Erin and Abby Delaney were born in joined at the head -- a rare early stages of development, an embryo only partially separates to form two babies. Conjoined twins are rare, occurring in about one out of every , live births, experts say. . The two Indonesian twin baby girls were successfully separated in a. May 31, - While conjoined twins are already a rarity, Abby and Brittany Hensel were “When children ask the girls if they have two heads, they say they.