Effects of Maternal Oxygen Supplementation on Fetal Oxygenation and Cardiopulmonary Haemodynamics in Lambs

November 7, 2026 Dr. Michael Lee – Health Editor Health

Maternal Oxygenation Alters Fetal Haemodynamics During Cord Clamping

Supplemental oxygen given to pregnant ewes significantly increases fetal arterial oxygen pressure and alters pulmonary blood flow during the transition to newborn life, according to a study. Researchers examined how varying maternal oxygen levels affect cardiopulmonary parameters in lambs both before and immediately after umbilical cord clamping.

    Key Clinical Takeaways:

  • Maternal oxygen supplementation significantly increases fetal PaO2, SaO2, and cerebral oxygenation compared to oxygen reduction groups.
  • End-diastolic pulmonary blood flow remains positive and significantly elevated in lambs receiving supplemental oxygen during the immediate transition phase prior to ventilation onset.
  • Ventilation onset triggers a rapid increase in carotid arterial pressure in oxygen-reduced lambs, highlighting distinct hemodynamic responses based on prenatal oxygen exposure.

Initial Assessments Show Uniform Fetal Characteristics and Baseline Parameters

Initial assessments established that fetal body weight, sex distribution, and proportion of twins showed no significant differences between the supplemental oxygen group and the reduction group. Before any alterations in maternal oxygen were introduced, baseline fetal parameters—including pH, partial pressure of carbon dioxide, partial pressure of oxygen, arterial oxygen saturation, and cerebral oxygenation—remained uniform across subjects. Core body temperature also stayed consistent throughout the investigation, averaging 37.3 degrees Celsius in the supplemental oxygen cohort and 37.6 degrees Celsius in the oxygen reduction cohort.

Physiological Responses to Maternal Oxygen Changes

Altering maternal oxygen delivery produced immediate, measurable shifts in maternal and fetal blood chemistry. Ewes receiving supplemental oxygen sustained a significantly higher maternal partial pressure of oxygen at 165.0 mmHg compared to 67.1 mmHg in the reduction group, while maternal oxygen saturation tended to increase similarly. Following these adjustments, maternal oxygen supplementation significantly elevated fetal partial pressure of oxygen, arterial oxygen saturation, and cerebral oxygenation.

While mean, systolic, and diastolic blood pressures in the mothers remained unaffected by the intervention, fetal pulmonary blood flow showed clear divergence. Maternal oxygen supplementation increased mean and end-diastolic pulmonary blood flow relative to the reduction group. Specifically, end-diastolic pulmonary blood flow showed positive values in five of the seven lambs receiving supplemental oxygen at the exact moment of cord clamping, indicating left-to-right shunting through the ductus arteriosus and low pulmonary vascular resistance. Conversely, end-diastolic pulmonary blood flow registered as negative in all seven lambs in the oxygen reduction group at cord clamping. Maternal oxygen reduction increased carotid arterial flow and heart rate compared to the supplemented group.

Cardiopulmonary Dynamics Between Cord Clamping and Ventilation Onset

During the critical sixty-second window separating umbilical cord clamping from the onset of mechanical ventilation, oxygen saturation and cerebral oxygenation declined across all subjects. Peripheral oxygen saturation in the supplemented lambs dropped from 75.3 percent to 40.0 percent, while the reduction group fell from 53.5 percent to 33.7 percent. Despite these declines, peripheral oxygen saturation remained significantly higher in the supplemental oxygen group for the first thirty seconds following cord clamping.

Hemodynamic changes during this interval included a significant rise in mean carotid arterial pressure among supplemented lambs, climbing from 52.6 mmHg prior to clamping to 68.2 mmHg. The reduction group experienced no significant alteration in mean blood pressure during this pre-ventilation phase. Mean, peak-systolic, and end-diastolic pulmonary blood flows remained significantly higher in the supplemented lambs from the moment of cord clamping until ventilation began.

Post-Ventilation Hemodynamic Adjustments

Initiating mechanical ventilation produced rapid physiological adjustments across both experimental cohorts, though distinct differences persisted based on prior oxygen exposure. Arterial blood gas parameters—including pH, partial pressure of oxygen, and partial pressure of carbon dioxide—showed no significant differences between groups after ventilation started. However, cerebral oxygenation remained higher in the supplemental oxygen group three to five minutes following ventilation onset.

Ventilation onset triggered a rapid increase in mean and diastolic carotid arterial pressures among the oxygen-reduced lambs, keeping those pressures significantly higher than those of the supplemented group during the initial four to five minutes. Pulmonary blood flow parameters stayed higher in the supplemental oxygen group for the first minute after ventilation began before equalizing between cohorts. Meanwhile, carotid arterial flow became significantly elevated in the oxygen-reduced lambs following ventilation onset.

Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.

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