The list of studies showing that the COVID-19 vaccines are safe during pregnancy continues to grow. In this post, we’ll discuss a study released by the United States Centers for Disease Control and Prevention (CDC) in January demonstrating that receiving the Pfizer, Moderna, or Johnson & Johnson COVID-19 vaccines during pregnancy was not linked to preterm birth or babies that were small for their gestational age. 
First, what is preterm birth? Most providers classify any baby born before 37 weeks of gestation as preterm or premature. And what does small for gestational age mean? Babies given this label are usually in the bottom 10 percent of birthweight of babies born at the same weeks of pregnancy. While most babies who are born a little bit early or are small when they are born end up just fine, for both groups of children, the risk of adverse effects increases. Adverse effects may include breathing problems, inability to regulate their temperature, immune system issues, and challenges regulating their blood sugar.
While that’s a scary list of possible issues, the good news is that researchers at the CDC have shown that the available COVID-19 vaccines do not increase the risk of preterm or small for gestational age babies. The research team analyzed data from more than 40,000 pregnancies.
They found that whether they compared the risk of preterm birth or small for gestational age to number of vaccine doses (one or two) or trimester of vaccination (first, second, third), vaccination did not carry an increased risk of either outcome, compared with pregnant people who did not receive a COVID-19 vaccine. In contrast, pregnant women who were unvaccinated had a higher risk of preterm birth. 7 percent of women who didn’t get vaccinated during pregnancy had babies who were born premature, as compared to 4.9 percent who received any COVID-19 vaccine during pregnancy.
Other studies have shown that pregnant people contract COVID-19 are much more likely to experience preterm labor and birth or have a baby who is small for their gestational age. In a study published in The Lancet Regional Health – Americas in October 2021, a team of researchers led by Deborah Karasek, an epidemiologist at the University of California, San Francisco, showed that risk of having a baby born very early—less than 32 weeks of pregnancy—was 60 percent higher and risk of having a baby born before 37 weeks was 40 percent higher for people who had COVID-19 during their pregnancy. 
And the vaccine has benefits other than protecting babies from the effects of COVID-19 infection in utero. In study published in the Journal of Perinatology in September 2021, researchers showed that antibodies against SARS-CoV-2, the virus that causes COVID-19 infection, were present in the umbilical cord blood of babies whose mothers had either been infected with or vaccinated against COVID-19 during pregnancy.  And in this study, vaccination led to more robust antibody production than natural infection did, meaning that the vaccination both protects the mother from infection and protects the baby with antibodies passed through the placenta. Scientists have shown that maternal antibodies can hang around for up to a year after baby is born, so if you get vaccinated during pregnancy, you might be protecting your baby for a while.
If you still have concerns about getting vaccinated for COVID-19 during pregnancy, the best person to talk to is your doctor or midwife. Aside from you, your care provider knows your situation the best and can thus advise you about the best course of action for vaccines during your pregnancy.
- S. Lipkind et al. “Receipt of COVID-19 Vaccine During Pregnancy and Preterm or Small-for-Gestational-Age at Birth — Eight Integrated Health Care Organizations, United States, December 15, 2020–July 22, 2021,” MMWR Morb Mortal Wkly Rep, 2022.
- Karasek, et al. “The association of COVID-19 infection in pregnancy with preterm birth: A retrospective cohort study in California,” Lancet Regional Health. Americas, 2021.
- Kashani-Ligumsky et al. “Titers of SARS CoV-2 antibodies in cord blood of neonates whose mothers contracted SARS CoV-2 (COVID-19) during pregnancy and in those whose mothers were vaccinated with mRNA to SARS CoV-2 during pregnancy.” Journal of perinatology: official journal of the California Perinatal Association, 2021.