You can have irregular cycles when you're stressed or ill, when you're breastfeeding, when you've stopped taking hormonal contraception, or when you're approaching menopause. Sometimes there is an underlying hormonal disorder or other problem that needs medical investigation.

After giving birth, most women experience a period of natural infertility that can last for many months if you breastfeed. The Billings Ovulation Method® enables you to recognise the months of infertility. So you can enjoy your sexual relationship without worrying about the effects on your milk and your baby of the synthetic hormones in chemical contraceptives.

If you've stopped hormonal contraception you may not show signs of fertility for some weeks or months until your own hormones return to normal function. You may have regular bleeds but not observe the normal mucus changes indicating fertility.

From about the age of fifty most women are infertile. The change from fertility to infertility is usually gradual, occurring over a number of years. During this time menstrual cycles often become extremely variable in length and mucus episodes less frequent.