Vaccine pregnancy data: The latest and greatest

Okay, mamas. I did some digging tonight and found all the data on we have, thus far, on COVID19 vaccines and pregnancy/lactating. There are currently three sources of rich information.

Bottom line: It’s looking good.

Note: This is important because pregnant and lactating people were excluded from vaccine trials (this is normal but this decision is consistently debated among scientists). So, we are at the mercy of time to see “real world” data. This post is based on mRNA vaccines; we do not have J&J data yet.


On March 1, the ACIP (Advisory Committee on Immunization Practices) at the CDC met to discuss updates on COVID-19 vaccines. The meeting minutes are here. Buried in those presentations, were slides regarding of safety data for vaccinated pregnant women:

American Journal of Obstetrics and Gynecology (AJOG)

On March 25, a study was published in a highly regarded scientific, OBGYN journal. The scientists enrolled 131 vaccinated women (84 pregnant, 31 lactating, and 16 non-pregnant) between December 17, 2020 and Feb 23, 2021. The scientists compared vaccinated pregnant women to two groups: 1) unvaccinated pregnant women and 2) “naturally” infected pregnant women.

This is what they found:

  • Among the pregnant and vaccinated, 13% received their first vaccine dose in the first trimester, 46% in the second trimester, and 40% in the third trimester.

  • Antibody levels were the same in pregnant and lactating compared to non-pregnant women

  • Antibody levels were higher among vaccinated compared to “naturally” infected pregnant women

  • Antibodies were present in all breastmilk samples

  • The second vaccine dose increased a specific type of antibody (IgG but not IgA) in maternal blood and breastmilk (which was expected)

  • Vaccine-related fevers/chills were reported by 32% of pregnant women after the second dose and 50% of non-pregnant

  • 13 people delivered babies during this study period

    • All 13 were vaccinated in the 3rd trimester (which makes sense, because they delivered during the study period, which was only 2 months)

    • Antibodies were present in all umbilical cord blood samples

    • One participant delivered 17 days after vaccine 1, with spontaneous preterm labor at  35 weeks’ gestation

  • Here is a figure from the paper. Don’t let it scare you off (it scared me off at first). I’ll walk you through two panels.

    • Panel A: At baseline (i.e. V0=no vaccine protection), antibodies were low across non-pregnant people, pregnant people, and lactating. When participants got the second dose (V1), antibodies were high across all three groups. Then, 2 weeks after the second dose (V2=fully protected), all three groups had even more antibodies. This is fantastic news.

    • Panel F shows that antibodies were higher among vaccinated (blue, purple, orange dots) compared to “naturally” infected people (yellow dots). Also, great news.

Developmental and Reproductive Toxicology Study (DART) studies

We do have data from Pfizer, Moderna, and J&J DART studies. These are small animal studies that are required before studying vaccines among pregnant humans. Scientists basically give pregnant rats the vaccine and see how they do. What did they find?

  • Rats did not have any adverse effects on female reproduction, fetal/embryonal development, or postnatal developmental. We are not surprised, but still good to know.

Other Helpful Links

  • Fertility and vaccine previous post here

  • Pregnancy and mRNA vaccine previous post here

  • Mom to baby transfer of antibodies previous post here

  • HERE is a great decision tool to help you (if you’re pregnant) decide whether or not you should get the vaccine. A group of experts in the fields of OB/GYN, Maternal-Fetal Medicine, Shared Decision-Making and risk communication, Emergency Medicine, and current COVID-19 research at the University of Massachusetts Medical School – Baystate made a decision aid to help individuals who are pregnant, lactating, or planning on becoming pregnant decide whether or not to receive a COVID-19 vaccine (in conjunction with their healthcare providers). At this site you can get the decision aid in 10 languages.

Hope this is helpful!

Love, YLE (and a fellow mama)