Uteri taken from 25 bitches at various times during the early stages of pregnancy were studies cytologically to determine how the implantation chamber developed and how fetal-maternal relations were established. On day 13 after the end of estrus, knobs of trophoblastic syncytium formed and became wedged between cells of the uterine luminal epithelium. The syncytium quickly spread along the uterine lumen and into the mouths of the glands, dislodging and surrounding maternal cells. As invasion continued trophoblastic villi, consisting of cores of cytotrophoblast covered by a continuous layer of syncytium, penetrated deeper into the endometrium. The syncytium spread to surround maternal vessels and decidual cells. By day 26 the trophoblast had extended down to the large lacunae. Here syncytial trophoblast covering tips of the villi degenerated, leaving cytotrophoblast exposed to the necrotic zone. These cells possessed characteristics of absorbing cells. Hematomas were formed by focal necrosis of fetal and endometrial tissue at the poles of the implantation sites. Large pools of extravasated blood accumulated and red blood cells were phagocytized by surrounding trophoblastic cells. Therefore, the endotheliochorial relationship in the canine placenta appeared to be established by syncytial trophoblast invading a cellular endometrium. In the necrotic zone and hematomas, cellular trophoblast may have lost its syncytial covering, but elsewhere maternal vessels and decidual cells in the placenta were in direct contact only with syncytial trophoblast.

No abstract

At five stages of gestation, mice were exposed dorsally to ultrasonic irradiation at 1 W/cm2 (spatial and temporal average), 2 MHz, and 34 and 37 degrees C (temperature at beginning of exposure). The results indicated that ultrasonic exposure up to at least 100 s is not hazardous to a pregnant mouse or its offspring in utero under the conditions of our experiment. Thresholds for both undesirable and lethal effects on the dam and its embryos or fetuses appeared between 100 and 200 s. Temperature rises in the uterus to more than 40 degrees C and similarity of results obtained with continuous-wave and burst modes of irradiation suggest a thermal mechanism as one cause of these effects. Preliminary conclusions are that thresholds for both tissue damage to the dam and deleterious effects on pregnancy were similar; however, they occurred at spatial average intensity and exposure levels far in excess of those used in clinical diagnostic medicine.

Pregnant mice were exposed to ultrasound (continuous wave, 2 MHz) on Day 8 of gestation to determine effects on the progeny. The most significant finding was a decrease in mean uterine weight of the female progeny. The thresholds for this effect were 140 s at 0.5 W/cm2 and 60 s at 1 W/cm2, which were below the thresholds previously reported for other effects in mice. We suggest that this indicates a delay or impairment of maturation of the mice exposed in utero. Exposure of the dams to spatial average intensity of 1 W/cm2 for 40 and 60 s had no effect on body weight of the progeny, compared with sham-treated controls. In this experiment the body weights of progeny from sham-treated controls were significantly lower than those from untreated controls on Days 10, 17, and 25 of age. After exposure in utero to 0.5 W/cm2 for 180 s, statistically significant decreases in mean body weights of the neonates were observed, but only on Day 25 of age, in both sexes compared with sham-treated controls. At necropsy at Day 25 of age, neonatal organ weights relative to body weights were not significantly affected for the thymus in either sex or for the seminal vesicles and tests ion comparison with sham-treated controls.