Chronic fetal and maternal instrumentation in pregnant sheep: Effect on gestation length and birthweight

Abstract

The objective was to compare gestation length in chronically instrumented (laboratory) pregnant sheep (n = 131) and in the breeding flock (n = 476) that provided the experimental sheep. In the breeding flock, gestation length was normally distributed and varied between 141 and 151 days (mean = 147 +/- 0.1 days). In the laboratory sheep, gestation length varied between 128 and 151 days (mean = 142 +/- 1 day), and was bimodal, with 35.9% delivering preterm (<141 days). To examine potential factors that contributed to the preterm birth, a severity score was used, which comprised surgery characteristics, number of experiments and maternal or fetal complications. There was a significant inverse linear relationship (P < 0.001) between the total severity score and gestation length. The median values for the surgical (15 v. 12), overall complication (6 v. 2), maternal complication (2 v. 0) and fetal complication (2 v. 2) components were significantly greater in the preterm compared with the term groups. There was no relationship between fetal number and gestation length in either group. It is concluded that in chronic pregnant sheep preparations, there is a significant incidence of preterm birth and that this is associated with the severity of the surgical intervention and with several maternal and fetal complications.

Changes in fetal lamb arterial blood gas and acid-base status with advancing gestation

“…The number of samples collected from an individual fetus ranged from 1 to 17 (mean ϭ 4.1 Ϯ 0.3) and the number of days over which sampling occurred was from 1 to 24 (mean ϭ 5.8 Ϯ 0.5) days. All operated fetuses survived until spontaneous delivery, although as reported previously (9), there was a significant incidence of preterm birth in the operated animals that was not present in the breeding flock from which the study animals were obtained. Birth weight averaged 3.84 Ϯ 0.13, 3.40 Ϯ 0.08, and 2.96 Ϯ 0.23 kg for singletons, twins, and triplets, respectively.…”

“…The breeding method and surgical and experimental procedures employed on the animals have been previously described in our study of the effect of chronic fetal instrumentation on gestational length and birth weight in sheep (9). None of the data presented in this paper were obtained during the experiments conducted on these sheep.…”

“…We hypothesized that in the fetal lamb, blood gas and acid-base variables would change in relation to gestational age in a manner similar to that in the human fetus. In addition, because the pregnant sheep studied carried singleton, twins, or triplets, we also examined the effect of fetal number on the variables and their relationships to gestational age, given that in pregnant sheep, birth weight decreases with increasing fetal numbers (9). We hypothesized that the alterations in fetal blood gas and acid-base status with advancing gestational age would be greater in the twins and triplets.…”

Real-Time Ultrasound Assessment of Body and Breathing Movements and Abdominal Diameter in Fetal Lambs From 55 Days of Gestation to Term

“…We have previously reported that surgical instrumentation of pregnant sheep results in a significant incidence of preterm birth; whereas there was no preterm birth in the breeding flock from which the sheep that were instrumented were obtained. 33 The results of this study suggested that neither the death of the operated fetus nor the shortened gestation length affected the motility characteristics of the nonoperated twins as the break points and slopes of the regression lines in the operated ewes were not different from those in the nonoperated sheep (Table 2). In contrast, the growth of the nonoperated fetuses was affected in late gestation, as the slope of the second-phase regression line was significantly less than that in the nonoperated group (Table 3).…”

“…Moreover, one-half of the animals were subject to fetal surgery at about 120 days of gestation. Previously we 33 and others 34 have reported the chronic instrumentation of fetal lambs is associated with a reduction in birth weight. In this study, ultrasound of the operated ewes with twins or triplets was done on fetuses not subject to surgery.…”