Influence of fetal death and fetectomy on gestation and the initiation of parturition in the ewe

Depressed function of the fetal hypothalamic-pituitary-adrenal axis results in prolonged gestation, and fetal death causes premature parturition. The objective of this experiment was to determine effects of death in utero of a sibling, or its removal, on the duration of gestation and concomitant changes in maternal serum concentrations of oestradiol (E) and progesterone (P). Ovine placental lactogen (oPL) was also determined as an index of placental viability. Blood samples were collected in the morning, beginning 3 days prior to surgery on Day 115 +/- 3 of gestation and continuing daily until 3 days post partum. Surgeries were performed via mid-ventral laparotomy to induce fetal death or to remove the fetus. Fetal death was induced by ligating the umbilicus. Duration of gestation was similar (P > 0.05) in control (C, n = 6) and sham-operated (S, n = 3) ewes (148 +/- 1.0 and 148.6 +/- 0.7 days, respectively). On the day of parturition, concentrations of P, E and oPL were 5.2 +/- 1.9 ng mL-1, 135 +/- 22 pg mL-1 and 153 +/- 54 ng mL-1, respectively, in ewes from combined C and S groups. Total fetectomy (n = 3) resulted in a rapid decrease (P < 0.05) in maternal serum concentrations of P, E, and oPL. Ligation of the umbilicus of both fetus(es) in utero (n = 4) induced fetal death, decreased (P < 0.05) length of gestation to 118.8 +/- 1.8 days and decreased (P < 0.05) serum concentrations of P and oPL prior to parturition and oPL on the day of parturition. In addition, maternal serum concentrations of E failed (P > 0.05) to increase at parturition. Length of gestation and concentrations of P, E and oPL at parturition were not affected (P > 0.05) by removal of one fetus when its sibling was undisturbed (n = 4) compared to control ewes. In contrast, death of one fetus with its sibling undisturbed (n = 5) decreased (P < 0.01) length of gestation (139.2 +/- 2.8 days), but did not affect P, E and oPL (P > 0.05) on all days tested. In conclusion, death of one fetus reduced the duration of gestation, but changes prepartum in maternal serum concentrations of P and oPL were similar to ewes delivering only live fetuses. The increase in maternal concentrations of E that normally occur at parturition was absent in ewes giving birth to only dead fetuses and, therefore, was not a prerequisite to parturition.