Figure 1. Ultrasonographic detection of superfetation.

(a) Late-pregnant females were ultrasonographically examined to detect a second set of new corpora lutea (white arrowheads), indicative of new ovulations during an ongoing gestation, next to the active corpora lutea (*) from the active pregnancy, in which (b) living fully developed fetuses are present inside the uterus (rib cage (white arrowheads) and part of thorax of a fully developed fetus next to placental tissue (*)). Frequent ultrasonographic examinations after delivery revealed (c) two sets of corpora lutea, the regressing ones from the previous pregnancy (*) and the now active ones (white arrowheads) from the gestation that resulted from superfetation, and (d) early embryonic structures (here, embryonic vesicles (white arrow heads) next to placental scars (*) from parturition 2 days ago), which were more developed than from fertilization after parturition would have been possible. The white size bar indicates 10 mm.