SYDNEY forward Gary Rohan has shared the sad news that one of the twins he and partner Amie are expecting will have its life cut short after being diagnosed with anencephaly.

The condition, which can be diagnosed during pregnancy, is a serious birth defect in which parts of the brain and skull are underdeveloped.

Rohan wrote on social media that talking about the situation had been therapeutic for the expectant parents.

"We would love for anyone who has been affected by anencephaly themselves or know of others affected by anencephaly to please contact us," he wrote on Instagram.

"Don't be afraid to talk to us about it. That's what we want, we want people to ask questions, we want to talk about it with others.

"We still need questions answered as much as everyone else. 

"And at the end of the day, we will always be parents to twins, our journey has just been written a little differently to others."

Rohan and his partner are expecting the birth of the surviving twin in May next year.