EXECUTIVE SUMMARY
Babies born to mothers who were vaccinated against human papillomavirus (HPV) during pregnancy did not exhibit a significantly higher risk for major birth defects, low birth weight, preterm birth, or stillbirth when compared to babies who were not exposed, according to data from a new study.
- Although HPV vaccination is not recommended in pregnancy, many women are vaccinated inadvertently early in the first trimester of unplanned or unrecognized pregnancies, and data on the safety of vaccination during pregnancy are limited.
- The CDC offers guidelines for the vaccines women need before, during, and after pregnancy. Some vaccines, such as the measles, mumps, rubella vaccine, should be administered one month or more before pregnancy, while the Tdap vaccine can be administered during pregnancy.
Babies born to mothers who were vaccinated against human papillomavirus (HPV) during pregnancy did not demonstrate a significantly higher risk for major birth defects, low birth weight, preterm birth, or stillbirth when compared to babies who were not exposed, data from a newly released study indicate.1
The HPV vaccine is recommended for all girls and women 9-26 years of age. Although HPV vaccination is not recommended in pregnancy, many women will be vaccinated inadvertently early in the first trimester of unplanned or unrecognized pregnancies, and there are limited data on the safety of vaccination during pregnancy.
To perform this study, scientists in the department of epidemiology research at the Copenhagen, Denmark-based Statens Serum Institut and the clinical epidemiology unit in the department of medicine at the Karolinska Institutet in Stockholm studied a cohort that included all the women in Denmark whose pregnancy ended between Oct. 1, 2006, and Nov. 30, 2013. Using nationwide registers, researchers linked information on vaccination, adverse pregnancy outcomes, and potential confounders among women in the cohort.
Women who were exposed to the vaccine during the prespecified time windows were matched for propensity score in a 1:4 ratio with women who were not exposed to the vaccine during the same time windows. Outcomes included spontaneous abortion, stillbirth, major birth defect, small size for gestational age, low birth weight, and preterm birth.
In matched analyses, exposure to the quadrivalent HPV vaccine was not associated with significantly higher risks than no exposure for major birth defect (65 cases among 1,665 exposed pregnancies and 220 cases among 6,660 unexposed pregnancies; prevalence odds ratio [OR], 1.19; 95% confidence interval [CI], 0.90-1.58), spontaneous abortion (20 cases among 463 exposed pregnancies and 131 cases among 1,852 unexposed pregnancies; hazard ratio [HR], 0.71; 95% CI, 0.45-1.14), preterm birth (116 cases among 1,774 exposed pregnancies and 407 cases among 7,096 unexposed pregnancies; prevalence OR, 1.15; 95% CI, 0.93-1.42), low birth weight (76 cases among 1,768 exposed pregnancies and 277 cases among 7,072 unexposed pregnancies; prevalence OR, 1.10; 95% CI, 0.85-1.43), small size for gestational age (171 cases among 1,768 exposed pregnancies and 783 cases among 7,072 unexposed pregnancies; prevalence OR, 0.86; 95% CI, 0.72-1.02), or stillbirth (two cases among 501 exposed pregnancies and four cases among 2,004 unexposed pregnancies; HR, 2.43; 95% CI, 0.45-13.21).1
“In a nationwide cohort study conducted in Denmark, we found that quadrivalent HPV vaccination during pregnancy was not associated with significantly greater risks of adverse pregnancy outcomes,” the researchers concluded. “Given the upper limits of the confidence intervals in our study, relatively higher risks of more than 58% for major birth defect, 14% for spontaneous abortion, 42% for preterm birth, 43% for low birth weight, and 2% for small size for gestational age are unlikely to be associated with quadrivalent HPV vaccination.”
Check Vaccine Safety in Pregnancy
Until recently, pregnant women largely have been excluded from clinical trials because they have been considered a vulnerable population, wrote Kathryn Edwards, MD, Sarah H. Sell and Cornelius Vanderbilt Professor of Pediatrics at the Vanderbilt University School of Medicine and scientific director of the Vanderbilt Vaccine Research Program, in an accompanying editorial. However, there has been a concerted effort during the past few years to include pregnant women in clinical studies of drugs and vaccines that are used in pregnancy to provide pertinent safety and effectiveness data.
“In the case of HPV vaccine or other vaccines that are not intended for pregnant women but are inadvertently administered to them, postmarketing safety evaluations assume great importance,” Edwards wrote. “The carefully conducted postlicensure safety study of HPV vaccine now reported ... is a model for others to emulate.”
The CDC offers guidelines for the vaccines women require before, during, and after pregnancy. Certain vaccines, such as the measles, mumps, rubella (MMR) vaccine, should be administered one or more months before pregnancy, while the Tdap vaccine, which protects against whooping cough, can be administered during pregnancy.
Flu shots can be administered before or during pregnancy, depending on if it is flu season when the woman is pregnant. New mothers may receive vaccines after giving birth, even while breastfeeding.
Providers soon may see data on vaccine safety in pregnant women. Recent updates to the Common Rule, the ethical framework that guides U.S. biomedical research, have removed the “vulnerable population” classification for pregnant women.
Also, the recently passed 21st Century Cures Act contains advocacy for the inclusion of pregnant women in clinical trials.3,4
REFERENCES
- Scheller NM, Pasternak B, Mølgaard-Nielsen D, et al. Quadrivalent HPV vaccination and the risk of adverse pregnancy outcomes. N Engl J Med 2017;376:1223-1233.
- Edwards KM. Ensuring vaccine safety in pregnant women. N Engl J Med 2017;376:1280-1282.
- Federal Policy for the Protection of Human Subjects (“Common Rule”). Washington, DC: Department of Health and Human Services, Office for Human Research Protections; March 18, 2016.
- H.R. 6 — 114th Congress: 21st Century Cures Act. Available at: http://bit.ly/1lTfwfU. Accessed April 17, 2017.
Many pregnant women are exposed to the vaccine inadvertently.
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