Pregnancy and COVID-19: Testing, Transmission, and Vaccines

As research around COVID-19 evolves, so too will the recommendations concerning pregnancy and COVID-19

Amanda Loudin

The questions surrounding COVID-19 and pregnancy are multilayered, from testing protocols to mortality rates, transmissibility to the fetus, and recommendations surrounding vaccines. As with many facets of this disease, finding answers to these issues is an ever-evolving challenge. Results from the latest research into pregnancy and COVID-19 reveal a mix of good and bad news.

Mortality rates

One of the most recent and sobering studies to dive into mortality rates among pregnant women who contracted COVID-19 found that mortality rates were 13 times higher in pregnant mothers than in similarly aged individuals. 

The study, published last month in the American Journal of Obstetrics and Gynecology (AJOG), followed 240 pregnant women between March and June 2020. In addition to higher mortality rates, the study also found that pregnant women with COVID-19 were 3.5 times more likely to require hospitalization than similarly aged peers who were not pregnant. 

Together, these findings clearly indicate that pregnant women should be considered as a unique population at higher risk of severe disease and mortality due to COVID-19.   

Testing protocols 

The decision if and when to test pregnant women for the presence of COVID-19 varies from one health care facility to another, as current American College of Obstetrics and Gynecology (ACOG) recommendations do not include a universal testing strategy. Rather, the organization’s practice advisory statement reads: “Pregnant women admitted for labor and delivery with suspected COVID-19, or who develop symptoms suggestive of COVID-19 during admission, should be prioritized for testing.” Many pregnant women also receive testing upon admission to hospitals according to standard operating procedures for newly admitted patients.

To date, it appears that the reliability of testing for pregnant women is on par with the general population. Christopher Zahn, MD, vice president of practice activities for ACOG, says “There’s no difference that we are aware of in terms of the reliability of the COVID tests currently authorized by the FDA for pregnant individuals versus nonpregnant individuals.” 

In terms of antibody testing, an article first published online in AJOG in May 2020 indicated that the case has yet to be made for antibody testing, whether in pregnant or nonpregnant individuals.

Vertical transmission to the fetus

For women who test positive for COVID-19, the question of whether vertical transmission of the disease to the fetus is feasible and/or common continues to be a research focus. Furthermore, researchers are working to determine the impact of the mother’s illness severity level on the fetus and whether or not that severity increases the likelihood of vertical transmission.

A September 2020 AJOG letter to the editor on the topic, written by Christina Penfield, MD, MPH, and colleagues from the division of maternal-fetal medicine at NYU Langone Health in New York City, concluded that the evidence of vertical transmissibility is still evolving. 

Earlier research found that COVID-19 was present in the placenta, which suggested vertical transmission was possible. “The presence of COVID-19 in the placenta does not necessarily mean the fetus was infected, although other studies have confirmed that vertical transmission, though rare, is possible,” says Penfield. 

Penfield’s own research published in AJOG looked at placental and membrane samples early on in the pandemic (during March and April 2020). At the time of sample collection, testing for antibodies wasn’t readily available at Langone. However, in their September 2020 letter to the editor, Penfield and colleagues wrote, “Our evaluation and understanding of vertical transmission of SARS-CoV-2 have evolved over time, and we agree that the use of these adjunct tests [for viral RNA load in maternal serum and detection of neonatal IgM antibodies] is valuable to generate evidence suggestive of vertical transmission.”

An August 2020 study of placental COVID-19 transmission in a pregnant woman in her third trimester suggested that it was the first such case of placental SARS-CoV-2 in a patient with mild COVID-19. But though the researchers detected SARS-CoV-2 throughout the placenta and found evidence of vasculopathy, the newborn tested negative for SARS-CoV-2 via RT-PCR 24 hours after birth. Since this woman was infected with the virus during her third trimester, the findings raise questions around whether timing of infection alters the likelihood of vertical transmission.   

While vertical transmission doesn’t appear to be common, the question that remains is how significant that transmission is when it does occur. Future studies will be necessary to determine the degree and clinical relevance of vertical transmission in COVID-19.

Vaccines

Another area of concern surrounding COVID-19 and pregnant women is whether or not they should receive current COVID-19 vaccines. Vaccinations during pregnancy can prevent maternal and infant morbidity from infectious diseases such as influenza and pertussis. Clinical data on the safety of these vaccines and pregnant women is well established. Whether or not the COVID-19 vaccines are similarly preventive of maternal and infant mortality has been a subject of debate.

An article published in JAMA this February reported that it is unclear whether a mother’s immunity actually protects her fetus from contracting COVID-19, as third trimester SARS-CoV-2 antibody transfer does not appear as efficient as the transfer of influenza or pertussis antibodies. Understanding how SARS-CoV-2-specific antibodies are transferred across the placenta will be important for designing COVID-19 vaccines that protect neonates in addition to mothers.

As most COVID-19 vaccine trials did not include pregnant women, very little data exists regarding the safety of the current mRNA vaccines in pregnant women. Despite the lack of evidence, in regards to Moderna’s COVID-19 vaccine, a World Health Organization (WHO) article updated on January 29, 2021, stated, “We don’t have any specific reason to believe there will be specific risks that would outweigh the benefits of vaccination for pregnant women.” For this reason, the organization recommends that pregnant women at high risk of exposure to COVID-19 talk to their health care providers to determine if and when to get a vaccine. 

As with most populations and COVID-19, there remains much uncertainty when it comes to the research surrounding the pregnant population. As the research continues to evolve, so too will the recommendations for pregnant women. 


Amanda Loudin

Amanda Loudin is a Maryland-based freelance writer specializing in science and health. Find her work in the Washington Post, NBC, and many other outlets.