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.

BACKGROUND: We estimated respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) illness incidences among pregnant women and examined the association between antenatal RSV illness and preterm birth and small-for-gestational-age (SGA) infant.

METHODS: Pregnant women aged ≥18 years were contacted twice weekly until the end of pregnancy to identify illness episodes with ≥1 of the following: myalgia, cough, runny nose/nasal congestion, sore throat, or difficulty breathing. Midturbinate nasal swabs were collected and tested for RSV and hMPV by real-time reverse transcription polymerase chain reaction. 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 2764 participants, the median age was 29 years (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%) participants sought medical care. Incidence rates per 10 000 pregnant woman-months were 57 (95% CI, 44-72) for RSV illnesses 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, 2.50; 95% CI, 1.04-6.00) but not SGA infant (adjusted HR, 0.79; 95% CI, .29-2.16).

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.