According to a new study, prolonged summer heat stress increases the risk of preterm birth for pregnant women. Several days in a row with temperatures of 30 degrees increased the risk for women in the 34th to 37th week of pregnancy by 20 percent, several days with more than 35 degrees even by 45 percent, according to a study led by researchers at the University Hospital Hamburg-Eppendorf (UKE) revealed.

The team led by professors Petra Arck and Anke Diemert analyzed more than 42,000 patient files from women who had given birth at the Hamburg clinic in the past 20 years.

From the third day

In the specialist journal “eBioMedicine”, the doctors found that expectant mothers apparently survive one or two hot days well. Premature labor only sets in more frequently on the third, fourth or fifth day without cooling down, especially if high humidity intensifies the perceived heat sensation.

The study only considered so-called spontaneous premature births and not those in which the child was born by caesarean section because of danger to himself or the mother, as Diemert explained.

According to the doctors, heat waves that last for days are extremely stressful for pregnant women. The abdomen presses on the main vein, which is why not as much blood arrives at the heart. The heat dilates the blood vessels and increases the effect. The supply of oxygen and nutrients to the baby in the uterus is also impaired. In addition, the pregnancy hormones decrease while the level of the stress hormone cortisol increases. In addition, there is a lack of sleep.

Normally, a pregnancy lasts an average of 40 weeks. The study was about so-called late premature births, in which the child is born between the 34th and 37th week of pregnancy. Unlike children born earlier, these babies are usually not about survival, Diemert said. But later in life, they would have an increased risk of health problems such as poor concentration, infections and obesity.

Not a good prognosis due to global warming

The number of late premature births is increasing in all industrialized countries. One reason for this could be global warming, suspects the Hamburg research team, which also includes meteorologists. In view of the climate forecasts for the next ten years, the proportion of children born prematurely could rise from a good 8 percent today to 15 percent in 2033.

It is true that this study cannot conclusively prove a direct causal connection between increasing summer heat and the increasing risk of preterm birth. “But due to the large amount of data, it is very difficult to imagine any other effect.”

study press release