Ambient Temperature Linked to Stillbirth and Short Pregnancies

A new study suggests that environmental factors may be a contributory cause of adverse birth outcomes, such as preterm births and stillbirths.

Researchers at the Queensland University of Technology (QUT; Australia) and the Norwegian University of Science and Technology (NTNU; Trondheim) examined the relation between ambient temperature and preterm birth and stillbirth in Brisbane (Australia), between 2005 and 2009. During this period a total of 101,870 births were recorded, of which 653 (0.6%) were stillbirths. The researchers used a Cox proportional hazards model with live birth and stillbirth as competing risks, comparing recorded weekly temperature, humidity, and air pollution levels for each pregnancy.

The results showed that higher ambient temperatures in the last four weeks of the pregnancy increased the risk of stillbirth; the lowest risks were in the coolest weeks, and warm temperatures with weekly means of 23 °C were just as dangerous as the hottest weeks. The hazard ratio for stillbirth was 0.3 at 12 °C, relative to the reference temperature of 21 °C; the temperature effect was greatest at less than 36 weeks of gestation. The researchers also found an association between higher temperature and shorter gestation, with a hazard ratio for stillbirth of 0.96 at 15 °C and 1.02 at 25 °C. This effect was greatest at later gestational ages. The study was published in the December 2011 issue of the American Journal of Epidemiology.

“We found that increases in temperature increased the risk of stillbirth, and this was particularly true in the earlier stages of pregnancy before 28 weeks,” said lead author associate professor Adrian Barnett, PhD, of the QUT Institute of Health and Biomedical Innovation (IHBI). “It is known that women should avoid hot tubs or Jacuzzis during pregnancy as this can cause a pregnancy termination, and that dehydration caused by heat stress and sweating could be harmful to a fetus and induce birth.”

Babies born before the 37th week of gestation are born prematurely. The risk of complications increases the earlier the baby is born, including immature lungs, pneumonia, apnea, bradycardia, jaundice, cerebral palsy, intraventricular hemorrhage (IVH), an immature gastrointestinal and digestive system, patent ductus arteriosus (PDA), anemia, retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), sepsis, and various infections.

Related Links:
Queensland University of Technology
Norwegian University of Science and Technology