A period can be about a week late before home pregnancy tests can accurately detect pregnancy, according to Central Carolina OB-GYN. If a woman is not pregnant, she may skip periods or have late periods for other reasons, notes pediatrician Jennifer Shu.
Causes of missed periods other than pregnancy include menopause, weight changes, side effects of medicines, hormonal disturbances and stress, Dr. Shu notes. After stopping birth control, women may miss several periods. Abnormal thyroid or adrenal glands, tumors and cysts can also cause changes in periods. A woman should visit her doctor if she misses several periods after having them regularly. A pelvic examination and an ultrasound may be given to determine the cause of missed periods.