Thoracoabdominal structures

Thoracoabdominal structures. Prior to 12.5 DPC, the fetal thorax could not be differentiated from the abdomen. This distinction became apparent at 12.5 DPC, and the echogenic lungs grew increasingly distinct from the more hypoechoic liver over the remaining course of gestation. The fetal stomach and urinary bladder were not discreetly identifiable until 17.5 DPC, when they appeared as hypoechoic structures (Figure 13).

Conclusion

It is possible that the anesthesia chosen for these types of studies could affect the growth or development (or both) of the fetus. This drawback was addressed for this report by designating 3 groups of dams, each of which underwent only 4 imaging sessions during the last half of gestation. Isoflurane was selected because of its rapid induction and recovery properties and because it is commonly used in veterinary cesarean sections. Toxicology studies investigating chronic daily exposure (4 h daily at no more than 0.6%) before and during pregnancy reported a negative effect on development at the 0.6% level.

Discussion - part 3

Power Doppler, also known as amplitude-mode Doppler, disregards directional information and codes blood flow according to the number of moving reflectors (red blood cells) in the field. The higher the number of moving red cells (blood flow), the higher the brightness value of the Doppler display. It is frequency-independent and has higher sensitivity to low velocity blood flow than does conventional Doppler. Conventional color Doppler imaging with the 15-MHz system therefore can be used to provide information on the direction of flow, and both the color Doppler and power Doppler applications allow for pulsed-wave quantification of velocity as well as comparative indices of systolic and diastolic flow.

Discussion - part 2

Current applications for the technique described here include counting early embryos in experimental animals. This practice will allow early confirmation of pregnancy in valuable animals, which can be removed from mating if already pregnant or recycled into mating if not. In addition, our technique can help determine whether fetal wastage has occurred between early pregnancy and delivery. For example, Becker and coworkers treated tumor-bearing pregnant mice with angiogenic inhibitors to determine whether there was any effect on pregnancy. The tumors went away, while pregnancies progressed. The authors were able to show that the number of early pregnancies was the same as the number of animals delivered, thereby demonstrating that there was no fetal wasteage. The system also can be used to document delayed development or growth retardation in mutant or manipulated animals compared with wild-type animals.

Discussion

Discussion
Here we describe the use of a commercially available ultrasound system to provide a simple and accurate method to stage and morphologically assess embryonic mouse development. Using a similar technique, Chang and coworkers found that decidual sac size is a reliable and accurate marker of GA. We used US measurements of CRL, BPD, and sac width to predict GA statistically by using formulas based on best linear fit to the data. CRL and BPD, in particular, are used routinely in the ultrasound staging of human gestational development, and many operators and investigators are likely to be familiar with them.

Musculoskeletal system

Musculoskeletal system. Limb buds were first apparent at 10.5 DPC in 10 of 27 (37%) fetuses, and in the remaining 17 fetal animals, limb buds became apparent the following day (Figure 9). Individual hind- and forelimb digits became discernible at 15.5 DPC; femur length could be measured at this time as well (Figure 10).

Cardiovascular system

Cardiovascular system. Fetal heart activity was detectable by use of gray-scale US at 10.5 DPC in all gestations. Blood flow within the umbilical cord was demonstrated at this time point as well by use of power Doppler color imaging. Power Doppler color imaging of the heart revealed the interventricular septum by 14.5 DPC and the atrial septum at 17.5 DPC. The interventricular septum could be detected by use of gray-scale at 16.5 DPC. By 11.5 DPC, blood flow could be demonstrated within the major thoracoabdominal arteries, and the circulation could be followed within the ascending, descending, and abdominal aorta and into the hypogastric arteries, umbilical cord, and placenta (Figure 6).