Patient's question:
Hello:I had my period on November 16, and then I had it again on December 17. On December 28, I had sex with my husband. Could I be pregnant? I'm very worried…………（How to determine the safe period）
In October, I had my period on the 12th.
Doctor's answer:
The method of calculating ovulation based on the menstrual cycle is also known as the calendar method. Both menstruation and ovulation are influenced by the endocrine hormones of the pituitary gland and ovaries, exhibiting cyclical changes. The lengths of both cycles are consistent, occurring once per month, with ovulation occurring between two menstrual periods. A woman's menstrual cycle can vary in length, but the interval between the day of ovulation and the start of the next menstrual period is relatively fixed, generally around 14 days. Based on this relationship between ovulation and menstruation, it is possible to calculate the ovulation period based on the menstrual cycle. The calculation method starts from the first day of the next menstrual period, counting backward 14 days or subtracting 14 days to determine the day of ovulation. The day of ovulation, along with the previous 5 days and the following 4 days, is collectively referred to as the fertile window. This is the theoretical basis for the safe period method of contraception. For example, a woman with a 28-day menstrual cycle has her first day of her current period on December 1. Her next menstrual period would then occur on December 29 (December 1 plus 28 days). Subtracting 14 days from December 29 gives December 15 as the day of ovulation. The fertile window, which includes the day of ovulation and the 5 days before and 4 days after, is from December 10 to December 19. All other times are considered the safe period.