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Researchers have identified local heat waves as a factor that can lead to an increased risk of preterm birth and stillbirth, according to a cohort study published in JAMA Network Open. Authors found a significant link between periods of high temperatures in some of the top metropolitan statistical areas in the United States and early deliveries. Looking at 53 million births from 1993 to 2017, they concluded that after 4 consecutive days of mean temperatures exceeding the 97.5th percentile, the rate ratio for preterm birth was 1.02 (95% CI, 1.00-1.03), and the rate ratio for early-term birth was 1.01 (95% CI, 1.01-1.02). In other words, heat waves were positively associated with daily rates of preterm and early-term births. 

Effects of heat: There are a few possible reasons for the early births, the authors surmise. Heat stress and dehydration can reduce uterine and placental blood flow, cause an inflammatory reaction that may affect the induction of labor, or possibly trigger the premature rupture of membranes. Additionally, heat waves may make the mother’s comorbid health conditions worse, causing fetal distress. Read more about pregnant patients in UC from the JUCM archives: Point Of Care Ultrasound Diagnosis Of Ruptured Ectopic Pregnancy In An Urgent Care Setting

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Heat Waves Increase Risk of Preterm Birth