Last menstrual period ultrasound dating

Gestational age is calculated from the first day of the mother’s last menstrual period and not from the date of conception.The baby can be measured as early as 5 or 6 weeks after the mother’s last menstrual period.Also, when providers all use the same LMP date, we are using one system that provides a standard convention.

If the mother has a regular period and knows the first day of her last menstrual period, gestational age can be calculated from this date.

Medical professionals use a standard set of up to three methods to date pregnancies: last menstrual period, ultrasound, and a physical exam.

That way, regardless of where they trained or where they practice, any two doctors dating a pregnancy will predict the same due date or gestational age.

From the Carolina Population Center, the Departments of Epidemiology, Maternal and Child Health, Nutrition, and Biostatistics, School of Public Health, and the Department of Obstetrics and Gynecology, School of Medicine, University of North Carolina at Chapel Hill Objective: The purpose of this study was to evaluate the accuracy of algorithms for the assignment of gestational age with the use of the last menstrual period and early ultrasound information.

Study Design: Gestational age estimates that are based on last menstrual period, ultrasound scanning, or their combination were compared among women who attended prenatal care clinics in central North Carolina (n = 3655) by an evaluation of digit preference in the last menstrual period dates and a comparison of mean gestational age, preterm and postterm categories with the use of κ statistics, difference between actual and expected delivery date, and birth weight among subgroups with discrepant assignments.

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