Although the overall risk is very low, a study released by the CDC early in the pandemic suggested that pregnancy increases the risk of more severe COVID-19 illness. The study compared pregnant to non-pregnant women, both groups with symptomatic COVID-19. The pregnant women were found to be three times more likely to be admitted to the intensive care unit (ICU) compared to non-pregnant women.
Since the introduction of vaccines for COVID-19, pregnant women have been strongly encouraged to get vaccinated and boosted. The CDC continues to compile evidence indicating that vaccination is safe and effective during pregnancy. But how serious is COVID-19 during pregnancy?
Pregnancy increases the risk for mother and baby
A living systematic review which included more than 140 studies sheds light on the specific risk factors associated with severe COVID-19. Serious illness—such as ICU admission, ventilation and death—was associated with being 35 years or older, having an increased body mass index (BMI 30 or more), high blood pressure or an underlying medical condition.
Pregnancy-specific risks such as pre-eclampsia and gestational diabetes also increase the risk of serious illness. Socioeconomic factors, such as ethnicity and poverty, also create disparities in access to timely, high-quality care, compounding the challenges for many women. All of these factors are known risks which predate the pandemic. The degree to which SARS-CoV-2 variants present similar risks is still being quantified, but another large review echoed these findings.
Severe COVID-19 disease associated with increased age, body mass index, high blood pressure, diabetes
Source: Allotey J, et al. BMJ 2020;370:m3320
Overall risk is very low
Keep in mind that the absolute risk of serious complications due to COVID-19 during pregnancy is very low. For example, among all the pooled studies in the systematic review, 0.8% of pregnant women with COVID-19 were admitted to the ICU compared to 0.6% among the non-pregnant women with COVID-19. The absolute risk difference introduced by COVID-19 is therefore about 0.2%. Looking at this another way, comparing pregnant women with and without COVID-19, the absolute risk difference introduced by COVID-19 is 3% (3.4% admitted to the ICU among those with COVID-19 vs. 0.4% for those without).
However, an important caveat to any study of COVID-19 in pregnant women may be due to differences in testing: non-pregnant women are tested when symptomatic whereas pregnant women are likely to be tested any time they receive medical care, regardless of symptoms. This difference in testing introduces potential bias and results should be interpreted with caution. In other words, COVID-19 may appear to introduce additional risk simply because it is universally screened in a way that is different from other infections.
Interestingly, this systematic review also found that approximately two-thirds of pregnant women infected with SARS-CoV-2 are asymptomatic. In fact, women who were pregnant were less likely to have fever, shortness of breath, cough and muscle aches compared to non-pregnant women with COVID-19. These findings may be artifacts of the testing bias—more asymptomatic infections are picked up with pregnancy given the increased contacts with the healthcare system during pregnancy.
What about transmission of infection to the baby during pregnancy?
Transmission of infection to the infant during pregnancy is rare, and infants who become infected are more likely to have been exposed during and just after delivery. A number of natural barriers to vertical transmission from mother to child may protect the baby during pregnancy, and the baby can begin developing its own antibodies between 12 and 20 weeks’ gestation.
After delivery, household contacts with any illness should take precautions around the baby in the first month or two as the infant’s immune system matures. Common-sense precautions include limiting close contact with the baby if unwell, avoiding crowded situations in closed areas with poor ventilation, and washing hands with soap and water.
Which trimester is best to get vaccinated?
For women who plan to get a booster, some may be interested in which trimester is best for the baby’s post-delivery protection. In a recent study of third-trimester booster vaccination, a longer duration of time between vaccination and delivery was correlated with waning maternal antibodies, but there was no effect on the level of antibodies in the baby at delivery. The primary goal of vaccination, though, is to protect the mother against increased risks during pregnancy.
Protection in the womb continues after birth
In a study among more than 1,700 women who delivered at Pennsylvania Hospital in Philadelphia between April and August 2020, antibodies were measured in both the woman and the baby. The researchers found that antibodies were transferred to the neonates even among mothers with an asymptomatic infection.
How safe is vaccination during pregnancy?
There is growing evidence that vaccination during pregnancy is safe and effective. The vaccine does not induce antibodies in the fetus, suggesting there is little chance that the vaccine will affect fetal development in the womb. There is also no evidence of increased miscarriage or still birth rates after vaccination.
Although the safety profile is very good, vaccines do have side effects. A recent Canadian study found that pregnant vaccinated females had four times the risk of a significant health event within seven days of dose two of Moderna compared to unvaccinated pregnant people. This increased risk was not present for either dose one or two of Pfizer nor dose one of Moderna.
Vaccination during pregnancy has been recommended for more than two decades for influenza and pertussis. Health officials have added a recommendation for vaccination against COVID-19 during pregnancy given the increased risk of COVID-19 illness and the safety of vaccination. At the moment, though, data is sparse regarding the additional benefit of vaccinating or boosting pregnant people who have already recovered from COVID-19.
Taken together, a reasonable conversation about vaccination risks and benefits might consider which vaccine (perhaps Pfizer vs. Moderna) and how many doses should be administered in the context of a woman’s unique health risks and prior COVID-19 infection. Antibodies from vaccination or prior infection offer protection to the mother and also the infant during the first six months of life when the immune system is rapidly developing.