What can cause a period to be late if you have a tubal ligation?

Menstrual cycle may vary. Acute sickness, extreme stress, etc. may cause period delay. Chance of pregnancy is extremely low after tubal ligation but it does rarely occur. If your partner has any doubt just do an early morning urine test to rule out pregnancy after 5 days of a missed period. For middle-aged woman, cycle could change drastically (long or short) when approaching pre-menopausal time.