Conjoined twins, conception, pregnancy, and delivery: a reproductive history of the pygopagus Blazek sisters (1878-1922).

Conjoined twins represent the most uncommon twinning mechanism in humans, with an incidence approaching 1:100,000 deliveries. Although several conjoined male twins have occasionally been reported, for unexplained reasons most cases of conjoined twins are female. Of all the female conjoined twin sets either documented by medical authorities or referenced in ancient literary sources, in only one case were pregnancy and delivery successfully achieved by the conjoined twins themselves. We describe the highly unusual circumstance of the Blazek sisters, an extreme developmental example of the terminal monogenital pygopagus type of conjoined twins in which one of the joined sisters conceived and underwent labor and childbirth. Although little information is known about their own birth, these conjoined twins paradoxically hold a unique place in the history of obstetrics. Information from formal anatomic examinations of the sisters and their exploitative circus exhibitions is outlined with a view to explain relevant reproductive events. We present the sensational conception, pregnancy course, and subsequent vaginal delivery of a healthy male infant as summarized from contemporary sources. Additionally, the significance of pygopagus twins is discussed with regard to other types of monozygous twinning. Although modern operative techniques have been a welcome advance in the science of conjoined twin separation, the Blazek case is another reminder that, even in the era before complex surgery, conjoined twins were not necessarily consigned to an incomplete reproductive career.