Learning Objectives and CME/Disclosure Information Show
CLINICAL ACTIONS:Historically, dating pregnancies and calculating due dates were left to weekly pregnancy calendars. However, ultrasound dating, in particular first trimester sonography, has greatly improved our ability to calculate the estimated due date (EDD). There will be times that dating based on LMP does not match the ultrasound date. ACOG recommends redating as follows:
SYNOPSIS:Clinical determination of EDD, 280 days after the last menstrual period (LMP) still plays a role but may not always be accurate due to variability in length of an individual woman’s cycle length or timing of ovulation. Accurate dating is vital to pregnancy management, as certain interventions and management decisions may be based on such information including timing of delivery in the case of pregnancy complications. KEY POINTS:
Learn More – Primary Sources:ACOG/AIUM/SMFM Committee Opinion 700: Methods for Estimating Due Date AIUM Practice Parameter for the Performance of Limited Obstetric Ultrasound Examinations by Advanced Clinical Providers ACOG AIUM Practice Bulletin 175: Ultrasound in Pregnancy Take a post-test and get CME credits TAKE THE POST TEST Related ObG Topics:
You have just attended our centre for an early pregnancy scan and your due date doesn’t match your last menstrual period (the LMP) and you are very certain of your dates. Your due date is important for many reasons. It will allow you to plan ahead for your baby’s arrival and it also helps your doctor know when certain prenatal tests should be performed to make sure your baby is developing normally. With so much being based on your expected due date it’s really important for it to be as accurate as possible. A gentle warning is that menstrual cycles are seldom that regular. Normal cycles can be between 21 to 35 days with some women outside of this guideline. Regularity is seldom that common and there is a fair chance the calculation will be off. But we still use your LMP as a guideline because the beginning of a period is an identifiable event where ovulation and fertilisation is not. It is very common when scanning an early pregnancy to find that the due date does not match the menstrual history. Sometimes the dates can be more than a week off and sometimes even as much as 4 weeks. An early obstetric ultrasound performed at approximately 8 weeks where a crown rump length (the CRL) is measured precisely predicts an estimated due date accurately. The accuracy of ultrasound measurements used to confirm the calculated due date will be much less accurate further into the pregnancy. On an early pregnancy ultrasound the embryo’s crown rump length is used to predict your estimated due date ONLY if the measurement falls outside of what your last menstrual period predicts. Measuring the embryo on ultrasound is accurate to within plus or minus five days of the due date. If the crown rump length falls outside of these five days we give you a new estimated due date based on the size of the embryo. Post navigationDisclaimerAll of the content and articles on our blog and website are intended for informational purposes only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team. Is ultrasound due date more accurate?Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.
Can ultrasound dates be wrong in pregnancy?It is very common when scanning an early pregnancy to find that the due date does not match the menstrual history. Sometimes the dates can be more than a week off and sometimes even as much as 4 weeks.
Why my due date is different from the ultrasound?“If dating is only based on the last menstrual period and a later ultrasound shows a discrepancy, then the due date may be changed,” Lamppa says. If your due date is confirmed by an ultrasound in the first trimester, it shouldn't change as the pregnancy progresses, even with additional ultrasounds, she says.
What is the most accurate way to determine your due date?You can calculate your due date if you know the first day of your last menstrual period (LMP) before you got pregnant. Your due date is 40 weeks after the day you started your last period. This method is a good way to estimate when your baby is due because many women people the day they started their period.
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How accurate is your due date by ultrasound
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