MATHIASEN, C.C.*; GILMAN, C.A.; WOLF, B.O.; University of New Mexico; University of New Mexico; University of New Mexico: Portable ultrasonography – developing a non-invasive technique to quantify reproductive effort in small mammals

Traditional methods of quantifying maternal reproductive effort in small animals under both laboratory and field conditions have required sacrifice and dissection to obtain fetal measurements such as skull dimension and body mass. In this study we show how a portable ultrasound imaging system can be used to obtain in-vivo virtual measurements of embryonic and fetal growth parameters as well as estimates of fetal mass for two rodent species. This non-destructive method opens avenues for repetitive sampling of the same individual over differing times scales, and allows the progressive quantification of energy invested a single reproductive event. We present data from 26 Rattus norvegicus and 10 Mus musculus pregnant females that were scanned with a SonoSite Titan portable ultrasound unit on days 12, 14, 16, 18 and 20 of gestation. For each female, we scanned and recorded virtual caliper measurements for skull and body dimensions of each fetus, then compared them against standard staging systems to assign a fetal development stage. To validate the suitability of using virtual fetal measurements as a proxy for maternal reproductive effort, dissections were performed immediately after the ultrasound procedure. Measurements taken via ultrasound probe were compared to the actual fetal measurements and the assigned gestational state verified. We show that ultrasound techniques using virtual measurements reflect actual dimensions and that fetal body mass can be estimated via virtual caliper measurements.