Childbearing and the risk of parathyroid adenoma--a dominant cause for primary hyperparathyroidism.

Objectives. To explore possible associations between the reproductive history amongst women and the risk of parathyroid adenoma (PA). Design. Two nationwide Swedish registries. The Fertility Register included data on more than 3.4 million livebirths between 1943 and 1992 amongst Swedish females born 1925-72, The Cancer Register encompasses more than 1800 women with a diagnosis of PA 1960 until 1992. Setting. All women resident in Sweden 1960-92. Subjects, Cases were all 1800 women born 1925-72 reported to the Swedish Cancer Registry with a histopathological diagnosis of PA. Five controls were selected at random for each case by matching for the month and year of birth. Conditional logistic regression was used to estimate relative risks of PA. Main outcomes. Parathyroid adenoma. Results. High parity (four or more live births) was associated with an increased risk of PA. Amongst women with a diagnosis of PA before menopause (i.e. the age of 50 years) there was an increased risk of PA with younger age at first childbirth. Nulliparous women were at increased risk for PA before menopause, and at decreased risk after menopause. Conclusions. There is an association between childbearing and the risk of PA, which has not previously been demonstrated, but the underlying biological mechanisms remain to be determined.