PLASMA PROSTAGLANDIN METABOLITE CONCENTRATIONS IN NORMAL AND DYSFUNCTIONAL LABOR

Objective To determine the concentrations of the metabolites of prostaglandin E2 (PGEM) and of prostaglandin F2alpha (PGFM) prior to the onset of labour and during spontaneous labour, and to correlate the changes in concentrations of these metabolites with labour outcome. Design Longitudinal study throughout labour. Setting Labour ward of a large maternity unit. Subjects Seven primigravid and 11 parous women in the late third trimester with no signs of labour, and 17 primigravid and 11 parous women in spontaneous labour. Interventions Six of the primigravid women required augmentation with oxytocin because of dysfunctional labour. Results Before labour, parous women had significantly higher concentrations of both PGEM (P<0.007) and PGFM (P<0.006) compared with primigravid women. During labour, PGFM concentrations were significantly higher in both primigravid (P<0.0002) and parous (P<0.0001) women compared with the concentrations of these metabolites in women not in labour; the same was true for PGEM in primigravid (P<0.003) but not in parous (P = 0.1) women. There was a small but significant increase (P<0.02) in PGEM as labour progressed in both the normal groups. Amniotomy was associated with a significant increase in PGFM in primigravid and parous women (P<0.002 and P<0.009, respectively). The concentration of PGFM one hour following amniotomy correlated inversely with the amniotomy to delivery interval in both the normal primigravid (r = -0.624; P = 0.04) and the parous (r = 0.745; P = 0.021) groups. Women with dysfunctional labour showed no significant rise in PGEM or PGFM. Their PGFM concentrations were significantly lower than those seen in normal labour (P<0.05). The concentration of PGFM in cord blood was significantly higher (P<0.0001) in the parous women who laboured than in women delivered by elective caesarean section. There was no difference in the corresponding concentrations of PGEM (P = 0.9). Conclusions These data show that spontaneous labour is associated with increased concentrations of prostaglandin metabolites in the maternal plasma, and are consistent with PGF2alpha being an important stimulator of uterine contractility, with a relative deficiency of PGF2alpha being associated with dysfunctional labour.