The measurement used for dating should be the mean of three discrete CRL measurements when possible and should be obtained in a true midsagittal plane, with the genital tubercle and fetal spine longitudinally in view and the maximum length from cranium to caudal rump measured as a straight line 8, Mean sac diameter measurements are not recommended for estimating the due date. Dating changes for smaller discrepancies are appropriate based on how early in the first trimester the ultrasound examination was performed and clinical assessment of the reliability of the LMP date Table 1.
For instance, the EDD for a pregnancy that resulted from in vitro fertilization should be assigned using the age of the embryo and the date of transfer. For example, for a day-5 embryo, the EDD would be days from the embryo replacement date. Likewise, the EDD for a day-3 embryo would be days from the embryo replacement date. Using a single ultrasound examination in the second trimester to assist in determining the gestational age enables simultaneous fetal anatomic evaluation. With rare exception, if a first-trimester ultrasound examination was performed, especially one consistent with LMP dating, gestational age should not be adjusted based on a second-trimester ultrasound examination.
How accurate was your ultrasound due date?
Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as. Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role. Date changes for smaller discrepancies 10—14 days are appropriate based on how early in this second-trimester range the ultrasound examination was performed and on clinician assessment of LMP reliability.
Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; therefore, decisions need to be guided by careful consideration of the entire clinical picture and may require close surveillance, including repeat ultrasonography, to ensure appropriate interval growth. The best available data support adjusting the EDD of a pregnancy if the first ultrasonography in the pregnancy is performed in the third trimester and suggests a discrepancy in gestational dating of more than 21 days.
As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. For the purposes of research and surveillance, the best obstetric estimate, rather than estimates based on the LMP alone, should be used as the measure for gestational age.
The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine recognize the advantages of a single dating paradigm being used within and between institutions that provide obstetric care. Table 1 provides guidelines for estimating the due date based on ultrasonography and the LMP in pregnancy, and provides single-point cutoffs and ranges based on available evidence and expert opinion.
No part of this publication may be reproduced, stored in a retrieval system, posted on the Internet, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Methods for estimating the due date. American College of Obstetricians and Gynecologists. Women's Health Care Physicians.
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Recommendations The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine make the following recommendations regarding the method for estimating gestational age and due date: As soon as data from the last menstrual period LMP , the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record.
Introduction An accurately assigned EDD early in prenatal care is among the most important results of evaluation and history taking. Clinical Considerations in the Second Trimester Using a single ultrasound examination in the second trimester to assist in determining the gestational age enables simultaneous fetal anatomic evaluation.
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Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as the biparietal diameter and head circumference measured in transverse section of the head at the level of the thalami and cavum septi pellucidi; the cerebellar hemispheres should not be visible in this scanning plane the femur length measured with full length of the bone perpendicular to the ultrasound beam, excluding the distal femoral epiphysis the abdominal circumference measured in symmetrical, transverse round section at the skin line, with visualization of the vertebrae and in a plane with visualization of the stomach, umbilical vein, and portal sinus 8 Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role.
Conclusion Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. Regression models using a combination of any two or three ultrasonic variables did not improve accuracy of prediction. When ultrasound was used instead of certain LMP, the number of postterm pregnancies decreased from Ultrasound was more accurate than LMP in dating, and when it was used the number of postterm pregnancies decreased.
Combining more than one ultrasonic measurements did not improve dating accuracy. We'd be really keen to know more about your studies — and what you have learned. You're right that we did include 'anecdotal stories' in our article. We used them to illustrate the key points we were making in the articles but the quotes we used were all centred on the real experiences of pregnant women posting in our forum. We are confident that we are not using these quotes to 'misinform women', as the key points in our article were all sourced from expert monographers.
It's interesting that you say that ultrasounds between 8 and 10 weeks are the most accurate.
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In the UK, most pregnant women don't have an ultrasound until they are at least 12 weeks pregnant. Perhaps you are based in the US, or another country, where ultrasound practice is a bit different?
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How accurate is an early ultrasound for dating? - Mothering Forums
Some of the information in this article disagrees with everything we have studied so far regarding dating pregnancies and ultrasound accuracy. An ultrasound between weeks is the most accurate, not Please do not misinform women on anectodal stories.
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Do drop us a line a bout your studies, please. We'd be really interested to hear more. You need to be logged in to do this Sign In Sign Up.