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No Link Between COVID-19 and Stillbirth Detected, But Placental Vascular Pathology is Worrisome

Key findings

  • In this study of more than 18,000 births across three years at three Boston hospitals, there was no change in the rate of third-trimester stillbirth during the first five months of the COVID-19 pandemic compared with equivalent periods in 2019 and 2018
  • Rates of fetal and maternal vascular malperfusion were higher during the early pandemic period than in the previous two years
  • Two women who experienced stillbirth were either proven to be or presumed to be infected with SARS-CoV-2, and both had signs of maternal vascular malperfusion
  • Since most of the stillbirths were not known to be associated with maternal SARS-CoV-2 infection, this study was unable to identify a definite association between stillbirth, placental pathology and SARS-CoV-2

There is mixed evidence about whether SARS-CoV-2 infection increases the risk of stillbirth. However, Schwartz and colleagues reported in Viruses that certain placental pathology (co-occurrence of chronic histiocytic intervillositis, perivillous fibrin and trophoblast necrosis) is a risk factor for placental infection with SARS-CoV-2 as well as for maternal–fetal viral transmission.

Residents Megan E. Bunnell, MD, and Kathleen J. Koenigs, MD, and Ilona Goldfarb, MD, MPH, maternal-fetal medicine specialist, all in the Department of Obstetrics and Gynecology at Massachusetts General Hospital; and Drucilla J. Roberts, MD, head of Obstetric and Perinatal Pathology at the Department of Pathology at Mass General; and colleagues recently became the first to examine changes in placental pathology as part of reviewing rates of stillbirth during the pandemic.

In Placenta, they report that rates of late-term stillbirth were unaffected during the first wave of COVID-19 in Boston, but rates of fetal and maternal vascular malperfusion increased.

Study Methods

Using data from two academic hospitals and a community hospital, the researchers compared third-trimester (≥28 weeks) stillbirth rates for February to July 2020 with those for equivalent time periods in 2019 and 2018. In 2020, 6,406 births were studied; the numbers in the other years were approximately the same.

Stillbirth Rates

In the five-month time period studied in 2020, the stillbirth rate was 12 of 6,406 (0.187%); rates were similar in the other five-month time periods (0.188% in 2019 and 0.150% in 2018).

Placental Pathology

In all cases of stillbirth, pathologists had examined the placenta for:

  • Maternal vascular malperfusion (MVM)—placental hypoplasia, accelerated villous maturation, distal villous hypoplasia, decidual arteriopathy, placental infarcts or increased perivillous fibrin
  • Fetal vascular malperfusion (FVM)—any grade

There was a trend toward an increase in vasculopathic pathology: 11 of 12 placentas were affected by either MVM or FVM in 2020, nine of 12 in 2019 and five of nine in 2018.

Stillbirth and SARS-CoV-2

Universal SARS-CoV-2 testing was not implemented until mid-April, but eight of the 12 women who experienced a stillbirth in 2020 were tested and two were either proven to be or presumed to be infected. Neither showed the SARS-CoV-2 placental pathology reported by Schwartz and colleagues but both had signs of MVM.


This study is unable to identify an association between stillbirth, placental pathology and SARS-CoV-2 because most of the stillbirths were not known to be associated with maternal SARS-CoV-2 infection.

However, COVID-19 is known to result in hypoxia and vascular insults to the placenta. These insults may not lead directly to fetal death but could cause micro-insults to the placenta throughout fetal development, leading to increased risk of stillbirth and other adverse pregnancy outcomes in later gestation. Increased antenatal surveillance may be warranted.

Recent reports from the U.K. and personal experience in the U.S. suggest that the B.1.1.6 and Delta variant may be both more infectious and damaging to the placenta with increased perinatal morbidity and mortality. Further studies on strain effects and perinatal outcomes are needed.

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