Can you get pregnant from having sex on the first day of your period?

In general, having sex on the first day of menstruation will not result in pregnancy. The detailed explanation is as follows:

Under normal circumstances, a woman's ovulation period usually occurs about 14 days before the next menstrual period. The first day of menstruation is far from the ovulation period; at this time, the ovaries generally do not release an egg. Without an egg, fertilization cannot occur, making the likelihood of pregnancy extremely low. Moreover, during menstruation, the uterine lining is shedding to allow menstrual blood to flow out, and this endometrial environment is unfavorable for embryo implantation. Even if unexpected ovulation occurs and fertilization takes place, successful implantation and development of the embryo within such a lining would be very difficult. Additionally, during menstruation, the vaginal environment changes—the normally acidic environment is diluted by menstrual blood, reducing resistance. This condition is not conducive to sperm survival or movement through the reproductive tract, further decreasing the chance of sperm meeting and fertilizing an egg.

However, it should be noted that although the probability of pregnancy on the first day of menstruation is very low, sexual intercourse during this time is still not recommended. During menstruation, the female reproductive system is more vulnerable, and intercourse can easily lead to infections such as vaginitis or pelvic inflammatory disease. It may also cause increased menstrual bleeding or prolonged periods, posing adverse effects on women's health.