The vanishing sac syndrome. Ultrasound evidence of pregnancy failure in multiple gestations, induced and spontaneous.

During a five-year period an ultrasound diagnosis of multiple gestations was made in 162 women. Four cases evidenced an empty gestational sac or sacs associated with viable, normal-appearing gestations. Three of the four patients had ovulation-induced pregnancies. Resorption of these empty sacs was documented. First- and early-second-trimester vaginal bleeding occurred frequently in these pregnancies and was a warning of the possible loss of one or more of the sacs.