Sorry to disappoint you BUT, a woman is NOT actually at her most fertile during her period of Menstruation.
Normally her MOST Fertile period is between the 11th. and the 14th days POST her last Menstruation.
When she is menstruating , her body, the Uterus in fact, is FLUSHING away the blood enriched lining it had built up in anticipation of conception and pregnancy occurring but did NOT occur.

@Triphid Maybe he meant the fact that a woman is menstruating means that she is fertile. Pre or post her years of menstruating she is not.

@Moravian Thank you, Alec. Yes, I wrote that "A menstruating woman is a FERTILE woman." That is likely to be true with most women. We all know that ovulation happens later in the month...don't we.

@Moravian That may be one context of it HOWEVER, just because a woman has her menstrual periods does NOT mean that she is actually FERTILE.
Basically the Hormones released control and trigger the Menstruations, Fertility relies solely upon ONE of the 2 Ovaries producing a viable, mature ovum and most human females are born with approx. 500 immature ova already in their ovaries, now things can happen and those ovaries may be affected by such things as P.C.O. S. (Polycystic Ovarian Syndrome), Venereal Diseases, infections, etc, etc, and even cancers elsewhere in the body, not just the Ovaries or the Genital region/s.
All of those and more can stop the Ovaries from producing and releasing a Mature Ovum but NOT stop the other glands, elsewhere in the body from producing the necessary hormones.
Now, PLEASE do NOT take this the wrong way, BUT did you guys EVER bother to learn ANYTHING about your wives, daughters, other women and how their body works and such things, OR did you merely grow up ( I use that term very loosely here btw) seeing women and girls as merely walking Sperm Deposit Slots, etc, etc, and thing to do 'cat-calls and wolf-whistles' at as they passed by?

@Triphid Thanks for the biology lesson. You have missed you vocation

@Moravian Already been there done that, kind of, Trained and Worked as a Nurse for years and as a Mid-Wife also.

@mischl Btw, Ovulation ALWAYS PRECEDES Menstruation by normally 5-7 days.
When the Menstruation Period ends, then the female body goes about slowly re-lining the walls of the Uterus ( Womb to those who are unfamiliar Medical terminology) in readiness for the next cycle of Ripening of an Ovum, release of it from the ovary, its descent along the Fallopian Tube to, hopefully, meet up with a suitable Male Sperm cell, suitable as in ACCEPTABLE to the Ovum that is, the fertilization of the Ovum and then, IF all goes well, its eventual implantation into the ready and waiting Uterine wall.
IF conception DOES NOT occur then the Uterus begins the slow process of readying itself to shed the blood engorged linings once again.

I think that's what women call PMS, aka "Putting up with Male Shit." LOL.

And pakistan, and malaysia, and everyfuckistan.

@AtheistInNC Check your OWN backyards, so to speak, as well.
The United State of Absurdity STILL have some 'cultures' that have such 'regulations'[ in place and operating, for example, The Amish, the Quakers to name just a few.
So I guess we can NOW change the United States of Absurdity to the United States of Anotherfuckedupistan then, can we.

@Triphid I'm pretty sure that the U.S. hasn't had a public stoning or honor killing (or rape) for a couple of hundred years. In India and Pakistan, it's weekly.

But I agree with you that the U.S. needs to eradicate all the 'cultures' that are misogynist as well.

@AtheistInNC No PUBLIC Stonings in the U.S.of A. BUT plenty of Mass Killings by Crazy/Crazed Gun Owners at schools, cinemas, etc, etc. though.