FETAL ENDOCRINE RESPONSES TO CHRONIC PLACENTAL EMBOLIZATION IN THE LATE-GESTATION OVINE FETUS

OBJECTIVE: The purpose of this study was to examine the effect of chro nic fetal Placental embolization on the fetal corticotropin, cortisol, and catecholamines concentrations and on myometrial contractility pat tern. STUDY DESIGN: Fourteen fetal sheep were studied (seven embolized , seven controls) for 10 days between 0.84 and 0.91 of gestation. Dail y injections of nonradioactive microspheres were performed to decrease fetal arterial oxygen content by 30% to 35% of the preembolization va lue. Umbilical artery Doppler flow velocity waveforms were measured da ily. RESULTS: Chronic fetal placental embolization produced progressiv e fetal hypoxemia (p < 0.001) with changes in umbilical artery Doppler flow velocity waveforms indicative of a 25% increase in placental vas cular resistance (p < 0.01). In response to chronic fetal hypoxemia th ere was a progressive increase in baseline fetal plasma norepinephrine concentration (p < 0.001). There was a transient lburfold to fivefold increase in baseline fetal plasma cortisol levels concomitant with a significant decrease in baseline immunoreactive corticotropin between days 7 and 9 of embolization (both p < 0.05), with a return to control values by day 10. There was a 57% increase in myometrial contracture frequency in the embolized group when compared with controls (p = 0.00 1). CONCLUSIONS: During repetitive chronic placental damage that led t o fetal hypoxemia, the fetal endocrine environment changed with time i n a direction that would prevent the onset of premature activation of the hypothalamic-pituitary-adrenal axis and premature delivery.