THE EFFECT OF PREGNANCY ON PERIPHERAL BLOOD IN THE MOUSE

¹ Radiological Research Laboratory, Department of Radiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032

1. Fifteen pregnant mice, time-mated so as to be simultaneously at the same stages of gestation, were weighed daily at the same time for the duration of their pregnancies. As expected, except for gestation day 2, there was a steady increment to 45 grams in the average total body weight of the 15 pregnant mice at day 18, as the fetuses are preparing for birth. The average total body weight almost doubled the original body weight of 25 grams.

2. The white blood cell counts of the pregnant mouse showed a rapid rise by the third day, possibly related to marshalling of leukocytes (neutrophils and macrophages) to phagocytize the invading spermatozoa, or to changes in the uterine mucosa anticipating implantation which usually occurs at day 4. There is a second peak in the peripheral white cell count at 9 days when the placenta is being organized. Thereafter the average white cell count remains below the normal level for this strain of mouse, with a slight rise of the average at 14 days and another at 16 days, but neither peak bringing the count up to normal.

3. The maternal erythrocyte count showed a steady decline almost from the day of conception, approaching the level of anemia but indicating possibly that the growing fetuses were depriving the mother of nutritive elements necessary for erythropoiesis.

4. The fetal blood at 17 days gestation, two days before birth, showed average deficiencies in the hemoglobin, red and white cell counts and in platelets. Adult type lymphocytes were about 50% of the adults and nucleated reds were still abundant.

5. In general there was evidence of a decreasing average of peripheral erythrocytes in the blood of pregnant mice as gestation progressed while the white cells showed several peaks of production probably related to major structural and functional changes of the intimate relation between fetus and mother. These structural changes related to implantation, placentation, and the functional changes to increasing hypoxia in the crowded condition of the gravid uterus.