Antenatal RSV and hMPV illnesses rates among pregnant women in Thailand and association between antenatal RSV and perinatal outcomes: A prospective cohort study.

Background: We estimated RSV and hMPV illness incidences among pregnant women and examined the association between antenatal RSV illness and preterm birth and small for gestational age (SGA).

Methods: Pregnant women aged ≥18 years were followed twice weekly until the end of pregnancy to identify illness episodes with >1 of myalgia, cough, runny nose/nasal congestion, sore throat, or difficulty breathing. Mid-turbinate nasal swabs were collected and tested for RSV and hMPV by real-time reverse-transcription PCR. Incidences were calculated. Cox proportional hazards regression was used to estimate hazard ratios (HRs) comparing participants with and without RSV illnesses for preterm birth (live birth before 37 weeks gestation) and SGA infant.

Results: Among 2,764 participants, the median age was 29 years (interquartile range [IQR] 24-34) and the median enrollment gestational age was 10 weeks (IQR 7-14). Overall, 71 (3%) and 29 (1%) cases of RSV and hMPV illnesses were identified, respectively. Among these, 30 (42%) and 10 (34%), respectively, sought medical care. Incidence rates per 10,000 pregnant woman-months were 57 (95% confidence interval [CI] 44-72) for RSV and 23 (95% CI 16-33) for hMPV illnesses. Antenatal RSV illness in the third trimester conferred an increased risk of preterm birth (adjusted HR [aHR] 2.50, 95% CI 1.04-6.00) but not having an SGA infant (aHR 0.79, 95% CI 0.29 to 2.16).

Conclusions: Antenatal RSV illness was associated with some adverse antenatal outcomes. Pregnant women had a 0.4-0.7% risk of RSV illness per pregnancy month, of which one third resulted in medical visits.