Circulating prostaglandin E2 concentrations decrease at birth in premature lambs

Rationale During pregnancy, prostaglandin E 2 (PGE 2 ) is released from the placenta and circulates in relatively high concentrations in the fetus. As PGE 2 suppresses breathing, PGE 2 concentrations must decrease after birth, but the timing and mechanisms behind this decrease are unknown. We hypothesised that both umbilical cord clamping and lung aeration contribute to the reduction in PGE 2 concentrations after birth. Materials and methods Instrumented premature lambs (138–141 days gestation) were randomised to receive either physiological-based cord clamping (PBCC; cord clamping after ventilation onset; n = 5) or immediate cord clamping (ICC; before ventilation onset; n = 6). PGE 2 concentrations were measured in pulmonary and carotid arterial blood 30 s after ventilation onset, after lung aeration and 30 s after cord clamping. All PGE 2 data are expressed relative to fetal PGE 2 concentrations. Results Relative to fetal concentrations, ventilation onset decreased PGE 2 concentrations in the carotid ( p = 0.036) and pulmonary arteries ( p = 0.052) in PBCC lambs, whereas cord clamping had no further additional effect on PGE2 concentrations in these lambs. In ICC lambs, cord clamping decreased PGE 2 concentrations, relative to fetal concentrations, in both the carotid ( p = 0.001) and pulmonary arteries ( p < 0.001). Ventilation onset further decreased PGE 2 concentrations in both the carotid ( p = 0.002) and pulmonary arteries ( p = 0.014). Conclusion Both umbilical cord clamping and ventilation onset independently decrease PGE 2 concentrations immediately after birth, which may enhance breathing activity, although the effect of cord clamping is reduced by ventilation onset.