Effects of wildfire disaster exposure on male birth weight in an Australian population

Abstract

Background and objectives: Maternal stress can depress birth weight and gestational age, with potential health effects. A growing number of studies examine the effect of maternal stress caused by environmental disasters on birth outcomes. These changes may indicate an adaptive response. In this study, we examine the effects of maternal exposure to wildfire on birth weight and gestational age, hypothesising that maternal stress will negatively influence these measures.

Methodology: Using data from the Australian Capital Territory, we employed Analysis of Variance to examine the influence of the 2003 Canberra wildfires on the weight of babies born to mothers resident in fire-affected regions, while considering the role of other factors.

Results: We found that male infants born in the most severely fire-affected area had significantly higher average birth weights than their less exposed peers and were also heavier than males born in the same areas in non-fire years. Higher average weights were attributable to an increase in the number of macrosomic infants. There was no significant effect on the weight of female infants or on gestational age for either sex.

Conclusions and implications: Our findings indicate heightened environmental responsivity in the male cohort. We find that elevated maternal stress acted to accelerate the growth of male fetuses, potentially through an elevation of maternal blood glucose levels. Like previous studies, our work finds effects of disaster exposure and suggests that fetal growth patterns respond to maternal signals. However, the direction of the change in birth weight is opposite to that of many earlier studies.

Keywords: birth weight; disaster; gestational diabetes; macrosomia; maternal stress.

Figure 1.

Means for birth weight arising from ANOVA analysis of males (only) at three levels of estimated fire exposure between 2002 and 2004, with the fire and fire aftermath (2003) shown by the shaded area. Babies born between the fire (18 January) and March 2003 are estimated to be exposed in the third trimester, those born between April 2003 and June 2003 as exposed in the second trimester and those born between July 2003 and September 2003 as exposed in the first trimester. Babies born between October 2003 and December 2003 would have been conceived in the fire aftermath

Figure 2.

Plot of the percentage of births in each weight category by fire exposure in 2003, a chi-square test indicates that these differences are significant at P = 0.02. In the severely affected area, there were increases in birth weights between 4000 and 5000 g, which were not offset by the increases in birth weights between 500 and 1500 g