![]() Last menstrual cycle, if known, should be used to estimate the gestational age before an ultrasound. First-trimester ultrasound has an accuracy of +/- 5 to 7 days. When the crown-rump length exceeds 84 mm (approximately 14 weeks and 0/7 days), the accuracy decreases, and full fetal biometry should be used to approximate the gestational age. The average of three crown-rump length measurements is used to improve accuracy. Crown-rump length is used for pregnancy dating the first trimester. ![]() First-trimester ultrasound can be performed either trans-vaginally or trans-abdominally. įirst-trimester ultrasound (ultrasound before 13 weeks and 6/7 days) is the most accurate method to establish or confirm gestation age in pregnancy. Uterine fibroids, amniotic fluid abnormalities, increased maternal body mass index (BMI), and fetal growth abnormalities are some examples of circumstances that can alter the accuracy of fundal height measurement. The assumption with fundal height measurement is that the measurement in centimeters from uterine fundus to pubic symphysis is equal to the patient's gestational age. The usefulness of fundal height measurement in any circumstance has varied widely throughout the literature but can be helpful in resource-poor areas for an estimation of gestational age. The most common use for fundal height measurement is recording the trend of this measurement to screen for appropriate fetal growth throughout gestation. Measurement should be performed using a non-elastic tape measure, and the patient should have an empty bladder. The distance from the uterine fundus to the pubic symphysis defines fundal height measurement. ![]() įundal height measurement is a physical exam parameter that can be used to estimate gestational age. This technique assumes that the patient has a normal 28-day menstrual cycle and ovulates on day 14 of that cycle. Adding seven days and then nine months to the patient’s last menstrual period (or 280 days) will give an estimated delivery date. The patient must be sure of the first day of their last menstrual period to use this method in establishing the due date. One method of estimating the delivery date is by using the patient's last menstrual cycle.
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