How heat exposure can influence fetal development during pregnancy?

Summer is coming! And high temperatures and heat waves followed. The frequency and intensity of heatwaves are increasing rapidly and may be set to escalate in the coming decades. Are you aware of the fetal health risks of heat exposure during pregnancy?

Pregnancy induces several physiological and anatomical changes in women such as changes in surface area-to-mass ratio, weight gain, high basal metabolic rate, higher fat deposits that retain heat, and reduced systemic vascular resistance, which can pose particular challenges to maternal thermoregulation. Previous studies showed that maternal exposure to heat was associated with an increased risk of preterm birth, low birth weight, and stillbirths. [ref] There are a couple of potential mechanisms that may contribute to fetal restricted growth. [ref]

Firstly, when pregnant women are in the context of high ambient temperature, peripheral vasodilation increases blood flow to the skin as a means to enhance heat loss via convection and evaporative capacity, which may occur at the expense of blood flow to the placenta. Adequate placental blood flow is an essential condition to maintain the metabolic demand and development of the growing fetus. Inadequate uteroplacental blood flow could reduce the transfer of water, oxygen, and nutrients to the fetus and the removal of metabolic waste from the fetus.

Secondly, experimental studies found that heat stress is associated with reduced substrate supply like glucose and amino acid to the fetus, which may have negative consequences for normal fetal growth and development. This finding is attributable to a smaller surface area of the placenta and a concomitant deficiency in the number and activity of glucose and amino acid transporters.

Thirdly, elevated ambient temperature could serve as a stressor capable of activating the maternal hypothalamic-pituitary-adrenal/ovary. Evidence showed that stress hormones (e.g., cortisol, estrogen) can produce related fetal developmental alterations, including restricted placental and fetal growth. Finally, heat stress results in upregulated expression of heat-shock proteins with associated increased production of inflammatory factors, which may play a potential role in leading to adverse birth outcomes.

In the BiSC project, we are going to explore if and how maternal exposure to heat could impact fetal physical and neurological development.

Thanks so much for the contribution of the BiSC family. Soon we will be able to provide more information on it, stay tuned!

This news has been written by Yu Zhao, a pre-doctoral student of the BiSC Project.