How accurate are ultrasounds in determining date of conception?
On One Hand: Margin of ErrorAccording to Dr. Arthur T. Ollendorf, a professor of obstetrics at the University of Cincinnati, estimated conception dates from ultrasounds performed during the first trimester of pregnancy are accurate within a week. Henci Goer, author of “The Thinking Woman’s Guide to a Better Birth,” states that conception dates determined by ultrasounds in the second and third trimesters can be off by as many as 10 days.On the Other: It’s a Best GuessMost doctors use a combination of ultrasounds, blood tests and the date of a woman’s last menstrual cycle to calculate a conception date. By using all of these methods to determine a date, the doctor increases the estimate’s accuracy. Because every woman has a uniquely timed cycle and the lifespan of sperm can vary, it’s nearly impossible to determine exact conception dates.Bottom LineWhile ultrasounds are not 100 percent accurate in determining conception dates, they are one of the best tools available for monitoring a pre