Maternal COVID-19 Test Positivity and Outcomes of Extremely Preterm Infants in the Neonatal Intensive Care Unit.

Objective: To describe the neonatal intensive care unit outcomes of infants born extremely preterm to mothers who test positive for SARS-CoV-2 during pregnancy.

Study design: Prospective study (3/1/2020-4/30/2023) at 16 NICHD Neonatal Research Network centers of inborn infants (birth weight 401-1000 grams and/or gestational age <29 weeks) born to mothers tested for SARS-CoV-2 during pregnancy. Frequency of maternal SARS-CoV-2 detection, vertical transmission rate, and association of maternal SARS-CoV-2 positivity during pregnancy with infant outcomes were determined.

Results: During the 38-month study, 4548 extremely preterm infants were born to 4072 mothers tested for SARS-CoV-2 during pregnancy. Overall, 7% (297/4072) of mothers had a positive SARS-CoV-2 test; 1% (2/181) of tested infants were positive at age <72 hours. The majority of outcomes (eg, bronchopulmonary dysplasia, retinopathy of prematurity) did not differ between infants of test-positive vs test-negative mothers. Infants of test-positive mothers were more likely to be diagnosed with necrotizing enterocolitis (NEC) than those of test-negative mothers (14% vs 11%; p=0.03). In adjusted analyses, infants born to test-positive mothers were more likely to develop NEC (risk ratio 1.40; 95% CI 1.03 -1.89; p=0.03) or the combined outcome of death within 12 hours of age or NEC (risk ratio 1.33; 95% CI, 1.09-1.62; p<0.01) but not death within 12 hours of age (risk ratio 1.22, 95% CI 0.92-1.62; p=0.16) or before discharge (risk ratio 0.83, 95% CI 0.55-1.26; p=0.38).

Conclusions: Among infants <29 weeks' gestation, vertical transmission of SARS-CoV-2 was infrequent. Maternal SARS-CoV-2 positivity was associated with NEC but not with other infant outcomes or mortality.