Neonatal histopathological findings enabling further understanding of the pathophysiological mechanisms of pregnancy failure in the common bottlenose dolphin (Tursiops truncatus)

Reproductive success is a critical component of the care of bottlenose dolphins (Tursiops truncatus) in managed care facilities and is vital in sustaining free-ranging dolphin populations. Despite well-established breeding programs with high reproductive success rates, pregnancy failures still occur in managed care just as they do in free ranging dolphin populations. Retrospective analysis from 1990-2019 enabled histopathology to be performed on neonatal tissue from 29 failed bottlenose dolphin pregnancy cases. Timing of the neonatal loss varied with three failures occurring during the 2nd trimester, 13 losses occurred in the 3rd trimester, seven neonates did not survive > 24 hours and six neonates did not survive > 30 days. These 29 cases were examined for signs of lung atelectasis, fetal distress, fetal pneumonia, and where available the placenta was also examined for signs of inflammation or pathological lesions. Fetal distress was defined as an increased number of amniotic squamous cells, with or without meconium, within the fetal bronchioles and alveoli. It was subjectively graded as mild, moderate or severe. Possible causes include: normally occurring birthing complications, infections that cause placental necrosis, fetal hypoxia secondary to placental abnormalities such as an umbilical cord torsion, decreased oxygen carrying capacity of the blood due to anemia or decreased food intake, maternal hypoxia, and maternal shock. This study aims to further elucidate the pathophysiological mechanisms of pregnancy failure in the bottlenose dolphin.繁殖成功率是人工圈养设施中宽吻海豚（Tursiops truncatus）养护工作的核心组成部分，同时对维持野生宽吻海豚种群的存续至关重要。尽管当前已建立起繁殖效率优异的成熟繁育体系，但人工圈养环境中仍会出现妊娠失败案例，野生种群亦存在此类情况。本研究对1990年至2019年间的29例宽吻海豚妊娠失败案例开展回顾性分析，对其新生幼崽组织进行组织病理学检查。新生幼崽的死亡时间分布存在差异：3例发生于妊娠中期，13例发生于妊娠晚期；7只新生幼崽存活时长不足24小时，6只存活时长不足30天。研究人员对这29例样本的肺不张、胎儿窘迫、胎儿肺炎相关征象进行了检测；若胎盘样本可获取，同时对其开展炎症或病理性损伤相关征象的检查。本研究将胎儿窘迫定义为胎儿细支气管与肺泡内羊膜鳞状细胞数量增多，伴或不伴胎粪存在，并采用主观分级法将其划分为轻度、中度与重度三个等级。可能的致病诱因包括：常见分娩并发症、引发胎盘坏死的感染、因胎盘异常（如脐带扭转）继发的胎儿缺氧、贫血或摄食量减少导致的血液携氧能力下降、母体缺氧以及母体休克。本研究旨在进一步阐明宽吻海豚妊娠失败的病理生理机制。