Background: The prevalence of idiopathic spontaneous premature labor or without an evident clinical cause, has not been reduced with tocolytic treatments, suggesting that premature labor has multiple causes and infections play a not well-defined role.
Aim: To perform microbiological studies of the amniotic fluid and of the lower genital tract in women with idiopathic premature labor and intact membranes, relating these findings with maternal and neonatal outcomes.
Patients and methods: Women with pregnancies between 24 and 34 weeks, with premature labor and without an evident clinical cause were enrolled. Amniotic fluid and genital tract samples were obtained for traditional microbiological cultures. This information was related with delivery events and neonatal outcome.
Results: Sixty-three patients were included. The overall frequency of microbial invasion of amniotic cavity was 23.8% and of cervical or vaginal infection was 63.5% (in 39.7% there was only cervical or vaginal infection without involvement of the amniotic sac). Absence of infection was documented in 36.5% of women. Compared to patients without infection, women with microbial invasion of amniotic cavity had a higher rate of prematurity (73.3% p < 0.05), a higher rate of prematurity of less than 34 weeks (60% p < 0.01), a higher frequency of preterm rupture of membranes (40% p < 0.001), a shorter admission-to-delivery interval (median 3.0 days p < 0.01) and lower gestational age at delivery (median 33 weeks p < 0.01). Clinical chorioamnionitis and endometritis (20% p < 0.01) was observed only in patients with amniotic cavity infections. Severe asphyxia (26.7% p < 0.05) and neonatal admission to Intensive Care Units (46.7% p < 0.05) were more frequent and neonatal weight was less in the offspring of women with microbial invasion of amniotic cavity (2020 g median p < 0.01).
Conclusions: In preterm labor with intact membranes, intraamniotic infection is the most frequent cause of prematurity and is associated with a higher prevalence of maternal and neonatal problems.