Can your pregnancy scan give the wrong due date?

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.

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.

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. Fetal Imaging Workshop Invited Participants. A comparison of recalled date of last menstrual period with prospectively recorded dates.

J Womens Health Larchmt ; Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol ; Last menstrual period versus ultrasound for pregnancy dating. Int J Gynaecol Obstet ; First trimester ultrasound screening is effective in reducing postterm labor induction rates: Ultrasound for fetal assessment in early pregnancy. Cochrane Database of Systematic Reviews , Issue 7. Predicting delivery date by ultrasound and last menstrual period in early gestation.

New charts for ultrasound dating of pregnancy and assessment of fetal growth: Ultrasound Obstet Gynecol ; First- and second-trimester ultrasound assessment of gestational age.

How Ultrasounds Can Date Your Pregnancy

First- vs second-trimester ultrasound: Br J Obstet Gynaecol ; Gestational age in pregnancies conceived after in vitro fertilization: Ultrasound dating at 12—14 weeks of gestation. A prospective cross-validation of established dating formulae in in-vitro fertilized pregnancies. Accuracy of gestational age estimation by means of fetal crown—rump length measurement. Estimation of gestational age by transvaginal sonographic measurement of greatest embryonic length in dated human embryos.

Ultrasound Obstet Gynecol ;4: Underestimation of gestational age by conventional crown—rump length dating curves. New crown—rump length curve based on over pregnancies. Standardization of sonar cephalometry and gestational age. Sonographic prediction of gestational age: Conceptional age, menstrual age, and ultrasound age: I've not even had my 20 week scan yet.

Wrong due date from ultrasound scan - why it happens | MadeForMums

I have scans every few weeks so it will probably keep on changing. My baby will come when it's ready anyway, maybe weeks before or maybe weeks after my due date.

These can be carried out from week 5 or 6 of pregnancy, which is a notoriously tricky time to be accurate on dates. Measurements at such an early stage aren't accurate which is why they wait for 12 weeks to date you. Expert Jan Steward, who is director of Ultrasound Direct and Babybond, agrees that early scans carry a much greater risk of inaccuracy. We always recommend mums get a definitive dating scan closer to 12 weeks as this will be much more accurate.

Just half a millimetre at such an early stage can change your date by a week. Your week scan will be far more accurate. The sonographer then said that I was only about 4. Then at the week scan I got an EDD of 15 march, so that early scan was completely out. Well, you'd think so, wouldn't you. At around 12 weeks you can get more accurate measurements. By talking to the health care professionals you should get a clearer picture as to what is happening. Thanks so much for your post — we always welcome feedback, positive or negative, as we always aim to make our articles as accurate and as helpful as possible.

Methods for Estimating the Due Date

We spent a lot of time talking to sonographers before writing this article, so we're surprised that you think what they're saying is not in line with what you have studied. 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.

How an Ultrasound Can Estimate Your Conception Date

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. In the UK, most pregnant women don't have an ultrasound until they are at least 12 weeks pregnant.

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