How to Use a Pregnancy Calculator

Video Transcript

STEVE ARKIN, MD: Hi! I'm Dr. Steve Arkin and I'm going to talk a little bit about how to use a pregnancy calculator. Calculating the gestational age which is approximately 270 days from conception of how long a woman is pregnant. A woman is pregnant for 40 weeks. This gets confusing because in the days when doctors dated pregnancies, they were based on the last menstrual period. So 40 weeks from the very first day of your menstrual cycle is the starting date of the 40-week calendar and this can be done several different ways. Many drug rep manufacturers had a pregnancy wheel and you spin the wheel and you put your first day of your last period, lets say March 26, then you look at 40 weeks from that date is and that would be your due date. There are also computer programs and Palm Pilot software that has this type of information when you put in your period date. Most people ovulate 2 weeks after their last period. However, some of them have 35-day cycles, some have 28-day cycles. So the 2-week rule does not apply to everybody but the gestational age is calculated that way. However, with the advent of ultrasound, most physicians including myself who have an early ultrasound, rely more on the ultrasound date as being more accurate than woman's recollection of her last period. Pregnancy calculations have been done this way for years, but just remember that if someone says they've been pregnant for 40 weeks, they're probably pregnant for 38, because it was really, they got pregnant two weeks after the date that we actually set the clock. That's my summary on pregnancy calculation.