Monitoring Pregnancy Through Ultrasonography

A 12.5-MHz ultrasound probe was used to monitor 11 pregnancies in 6 queens from a breeding colony, and results were compared to previous findings using 5-, 7.5-, and 10-MHz probes. Cats were monitored daily from day 7 to day 28; the mean duration of the pregnancies was 65.2 days ± 0.7 days. The first embryonic vesicle was seen on different days depending on which probe was used; the higher MHz probes provided the earliest detection (day 11) compared with the 5-MHz probe (day 16-17). There was also delayed visualization of embryos with the 5-MHz probe (day 20) vs the higher MHz probes (days 14-16). Measuring the length of the embryonic vesicle after day 11 or the crown-rump length after day 17 could be used to evaluate stage of gestation; however, this became less reliable after day 25. Visualization of the limbs, neural tube, and stomach when using the 12.5-MHz probe indicated a pregnancy of at least 19, 20, and 26 days, respectively. The use of the 12.5-MHz probe did not improve the diagnosis of pregnancy in comparison with the 7.5- or 10-MHz probes but allowed significantly earlier diagnosis than the 5-MHz probe.

Ultrasonography is routinely used for diagnosis and evaluation of pregnancy in queens, including establishment of gestational age when the breeding date is unknown. This study added to the body of knowledge related to gestational aging in queens using a higher frequency probe than previously studied. The application of the results is limited to the equipment and skill of the operator as well as compliance of the patient. Further studies should focus on the ultrasonographic appearance of abnormal pregnancies, including characterization of the normal and abnormal placenta and potential normal variation between breeds.—Milan Hess, DVM, MS, DACT