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Charlotte Lozier Institute

Phone: 202-223-8073
Fax: 571-312-0544

2776 S. Arlington Mill Dr.
#803
Arlington, VA 22206

The
Voyage of Life

Vaccines and Immunity that Pass from Mother to Baby

Dive Deeper
Covid-19 coronavirus particle, illustration. The coronavirus SARS-CoV-2 virus causes a mild respiratory illness (Covid-19) that can develop into pneumonia and be fatal in some cases. The coronaviruses take their name from their crown (corona) of surface proteins, which are used to attach and penetrate their host cells. Once inside the cells, the particles use the cells' machinery to make more copies of the virus. COVID-19 vaccines target the outer spike proteins that give the coronavirus its distinctive shape. (Image Credit: Science Source)
How does immunity from the mother get passed to the fetus?

The membranes of the placenta create a barrier that allows some substances to cross to the fetus while keeping other substances out. For example, the placenta does not allow bacteria to enter the fetal bloodstream,1  and can even provide a barrier against some viruses.2 In contrast, the placenta allows water, gases, and nutrients to pass to the fetus. It even transfers some large molecules, like maternal antibodies, to the fetus. These include antibodies against tetanus, diphtheria, and measles,3  but not polio.4 Antibodies are enormous compared to the molecules and chemicals that commonly cross the placenta. Therefore, they need a specific receptor, called the FcRN receptor, to actively move them into the umbilical cord and fetal blood stream.5 While there are five different classes of antibodies, the FcRN receptor moves the smallest type best, the IgG antibody.6 IgG antibodies circulate in the fetus’s blood and provide protection against specific germs and toxins.

8
Weeks
Researchers have seen maternal antibodies in the umbilical cord as early as 8 to 10 weeks gestation, and the concentrations of maternal antibodies in the umbilical cord increase throughout pregnancy.7
Can a mother influence how much protection she gives to her baby?

The more antibodies that the mother has circulating in her own bloodstream, the more antibodies that will transfer to her baby. That is why doctors recommend getting a vaccine against tetanus, diphtheria, and pertussis (Tdap)  between 27 and 30 weeks gestation every time a mother is pregnant, whether or not she already has had the vaccine.8 The vaccine stimulates the mother’s immune system to create more antibodies; therefore, more antibodies transfer to the fetus, helping protect him from whooping cough, caused by the pertussis virus, after birth.  Similarly, when mothers get the flu vaccine in the second or third trimester, most of their babies have enough antibodies to avoid getting the flu for 6 months after birth!

Similarly, when mothers get the flu vaccine in the second or third trimester, most of their babies have enough antibodies to avoid getting the flu for 6 months after birth!9

Pregnant women appear to be more susceptible to COVID-19, and are at higher risk of serious illness, due to the extra oxygen they need to sustain the fetus.10 Therefore, the CDC recommends that pregnant women get vaccinated against COVID-19. Preliminary studies suggest that the vaccine is safe for pregnant women.11

Since mothers can pass antibodies to their children while they are still pregnant, some researchers have tried to develop vaccines against harmful diseases that can be deadly to newborns, such as group B strep and respiratory syncytial virus (RSV), which can cause colds and pneumonia.12 Currently, a vaccine against Group B strep is in clinical studies with the goal of passing immunity to the young infants,13 and a maternal vaccine against RSV is currently under priority review at the Food & Drug Administration.14

Why do some antibodies cross the placenta while others don't?

Researchers are still investigating the reasons why some antibodies transfer to the fetus efficiently while others do not, although two theories have emerged. First, the FcRN receptor moves more IgG1 antibodies than any other kind. These antibodies identify foreign proteins. This means that the fetus will have better immunity against diseases where the antibodies recognize microbial proteins.15 Second, the placenta selectively transfers antibodies that stimulate the fetus’s own immune system to make natural killer cells.16 Therefore, the placenta is designed to selectively transfer maternal antibodies that will best train the fetus’s immune system to fight future infections itself.

How do antibodies in the breastmilk protect the baby?

Even after birth, the infant continues to get maternal antibodies through the breastmilk. The most common antibody in breastmilk is IgA, which protects against germs in the respiratory system and gut. The IgA molecules in breastmilk come attached to proteins that protect them from getting digested.17 These IgA molecules attach to the lining of the intestine and protect the infant against ingested bacteria. Infants do not make significant quantities of IgA on their own until several weeks after birth, so the maternal IgA from the breastmilk provides the best defense against germs.18 Maternal antibodies do not pass into the newborn’s bloodstream after birth, but substances in the breastmilk help strengthen a newborn’s own immune responses.19

Back to The Voyage of Life
Sources
  1. Moore, Keith, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  2. Roger Pique-Regi et al., “Does the Human Placenta Express the Canonical Cell Entry Mediators for SARS-CoV-2?,” ed. Stephen CJ Parker and Marianne E Bronner, ELife 9 (July 14, 2020): e58716, https://doi.org/10.7554/eLife.58716.
  3. Moore, Keith, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  4. Madeleine F. Jennewein et al., “Fc Glycan-Mediated Regulation of Placental Antibody Transfer,” Cell 178, no. 1 (June 27, 2019): 202-215.e14, https://doi.org/10.1016/j.cell.2019.05.044.
  5. Genevieve G Fouda et al., “The Impact of IgG Transplacental Transfer on Early Life Immunity,” ImmunoHorizons 2, no. 1 (January 1, 2018): 14–25, https://doi.org/10.4049/immunohorizons.1700057.
  6. Fouda et al., “The Impact of IgG Transplacental Transfer on Early Life Immunity,” 2018; Patricia Palmeira et al., “IgG Placental Transfer in Healthy and Pathological Pregnancies,” ed. Andres Salumets, Clinical and Developmental Immunology 2012 (October 1, 2011): 985646, https://doi.org/10.1155/2012/985646.
  7. Genevieve G Fouda et al., “The Impact of IgG Transplacental Transfer on Early Life Immunity,” ImmunoHorizons 2, no. 1 (January 1, 2018): 14–25, https://doi.org/10.4049/immunohorizons.1700057.
  8. Geeta K Swamy and R Phillips Heine, “Vaccinations for Pregnant Women,” Obstetrics and Gynecology 125, no. 1 (January 2015): 212–26, https://doi.org/10.1097/AOG.0000000000000581.
  9. Geraldine Blanchard-Rohner et al., “Influenza Vaccination Given at Least 2 Weeks Before Delivery to Pregnant Women Facilitates Transmission of Seroprotective Influenza-Specific Antibodies to the Newborn,” The Pediatric Infectious Disease Journal 32, no. 12 (2013), https://journals.lww.com/pidj/Fulltext/2013/12000/Influenza_Vaccination_Given_at_Least_2_Weeks.24.aspx; Swamy and Heine, “Vaccinations for Pregnant Women.”
  10. Francesca Donders et al., “ISIDOG Recommendations Concerning COVID-19 and Pregnancy,” Diagnostics 10, no. 4 (April 2020): 243, https://doi.org/10.3390/diagnostics10040243.
  11. Tom T. Shimabukuro et al., “Preliminary Findings of MRNA Covid-19 Vaccine Safety in Pregnant Persons,” New England Journal of Medicine 0, no. 0 (April 21, 2021): null, https://doi.org/10.1056/NEJMoa2104983.
  12. Geeta K Swamy and R Phillips Heine, “Vaccinations for Pregnant Women,” Obstetrics and Gynecology 125, no. 1 (January 2015): 212–26, https://doi.org/10.1097/AOG.0000000000000581.
  13. Monica Fabbrini et al., “Functional Activity of Maternal and Cord Antibodies Elicited by an Investigational Group B Streptococcus Trivalent Glycoconjugate Vaccine in Pregnant Women.,” The Journal of Infection 76, no. 5 (May 2018): 449–56, https://doi.org/10.1016/j.jinf.2018.01.006.
  14. https://www.biopharma-reporter.com/Article/2023/02/21/FDA-decision-on-Pfizer-s-maternal-RSV-vaccine-expected-in-August
  15. Patricia Palmeira et al., “IgG Placental Transfer in Healthy and Pathological Pregnancies,” ed. Andres Salumets, Clinical and Developmental Immunology 2012 (October 1, 2011): 985646, https://doi.org/10.1155/2012/985646.
  16. Madeleine F. Jennewein et al., “Fc Glycan-Mediated Regulation of Placental Antibody Transfer,” Cell 178, no. 1 (June 27, 2019): 202-215.e14, https://doi.org/10.1016/j.cell.2019.05.044.
  17. A. S. Goldman, “The Immune System of Human Milk: Antimicrobial, Antiinflammatory and Immunomodulating Properties.,” The Pediatric Infectious Disease Journal 12, no. 8 (August 1993): 664–71, https://doi.org/10.1097/00006454-199308000-00008.
  18. Jack Newman, “How Breast Milk Protects Newborns,” KellyMom, 2018, https://kellymom.com/pregnancy/bf-prep/how_breastmilk_protects_newborns/.
  19. Jack Newman, “How Breast Milk Protects Newborns,” KellyMom, 2018, https://kellymom.com/pregnancy/bf-prep/how_breastmilk_protects_newborns/.
See Full Bibliography

All images and illustrations on The Voyage of Life were reviewed by credentialed scientists for accuracy.

Medical art animation was used to provide a schematic representation of fetal development, with some features, including timing, not to scale. The animation was chosen as an ethically uncompromised guide to fetal development. There are many real human images at each developmental age showing the most accurate fetal forms throughout development. A concerted effort was made to use images and material in which the human embryo or fetus did not undergo any known harm.

Page last updated on June 7, 2023