Scientists examine risk of poor birth outcomes following H1N1 vaccination

July 10, 2012

In studies examining the risk of adverse outcomes after receipt of the influenza A(H1N1) vaccine, infants exposed to the vaccine in utero did not have a significantly increased risk of major birth defects, preterm birth, or fetal growth restriction; while in another, study researchers found a small increased risk in adults of the nervous system disorder, Guillain-Barre syndrome, during the 4 to 8 weeks after vaccination, according to 2 studies in the July 11 issue of JAMA.

In the first study, Björn Pasternak, M.D., Ph.D., of the Statens Serum Institut, Copenhagen, Denmark and colleagues investigated whether exposure to an adjuvanted influenza A(H1N1)pdm09 during pregnancy was associated with increased risk of major birth defects, preterm birth, and . According to background information in the article, the 2009 influenza A(H1N1) pandemic put pregnant women at increased risk of illness, death, and poor pregnancy outcomes. "Pregnant women were among the main target groups prioritized for vaccination against influenza A(H1N1)pdm09, and an estimated 2.4 million women were vaccinated during pregnancy in the United States alone. However, assessment of the fetal safety of H1N1 vaccination in pregnancy has been limited to a few pharmacovigilance reports and descriptive cohort studies."

The registry-based study included all live-born singleton infants in Denmark delivered between November 2, 2009, and September 30, 2010. The researchers estimated the prevalence odds ratios of adverse fetal outcomes, comparing infants exposed and unexposed to an AS03-adjuvanted influenza A(H1N1)pdm09 vaccine during pregnancy. Following exclusions, a group of 53,432 live-born infants was identified with 6,989 (13.1 percent) exposed to the vaccine during pregnancy.

In a propensity score-matched analysis of 330 infants exposed to the vaccine in the first trimester of pregnancy and 330 unexposed, there were 18 infants (5.5 percent) diagnosed with a major birth defect among those exposed compared with 15 (4.5 percent) among the unexposed. Among infants exposed to the H1N1 vaccine in the first trimester, 31 (9.4 percent) were born preterm compared with 24 (7.3 percent) among the unexposed. Preterm birth occurred in 302 of 6,543 infants (4.6 percent) with second- or third-trimester exposure, compared with 295 of 6,366 unexposed infants (4.6 percent). "Taking gestational age into account, there was no increased risk of small size for gestational age associated with vaccination in the first (25 [7.6 percent] exposed vs. 31 [9.4 percent] unexposed) or the second or third trimester (641 [9.7 percent] exposed vs. 657 [9.9 percent] unexposed)," the researchers write.

"In conclusion, this nationwide cohort study in Denmark found no significant associations between exposure to an AS03-adjuvanted A(H1N1)pdm09 vaccine in pregnancy and risk of adverse fetal outcomes including major birth defects, preterm , and growth restriction. Although the data provide robust evidence of safety with respect to outcomes associated with second- or third-trimester exposure, results from analyses of first-trimester exposure should be viewed as preliminary and need confirmation. Further research also needs to address risk of specific as well as effectiveness of H1N1 vaccination in pregnancy."

Explore further: Prenatal use of newer antiepileptic drugs not associated with increased risk of major birth defects

More information: JAMA. 2012;308[2]:165-174.

Related Stories

Prenatal use of newer antiepileptic drugs not associated with increased risk of major birth defects

May 17, 2011
Use of newer-generation antiepileptic drugs, which are also prescribed for bipolar mood disorders and migraine headaches, during the first trimester of pregnancy was not associated with an increased risk of major birth defects ...

Link between influenza vaccination in pregnancy and reduced risk of premature birth

June 1, 2011
A study published in this week's PLoS Medicine suggests that there might be an association between maternal immunization with inactivated influenza vaccine during pregnancy and reduced likelihood of prematurity and the baby ...

Flu shot during pregnancy shows unexpected benefits in large study

May 22, 2012
Getting a flu shot during pregnancy provides unanticipated benefits to the baby, according to the authors of a large population-based study examining the issue. Specifically, the study showed that H1N1 vaccination during ...

Research demonstrates link between H1N1 and low birth weight

May 2, 2011
In 2009, the United States was gripped by concern for a new winter threat: the H1N1 strain of influenza. According to research conducted through that winter, pregnant women were right to be concerned.

Rheumatoid arthritis drug not linked to specific birth defects

July 3, 2012
(HealthDay) -- The rheumatoid arthritis drug leflunomide is not a major cause of birth defects in women who inadvertently become pregnant while taking the drug, although pregnancy should be avoided, according to a study in ...

Recommended for you

Population health impact of infants born small for gestational age in low- and middle-income countries

August 18, 2017
In low-and middle-income countries, it is common for babies to be born of low birth weight, due to either inadequate growth in utero (fetal growth restriction) and/or preterm birth, (birth before 37 weeks gestation). Maternal ...

Hormone from fat tissue can give protection against polycystic ovary syndrome

August 10, 2017
Obesity and reduced insulin sensitivity are common in polycystic ovary syndrome, PCOS. New research based on animal studies, and to be published in the journal PNAS, reveals that the hormone adiponectin can protect against ...

Study in mice may reveal insights into causes of miscarriages for some women

August 9, 2017
Researchers at St. Michael's Hospital have identified how natural killer cells in the mouse placenta can cause a fetus to fail to grow in the womb or cause miscarriages.

Insomnia, sleep apnea nearly double the risk of preterm delivery before 34 weeks

August 9, 2017
Pregnant women who are diagnosed with sleep disorders such as sleep apnea and insomnia appear to be at risk of delivering their babies before reaching full term, according to an analysis of California births by researchers ...

Elective freezing of IVF embryos linked to higher pregnancy rates in some cases

August 1, 2017
A delay in transferring embryos to the mother improves the success of in vitro fertilization in certain cases, according to a study by scientists at the Stanford University School of Medicine, Celmatix Inc. and several other ...

Negative birth outcomes linked to air pollution exposure early in pregnancy, study finds

July 27, 2017
Exposure to air pollution early in a pregnancy could increase risk for preterm birth and low birth weight, according to a study led by researchers at NYU School of Medicine, and published on July 27 in Environmental Health ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.