Juliet is a fertility doctor for ANIMALS... hence her being clueless when trying to help Jack operate.

Henry Gale was brought to the island as a baby becuase of his funked up spine. The island keeps him ( and the others, who probably all have some ailment) alive. I always thought Ethan looked like he had down syndrome or something.

I would be sterile too if all i had to do was join the book club on that island or keep the hottest women on the island in a cage!