ACCUMULATION OF INTERLEUKIN-1-BETA AND INTERLEUKIN-6 IN AMNIOTIC-FLUID - A SEQUELA OF LABOR AT TERM AND PRETERM

From the finding of micro-organisms or inflammatory mediators, or both , in amniotic fluid (AF), it has been proposed that intrauterine infec tion is one cause of preterm labour (PTL, intact fetal membranes); Thi s theory, however, remains unproved, i.e. the accumulation of micro-or ganisms and inflammatory mediators in AF after labour is in progress m ay be the consequence, not the cause, of labour both at term and prete rm. This study was conducted to evaluate this possibility by a compari son of the concentrations of interleukin (IL)-1 beta and IL-6 in AFs c ollected before and during PTL (<34 weeks gestation) with those in AFs collected at term (before labour and from the forebag and upper compa rtments of the amniotic sac during labour). The concentrations of IL-1 beta and IL-6 in AF were also analysed as a function of the duration of labour (term or preterm) before fluid collection. In addition, stud ies were conducted to define the source of IL-1 beta in AF. A total of 666 AFs mere evaluated. IL-1 beta was not detected (<50 pg/ml) in AFs collected before the onset of labour at any stage of gestation (n = 3 20), including 170 fluids obtained at term. During labour, IL-1 beta w as detected (<50 pg/ml) in 58 out of 106 (54.7 %), 17 out of 64 (26.6 %) and 60 out of 176 (34 %) of AF samples obtained during PTL, term la bour (upper compartment) and term labour (forebag) respectively. AF sa mpling, as well as labour and delivery, were completed in <18 h in all term pregnancies. However, labour (with cervical dilation) was in pro gress for >18 h before AF was collected in 39 out of 106 (37 %) PTL pr egnancies. The incidence of IL-1 beta-positive samples among AFs colle cted before 18 h of PTL (23 out of 67; 34%) was indistinguishable from that in AFs collected during labour at term. However, in AFs collecte d after >18 h PTL, the incidence of IL-lp-positive samples was 35 out of 39 (89.7 %) The concentrations of IL-1 beta (pg/ml; mean +/- SEM) i n AFs collected during PTL (2680 +/- 730; n = 106) were greater than t hose in AFs collected from the upper compartment and forebag during te rm labour (436 +/- 244, n = 64; and 468 +/- 119, n = 176) respectively ; this difference, however, was attributable to very high concentratio ns of IL-1 beta in AFs in which PTL was in progress for >18 h before A F collection (6021 +/- 1832; n = 39). The concentrations of IL-6 in AF were correlated with those of IL-1 beta (P < 0.001). We conclude that IL-1 beta and IL-6 accummulate in AF in a similar proportion of pregn ancies during the first 18 h of term and preterm labour. Therefore, th e accumulation of these cytokines in AF cannot be taken as evidence fo r a role for infection in the pathogenesis of PTL.