One in 10 Pregnant Women Test Positive for COVID-19, and Most Are Asymptomatic

Kate Johnson

September 10, 2020

One of every 10 pregnant or recently pregnant women in hospital was diagnosed with COVID-19, yet up to three-quarters were asymptomatic at the time of diagnosis, according to a living systematic review from the PregCOV-19 Living Systematic Review Consortium.

The study, published in BMJ, shows an increased risk of preterm delivery, as well as the need for invasive ventilation in these women, wrote John Allotey, PhD, of the University of Birmingham (England) and colleagues. The findings "will produce a strong evidence base for living guidelines on COVID-19 and pregnancy," they noted.

The systematic review included 77 studies, one-third each from the United States and China, with the remaining studies from Belgium, Brazil, Denmark, France, Israel, Italy, Japan, Mexico, the Netherlands Portugal, Spain, and the United Kingdom.

The studies included women with COVID-19, of whom 13,118 were either pregnant or in the postpartum or postabortion period and 83,486 were of reproductive age but not pregnant. Some studies also included healthy pregnant women for comparison.

In the pregnant and recently pregnant women, the most common COVID-19 symptoms were fever (40%) and cough (39%), with lymphopenia (35%) and raised C reactive protein levels (49%) being the most common laboratory findings. Pregnant and recently pregnant women with COVID-19 were less likely to have fever (odds ratio, 0.43) and myalgia (OR, 0.48), compared with nonpregnant women of reproductive age with COVID-19, reported the authors.

The overall preterm and spontaneous preterm birth rates in the COVID-19–positive women were 17% and 6% respectively. Dr. Allotey and authors noted that "these preterm births could be medically indicated, as the overall rates of spontaneous preterm births in pregnant women with COVID-19 was broadly similar to those observed in the pre-pandemic period." There were 18 stillbirths and 6 neonatal deaths in the COVID-19 cohort.

Overall, 73 (0.1%) of pregnant women with confirmed COVID-19 died from any cause, and severe COVID-19 infection was diagnosed in 13%. Maternal risk factors associated with severe infection included older age (OR, 1.78), high body mass index (OR, 2.3), chronic hypertension (OR, 2.0), and preexisting diabetes (OR, 2.51). Compared with nonpregnant women with COVID-19, pregnant or recently pregnant women with the infection were at increased risk of admission to intensive care (OR, 1.62) and needing invasive ventilation (OR, 1.88).

The report included studies published between December 1, 2019, and June 26, 2020, but the living systematic review will involve weekly search updates, with analysis performed every 2-4 weeks and reported through a dedicated website.

The Value of a Living Meta-Analysis

Asked to comment on the findings, Torri Metz, MD, a maternal-fetal medicine subspecialist at the University of Utah, Salt Lake City, expressed surprise at the 10% rate of infection in the pregnant or recently pregnant population. "This is higher than currently observed at many hospitals in the United States," she said in an interview. "This may overestimate the actual risk as many of these studies were published early in the pandemic and did not universally sample women who were pregnant for SARS-CoV-2."

She noted the value of a living meta-analysis in that it will be updated on a regular basis as new evidence emerges. "During this time of rapidly accumulating publications about COVID-19 infection, clinicians will find it useful to have a resource in which the available data can be combined in one source."

And there are still some outstanding questions that new studies hopefully will shed light on, she added. "The authors found that many of the risk factors for severe disease, like diabetes, obesity and high blood pressure, in nonpregnant adults are the same in the pregnant population. What remains unknown is if pregnant patients with COVID-19 infection are at higher risk than those who are not pregnant. The authors note that this information is still limited and largely influenced in this published analysis by a CDC [Centers for Disease Control and Prevention] study in which the majority of patients had unknown pregnancy status. We also do not know if COVID-19 infection is associated with any birth defects since the majority of women with COVID-19 infection in the first trimester have not yet delivered."

Malavika Prabhu, MD, an obstetetrician/gyneologist at Weill Cornell Medicine in New York City added that "this systematic review and meta analysis, which is a compilation of other studies done around the globe, confirms that pregnant women with preexisting medical conditions such as diabetes, hypertension, and obesity, are at increased risk of severe COVID-19 and that pregnant women with COVID-19 are at increased risk of invasive ventilation, compared to nonpregnant women with COVID-19, particularly if they have a preexisting medical condition."

She said the preterm delivery rate of COVID-positive women is "challenging to interpret given that the total preterm birth rate potentially included many medically indicated preterm deliveries – which is to be expected – and there is no comparison group for spontaneous preterm birth presented".

Other outstanding questions about COVID-19 pregnancies include whether they are associated with preeclampsia or smaller/growth restricted infants and why the cesarean delivery rate is high, she said. "But some of these questions are tough to answer with this data because it primarily reflects a COVID infection close to the delivery, not one that occurred several months prior to a delivery."

Deborah Money, MD, professor of obstetrics and gynecology, medicine, and the school of population and public health, University of British Columbia, Vancouver, commented that "this is a group that have been doing ongoing living systematic reviews of the literature scanning for pregnancy outcomes. They post their information in real time on their website, so many of us in this area follow these postings as their methodology is robust and they work hard to only include high-quality literature and avoid duplication of cases in multiple papers. There has been a problem of re-reporting the same severe cases of COVID-19 in the literature."

This "amplifies the importance of collecting Canadian-specific data to ensure that we understand if these kind of outcomes will also be found in Canada. The data presented in this paper represent outcomes from a broad range of countries with different methods of collecting information on pregnancy and highly variable prenatal care systems. This makes our pan-Canadian study of outcomes of COVID-19 for pregnant women and their infants, CANCOVID-Preg, even more important," she said.

"Globally, we all must continue to monitor outcomes of COVID-19 in pregnancy to minimize adverse impact on women and their infants," said Dr. Money, who was not involved in the study.

The study was partially funded by the World Health Organization and supported by Katie's Team, a dedicated patient and public involvement group in Women's Health. Dr. Metz is principal investigator for the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network COVID-19 study; the study is funded by NICHD and enrollment is ongoing. Dr. Prabhu had no relevant financial disclosures. Dr. Money received funding from the Canadian Institutes for Health Research and the Public Health Agency of Canada and received a small grant from theBC Women's Foundation for COVID-19 in pregnancy research.

SOURCE: Allotey J et al. BMJ. 2020;370:m3320.

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