To compare gestational age (GA) estimates in early pregnancy, determined by last menstrual period (LMP), human chorionic gonadotropin (h CG) concentration, ultrasound crown–rump length (Hadlock formula), and ovulation day (luteinizing hormone surge plus 1 day).Female volunteers seeking to conceive (at 5 US sites) collected daily early-morning urine for up to 3 menstrual cycles. Conception cycle urine was quantitatively assessed for luteinizing hormone and h CG.Ask your GP if you want the reassurance of an early scan. The scan's main purpose is to work out accurately how many weeks pregnant you are and estimate your due date.You may have calculated the length of your pregnancy from the first day of your last menstrual period (LMP).Or perhaps she had irregular cycles and needs to pinpoint a more specific date in a timeline to accurately plan for the baby's birth. Using a calendar type system, you figure a due date by adding 280 days to last menstrual period, or equaling 40 weeks. That's great if you have regular, 28 day cycles and ovulate predictably on day 14. "New Guidelines For Estimating Women's Due Dates Issued By OB-GYN Group." The Huffington Post. Of course, the primary reason for most women to need the answer is to estimate the due date of the baby. But there can be other issues at play, such as when a woman has had sex with two men since her last menstrual period, for instance.
Correlation between GA determined by ultrasound and ovulation day was excellent (maximum difference 10 days); however, pregnancies dated by ultrasound were 3 days advanced.
The accuracy of h CG measurement in determining the week since conception was more than 93%.
Methods for establishing pregnancy duration vary in their accuracy and their GA estimates.
The guidelines give precedence to the findings of an early ultrasound over other methods, including date of last menstrual period or LMP.
Having a scan in the first few months of pregnancy can be a thrilling experience.
In September 2014, the American College of Gynecologists and Obstetricians along with the American Institute of Ultrasound in Medicine and the Society for Maternal-Fetal Medicine, released new guidelines for physicians and other health care providers for accurately estimating due dates for pregnant women.