Adjective
monoamniotic (not comparable)
English Wikipedia has an article on:monoamnioticWikipedia
(biology, of twins) Sharing the same amniotic sac within their mother's uterus.
Monoamniotic twins share a hormonal environment, but can suffer from the 'twin to twin transfusion syndrome' in which one twin is "relatively stuffed with blood and the other exsanguinated". Source: Internet