Has the human papillomavirus (HPV) immunization programme improved obstetric outcomes in spontaneous delivery? An ecological study

Objective: To measure the rates of adverse obstetric outcomes in spontaneous delivery in a population of young women with high uptake of the bivalent human papillomavirus (HPV) vaccine.

Study design: This was a population-based ecological study with data from the Aberdeen Maternity and Neonatal Databank, UK. All women born between 1986-1996 with spontaneous singleton live birth at age 20-30 years were included for analysis. Exposure was defined according to maternal year of birth and HPV immunisation eligibility: pre-immunisation cohort (1986-1990), catch-up immunisation cohort (1991-1994) and routine immunisation cohort (1995-1996). Outcomes were defined as spontaneous preterm birth (PTB), low birth weight (LBW) and pre-labour preterm rupture of membranes (pPROM). Generalized estimating equation models were applied, adjusted for deprivation, smoking status, marital status, body mass index, parity, maternal age and year of infant delivery.

Results: A total of 6515 spontaneous singleton live births were included in final analysis, with 5134 births included in the pre-immunisation cohort, 1250 in the catch-up immunisation cohort and 131 in the routine immunisation cohort. Compared with the pre-immunisation cohort, no statistically significant reduction on PTB, LBW or pPROM were observed in either immunised cohorts. The adjusted odds ratio (aOR) on PTB was 0.64 (95 % confidence interval, 0.40-1.03) in the catch-up cohort and 0.71 (0.28-1.77) in the routine cohort. The corresponding aOR were 0.88 (0.54-1.45) and 0.51 (0.16-1.62) for LBW and 1.62 (0.58-4.54) and 1.51 (0.21-11.01) for pPROM.

Conclusions: We did not observe a significant reduction on PTB, LBW or pPROM among spontaneous singleton live birth in either HPV immunised cohorts, although the additional benefit in improving obstetric outcomes cannot be excluded because of the limits of the sample size and the study design. Further demonstration is warranted when more women in the fully HPV immunised cohorts embark on pregnancy.