It is possible to be pregnant during breastfeeding without a period. Ovulation resumes earlier than menstruation during breastfeeding, so even having sex during a time period when you don’t have a period can lead to pregnancy. Because higher levels of prolactin during breastfeeding inhibit the onset of menstruation, ovulation is often restored before the onset of menstruation and ovulation occurs. Moreover, because ovarian function has not fully returned to normal at this time, ovulation is irregular and the time of ovulation is not easy to deduce. If sexual intercourse occurs during ovulation and no contraceptive measures are taken, it is very likely that another pregnancy will occur. Therefore, it is also emphasized that contraceptive measures should be taken during breastfeeding to avoid unwanted pregnancy. It is usually recommended to choose to use condoms or place an intrauterine device (IUD), and contraceptive pills are not recommended to avoid interfering with breastfeeding. If a woman does not have a period during breastfeeding and has had sex without reasonable contraception, she can go to the hospital for a blood test to determine whether she is pregnant or not. And it is usually recommended that breastfeeding women are advised to review the ultrasound, blood test, and leukorrhea routine on the 42nd day after delivery to make sure that there is no abnormality before having intercourse.