IntroductionDespite a growing body of research on the risks of SARS-CoV-2 infection during pregnancy, there is continued controversy given heterogeneity in the quality and design of published studies.MethodsWe screened ongoing studies in our sequential, prospective meta-analysis. We pooled individual participant data to estimate the absolute and relative risk (RR) of adverse outcomes among pregnant women with SARS-CoV-2 infection, compared with confirmed negative pregnancies. We evaluated the risk of bias using a modified Newcastle-Ottawa Scale.ResultsWe screened 137 studies and included 12 studies in 12 countries involving 13 136 pregnant women.Pregnant women with SARS-CoV-2 infection—as compared with uninfected pregnant women—were at significantly increased risk of maternal mortality (10 studies; n=1490; RR 7.68, 95% CI 1.70 to 34.61); admission to intensive care unit (8 studies; n=6660; RR 3.81, 95% CI 2.03 to 7.17); receiving mechanical ventilation (7 studies; n=4887; RR 15.23, 95% CI 4.32 to 53.71); receiving any critical care (7 studies; n=4735; RR 5.48, 95% CI 2.57 to 11.72); and being diagnosed with pneumonia (6 studies; n=4573; RR 23.46, 95% CI 3.03 to 181.39) and thromboembolic disease (8 studies; n=5146; RR 5.50, 95% CI 1.12 to 27.12).Neonates born to women with SARS-CoV-2 infection were more likely to be admitted to a neonatal care unit after birth (7 studies; n=7637; RR 1.86, 95% CI 1.12 to 3.08); be born preterm (7 studies; n=6233; RR 1.71, 95% CI 1.28 to 2.29) or moderately preterm (7 studies; n=6071; RR 2.92, 95% CI 1.88 to 4.54); and to be born low birth weight (12 studies; n=11 930; RR 1.19, 95% CI 1.02 to 1.40). Infection was not linked to stillbirth. Studies were generally at low or moderate risk of bias.ConclusionsThis analysis indicates that SARS-CoV-2 infection at any time during pregnancy increases the risk of maternal death, severe maternal morbidities and neonatal morbidity, but not stillbirth or intrauterine growth restriction. As more data become available, we will update these findings per the published protocol.

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Background Inflammation during pregnancy may aggravate iron deficiency by increasing serum hepcidin and reducing iron absorption. This could restrict iron transfer to the fetus, increasing risk for infant iron deficiency and its adverse effects. Objectives To assess whether iron bioavailability and/or iron transfer to the fetus is impaired in overweight/obese (OW) women with adiposity-related inflammation, compared to normal weight (NW), pregnant women. Design In this prospective study, we followed NW (n = 43) and OW (n = 40) pregnant women who were receiving iron supplements from the 14th gestational week to term and followed their infants to age six months. We administered 57Fe and 58Fe in test meals mid-2nd and mid-3rd trimester, and measured tracer kinetics throughout pregnancy and infancy. Results 38 NW and 36 OW completed the study to pregnancy week 36 and 30 NW and 27 OW mother infant pairs completed the study to six months postpartum. Both groups had comparable iron status, hemoglobin and serum hepcidin throughout pregnancy. Compared to the NW, the OW pregnant women had: 1) 43% lower fractional iron absorption in the 3rd trimester (P = 0.033) with median (IQR) 23.9 (11.4–35.7) and 13.5 (10.8–19.5) %; and 2) 17% lower maternal-fetal iron transfer from the first tracer (P = 0.051) with median (IQR) 4.8 (4.2–5.4) and 4.0 (3.6–4.6) %. Compared to the infants born to NW, infants born to OW had lower body iron stores (BIS) with median (IQR) 7.7 (6.3–8.8) and 6.6 (4.6–9.2) mg/kg body weight at age six months (P = 0.024). Prepregnancy BMI was a negative predictors of maternal-fetal iron transfer (β = –0.339, SE = 0.144, P = 0.025) and infant BIS (β = –0.237, SE = 0.026, P = 0.001). Conclusions Compared to NW, OW pregnant women fail to upregulate iron absorption in late pregnancy, transfer less iron to their fetus, and their infants have lower BIS. These impairments are associated with inflammation independent of serum hepcidin. The study was registered at clinicaltrials.gov (NCT02747316).

What are the novel findings of this work?In pregnant women who have recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, anti-SARS-CoV-2 immunoglobulin G (IgG) concentrations at delivery increased with increasing viral load during infection and decreased with increasing infection-to-delivery interval. The median transplacental transfer ratio of IgG was 1.3 and it decreased with increasing viral load during infection. What are the clinical implications of this work?Even though high viral load during SARS-CoV-2 infection is associated with higher concentration of anti-SARS-CoV-2 IgG antibodies in recovered mothers, it affects negatively the transplacental transfer of IgG to the fetuses.