Usually animals are categorized as male and female based on what type of gametes their gonads produce. So male sea horses produce sperm.

Not sure how to count the “pregnancy” though, as these are fish and because of the following:

The male seahorse is equipped with a brood pouch on the ventral, or front-facing, side of the tail. When mating, the female seahorse deposits up to 1,500 eggs in the male’s pouch. The male carries the eggs for 9 to 45 days until the seahorses emerge fully developed, but very small. The young are then released into the water, and the male often mates again within hours or days during the breeding season

From Wikipedia

I could see how this could be seen as pregnancy.