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A twin pregnancy in which a single fetal death was diagnosed in the first trimester is described. Continued growth of the nonviable twin suggested the occurrence of the twin reversed arterial perfusion syndrome.

Three cases of monozygous male twins having exencephaly, anencephaly, and acephaly, with their cotwins being normal, are reported. Monozygosity of the twins was demonstrated by pathologic examination and in one case corroborated by blood group antigen testing. A constellation of abnormalities including adrenal hypoplasia in one of a pair of monozygous male twins with chorionic vascular anastomoses, together with the unusual racial background in each case, are in support of the possibility that environmental factors may play an etiologic role.

Previously we reported that the human fetal adrenal gland secreted various prostaglandins and that prostaglandin secretion was inhibited by endogenously synthesized glucocorticoids. Furthermore, we reported that the neocortex secreted larger quantities of prostaglandins than did fetal zone tissue and that the pattern of secretion of prostaglandins of the two zones differed. In the present investigation the rate and pattern of prostaglandin secretion by adrenal tissue of anencephalic fetuses were assessed and compared to either whole or separated zones of human fetal adrenal tissue. The rate of prostaglandin secretion into the culture medium was determined by measuring prostaglandin E2 or prostaglandin F2 alpha with use of specific radioimmunoassays in media collected at 24-hour intervals. The rate of prostaglandin E2 secretion by adrenal glands obtained from two anencephalic fetuses declined rapidly from 1.71 +/- 0.65 ng/mg-1 of protein per 24 hours and 0.82 +/- 0.46 ng/mg-1 of protein per 24 hours on day 1, respectively, to 0.36 +/- 0.03 and 0.12 +/- 0.04 ng/mg-1 of protein per 24 hours by the fifth day in culture. The rate and pattern of prostaglandin F2 alpha secretion by anencephalic tissue was similar to that of prostaglandin E2. The pattern of prostaglandin secretion by anencephalic adrenal tissue was similar to that observed in neocortex tissue, but the rate of prostaglandin secretion was less. When the rates of prostaglandin secretion by anencephalic and neocortex adrenal tissue were compared to the rates of secretion of cortisol, an inverse relationship was observed. Finally, when whole human fetal adrenal glands or anencephalic tissues were incubated in the presence of adrenocorticotropic hormone, dexamethasone, metyrapone, or SU 10603, the data obtained seemed to suggest that the rate of prostaglandin secretion was regulated in both tissues by endogenously synthesized glucocorticosteroids. In summary, the pattern of secretion of prostaglandins by the anencephalic adrenal gland was similar to that of neocortex tissue, and the rate of secretion of prostaglandins was inhibited by endogenously synthesized cortisol.

The adrenal glands of 12 anencephalic fetuses and 17 normal fetuses of 11 to 21 weeks' gestation were examined histometrically. The volume of the adrenal gland occupied by the fetal zone in the anencephalic fetuses was 57.5% compared with 76.5% in normal fetuses. The fetal zone in anencephaly showed involution in all specimens, which suggests that this involution begins well before 20 weeks' gestation.