Okay, let's assume your premise: birth is rare. Unless that is not what you are saying. If not, can you clarify a more precise statement/conclusion. And, also present a statistic/data. Be much obliged to read it ;) 

Not to be rude, but you used some and most. So if "most mammas" reproduce yearly, does that include human mammals? 

I wouldn't say your concern/wisdom on women who may have their systems depleted for excessive childbirth is a bad outlook on reproduction. Unfortunately, that can be a health factor in having children. In fact Natural Family Planning utilizes the cycles and careful planning/care in having children by your prudential view. Though you may disagree with human beings making a decision to live chaste lives with their spouses for the time being between the best opportunities having children, the cooperation in planning still follows the same course of responsibly not having excessive births - just good prudence. You prefer contraception/abortion instead.