Ultrasound BioMicroscopy (UBM) in monitoring placental and fetal development in mice.

Laboratory mouse has emerged as model to study fetal growth, placental function and to better understand human congenital diseases. High Resolution Biomicroscopy emerged as non invasive and accurate method to monitor embryonic and placental growth in developmental biology studies. The objectives of this study were to characterize, by UBM, development of placental and principal organ systems in CD1 mouse embryo and fetuses throughout pregnancy. Methods and Materials 13 CD1 female mice were examinated from 6.5 to 16.5 embryonic day (E) with a 40 MHz linear transducer (30-40 ?m axial and 70-90 ?m lateral resolution). During ultrasound examination, pregnant mice were lightly anesthetized using isoflurane (4% induction dose, 2.0-1.5% maintenance dose) plus oxygen (1Lt/min). Embryos were imaged transcutaneously through the maternal abdominal. Images of implantation sites, developing organs and measurements of fetal size were obtained in B-mode. Cardiac function was evaluated by pulsed-wave Doppler. Results At E6.5 an echogenic ectoplacental cone region and a small echolucent cavity containing embryo was visualized inside decidua. At E7.5, the three cavities of the embryo can be detected: the amniotic, the coelomic cavity, and the ectoplacental cavity. On day 9.5, the amniotic membrane, amniotic and yolk sac cavities, brain, cerebral ventricles and heart were visible. Placental development was monitored from E6.5 to E15.5 and its length and thickness at the level of umbilical vessels insertion were measured from E10.5 to E15.5. Placental lenght increased from 3.48±0.31 at E10.5 to 6.28±0.83 mm at a E15.5. Placental thickness raised from 1.94±0.1 at E10.5 to 3.81±0.71 mm at a E15.5. Brain, eye, limbs, tail, heart, lungs, liver, stomach and kidneys were gradually visible from E8.5 to E16.5. Bone ossification became evident from E14.5. Biparietal diameter increased from 1.9±0.4 at E11.5 to 4.83±0.12 mm at E16.5. Crown-rump length raised from 0.5±0.24 at E7.5 to 10.6±1.9 mm at E14.5. Cardiac contractions was detectable early at E8.5. The "U"-shaped heart tube was clearly visible at E9.5 and doppler waveforms was recorded for the first time. Atria and ventricles can be easily distinguished at E12.5 and at E14.5 ventricular septal definition is completed. Heart rate increased from 92.7 at E9.5 to 165 bpm at E16.5. Myocardial performance index decreased from 1.42 at E11.5 to 0.42 at E15.5. The dorsal aorta was identified based on the hyperechoic streaming patterns within the lumen and the corresponding doppler spettral trace exhibits a rapid upstroke and return to zero velocity during diastole.