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Slight cramping during pregnancy is due to stretching of uterine ligaments as the foetus grows to accomodate itself.But if it is associated with any other symptoms as increasing cramps,bleeding,discharge etc then consider rushing to your treating Gynaecologist for evaluation.
It might require pelvic examination to comment regarding the exact cause.Have healthy balanced diet and avoid any strenous activity.Maintain adequate hydration and completely avoid smoking and alcohol.
Take care!