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Since your last menstrual period was on , your baby's estimated birth date is .

How is a baby's estimated birth date calculated?

Naegele's Rule (Standard Pregnancy Dating Method)

In about 1850, Dr. Naegele determined that the average length of human gestation was approximately 38 weeks (266 days) from conception. This equates to 40 weeks (280 days) after the first day of the last menstrual period. When making this determination he assumed that the average woman had cycles that lasted 28 days and that she ovulated on day 14 of her cycle. Therefore, the egg could not be fertilized until 2 weeks after the first day of the menstrual cycle. He used his data to come up with a mathematical calculation for due dates.

Today, most authorities agree that many factors affect a due date. Your healthcare provider can use ultrasound, and other techniques, to help estimate your due date.