*LMP date may be adjusted if unknown or following ultrasound.Įach of these methods will give you the gestational age of your pregnancy. LMP + Time Passed = How Far Along I Am (Gestational) The age of pregnancy may be revised following your The LMP formula is good for working out an initial age of pregnancy but Historically, the first day of the last menstrual period (LMP) became the date from which pregnancy is counted even though conception occurs about two weeks later.

Pregnancy is counted from a women's last menstrual period because the start of a period is easily observable and usually known to a woman whereas theĭate of conception is much less likely to be known. Why Pregnancy is Counted from the Last Menstrual Period (LMP) Read more about ultrasound on this page or ourĭue date page. This initial estimation may then be superseded or confirmed by an ultrasound. Generally, obstetricians or physicians initially calculate pregnancy from your last period without adjusting for an irregularĬycle length. Irregular menstrual periods are generally calculated by early ultrasound. One for you, most likely based on ultrasound measurements. If you don't have a valid last menstrual period date for any reason, your doctor will provide (270 days) to 41 weeks and three days (290 days) with a probability of 70%. The reference above provides a delivery birth range of 38 weeks and four days More than ten days before the due date or more than ten days after. Just 4% of babies are born on their estimated due date, whileħ0% are born within ten days. Pregnancy is estimated to be 38 weeks or 266 days from conception.

Pregnancy is estimated to be 40 weeks or 280 days from the first day of a woman's last menstrual period (LMP).

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