Pregnancy diagnosis and fetal monitoring in Yangtze finless porpoises

The Yangtze finless porpoise Neophocaena asiaeorientalis asiaeorientalis is a Critically Endangered species endemic to the Yangtze River and connecting lakes. Understanding the reproductive biology, fetal development, and physiology of this species is essential to ensure the successful development of a captive-breeding program. We studied pregnancy and fetal development in this species using endocrine monitoring and ultrasonographic imaging. Plasma progesterone concentrations increased significantly from non-pregnant (0.61 ± 0.43 ng ml-1) to pregnant (37.44 ± 16.18 ng ml-1) phases. Based on progesterone variation, we estimate gestation length to be approximately 12 mo. Fetal growth patterns are well described by linear regressions of thorax diameter, thorax circumference, and total body length plotted against days from parturition. Fetal growth models may be used to estimate fetal age and predict parturition date with more data in the future. Our findings provide fundamental information on pregnancy dynamics and fetal development in this Critically Endangered species to improve existing and benefit the establishment of new captive-breeding programs for Yangtze finless porpoises.