If a woman’s menstrual cycle is regular and she is pregnant, the estimated date of delivery is usually calculated from the first day of the last menstrual period, not from the end of the period. If a woman’s menstrual cycle is very irregular, such as patients with polycystic ovary syndrome (PCOS), who sometimes do not have a period for half a year, how is the expected date of delivery calculated for this group of patients. Usually, it is based on the early pregnancy ultrasound examination, measuring the size of the gestational sac, the size of the embryo bud, the size of the parietal diameter, to estimate the actual gestational week, and based on the ultrasound examination to estimate her expected date of delivery. Because this part of the patient’s fertilized egg is usually later, under normal circumstances, women can see the gestational sac when the ultrasound is done at about five weeks of pregnancy, but this part of the patient may have to be pushed to 7-8 weeks before the gestational sac can be seen, which is directly related to the usual long menstrual cycle, ovulation is later.