How long is too long for a menstrual cycle? And what can be the causes of irregular periods? India talks to Dr Anita Mitra and Dr Dornu Lebari about what's 'normal' as well as the hormonal imbalance that arises from the condition polycystic ovary syndrome. India also finds out about some unusual animal cycles.

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Special thanks to all contributors and audio diarists.

A Listen production for BBC Radio 4 and BBC Sounds.