Variations in Serum Calcium and Phosphorus. During Pregnancy

The serum calcium and phosphorus were followed in a series of 579 dispensary patients throughout the course of their pregnancy. 3501 determinations were made in the interval between 28 weeks before delivery and 7 weeks postpartum.

Two factors were found to influence the calcium, the development of the pregnancy and the season. As the pregnancy progressed there was a gradual decline which reached a maximum a few weeks before delivery. This decline was not so sharp, from 9.86 mg. to 9.64 mg., during the first 4 months of the year, a season of low values, as during the remaining months, 10.46 mg. to 9.90 mg., but the drop is still significant. The last few weeks preceding delivery show a slight rise in both cases, succeeded immediately after the delivery by a marked increase, to 10.20 mg. and 10.40 mg. respectively, which was maintained to the end of the study, 5 to 7 weeks postpartum.

The seasonal effect is illustrated by the distinctly lower values found in blood drawn during the first 4 months of the year, the winter months, compared with those of the same stage of pregnancy drawn during the remaining 8 months. The 2 curves, based on averages for each season, are shown in Fig. 1. The depleted state found during the winter months is clearly demonstrated by the fact that the entire curve, up to the time of delivery, lies below the lower limits of the normal range, 10.0 mg. to 11.5 mg. per 100 cc. of serum, as determined by the authors. 1 The May to December averages are higher, though even these never rise above the lower third of the normal range. The differences between the curves although small at some stages, are in every case significant.