Ultrasonographic evaluation of fetal development in the rat

The study objectives were to measure gestational sac (GS) diameter and crown-to-rump (CR) length in conscious pregnant rats and to determine the chronological ultrasonographic appearance of heart beat and fetal organogenesis. The study formed part of a unilateral surgical salpingectomy trial with 16 female Sprague-Dawley rats (Rattus norvegicus). Ten rats were operated on with six controls before all were mated at 8-10 weeks of age. Gestation length was taken as 22 days. Rats were manually restrained for abdominal ultrasonography and were scanned from day 7 until day 19 or 20 post-mating followed by immediate euthanasia. Measurements’ were taken from two GSs per rat. The presence of several early GSs in a row were described as a “string of pearls”. As a fetus developed features of organogenesis were recorded. There was no significant difference in GS diameters and CR length between the test and control groups. Mean GS diameters ranged from 2.9 mm (day 7) to 18.1 mm (day 20). A string of pearls was seen on days 8-11. The CR length ranged from 1.6 mm (day 11) to 26.4 mm (day 20). A heart beat was first seen on day 11 and the echogenic vertebral column at day 14-15. From day 16, ribs, feet and the isoechoic lungs and liver were seen. The lungs became hyperechoic to the liver from day 18-19. The tail and mandible were visible on day 18 and the aorta and caudal vena cava were seen on day 19, as well as an occasional bladder. These measurements and staged in utero ultrasonographic appearance of various organ and skeletal structures will assist in a reasonably accurate prediction of the day of impending parturition by laboratory personnel and researchers.

本研究的旨在测量意识清醒的妊娠大鼠的妊娠囊（GS）直径和头体长（CR），并确定心脏跳动和胎儿器官发生的超声成像的时序特征。该研究作为一项涉及16只雌性Sprague-Dawley大鼠（Rattus norvegicus）的单侧性输卵管切除术试验的一部分。在所有大鼠于8-10周大时配对之前，对其中10只大鼠进行了手术操作，并与6只对照组进行了比较。妊娠长度定为22天。大鼠在腹部超声检查时被手动固定，从交配后的第7天至第19天或20天进行扫描，随后立即实施安乐死。每只大鼠从两个GS中取测量值。连续出现多个早期GS被描述为“珍珠串”。随着胎儿的发育，记录了器官发生的特点。在实验组和对照组之间，妊娠囊直径和CR长度的差异并无统计学意义。平均妊娠囊直径从第7天的2.9毫米至第20天的18.1毫米不等。在第8-11天可见“珍珠串”。CR长度从第11天的1.6毫米至第20天的26.4毫米不等。心脏跳动首次在第11天出现，第14-15天的声学椎骨。从第16天起，可见肋骨、足部以及同声学回声的肺和肝脏。从第18-19天开始，肺的回声高于肝脏。第18天可见尾巴和下颌骨，第19天可见主动脉和下腔静脉，偶尔可见膀胱。这些测量值以及胎儿体内不同器官和骨骼结构的超声成像分期，将有助于实验室人员和研究人员对即将分娩的日期进行较为准确的预测。