A study published in JAMA Network Open shows that there was no maternal viremia, placental infection, or vertical transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a cohort of pregnant women with coronavirus disease 2019 (COVID-19). In addition, compromised transplacental transfer of anti–SARS-CoV-2 antibodies with robust transfer of influenza-specific immunity and nonoverlapping placental expression of SARS-CoV-2 receptors angiotensin-converting enzyme 2 and transmembrane serine protease 2 were noted.
“This report of maternal viral load, transplacental antibody transmission, and placental pathology in 127 pregnancies during the SARS-CoV-2 pandemic provides needed data about maternal viral control, reduced transplacental transfer of anti–SARS-CoV-2 antibodies, and lack of vertical transmission in mother-neonate dyads,” wrote Andrea G Edlow, MD, Harvard Medical School, Boston, Massachusetts, and colleagues. “These findings can immediately inform clinical care and vaccine development and deployment strategies to maximize benefit for pregnant women and their neonates.”
From April 2 through June 13, 2020, samples were obtained from 127 pregnant women presenting for care at 3 tertiary care centers in Boston, Massachusetts. Of the pregnant women, 64 (mean age, 31.6 years) had RT-PCR results positive for SARS-CoV-2 and 63 (mean age, 33.9 years) with RT-PCR results negative for SARS-CoV-2. Of women with SARS-CoV-2 infection, 23 (36%) were asymptomatic, 22 (34%) had mild disease, 7 (11%) had moderate disease, 10 (16%) had severe disease, and 2 (3%) had critical disease.
The main outcomes were SARS-CoV-2 viral load in maternal plasma or respiratory fluids and umbilical cord plasma, quantification of anti–SARS-CoV-2 antibodies in maternal and cord plasma, and presence of SARS-CoV-2 RNA in the placenta.
In viral load analyses among 107 women, there was no detectable viremia in maternal or cord blood and no evidence of vertical transmission. No neonates born to women with confirmed SARS-CoV-2 infection had positive test results for SARS-CoV-2. Meanwhile, respiratory viral loads were quantified in 78 women. Among these, 11 women had detectable viral load in respiratory specimens.
In antibody analyses among 37 women with SARS-CoV-2 infection, anti–receptor binding domain (RBD) immunoglobulin (Ig) G was detected in 24 women (65%) and anti-nucleocapsid (N) was detected in 26 women (70%). Compared with nonpregnant hospitalized women of reproductive age, there was no significant difference in mean antibody titers between pregnant and nonpregnant women.
Among umbilical cords from mothers with SARS-CoV-2 infection, 23 (62%) had detectable anti-RBD IgG and 22 (59%) had detectable anti-N IgG. Meanwhile, N-specific IgM was observed in a single SARS-CoV-2 umbilical cord sample. Compared with influenza, mean antibody transfer ratios were significantly reduced for anti–SARS-CoV-2 IgG against RBD (0.72; P < .001) and N (0.74; P < .001). Further, the researchers found that maternal transplacental antibody transfer did not differ significantly by maternal disease severity or maternal medical comorbidities such as obesity, hypertension, or diabetes.
Among 88 placentas tested, SARS-CoV-2 RNA was not detected in any. Additionally, nonoverlapping placental expression of SARS-CoV-2 receptors angiotensin-converting enzyme 2 and transmembrane serine protease 2 was observed, which, said the authors, may serve as protective mechanisms against vertical transmission.
“To our knowledge, this is the first report of reduced transplacental transfer of antibodies to SARS-CoV-2,” the authors wrote. “These data point to a potential alteration in SARS-CoV-2–specific antibodies, which may result in compromised transfer. Whether altered transfer is related to infection-associated differences in SARS-CoV-2 antibody glycosylation or to differences in vaccine-elicited (HA) vs natural infection (SARS-CoV-2)–generated antibodies remains unclear.”
“These findings suggest that, although low rates of maternal viremia and patterns of placental SARS-CoV-2 receptor distribution may underlie the rarity of vertical transmission, reduced transplacental transfer of anti–SARS-CoV-2 antibodies may leave neonates at risk for infection,” the authors added.