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# How do you calculate the estimated pregnancy due date?

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A woman can estimate a pregnant woman’s due date by using an ultrasound test, measuring the size of the uterus and determining the first day of the woman’s last menstrual period, states WebMD. Most women’s due dates are approximately 40 weeks after the first day of their last menstrual cycle.

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The most common method of determining a woman’s due date without visiting a doctor is to use the woman’s last menstrual period as a tool of reference, according to WebMD. It is the first day of the woman’s last menstrual period, after which seven days and nine months are added. If the woman knows her day of conception, she can add 40 weeks to this date to come up with an estimated due date.

A doctor can diagnose a woman’s due date by looking at the size of her uterus, according to WebMD. Around 12 weeks of pregnancy, the uterus can be felt by palpating the pelvic rim. At 20 weeks, the uterus typically grows and reaches the belly button. Trained professionals can use the size and location of the uterus to determine the progress of the pregnancy and the estimated due date.

An ultrasound is a rather accurate tool that doctors use to estimate a woman’s due date, according to WebMD. This instrument uses sound waves to determine the size of the fetus. Most women deliver their babies within two weeks of their due dates, according to WebMD.

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