TL;DR
Get workout gear delivered free with Prime
- Fast, free delivery on millions of items
- Prime Video, Amazon Music and more included
- Member-only deals all year
A Swedish national case-control study found lower odds of preterm, very preterm and spontaneous preterm birth among women vaccinated against HPV before pregnancy. The observational findings do not establish that vaccination caused the differences, and the associations weakened after researchers accounted for high-grade cervical lesions.
A study of 624,713 births in Sweden found that women who had received a quadrivalent HPV vaccine before pregnancy had lower odds of preterm, very preterm and spontaneous preterm birth than unvaccinated women. The national case-control study, published in The BMJ, reports an association, not proof that vaccination caused the differences.
Researchers led by Jiayao Lei of the Karolinska Institute examined nationwide register data on singleton births to women ages 16 to 35 who had not previously given birth. The births occurred from 2006 through 2023. Among eligible births, 14.8% of women had received a quadrivalent HPV vaccine before pregnancy. The study excluded women whose first HPV vaccine was a bivalent or nonavalent product.
Compared with women who had not been vaccinated, vaccinated women had lower adjusted odds of preterm birth (adjusted odds ratio, or aOR, 0.95), very preterm birth (aOR 0.85) and spontaneous preterm birth (aOR 0.95). The researchers also reported lower odds of preterm prelabor rupture of membranes (aOR 0.93) and a severely small-for-gestational-age infant (aOR 0.92). These are relative odds estimates; the study summary does not give the absolute risk difference for each outcome.
Associations for some outcomes were stronger among women vaccinated before age 17: adjusted odds were lower for preterm birth (aOR 0.90), spontaneous preterm birth (aOR 0.89), preterm prelabor rupture of membranes (aOR 0.86) and severe small-for-gestational-age birth (aOR 0.91). Researchers found no significant differences for premature rupture of membranes, stillbirth or neonatal mortality in the overall vaccinated group. The reported results do not establish that vaccination at a particular age prevents these outcomes.
Possible Benefits Beyond Cancer Prevention
The findings raise the possibility that HPV vaccination’s benefits could extend beyond preventing HPV infections and related cancers, with potential relevance to pregnancy outcomes and public health planning. The researchers said that even relatively modest differences for individuals could matter across a population, but the study does not quantify an overall economic effect or show that vaccination should be presented as a way to prevent pregnancy complications.
The age pattern may also inform questions about when vaccination is offered. The researchers suggested that earlier vaccination could provide protection before potential HPV exposure and for a longer period before reproductive years. That is a proposed explanation, not a result that this study directly tested. The established purpose of HPV vaccination remains protection against HPV-related disease; these observational findings alone do not change clinical guidance.
Products Worth Considering
Withings BPM Connect Smart Blood Pressure Monitor
Withings BPM Vision Blood Pressure Monitor with Wi-Fi and Bluetooth
Fitbit Sense 2 Health and Fitness Smartwatch – Shadow Grey/Graphite
As an affiliate, we earn on qualifying purchases.
How Cervical Lesions May Fit
HPV vaccination is primarily used to prevent infection with HPV types associated with cervical and other cancers. In the United States, the American Academy of Pediatrics recommends a two-dose series of the nine-valent vaccine beginning between ages 9 and 12. The Swedish study examined the quadrivalent vaccine, so its results should not automatically be treated as direct evidence about every vaccine formulation or schedule.
The researchers considered whether cervical lesions could help explain the pregnancy associations. Before childbirth, high-grade cervical lesions had been diagnosed in 0.6% of vaccinated women and 3.7% of unvaccinated women in the study population. When the analysis adjusted for such lesions, the associations with preterm-birth outcomes weakened. The authors said prevention of lesions and subsequent cervical treatment could partly account for the pattern, but the study lacked detailed information on cervical treatment.
To address differences between groups, the team matched each adverse-outcome case with as many as 10 controls without that same outcome and adjusted its analyses for measured factors. Those methods can reduce some sources of bias, but they cannot remove all differences between vaccinated and unvaccinated participants.
“Our findings highlight the importance of timely HPV vaccination and suggest that its potential benefits may extend beyond cancer prevention to reproductive health.”
— Jiayao Lei and Zhongsong Zhang of the Karolinska Institute, speaking to MedPage Today
Association Does Not Prove Cause
The study was observational, so it cannot establish that HPV vaccination itself lowered pregnancy risks. Residual confounding remains possible, including differences in prior HPV exposure and sexual or reproductive behavior. The authors highlighted particular uncertainty around women vaccinated at age 17 or older, whose vaccination may have occurred as catch-up or opportunistic care.
Researchers also lacked detailed data on cervical treatment and could not fully assess differences in preventive interventions for preterm birth. The study summary does not provide absolute outcome risks or show whether the findings apply to other HPV vaccine formulations, populations outside Sweden, or people with different pregnancy histories. The results should not be read as evidence that vaccination directly prevents preterm birth, stillbirth or neonatal death.
Further Evidence and Policy Review
The study authors said policy and cost-effectiveness analyses should account for HPV vaccination’s cancer-prevention benefits and consider whether possible reductions in pregnancy complications affect the overall calculation. That is a recommendation for future analysis, not a finding that this study has already established economic savings.
Further research would need to test whether the associations hold in other populations and vaccine cohorts, and to examine cervical lesions, treatments and other potential confounders in more detail. Until then, the reported pregnancy differences remain an area for investigation rather than a new clinical guarantee. The study does not report a specific next publication date or planned follow-up.
Key Questions
Does the study prove that HPV vaccination prevents preterm birth?
No. It found lower adjusted odds of several outcomes among vaccinated women, but its observational design cannot show that vaccination caused the differences.
Which pregnancy outcomes were associated with vaccination?
The study reported lower odds of preterm, very preterm and spontaneous preterm birth, as well as preterm prelabor rupture of membranes and severe small-for-gestational-age birth. It found no significant overall difference for premature rupture of membranes, stillbirth or neonatal mortality.
Were the associations stronger for women vaccinated at younger ages?
For several outcomes, including preterm and spontaneous preterm birth, the associations were stronger among women vaccinated before age 17. This does not prove that earlier vaccination caused the lower odds.
Could cervical lesions explain the results?
Possibly, but that remains uncertain. The associations weakened after researchers adjusted for high-grade cervical lesions, and the authors said lesion prevention or subsequent treatment could partly explain the pattern. They lacked detailed treatment data, so this explanation is exploratory.
Does this change HPV vaccine recommendations?
The study does not establish a new pregnancy-related indication or change vaccination guidance. It examined a quadrivalent vaccine in a Swedish population; current vaccine recommendations should be discussed with a qualified health professional.
Source: rss
