Which day is considered to be the 1st day of the female reproductive system

The day one starts with the first day of your periods when the blood and tissue lining the uterus (womb) break down and leave the body is considered to be the '1st day' of the 'female reproductive system'.

Explanation:

The periods, that is the 'first day of female reproductive system' starts during puberty and stops 'permanently at menopause'. The menstrual cycle starts with the 'first day of bleeding', which is counted as 'day one'. The menstrual cycle stops just before the "next menstrual period". Menstrual cycle normally ranges from 25 to 36 days. The periods may last anywhere from '3 to 8 days', but '5 days' is average.