Abstract

Reproductive success is vital in sustaining free-ranging bottlenose dolphin (Tursiops truncatus) populations and is a critical component of managed care. Ultrasonography is invaluable in wild dolphin health assessments and marine mammal preventive medicine. It is also a non-invasive standard of care in assessing the fetomaternal unit in humans and animals, including dolphins and horses. The purpose of this prospective longitudinal study was to develop a protocol for fetomaternal ultrasonographic monitoring in Tursiops truncatus and to report normal measurements and descriptive findings correlated with a positive outcome. From 2010–2017, serial ultrasonographic evaluations of 12 healthy dolphins in managed care were performed over the course of 16 pregnancies. A total of 203 ultrasound exams was included in the study. Several metrics were practical to obtain and accurate in predicting fetal age. Fetal biparietal diameter (BPD), thoracic width in dorsal and transverse planes, thoracic height in a sagittal plane, aortic diameter, and blubber thickness all demonstrated a high correlation with date of gestation (r>0.94, p<0.00001). Regional uteroplacental thickness significantly increased with each trimester (range 0.22–0.40 cm; p<0.00011 cranial uterus, p<0.00057 mid, and p<0.000011 caudal). Lung:liver mean pixel intensity was 2.57±0.46 (95% CI 2.47–2.67). Ultrasonographic characteristics of normal pregnancy in dolphins are described, and an updated equation for prediction of parturition date in Tursiops is reported: days to parturition=348.16-(26.03∗BPD[cm]) (R²=0.99). Future applications of these normal data will help identify in utero abnormalities indicative of fetal distress and morbidity, and further improve understanding of reproductive failure in wild and managed populations.