(Published 2 March 2010)
Objective To assess whether vaccination against human papillomavirus (HPV) increases the risk of miscarriage.
Design Pooled analysis of two multicentre, phase three masked randomised controlled trials
Setting Multicentre trials in several continents and in Costa Rica.
Participants 26 130 women aged 15-25 at enrolment; 3599 pregnancies eligible for analysis.
Interventions Participants were randomly assigned to receive three doses of bivalent HPV 16/18 VLP vaccine with AS04 adjuvant (n=13 075) or hepatitis A vaccine as control (n=13 055) over six months.
Main outcome measures Miscarriage and other pregnancy outcomes.
Results – The estimated rate of miscarriage was 11.5% in pregnancies in women in the HPV arm and 10.2% in the control arm. The one sided P value for the primary analysis was 0.16; thus, overall, there was no significant increase in miscarriage among women assigned to the HPV vaccine arm. In secondary descriptive analyses, miscarriage rates were 14.7% in the HPV vaccine arm and 9.1% in the control arm in pregnancies that began within three months after nearest vaccination.
Conclusion There is no evidence overall for an association between HPV vaccination and risk of miscarriage.
Nonetheless, we cannot completely rule out the possibility of an increased risk among pregnancies conceived within three months of vaccination. It is unlikely that postmarketing surveillance will find small but important effects of vaccination on miscarriage because of the difficulties of ascertaining miscarriages in comparable unvaccinated women and determining timing of last menstrual period in vaccinated women, which is needed to investigate whether any effect is restricted to pregnancies conceived near vaccination.