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Regestrone is Norethisterone
and is used for postponement of menses;menstrual disorders;DUB;and also as a contraceptive
so as long as you take Regestrone you will not get pregnant.If your periods are normal;fallopian tubes are patent;follicular study
normal;and the semen analysis
of your husband is normal then you can get pregnant.For better chances do alternate days intercourse from 10th to 21 day from start of menses.
All the best.