Antenatal Respiratory Syncytial Virus and Human Metapneumovirus Illness Rates Among Pregnant Women in Thailand and the Association Between Antenatal Respiratory Syncytial Virus and Perinatal Outcomes: A Prospective Cohort Study.

Summary

Among 2764 pregnant women (median enrollment GA 10 weeks), RSV and hMPV illness incidences were 57 and 23 per 10,000 pregnant woman-months, respectively; 42% and 34% sought medical care. Third-trimester antenatal RSV illness was associated with increased preterm birth risk (adjusted HR 2.50; 95% CI 1.04–6.00), but not SGA (aHR 0.79; 95% CI 0.29–2.16).

Key Findings

• Incidence: RSV 57 and hMPV 23 per 10,000 pregnant woman-months.
• Medical care sought by 42% (RSV) and 34% (hMPV) illnesses.
• Third-trimester RSV illness associated with preterm birth (aHR 2.50; 95% CI 1.04–6.00).
• No association between antenatal RSV illness and SGA (aHR 0.79; 95% CI 0.29–2.16).

Clinical Implications

Supports prioritizing maternal RSV vaccination and heightened surveillance in late pregnancy; obstetricians should consider recent RSV illness when assessing preterm birth risk.

Limitations

• Single-country cohort may limit global generalizability
• Illness capture based on symptom-triggered sampling could miss asymptomatic infections

Future Directions

Evaluate maternal RSV vaccine effectiveness against preterm birth endpoints, assess mechanisms linking maternal infection to parturition timing, and extend surveillance across diverse settings.