I agree with you entirely. But, try to find a report that quantifies what percentage (or even number) of women actually get pregnant while at sea - It's nowhere to be found. They do publish the statistics for women that are pregnant while at sea, and that number is around 11% (last figures I saw were from 2007). I'm assuming that some of them became pregnant before deploying, and didn't find out they were pregnant until after they were at sea.
Whatever the case, a 11% "casualty" rate (and that's what it is with respect to mission readiness and capability), is a BIG problem for ship's captains as well as Navy HQ. I can only imagine, having never served aboard a sub, that "casualties" on such a ship with such a limited crew, become even more corrosive to the ship's readiness and morale.
You're right---the Navy doesn't even go there, or even if it does, such statistics are treated like classified information.
A few years ago I read a letter written in the Naval Institute Proceedings by a chief who lamented the fact that so many of his ship's female sailors had gotten pregnant that the vessel had been rendered wholly dysfunctional.
Nothing more was ever said about it in the Proceedings and that's the way the Navy is content to have it.
Bob Dornan tried to get these statistics service wide; he was stonewalled and at this point they may not exist at all. From personal experience, I can tell you that the 7th Transportation group had upwards of 100 women either pregnant or post partum carried as nondeployable througout the 60 months I was familiar with the situation. The figure was static, some go, some leave and some get pregnant again.