Increased deaths due to endocrine system diseases and allergies among mothers of dizygotic twins.

To test the hypothesis that mothers of DZ twins, who seem to represent a separate population from mothers of singletons in terms of levels of pituitary gonadotropins, height and weight, and reproductive and menstrual characteristics, have different patterns of disease and mortality, causes of non-cancer deaths were examined. Study subjects were 3,982 mothers of unlike-sexed (DZ) twins and other polyzygous multiple births, and a matched comparison group of 3,982 mothers of singletons only. A significantly increased risk of death due to diseases in ICD Group III, Allergic Endocrine System, Metabolic and Nutritional Diseases, was found among mothers of DZ twins (relative risk (RR) = 2.4, exact two-tail P = 0.024, exact 95% confidence limits 1.11 to 5.62). Of the 24 deaths among mothers of DZ twins, 18 were due to diabetes, 2 to diseases of the adrenal glands, 1 to a thyroid gland and, 3 to asthma. Of the ten deaths in the comparison group, nine were due to diabetes and one to asthma. Excluding the asthmas, the RR for endocrine system diseases is 2.33, exact two-tail P = 0.042, exact 95% CL 1.02 to 5.79. These observations are consistent with evidence in the literature which shows an association between endocrine system diseases and twinning, and between gonadotropic hormones and diabetes.