What the female reproductive system “naturally does” is to get pregnant almost immediately upon reaching puberty, and produce a baby approximately every 18 months, killing a huge percentage of mothers (and full term babies) in the process. What we take for granted in these modern times — women routinely having healthy babies with only a tiny risk of death for themselves — is attributable to the efforts of the medical profession. The natural death rate from childbirth is about 1 per 100 births, multiplied by the number of births per woman to get a lifetime risk of death from childbirth of over 5%. Currently in the US, the actual death rate is about 1 in 10,000 births, while in places like sub-Saharan Africa and Afghanistan, it remains at the natural rate due to the near-complete absence of medical care. “Natural” doesn’t automatically translate into “safe” or “good”.
In fact, the “female reproductive system” does not get pregnant almost immediately at puberty and then spit out a baby every 18 months. Unless of course, the female who owns the reproductive system in question is for some odd reason having coitus exactly from that moment on with virtually no let up. Part of the “naturalness” of the reproductive system is that it depends on coitus, which, barring the commission of a criminal act, is generally voluntary.
So we have a choice here. Tell people not to screw around and they won’t get pregnant—just like we tell them to eat less, not smoke, etc. Or tell them g’head, KEEP screwing around so then we can pump you full of synthetic estrogen and screw up your menstrual cycle.
I am not down on the medical profession for what it does well, and to be sure, it has saved a lot of lives and done lots of goods for mothers and babies. What I am saying is that its uncritical acceptance of the Pill is inherently contradictory and flies in the face of “first do no harm.”
Documentation, please. Part of the problem is the choices we make. Girls should not be engaging in sex "immediately upon reaching puberty." There are consequences to all behavior that does not line up with God's truths. God's design for the female body was and is perfect.