COVID-19 Severity in Pregnancy Appears Lower Than H1N1

What your doctor is reading on

MAY 18, 2020 — Unlike past respiratory illnesses, pregnancy does not seem to put women at risk of worse outcomes from COVID-19, according to the first 6 weeks of births to women in the UK during the COVID-19 era.

“When we actually looked at our data in nonpregnant women of the same age, the outcomes look to be pretty similar for [mothers]” with COVID-19, study coauthor Marian Knight, MBChB, DPhil, professor of maternal and child health at the University of Oxford, United Kingdom, told Medscape Medical News.

The data, currently available on a pre-print database, also suggest that more severe outcomes are more likely in later pregnancy, which Knight said should support guidance that women in the third trimester be vigilant with physical distancing, masking, and hand hygiene to avoid acquiring SARS-CoV-2 in the first place. The paper has not been peer-reviewed and therefore the findings should be taken as preliminary until it is accepted.

The data may also temper concerns raised in early case reports on miscarriage and other poor outcomes.

“Most of the publications in pregnancy have been case series, and we’ve really had no idea how representative they are of all the women affected,” she said. “These results can be reassuring” that poor outcomes may indeed be less common than the current literature suggests.

One, Two, 400 Cases

Back in 2012, Knight was doing surveillance on pregnancy during another pandemic: the H1N1 flu. It turned out to be vital for understanding that disease’s spread. When that pandemic subsided, the UK National Institute of Health Research asked researchers to be prepared to conduct similar surveillance when the next pandemic arose. Knight and colleagues were among those who geared up for when the day came.

And then SARS-CoV-2 arrived in the UK. At the end of February, Knight got the call to start monitoring the UK’s 194 obstetric units for COVID-19 hospitalizations and their outcomes.

“I was asked to start collecting data on the Friday and we started on the Monday,” she said.


Between March 1 and April 15, a total of 86,293 women gave birth. Only 427 of the births were to women with diagnosed COVID-19 that was serious enough for them to be hospitalized. The study does not include all women in the UK with SARS-CoV-2, as universal testing is unavailable, she said. Knight’s results only look at hospitalized women with confirmed SARS-CoV-2 infection and serious disease.

These are likely not all the women in the UK who gave birth while positive for SARS-CoV-2, said Knight, so the data still represent a small slice of the overall infection rate.

“What we can’t see is what potential impact a mild or indeed asymptomatic infection, if such a thing exists, has on the pregnancy,” Knight said. “I cannot from this study give you an infection rate. But I can give you a ‘hospitalized with infection’ rate.”

That rate is 4.9 per 1000 maternities. By comparison, the hospitalization rate — a marker of disease severity — of pregnant women with H1N1 was 8 per 1000 maternities.

This is notable and unexplained, said Christopher Zahn, MD, vice president of practice activities at the American College of Obstetricians and Gynecologists.

“It’s interesting because looking back at some of the other infectious outbreaks, such as H1N1, where pregnant women were at increased risk,” he told Medscape Medical News. “But with H1N1, pregnant women were at increased risk. But that’s not been identified in COVID either in international data or the emerging US data.”

Indeed, Lynne Mofenson, MD, senior HIV technical advisor to the Elizabeth Glaser Pediatric AIDS Foundation, saw Knight’s data, and has been tracking all the current studies on COVID-19 and pregnancy;

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