(CNN) --The deaths of two conjoined Iranian twins following unprecedented surgery to separate them has prompted an outpouring of grief around the world. Ladan Bijani died when her blood ...

Conjoined fetuses are a rare type of identical twins that share a placenta and an amniotic sac, when the embryo divides at 13-15 days from conception. The incidence ranges from 1/50,000-1/100,000 ...