100 Relationship between corpus luteum blood flow evaluated via colour Doppler ultrasound and pregnancy rate in bovine embryo transfer recipients

Abstract

The advent of colour Doppler ultrasound has allowed evaluation of blood flow to bodily tissues. This novel technology is being tested as a tool to improve efficiency in a variety of livestock reproduction programs. The objective of the present study was to evaluate the relationship between blood flow to the ovarian corpus luteum (CL), imaged via colour Doppler ultrasound, and pregnancy rate in crossbred dairy recipients for embryo transfer (ET). Oestrous cycles of Bos indicus × Bos taurus dairy heifers (n = 90, 16-24 months of age) were synchronized for embryo transfer on Days 7-8. Immediately before ET, heifers were palpated for the presence of ovarian CL and CL papillae. Presence of CL, CL papillae, and CL lacunae were confirmed via transrectal B-mode ultrasound (Ibex EVO I, E. I. Medical Imaging). Transrectal colour Doppler ultrasound (Ibex EVO I, E. I. Medical Imaging) was used to evaluate blood flow to the CL. In vitro-produced (IVP) blastocysts (qualities I and II) were transferred to the uterine horn ipsilateral to the CL. All palpation, imaging, and embryo transfer was performed by a single technician. Pregnancy was determined via transrectal ultrasound 24-32 days post-embryo transfer (31-39 days of embryo age). Blood flow to the CL was split into three categories: high, median, and low. Presence or absence of two additional CL structures, CL papillae and lacunae, were recorded. Fisher's exact test was used to evaluate data. Statistical differences were considered significant at P < 0.05. The overall pregnancy rate was determined to be 40%, 36 out of 90. Pregnancy rates were similar in high (33.9%, 20 of 59), median (59.09%, 13 of 22), and low (33.33%, 3 of 9) blood flow categories. Consistent with previous studies, absence of CL papillae and presence of CL lacunae at the time of ET did not affect pregnancy rate. Doppler blood flow, papillae, and lacunae were also evaluated together in each possible combination. Only one outlier was present; all other differences were not significant. The highest pregnancy rate (66.67%, 10 of 15) was observed in recipients with CLs with median Doppler blood flow, a palpable CL papillae, and no CL lacunae. A larger sample size is required to determine the accuracy of this measurement. In conclusion, recipients with high to low CL blood flow are suitable for IVP embryo transfer programs. Alone, colour Doppler imaging of the CL does not predict pregnancy rate.