Ultrasound accuracy for dating
Perkins also has extensive experience working in home health with medically fragile pediatric patients.Before the advent of routine ultrasound in pregnancy, medical personnel estimated a baby’s due date by the date of the last menstrual period and by feeling the uterus and determining the size to see if it matched the given due date.With transvaginal ultrasound, checking for embryonic development known to occur within a certain time frame more accurately dates a pregnancy.Transvaginal ultrasound can see embryonic development about a week before transabdominal ultrasound, the American Pregnancy Association (APA) states.5 ½ weeks gestation means 5 ½ weeks from the first day of the last menstrual period, which is usually about 3 ½ weeks from the date of conception (confusing, isn’t it!
A registered nurse with more than 25 years of experience in oncology, labor/delivery, neonatal intensive care, infertility and ophthalmology, Sharon Perkins has also coauthored and edited numerous health books for the Wiley "Dummies" series.Ultrasounds performed after 22 weeks gestation cannot be used to estimate the due date of the baby because the size no longer reflects the age very well.Even average babies can differ by up to 2 to 3 "weeks of growth";.However, the accuracy of the ultrasound examination is always dependent on the skill of the sonographer and the quality of the equipment.Usually the expected date of delivery (EDD or EDC) is calculated from your last menstrual period - if the early dating scan calculates the EDD to be within 5 days of the EDD from your last menstrual period.
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Most dating scans are done with a trans-abdominal transducer and a fullish bladder.