Pregnant women with COVID-19 are at higher risk of severe illness than other women, and may be at risk of preterm birth, but the full effect of SARS-CoV-2 infection in pregnancy was unknown. Through the Surveillance for Emerging Threats to Mothers and Babies Network (SET-NET), 16 jurisdictions gathered extra information on 5,252 women with laboratory-confirmed infection reported from March 29 to October 14, 2020. This report, first posted on November 2, 2020, covers the 4,442 whose pregnancies had ended.
The jurisdictions: California (excluding Los Angeles County), Georgia, Houston, Los Angeles County, Massachusetts, Michigan, Minnesota, Nebraska, New Jersey, New York (excluding New York City), North Dakota, Oklahoma, Pennsylvania (excluding Philadelphia), Puerto Rico, Tennessee and Vermont.
The mothers
- Median age 28.9; 46.0% Hispanic or Latina.
- 1,564 had at least one underlying condition — most often obesity before pregnancy.
- 84.4% were infected in the third trimester.
- Of the 2,691 whose symptoms were known, 376 (14.0%) had no symptoms.
The babies
Of 4,527 fetuses and infants, 4,495 (99.3%) were born alive (including 79 sets of twins and one set of triplets); there were 12 pregnancy losses before 20 weeks and 20 at 20 weeks or later.
| Outcome | |
|---|---|
| Preterm (before 37 weeks), of 3,912 with gestational age known | 506 (12.9%) — 149 before 34 weeks, 357 at 34–37 weeks |
| U.S. preterm rate, 2019, for comparison | 10.2% |
| Small for gestational age, of 3,486 with the data | 198 (5.7%) |
| Any birth defect | 28 (0.6%) — of 23 with known timing, 17 mothers infected in the third trimester |
| Deaths in hospital after birth | 9 (0.2%) |
| Full-term babies admitted to intensive care | 9.3% (reasons often missing) |
Preterm birth was no more common when the mother had symptoms than when she did not — including among mothers hospitalized at the time of infection.
Did the babies catch it?
Thirteen jurisdictions reported on testing of babies. Of 923 babies with information, 313 were not tested. Of 610 with results, 16 (2.6%) were positive:
- 4.3% (14 of 328) when the mother's infection was found within 14 days of delivery;
- 0% (0 of 84) when it was found more than 14 days before.
Eight of the positive babies were preterm (26–35 weeks), all admitted to neonatal intensive care. Of the eight full-term positive babies, one went to intensive care with fever and needed oxygen, six did not, and one had no information. With no antibody or placenta tests reported, how the babies were infected — before, during or after birth — could not be told.
What it means
The higher share of preterm births (12.9% vs 10.2%) suggests infection in pregnancy may raise the risk of preterm delivery, in line with earlier CDC reports on hospitalized women and a living systematic review — though one cohort study of 253 infants found no difference, perhaps because of differences in methods and size. Studies comparing pregnant women with and without COVID-19 are needed. The data are preliminary and mostly cover later-pregnancy infections.
Black and Hispanic women were overrepresented. Racial and ethnic disparities already exist in maternal illness, death and birth outcomes, and COVID-19's heavier toll on women of color may widen them.
Newborn infection was uncommon and mostly followed infection within a week of delivery. The American Academy of Pediatrics and CDC recommend testing all babies of mothers with suspected or confirmed COVID-19, yet few results were reported. Evidence suggests most full-term newborns who are infected have no or mild illness, but long-term effects are unknown. SET-NET will follow babies to 6 months.
Advice: providers should tell pregnant women that infection may raise the risk of preterm birth. Pregnant women and their households should wear masks, keep their distance and wash hands often when out or with others, keep up prenatal care, and get their yearly flu vaccine.
Limits
- Data completeness varied by jurisdiction; symptom status was often missing.
- Testing and reporting may be more common with severe illness or bad outcomes.
- The data are not nationally representative, with more Hispanic women than national case data.
- Pregnancy losses may be undercounted.
- Few women infected in the first trimester had finished pregnancies, limiting what can be said about birth defects.
- Other preterm risk factors were not assessed.
- Positive results are reportable, so if negative results went unreported, the 2.6% is likely an overestimate.
Sources
Based on Woodworth KR, O'Malley Olsen E, Neelam V, et al., "Birth and Infant Outcomes Following Laboratory-Confirmed SARS-CoV-2 Infection in Pregnancy — SET-NET, 16 Jurisdictions, March 29–October 14, 2020," MMWR Morbidity and Mortality Weekly Report, volume 69, Centers for Disease Control and Prevention; a work of the United States government in the public domain. Some of the report's percentages (of women with underlying conditions, and of infants tested) rest on bases it does not state, so only their counts are given here.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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