For patients who have had a spontaneous miscarriage, if their menstrual cycle is usually regular, the first day of the spontaneous miscarriage is the time when their next period would begin. However, if the miscarriage is incomplete and a dilation and curettage (D&C) procedure is required, the first day after the D&C is considered the start date for the next menstrual cycle.

Some people experience spontaneous miscarriages due to menstrual irregularities and an irregular menstrual cycle, which may be caused by hormonal imbalances. In such cases, the timing of the next period after a miscarriage is uncertain.

If the menstrual cycle is regular, the next period can be estimated based on the aforementioned timings. However, if the cycle is irregular, the timing of the next period post-miscarriage primarily depends on the condition of the endometrium. If the endometrium has recovered to a thickness of 1.0 or more, menstruation is likely to occur. If the endometrial lining is thin, menstruation may not occur for the time being.

Therefore, the length of time until menstruation resumes following a spontaneous miscarriage also requires monitoring of the hormonal balance and the regularity of the usual menstrual cycle.