Transvaginal ultrasonographic (TVS) evaluation of baboon gestation from 37-62 days postconception

Our objective was to determine the growth of the embryo and surrounding structures during baboon (Papio anubis) gestation using transvaginal sonography (TVS). To this end, we evaluated 19 timed-mated baboons using TVS between 37 and 62 days of gestation. After visualization of the gestational sac, amniotic sac, and yolk sac, the three largest diameters of each of these extra embryonic structures were measured using longitudinal and transverse views. Embryonic crown-rump length (CRL) was also recorded. Embryonic heart rates were determined using the M-mode function of the ultrasound equipment. All 19 gestations developed without complications. No significant trend could be demonstrated for heart rate or yolk sac diameters over the 37-62 day gestational age period. Mean (SD) gestational age in days, heart rate, and yolk sac diameter, respectively, for the group were 48 (7.8) days (range: 37-61), 180 (15) beats per minute (range: 156-221) and 5 (0.1) mm (range: 3-8). Significant correlations (P < 0.0001) were determined between gestational age and CRL and gestational and amniotic sacs. We conclude that TVS allows a clear visualization of the embryo proper and all the cavities within the gestational sac of the baboon gestation. This study has determined the normal pattern of changes of these cavities from 37-62 days of gestation. Future applications of these findings may include sampling fluid from these cavities for biochemical, cytological, and metabolic studies.