Fetal heart and surroundings: umbilical cord traction triggers sympathetic heart rate surge in fetal lambs in the artificial womb.

OBJECTIVE

To investigate whether umbilical cord traction triggers a unique umbilico-neuro-cardio reflex via sympathetic autonomic nervous system (ANS) activation, potentially explaining fetal heart rate (FHR) increases such as the double mountain peak sign and unexplained tachycardia outside labor.

DESIGN

Experimental physiological study using the EXTrauterine Environment for Neonatal Development (EXTEND) system.

SETTING

Controlled laboratory environment at The Children's Hospital of Philadelphia with fetal lambs supported by the EXTEND system.

POPULATION OR SAMPLE: Twenty-nine experiments were performed on three fetal lambs: 5 ANS-immature (<110 days gestational age) and 24 ANS-mature (>110 days GA), including subgroups for pharmacological intervention.

METHODS

Umbilical cord traction was performed in 20 experiments (5 ANS-immature, 15 ANS-mature). To investigate autonomic modulation, nine ANS-mature experiments included administration of either periumbilical capsaicin or intravenous propranolol. FHR changes were measured, and norepinephrine levels were sampled before and after interventions.

MAIN OUTCOME MEASURES: Change in FHR (bpm) and circulating norepinephrine concentrations in response to umbilical cord traction and pharmacologic modulation.

RESULTS

Cord traction significantly increased FHR in ANS-mature lambs (mean +42 bpm, p < 0.001), but not in ANS-immature lambs (mean +1 bpm, p = 0.770). Capsaicin also elevated FHR and norepinephrine, while propranolol inhibited both responses.

CONCLUSION

Umbilical cord traction appears to activate an umbilico-neuro-cardiac reflex through sympathetic ANS pathways in ANS-mature fetuses. This mechanism may underlie clinical CTG features such as the double mountain peak sign and fetal tachycardia outside of labor.