Last menstrual period: February 27 — What is the estimated due date?

        Last menstrual period (LMP) was February 27; the estimated due date (EDD) is December 4. However, this method is unreliable for women with irregular menstrual cycles. Details are as follows:

        Generally, the EDD is calculated from the first day of the LMP: subtract 3 months (or add 9 months) and add 7 days to the date. For example, if the first day of the LMP was January 1, the EDD would be October 8. In fact, the EDD is not an exact delivery date; statistical data indicate that only approximately 53% of women deliver on their EDD.

        For women with irregular menstrual cycles, it is recommended to undergo an ultrasound examination between gestational weeks 11 and 13 to confirm gestational age. Subsequently, a more accurate gestational age—and thus EDD—can be determined based on menstrual regularity and the crown-rump length (CRL) measured during this ultrasound. For instance, if the CRL at week 11 corresponds to a gestational age one week smaller than expected, the EDD should be postponed by one week. This adjustment is valid because embryonic development is highly synchronized before approximately 20 weeks’ gestation, allowing reliable gestational age estimation via ultrasound. Additionally, basal body temperature (BBT) charts may also be used for calculation.