Circulating prostaglandin E₂ concentrations decrease at birth in premature lambs

During pregnancy, prostaglandin E₂ (PGE₂) is released from the placenta and circulates in relatively high concentrations in the fetus. As PGE₂ suppresses breathing, PGE₂ 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 PGE₂ concentrations after birth.

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). PGE₂ concentrations were measured in pulmonary and carotid arterial blood 30 s after ventilation onset, after lung aeration and 30 s after cord clamping. All PGE₂ data are expressed relative to fetal PGE₂ concentrations.

Relative to fetal concentrations, ventilation onset decreased PGE₂ 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 PGE₂ concentrations, relative to fetal concentrations, in both the carotid (p = 0.001) and pulmonary arteries (p < 0.001). Ventilation onset further decreased PGE₂ concentrations in both the carotid (p = 0.002) and pulmonary arteries (p = 0.014).

Both umbilical cord clamping and ventilation onset independently decrease PGE₂ concentrations immediately after birth, which may enhance breathing activity, although the effect of cord clamping is reduced by ventilation onset.