The more severely infected an expectant mother is with COVID-19, the more likely she is to give birth prematurely. That's according to researchers at the Wayne State University School of Medicine and the National Institutes of Health's Perinatology Research Branch in Detroit.

"The more severe the SARS-CoV-2 infection, the greater the risk of preterm birth," said Roberto Romero, MD, DMedSci, chief of the Perinatology Research Branch and professor of Molecular Obstetrics and Genetics at the Wayne State University School of Medicine. "There was a dose-dependent relationship between the severity of SARS-CoV-2 infection and the risk of prematurity."

The report in the American Journal of Obstetrics and Gynecology, based on a retrospective observational study, used data from 14 National Health Service maternity hospitals in the United Kingdom to assess the effects of SARS-CoV-2 infection in pregnancy.

Public-health officials have strongly urged pregnant women to be vaccinated against the novel coronavirus because of greater risks of adverse outcomes for the women and their babies.

Of the 1,223 participants, 4.2% had preeclampsia, 1.3% had a miscarriage, and 17.6% had preterm birth. In addition, 10 fetal deaths (0.81%) occurred.

An Israeli study, meanwhile, also found an increased risk of adverse outcomes for both newborns and their COVID-19—symptomatic mothers. The study was published in the Journal of Maternal-Fetal & Neonatal Medicine.

The Detroit study, conducted in collaboration with the Fetal Medicine Foundation of London, concluded that the excess rate of premature birth was largely due to medically induced preterm birth brought about by concerns for the health of the mother, such as preeclampsia.

The authors pointed out that preterm birth (defined as a delivery that occurs before 37 weeks' gestation) is the leading cause of perinatal morbidity and mortality worldwide. One-third of cases are related to medical conditions that affect either the mother or the unborn baby, such as preeclampsia (a sudden increase in blood pressure after the 20th week of pregnancy).

The study found that the more severe the COVID-19 infection, the greater the risk of preeclampsia. In the study, women with severe COVID-19 tended to be older and had a higher body-mass index. More than one-half of the 51 cases of preeclampsia—23—were diagnosed after SARS-CoV-2 infection. Of the 30 cases included in the analysis, 13 had preterm preeclampsia (<37 weeks) and 17 had term preeclampsia.

The researchers noted that, in the cohort studied, physicians appeared to be medically inducing early delivery to save the lives of mothers infected with COVID-19. They emphasized that the possibility that COVID-19 infection causes preeclampsia must be considered.

"The principal finding is that there is a dose-response relationship between the severity of SARS-CoV-2 infection and the risk of subsequent development of preeclampsia and preterm birth," Dr. Romero said. "Patients with severe COVID-19 have a five-fold greater risk of preeclampsia than asymptomatic patients. Moreover, the relative risk of developing preeclampsia in women with moderate or severe COVID-19 was 3.3-fold higher than in those with asymptomatic or mild infection."

The Israeli study assessed 2,471 women in the third trimester of pregnancy and found "significant differences" for symptomatic COVID-19 patients. Differences included higher rates of gestational diabetes, lower white blood cell counts, and heavier bleeding during delivery. Researchers also identified respiratory complications in the offspring.

Of the 172 COVID-positive women—56 them symptomatic—monitored at the Mayanei Hayeshua Medical Center in Israel, only one woman needed mechanical ventilation, and no deaths occurred.

"Our analysis finds there were no significant increase in Cesarean delivery in women, who were COVID-19 positive and the incidence of preterm deliveries was not significantly different among the three groups (healthy, covid positive asymptomatic, covid positive symptomatic). Most pregnancy and delivery outcomes were similar between COVID-19-positive and -negative parturients (a woman about to give birth; in labor)," noted the study authors. "However, there were significant differences between the COVID-19-positive and healthy controls included higher rates of GDM (gestational diabetes), low lymphocyte counts (white blood cell count) which were significantly lower, postpartum hemorrhage (bleeding during birth), and neonatal respiratory complications."

The study looked at births at the hospital between March 26 and September 30, 2020. On average, the increased risk of incidence of adverse outcomes was 13.8% higher for asymptomatic COVID-19 patients and 19.6% higher for those showing symptoms, according to the study.

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