20Due Date Defining
As soon as that pink line shows up on a pregnancy test, some women rush to an online due date calculator to find out what their due date might be. But even after factoring the first day of the last menstrual cycle, doctors prefer to set the due date after
doing a first-trimester ultrasound.
During those first 12 weeks, an embryo follows a very predictable growth pattern, so the measurement can determine when the baby is expected, even if mom doesn't remember her last cycle. The date is defined in that initial ultrasound, although moms need to remember that only about 2 percent of newborns actually arrive on that date.