Sonographic appearance of late pregnancy sheep fetal intestine and kidney

Objective was to identify changes in sonographic characteristics of late pregnancy ovine fetus associated with fetal maturity. Ewes were synchronized, ram bred, and confirmed pregnant (n = 18) for potential cesarian section (c-section) at day 145 of pregnancy (d 0). Transabdominal ultrasonography was performed at days (d) 22, 15, 10, 7, 4, 1, and 0 prepartum to assess fetal heart rate (HR), abdominal diameter, renal volume, corticomedullary distinction (CMD), and gastrointestinal peristalsis (GIP). At day 1, 12 ewes were induced with 20 mg dexamethasone IM and underwent elective c-section on day 0. At birth, lambs were assigned a vigor score (1 - 10) based on HR, respiratory rate, muscle tone, irritability reflex, and mucous membrane color. A total of 19 live and 3 dead lambs were delivered with an average vigor score of 7 ± 0.6. Statistical analyses were performed using R. Mean days prepartum were assessed using ANOVA. Pearson’s correlation analysis was used to assess associations. Both CMD and GIP were strongly correlated with days prepartum (r = 0.7, p < 0.001), whereas low correlation was observed with renal volume (r = 0.27, p = 0.006) and abdominal circumference (r = 0.25, p = 0.009). Days prepartum differed for CMD categories (absent: 22 ± 0, indistinct: 9.1 ± 0.6, distinct: 0.5 ± 0.1; p < 0.001). Days prepartum also differed for GIP categories (no peristalsis: 12 ± 0.7, occasional peristalsis: 2.3 ± 0.4, frequent peristalsis: 0.6 ± 0.1; p < 0.001). Days prepartum did not differ when fetal HR measured :

• < 130 bpm (7.1 ± 0.7) or 130 - 149 bpm (8.8 ± 1.1; p = 0.43), but differed when fetal HR measured
• > 150 bpm (15 ± 1.5; p < 0.001). Fetal HR prior to induction (day 1) was moderately correlated with vigor scores at birth (r = 0.55, p = 0.07).

In summary, qualitative sonographic characteristics, such as onset of fetal GIP and CMD were superior to quantitative measurements in determining fetal maturity. Additionally, ultrasonographic assessment of fetal HR before induction may help to predict neonate survivability.

Keywords: Ewe, pregnancy, GI peristalsis, renal development, ultrasonography

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.