Acid-base balance in pregnancy

Abstract

In recent years considerable discussion has centered around the reaction of the blood during normal pregnancy, since findings in abnormal conditions, notably in the toxemias of pregnancy, must of necessity be compared with the normal. The various observers cited in this abstract all agree that plasma bicarbonate is lowered during pregnancy. Hasselbalch and Gammeltoft 1 confirmed earlier observations of the lowering of carbon dioxide tension of the blood during pregnancy, and Rowe 2 has recently determined the decrease in alveolar tension of carbon dioxide in a large series of cases.

During the past four months we have carried out plasma pH determinations on a series of thirty-three normal pregnant women. The series includes one to three determinations before delivery and one after delivery. Up to the present, 58 of the determinations before delivery, and 23 following delivery have been completed.

Plasma carbon dioxide content was lower during pregnancy than during the puerperium in all of the twenty-three cases which have been delivered, the average difference being 8.2 volumes per cent. The pH determinations were done by the method of Myers, Schmitz, and Booher. 3 The values before delivery extend over a range from 7.35 to 7.47, the mode lying between 7.38 and 7.42. Those following delivery cover the range from 7.34 to 7.42., the mode being 7.38 to 7.40. Taking into account all variations from 0.01 upwards, the pH was higher before than following delivery in 15 cases, by an average of 0.04; lower before than after delivery in 6 cases, by an average of 0.02; and unchanged in 2 cases. Study of the variations encountered does not as yet convince us that the blood is definitely more alkaline before than after delivery, although the evidence slightly favors that view.