Introduction Hyperparathyroidism (HPT) during pregnancy is rare but poses a significant danger to mother and baby yet the incidence of pregnancy loss and its relationship to the degree of calcium elevation is not known.
Design A retrospective patient series from a single practice examined the past and current obstetrical histories of pregnant patients with primary HPT.
Results Over a period of 6-years, 32 women age ranging from 19 to 40 years had a total of 77 pregnancies while having elevated serum calcium levels because of primary HPT (incidence 0·7% of all women with primary HPT). Fifteen patients underwent parathyroidectomy during the second trimester resulting in an uneventful delivery of a healthy infant between 36 and 40 weeks gestation. There were no maternal or infant complications at surgery or during the subsequent delivery. Thirty of the remaining 62 pregnancies (48%) were lost, a rate that is 3·5-fold higher than expected (P < 0·05). In those who did not have the HPT addressed after the first miscarriage, one-third lost one or more additional pregnancies. Pregnancy loss occurred typically in the late first or early second trimester, with second trimester losses (30%) being sixfold higher than expected (P < 0·01) and over 4 weeks later than typical (P < 0·05). Foetal loss was seen at all levels of elevated maternal calcium but most were above 11·4 mg/dl (2·85 mmol/l). The rate of foetal loss increased directly with increasing maternal serum calcium levels (R = 0·972).
Conclusions HPT during pregnancy is under recognized and is associated with a 3·5-fold increase in miscarriage rates. Pregnancy loss often occurs in the second trimester and is associated with multiple miscarriages when not addressed. Pregnancy loss is more common as calcium levels exceed 11·4 mg/dl (2·85 mmol/l), but can be seen at all elevated calcium levels. Emphasis is placed on earlier recognition and surgical cure before becoming pregnant, however, once pregnant, surgery should be offered early in the second trimester for those with calcium levels above 11·4 mg/dl.