Transitory thrombocytopenia in newborn mice after intrauterine hypoxia.

Pregnant mice were exposed to hypobaric hypoxia (0.7 atmospheres) continuously during days 13 to 20 of pregnancy. In the newborn offspring, the body weights were decreased, and liver weight/body weight ratios were increased compared to nonhypoxic control animals (P < 0.001). After intrauterine hypoxia, the newborn animals were polycythemic, and a postnatal transitory thrombocytopenia lasting 7 days occurred. A rebound thrombocytosis appeared on days 13 to 15 after birth. Bone marrow megacaryocyte concentrations were increased in the hypoxic animals on days 5 to 15 after birth compared to the nonhypoxic controls. These findings may be explained by a competitive mechanism on common stem cells. Increased demand for erythropoiesis during hypoxia may shunt hematopoietic cells in direction of erythropoiesis at expense of thrombopoiesis.