Fig. 3.

Heat stress particularly affects pregnancies with a female fetus. Relative risk of preterm delivery after heat exposure stratified for fetal sex. Heat events defined by the daily maximum temperature (a) and the daily apparent temperature (b) in pregnancies with a female offspring, and male offspring (c, d) respectively (female n = 12,552, male n = 12,954). The number of preterm births per category and fetal sex is shown on the Y-axis; X-axis is displayed in log scale; RR, 95% CI; Pearson χ2.