New data show low rates of COVID-19 in pregnant women

A research letter published yesterday in JAMA revealed a 3.9% prevalence of COVID-19 among women giving birth at three Yale New Haven hospitals in Connecticut.

A separate study published today in Infection Control & Hospital Epidemiology found a 7.9% prevalence of the novel coronavirus among symptomatic obstetric patients and a 1.5% prevalence among asymptomatic patients (those not having COVID-19 symptoms) at four Boston hospitals.

Positive test results in 2.9% of asymptomatic patients

In the JAMA study, the authors tested 782 pregnant women for COVID-19. Twelve (1.5%) had been previously tested positive for SARS-CoV-2, the virus that causes COVID-19. Of the remaining 770 patients, 30 (3.9%) tested positive, 22 (73.3%) of whom were asymptomatic. Overall, 22 of 756 (2.9%) of asymptomatic patients tested positive.

The prevalence of positive test results among patients with no symptoms increased from 0.6% (2 of 355) to 5% (20/401) from the first 2 weeks of the study (Apr 2 to 15) to the next 2 weeks (Apr 16 to 29), while the prevalence of patients with symptoms who tested positive in all patients hospitalized for childbirth fell from 1.4% (5/365) to 0.7% (3/405).

Eight of 14 patients with symptoms (57%) tested positive for COVID-19. Among asymptomatic patients who tested negative, none developed symptoms or needed further testing.

Clinicians, patients, and birth partners wore face masks, and women were limited to one birth partner. If a patient had COVID-19 symptoms or tested positive, clinicians wore N95 respirators and other appropriate personal protective equipment (PPE).

For patients who tested positive or for whom results were unavailable, clinicians wore full PPE and N95 respirators for the second stage of labor and birth. No obstetric healthcare workers were sent home because of known or possible exposure to an infected patient.

The authors noted an Apr 13 study that found a 13.5% prevalence of coronavirus infection in women giving birth in New York City.

The authors wrote that Connecticut has had the third-highest COVID-19 death rate of all US states, indicating a significant disease burden. "The increasing prevalence of positive SARS-CoV-2 test results in the asymptomatic population, while the prevalence of symptomatic infections decreased, may indicate that universal testing identifies patients in a convalescent period, in addition to those with subclinical active infection," they wrote.

They recommended balanced screening and testing of patients and a rational use of PPE on obstetric units.

Lower asymptomatic infection rates than in New York City

In the second study, the authors mined the electronic health data of all women giving birth at two academic and two community hospitals affiliated with Mass General Brigham Health from Apr 18 to May 5 for COVID-19 test results.

Of 763 hospitalized pregnant women, 757 (99.2%) were tested. Of the139 who had symptoms consistent with the coronavirus, 11 (7.9%) tested positive, while 9 of 618 of asymptomatic patients (1.5%) tested positive.

Nine (45%) of 20 patients who tested positive for COVID-19 had no symptoms at admission. Of asymptomatic patients, 2.7% and 1.5% in the two teaching hospitals tested positive, while 1.8% and 0.6% were confirmed in the two community hospitals.

No asymptomatic patients who tested positive developed coronavirus symptoms during hospitalization, and all nine newborns tested negative.

The authors noted that the rate of asymptomatic infections in pregnant women in their study was much lower than that of New York City, despite having similar per-capita case counts.

They say that could be because the Boston hospitals began testing more than 30 days after the state declared a lockdown, meaning that they had sampled at a time when community spread was slowing; Boston is less densely populated; and some New York City hospitals temporarily barred, or considered barring, birth partners, leading some women to not report their symptoms.

Testing asymptomatic obstetric patients gives a good indication of community COVID-19 disease burden, which can help public health officials decide, when, where, and how to strengthen or relax physical distancing measures, the authors said. "These data may, therefore, guide decision making about moving between mitigation versus containment measures and thoughtfully resuming both healthcare and non-healthcare operations," they wrote.

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