A case of simultaneous interstitial bilateral pregnancy.

Twin pregnancies may present tubal involvement in the following cases: (1) simultaneous intra- and extrauterine pregnancy; (2) interstitial bilateral pregnancy (either simultaneous or not); (3) multiple pregnancy in the same tube; and (4) simultaneous interstitial and ovarian pregnancy. Interstitial bilateral pregnancy appears to be by far the rarest kind of tubal twin pregnancy, apparently only one case having been reported in the literature, and this referring to a nonsimultaneous pregnancy. A case is now reported that therefore appears to represent the first observation of simultaneous interstitial bilateral pregnancy.