Figure 3. Cardiovascular responses during spontaneous uterine contractions in a near‐term fetal sheep (0.85 of gestation) .

Fetal heart rate (FHR beats min⁻¹ (bpm)), mean arterial pressure (MAP, mmHg) and amniotic pressure (mmHg) during uterine contractions resulting in a deep deceleration (left panels) and multiple moderate decelerations (right panels). Labour was induced by the administration of betamethasone (11.4 mg, i.m. to the ewe x2, 24 h apart) as previously described (Liggins, 1969). Contractions began approximately 48 h after the first dose of betamethasone. Note in the left panels that the deep deceleration occurred despite an initial mild fall in MAP at the start of contraction while delayed hypertension develops late in the deceleration, consistent with the data presented in Figs 1 and 2 during complete umbilical cord occlusion. Only the second to last contraction in the right panels was associated with an increase in MAP at the start of the deceleration. Thus the baroreflex cannot be a consistent trigger of decelerations. Data are 1 s averages.