In AN 5.191 and AN 5.192, utuni has been translated, somewhat cumbrously, “the fertile half of the month that starts with menstruation”.
In MN 93 and MN 38 it is more elegantly and idiomatically rendered “the fertile part of her menstrual cycle”. This is perhaps a little less precise according to what you write in this essay, but much more readable in my opinion. And does still justice to the matter.