Aim: To measure fetal cardiac output prior to labour and assess the risk of adverse obstetric and neonatal outcome in singleton pregnancies with appropriately grown for gestational age (AGA) fetuses at term.

Methods: This was a prospective observational study conducted at Queen Charlotte’s and Chelsea Hospital, London UK. Fetal cardiac output and fetal cerebroplacental ratio (CPR) was measured within 72 hours before birth in 200 nulliparous women having singleton pregnancies with AGA fetuses. Scan details were not available to the clinicians and delivery was managed per the local protocol and guidelines. Obstetric and neonatal outcomes were obtained from case notes and correlated with the ultrasound findings.

Results: Delivery was vaginal in 129 (64.5%) cases and by caesarean section in 71 (35.5%), including 34 (17.0%) for fetal distress and 37 (18.5%) for failure to progress. Fetuses delivered by caesarean section for fetal distress, compared to the remaining fetuses, had a lower median left cardiac output(LCO) (152.3 vs. 191.7 mL/min/kg; p=0.003), higher difference in the median ratio between the right to left cardiac output (RCO to LCO ratio) 1.925 vs. 1.340; p=0.002) and lower CPR (1.222 vs. 1.607; p<0.0001). In screening for emergency caesarean section for fetal distress, for a 10% false positive rate, the detection rate with the RCO to LCO ratio was higher that with the LCO (41% vs. 29%) and with the CPR (41% vs. 27%). Similarly, the positive predictive value for the RCO to LCO ratio (45%) was higher than LCO (37%) and the CPR (35%).

Conclusion: In AGA fetuses at term that develop intrapartum distress, there is evidence of prelabour redistribution of the cardiac output. The RCO to LCO ratio is superior to the LCO and CPR in predicting intrapartum fetal distress. Such assessments may be useful in stratifying patients for the intensity of monitoring during labour.