal health and environmental exposures like air pollution, heat, and even noise during pregnancy. Unlike genetics, expecting parents have some degree of control of their environment. If we can identify the critical time windows during pregnancy in which women are more vulnerable to the harmful effects of exposures, we can target interventions to reduce exposure that may be harmful. This study investigated how higher air pollution and heat exposures during different stages of pregnancy lead to an increased risk of lower birthweight among babies born at term.
What did we find?
In collaboration with researchers from the Harvard School of Public Health, Soroka University Medical Center and Ben-Gurion University, Dr. Yitshak-Sade and co-authors Dr. Allan Just and Prof. Itai Kloog, found that exposure to heat and air pollution was associated with lower birth weight. This was regardless of the pregnancy week at birth, season of birth, newborn sex, maternal socioeconomic status, smoking, and chronic conditions. For example, in pregnancies exposed to an average temperature of 75.2 degrees Fahrenheit (24 degrees Celsius), the newborn’s birth weight was about 8 grams smaller compared to pregnancies exposed to an average temperature of 73.4 degrees Fahrenheit (23 degrees Celsius). In addition, in pregnancies exposed to higher air pollution levels, babies were about 4 grams smaller on average. These birth weight differences may seem insignificant to the individual, but from a public health perspective has notable implications.
“A newborn’s birth weight was more affected by the adverse air pollution and heat effects towards the final weeks of pregnancy. This suggests that exposure to hotter temperatures in the 36th week of pregnancy will have more effect on birthweight than exposure in the second trimester,” says Dr. Yitshak-Sade. “We also found that higher air pollution exposure was associated with larger odds of being born small for gestational age – which means these babies were smaller compared to others born at the same pregnancy week”.
“A newborn’s birth weight was more affected by the adverse air pollution and heat effects towards the final weeks of pregnancy. This suggests that exposure to hotter temperatures in the 36th week of pregnancy will have more effect on birthweight than exposure in the second trimester”Dr. Maayan Yitshak Sade
Why is it important?
During prenatal care visits, parents are provided with information on a wide range of risk factors during pregnancy: infections, nutrition, exposure to violence, nutrition, medication consumption during pregnancy, and more. However, despite the growing evidence of harmful climate and air pollution effects, parents are still not advised about heat and air pollution exposure during pregnancy. Health care providers should convey these critical windows of vulnerability to heat and air pollution exposure to pregnant women during routine prenatal visits. This may increase awareness and hopefully motivate the expecting parents to reduce exposure as much as possible, especially in the final weeks of pregnancy.
What does this mean for pregnant women?
It is important to note that “the higher the better” is not always the case when it comes to birth weight. Also, lower weight within the normal range is not necessarily worse. Normal weight range depends on multiple variables in addition to environmental exposures: from genetics to nutrition and the length of gestation. Women are exposed to numerous environmental exposures during pregnancy and every step taken to reduce harmful exposures might help increase the chances of having a normal weight baby. The study suggests that women should be advised to limit their exposure to air pollution. They can do so, for example, by avoiding exercising near main roads and maintain proper ventilation indoors – especially when cooking. Women should also be advised to avoid exposure to heat, not necessarily extreme heat, when possible, and remain in cooler places.
Newborns health is affected by many environmental exposures during pregnancy, and these risks may be more significant among disadvantaged populations. In future studies, the research team is planning to take an exposomic approach and disentangle the complex relationship between the social and economic environment, environmental exposures, and birthweight, and to identify population groups that are more vulnerable to the effects of air pollution, heat, noise, and other exposures.
The information is for educational purposes only and is not intended as a substitute for medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you have regarding your medical care.