A question that most women have after being told that they are pregnant is ''When am I due?'' To calculate the expected date of confinement (EDC), first determine the date of the onset of the last menstrual period (LMP) and then calculate the EDC as follows:
Alternatively, the EDC can be calculated by adding 9 months and 7 days to the first day of the LMP. This calculation is based on a gestation of 280 days and is known as Ndgele's rule. By knowing the EDC, the examiner can predict the size of the uterus on physical examination, provided that the LMP is correct and that conception actually occurred at that time. If the size of the uterus differs significantly from that expected according to the EDC, the causes must be determined. Ultrasonography and other diagnostic tests can be helpful in dating a pregnancy.
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