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While previous reports of COVID-19 illness in pregnant women show generally good outcomes, the risk to expecting mothers and their infants isn't zero, researchers said.

For example, a pregnant woman in Switzerland delivered a stillborn infant at 19 weeks' gestation after testing positive for COVID-19, reported David Baud, MD, PhD, of the Lausanne University Hospital in Switzerland, and colleagues.

"This case of miscarriage during the second trimester of pregnancy in a woman with COVID-19 appears related to placental infection with SARS-CoV-2, supported by virological findings in the placenta," Baud's group wrote in a research letter in .

After delivery, swabs and biopsies of the placenta tested negative for bacterial infection, but positive for SARS-CoV-2. The placenta remained positive at 24 hours after delivery. No other causes of fetal demise were found.

Baud and colleagues noted that placental infection resulting in miscarriage or fetal growth abnormalities were observed in 40% of maternal infections with SARS and MERS coronaviruses. Further investigation is needed, they said, to determine whether SARS-CoV-2 crosses the placental barrier, and risk of adverse outcomes.

Growing Evidence of Maternal Death

Another case series indicated mothers are at risk, too: seven pregnant women testing positive for COVID-19 died of cardiopulmonary complications, reported Kjersti Aagaard, MD, PhD, of the Baylor College of Medicine in Houston, and colleagues in .

Nine women in the series endured a range of cardiopulmonary complications including acute hypotension, persistent hypoxia, organ failure, acute respiratory distress syndrome, and cardiac arrest. Only one recovered; besides the seven who died, one remained critically ill and on ventilator support at the time of publication. This report was the first to document maternal deaths related to COVID-19.

Aagaard said this case series does not establish risk; rather, documenting these cases cautions against assuming a low risk before solid data become available.

"The maternal mortality rate is unknown," Aagaard said in an interview with 麻豆传媒. "In the here and now, what this report tells us is the mortality rate among pregnant women due to COVID-19 disease is not zero."

Women in this retrospective case series were not selected by any form of systematic surveillance, but were voluntarily reported cases of maternal morbidity and mortality in patients with severe COVID-19 disease. The cases came from seven high-level maternity care centers in Iran.

Initial reports on more than 150 pregnant women from China indicated only one case of severe cardiopulmonary morbidity, Aagaard and colleagues observed. Traditionally, though, pregnant women have fared worse during viral outbreaks.

They experienced higher hospitalization and fatality rates during the 2002-2003 SARS epidemic and 2009 H1N1 pandemic, for example. While the SARS mortality rate in the general population was 10.5%, for pregnant women it was 25%. During the H1N1 pandemic, pregnant women accounted for around 5% of all deaths, but only 1% of the population.

Based on historical evidence and the documented cases of maternal death, Aagaard said she hopes this report will caution against complacency, reminding clinicians to stay vigilant when providing care to pregnant patients.

Sonja Rasmussen, MD, MS, a professor in the department of pediatrics and epidemiology at University of Florida in Gainesville, told 麻豆传媒 she expected early COVID-19 data on pregnant women from China to reveal some cases of severe illness and death.

Rasmussen, who previously worked on pandemic planning efforts for pregnant women at the CDC, added that fatality rates for pregnant women during SARS and H1N1 were cause for concern when predicting how SARS-CoV-2 might affect this population. While the new reports don't indicate how pregnant women fare compared to the general population, it's nevertheless clear that severely adverse outcomes are possible.

"I think these data here really remind us that we need a lot more information before we can say pregnancy doesn't increase your risk," said Rasmussen, who was not involved in the study.

While pregnant women are not exactly immunocompromised, Rasmussen said that their immune systems must adapt to tolerate the fetus. Shifts in the immune system, as well as other anatomical changes, may increase pregnant women's vulnerability to infection.

David Schwartz, MD, MS Hyg, a specialist in global maternal health and emerging infections at Augusta University in Georgia, identified several reasons that pregnant women have endured higher hospitalizations and fatality rates from previous viral infections, such as SARS and MERS.

"A lot of these reasons are based not just on the virus, but on the host," Schwartz told 麻豆传媒.

Physiological changes that go with pregnancy -- involving cardiac and respiratory systems and immune status -- may result in worse outcomes from some viral infections, he said. "The whole compendium of these changes can make pregnant women more vulnerable to having adverse outcomes."

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