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Studies: Preterm births, severe illness higher in some pregnant women with COVID-19 :

November 2, 2020

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COVID-19 has the potential to raise the risk of severe maternal illness and preterm birth in certain populations, according to two studies published today in Morbidity and Mortality Weekly Report.

The results highlight differences in how COVID-19 affects various populations during pregnancy and birth and the need for ongoing, improved data to understand the potential impact on pregnant women and infants.

Birth and Infant Outcomes Following Laboratory-Confirmed SARS-CoV-2 Infection in Pregnancy — SET-NET, 16 Jurisdictions, March 29-October 14, 2020” is the first report on Surveillance for Emerging Threats to Mothers and Babies Network (SET-NET) outcomes, including preterm delivery and SARS-CoV-2 infection in neonates. SET-NET will continue to follow women affected by the virus through completion of pregnancy and infants until age 6 months.

The SET-NET study involved data from 16 jurisdictions reporting on birth and infant outcomes of women with laboratory-confirmed SARS-CoV-2 infection (during the second and third trimester) between March 29, 2020, and October 14, 2020. The Centers for Disease Control and Prevention (CDC) cautions that this is not a nationally representative sample of pregnant women (46% were Hispanic or Latina, and 45% had an underlying medical condition, most often obesity [body mass index >30 kg/m2]). Among the 3,912 live births with data on gestational age, 12.9% of infants were born preterm — higher than national estimates of 10.2% in 2019. It is unknown if other factors contributed to the higher rate of preterm birth for this cohort.

For 3,486 live births with known weight, gestational age and sex:

  • 198 (5.6%) were small for gestational age;
  • 28 (0.6%) were reported to have birth defects;
  • 9 (0.2%) died in the hospital; and
  • 9.3% of infants born at >37 weeks’ gestation were admitted to an intensive care unit (ICU); the reason for admission often was missing and may have been due to the need to isolate from other infants.

Although the AAP and CDC recommend testing all infants born to mothers with suspected or confirmed COVID-19, results were infrequently reported in this cohort.

Information on SARS-CoV-2 testing was provided for 923 infants from 13 jurisdictions:

  • 313 (34%) were not tested;
  • 610 (21.3%) had molecular test results with 26 (2.6%) positive; and
  • percent positivity was 4.3% for infants born to women with infection identified ­<14 days before delivery. None of the 84 infants born to mothers with infection identified more than 14 days before delivery were positive. The percent positive likely is an overestimate if negative testing was less often reported, authors noted.

Most of the term neonates were asymptomatic or had mild disease. Authors highlighted the need for more surveillance, reporting by more jurisdictions and analysis of outcomes by race and ethnicity to guide public health action.

The data also highlight the inequities in maternal and birth outcomes.

“Longer-term investigation into solutions to alleviate underlying inequities in social determinants of health associated with disparities in maternal morbidity, mortality, and adverse pregnancy outcomes, and effectively addressing these inequities, could reduce the prevalence of conditions and experiences that might amplify risks from COVID-19,” authors noted.

Update: Characteristics of Symptomatic, SARS-CoV-2 Positive Women of Reproductive Age by Pregnancy Status — United States, January 22-October 3, 2020” provides national case surveillance data on 409,462 symptomatic women of reproductive age with laboratory-confirmed COVID-19. The study updates a previous national surveillance study with data from Jan. 22 to June 7 (

Of the 30,415 known pregnant women with COVID-19 during the study period, 23,434 (77%) were symptomatic. Pregnant women were significantly more likely to be admitted to an ICU (10.5 pregnant vs. 3.9 non-pregnant women with COVID-19 per 1,000).

“Although the absolute risks for severe COVID-19-associated outcomes among women were low, pregnant women were at significantly higher risk for severe outcomes compared with nonpregnant women,” authors wrote.

Race and ethnicity and age group put some women at higher risk of complications or death. For example, nine of the 34 pregnant women who died were Black. Non-Hispanic Asian women and non-Hispanic Native Hawaiian/Pacific Islander women had increased risk for ICU admission. Pregnant women ages 35-44 years with COVID-19 were four times as likely to need mechanical ventilation and twice as likely to die as their non-pregnant counterparts.

Authors said pregnant women should be counseled on risks of illness, including potential adverse outcomes such as preterm labor. They also should be reminded about COVID-19 preventive measures, such as wearing a cloth face covering, physical distancing and limiting interactions with people outside the household, and washing hands frequently.

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