Dating scan accuracy

Methods for Estimating the Due Date

Number 700 (Replaces Committee Opinion Number 611, October 2014. Reaffirmed 2022)

Committee on Obstetric Practice

American Institute of Ultrasound in Medicine

Society for Maternal–Fetal Medicine

This Committee Opinion was developed by the American College of Obstetricians and Gynecologists’ Committee on Obstetric Practice, in collaboration with members Christian M. Pettker, MD; James D. Goldberg, MD; and Yasser Y. El-Sayed, MD; the American Institute of Ultrasound in Medicine’s liaison member Joshua A. Copel, MD; and the Society for Maternal–Fetal Medicine.

This document reflects emerging clinical and scientific advances as of the date issued and is subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed.

ABSTRACT: Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. As soon as data from the last menstrual period, the first accurate ultrasound examination, or both are obtained, the gestational age and the estimated due date (EDD) should be determined, discussed with the patient, and documented clearly in the medical record. Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record. A pregnancy without an ultrasound examination that confirms or revises the EDD before 22 0/7 weeks of gestational age should be considered suboptimally dated. When determined from the methods outlined in this document for estimating the due date, gestational age at delivery represents the best obstetric estimate for the purpose of clinical care and should be recorded on the birth certificate. For the purposes of research and surveillance, the best obstetric estimate, rather than estimates based on the last menstrual period alone, should be used as the measure for gestational age.

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:

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.
If pregnancy resulted from assisted reproductive technology (ART), the ART-derived gestational age should be used to assign the estimated due date (EDD). 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.
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. Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record.
When determined from the methods outlined in this document for estimating the due date, gestational age at delivery represents the best obstetric estimate for the purpose of clinical care and should be recorded on the birth certificate. 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.
A pregnancy without an ultrasound examination that confirms or revises the EDD before 22 0/7 weeks of gestational age should be considered suboptimally dated.

Introduction

An accurately assigned EDD early in prenatal care is among the most important results of evaluation and history taking. This information is vital for timing of appropriate obstetric care; scheduling and interpretation of certain antepartum tests; determining the appropriateness of fetal growth; and designing interventions to prevent preterm births, postterm births, and related morbidities. Appropriately performed obstetric ultrasonography has been shown to accurately determine fetal gestational age 1. A consistent and exacting approach to accurate dating is also a research and public health imperative because of the influence of dating on investigational protocols and vital statistics. This Committee Opinion outlines a standardized approach to estimate gestational age and the anticipated due date. It is understood that within the ranges suggested by different studies, no perfect evidence exists to establish a single-point cutoff in the difference between clinical and ultrasonographic EDD to prompt changing a pregnancy’s due date. However, there is great usefulness in having a single, uniform standard within and between institutions that have access to high-quality ultrasonography (as most, if not all, U.S. obstetric facilities do). Accordingly, in creating recommendations and the associated summary table, single-point cutoffs were chosen based on expert review.

Background

Traditionally, determining the first day of the LMP is the first step in establishing the EDD. By convention, the EDD is 280 days after the first day of the LMP. Because this practice assumes a regular menstrual cycle of 28 days, with ovulation occurring on the 14th day after the beginning of the menstrual cycle, this practice does not account for inaccurate recall of the LMP, irregularities in cycle length, or variability in the timing of ovulation. It has been reported that approximately one half of women accurately recall their LMP 2 3 4. In one study, 40% of the women randomized to receive first-trimester ultrasonography had their EDD adjusted because of a discrepancy of more than 5 days between ultrasound dating and LMP dating 5. Estimated due dates were adjusted in only 10% of the women in the control group who had ultrasonography in the second trimester, which suggests that first-trimester ultrasound examination can improve the accuracy of the EDD, even when the first day of the LMP is known.

Accurate determination of gestational age can positively affect pregnancy outcomes. For instance, one study found a reduction in the need for postterm inductions in a group of women randomized to receive routine first-trimester ultrasonography compared with women who received only second-trimester ultrasonography 5. A Cochrane review concluded that ultrasonography can reduce the need for postterm induction and lead to earlier detection of multiple gestations 6. Because decisions to change the EDD significantly affect pregnancy management, their implications should be discussed with patients and recorded in the medical record.

Clinical Considerations in the First Trimester

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 3 4 7 8 9 10. Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11 15 16 17 18. 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 11. Mean sac diameter measurements are not recommended for estimating the due date. Beyond measurements of 84 mm (corresponding to approximately 14 0/7 weeks of gestation), the accuracy of the CRL to estimate gestational age decreases, and in these cases, other second-trimester biometric parameters (discussed in the following section) should be used for dating. If ultrasound dating before 14 0/7 weeks of gestation differs by more than 7 days from LMP dating, the EDD should be changed to correspond with the ultrasound dating. 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, before 9 0/7 weeks of gestation, a discrepancy of more than 5 days is an appropriate reason for changing the EDD. If the patient is unsure of her LMP, dating should be based on ultrasound examination estimates (ideally obtained before or at 13 6/7 weeks of gestation), with the earliest ultrasound examination of a CRL measurement prioritized as the most reliable.

If pregnancy resulted from ART, the ART-derived gestational age should be used to assign the EDD. 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 261 days from the embryo replacement date. Likewise, the EDD for a day-3 embryo would be 263 days from the embryo replacement date.

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. However, the range of second-trimester gestational ages (14 0/7 weeks to 27 6/7 weeks of gestation) introduces greater variability and complexity, which can affect revision of LMP dating and assignment of a final EDD. 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. 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.

Gestational age assessment by ultrasonography in the first part of the second trimester (between 14 0/7 weeks and 21 6/7 weeks of gestation, inclusive) is based on a composite of fetal biometric measurements and has an accuracy of  7–10 days 19 20 21 22. If dating by ultrasonography performed between 14 0/7 weeks and 15 6/7 weeks of gestation (inclusive) varies from LMP dating by more than 7 days, or if ultrasonography dating between 16 0/7 weeks and 21 6/7 weeks of gestation varies by more than 10 days, the EDD should be changed to correspond with the ultrasonography dating Table 1.Between 22 0/7 weeks and 27 6/7 weeks of gestation, ultrasonography dating has an accuracy of ± 10–14 days 19. If ultrasonography dating between 22 0/7 weeks and 27 6/7 weeks of gestation (inclusive) varies by more than 14 days from LMP dating, the EDD should be changed to correspond with the ultrasonography dating Table 1. 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. Of note, pregnancies without an ultrasound examination that confirms or revises the EDD before 22 0/7 weeks of gestational age should be considered suboptimally dated (see also Committee Opinion 688, Management of Suboptimally Dated Pregnancies 23).

Clinical Considerations in the Third Trimester

Gestational age assessment by ultrasonography in the third trimester (28 0/7 weeks of gestation and beyond) is the least reliable method, with an accuracy of ± 21–30 days 19 20 24. 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.

Conclusion

Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. 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. Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record. When determined from the methods outlined in this document for estimating the due date, gestational age at delivery represents the best obstetric estimate for the purpose of clinical care and should be recorded on the birth certificate. 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. A pregnancy without an ultrasound examination that confirms or revises the EDD before 22 0/7 weeks of gestational age should be considered suboptimally dated.

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.

Copyright May 2017 by the American College of Obstetricians and Gynecologists. All rights reserved. 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.

Requests for authorization to make photocopies should be directed to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400.

ISSN 1074-861X

The American College of Obstetricians and Gynecologists 409 12th Street, SW, PO Box 96920, Washington, DC 20090-6920

Methods for estimating the due date. Committee Opinion No. 700.American College of Obstetricians and Gynecologists. Obstet Gynecol 2017;129:e150–4.

Wrong due date from ultrasound scan - why it happens

Listening to MFM mums, it's clear lots of you leave your scan with a nagging feeling that what you've been told that day doesn’t seem quite right. Perhaps you’ve been given a due date that seems totally out of sync with the date that you thought you were going to have your baby.

Despite the fact that sonographers are experts in their field, estimated due dates (EDD) calculated from pregnancy scans can be incorrect, as Ollysmum76 discovered.

“My due date got put back by 2 weeks at the 12 week scan. Original date given was 18 December but at the scan it was moved to 31 Dec. It just doesn't quite add up by my reckoning of when I think I ovulated and when I know we did the deed!”

"I had an early scan at 8 weeks, which put me back a week," adds AbnormalKitty. "Then at my 12 week scan, they put me forward by 4 days."

When do you normally have a dating scan?

Unless you have an early pregnancy scan most of you will be given your estimated due date at the 12-week scan. It’s at this time that you will be told how many weeks pregnant you are.

Of course you have probably already used an online due date calculator. This is where you discover that your due date isn't based on the date you conceived, it's actually calculated from when your last menstrual period started (your LMP). Weird huh? It's because it gives a definite date for health professionals to work with. There would be so many variables if it was calculated from when you think you conceived, especially as everyone's cycles are different and the fact that you don't necessarily conceive on the day you have sex!

Try the MFM due date calculator

Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period, explains NHS Choices. But this will only give you a rough idea. This is especially true if you have an irregular cycle or have been on the Pill for example.

“Scans are an accurate way to give you a due date,” confirms Nigel from the Society and College of Radiographers. “If the scan date differs from your LMP dates, then the scan dates will be used, but do discuss with your midwife if you are concerned. The best time to establish this date is at the scan you are offered between 11 weeks and 2 days and 14 weeks plus 1 day,”

Just how accurate (or not) can the dating scan be?

Experts say that the scan date can sometimes come out as less pregnant than suggested by your LMP. This was the case for HowieMumma.

“My 1st scan with this baby put me 1 week earlier than I thought I was. But then again with my first baby I was spot on with dates, he always measured big and he was a week overdue... these babies like to be tricky! Babies are ready when they're ready - try not to worry (easier said than done).”

But Nigel also says that the estimated (and that is all it is) date is normally accurate plus or minus about a week.

“The due date is estimated by measuring the ‘crown rump length’ of your baby which is essentially their length from head to bottom. The healthcare professionals will stick to this date as far as possible because it is then used as the baseline for growth throughout pregnancy. "

So can my due date change during my pregnancy?

While the professionals like to try and stick with the date that you’re given at your dating scan, it can and does change.

This was certainly LH86's experience. “Trust me your due date might change. Your baby's growth can slow down and then have spurts.

"I'm 16+5 and have already been given 3 due dates and its changed for a 4th time back to the 2nd estimated due date! I've not even had my 20 week scan yet. 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."

What about early scans?

Like MFMer LH86 above, some of these first EDD are derived from early pregnancy scans (pic above). These can be carried out from week 5 or 6 of pregnancy, which is a notoriously tricky time to be accurate on dates. Understandably, when it is such early days it’s easy to worry when the scan dates are different to what you were expecting.

As Loobylou77 explains, it's really common for these to change when it comes to the dating scan at around 12 weeks.

“I was measured at 6+6 (6 weeks and 6 days) when I should have been 8 weeks. Measurements at such an early stage aren't accurate which is why they wait for 12 weeks to date you.

"At my 12 week scan I was back to bang on dates for my last period and was told to ignore the previous two scans, which they said were to check for 'viability' as opposed to dates. I know it’s hard, but please try not to worry.”

AdamsMum also found the date that she was given at an early dating scan was changed when she got to her dating scan.

“All the dates I was given were wrong up until my 12 week scan - which gave my EDD as one day before the date I had calculated myself!”

Expert Jan Steward, who is director of Ultrasound Direct and Babybond, agrees that early scans carry a much greater risk of inaccuracy. “At our clinics we scan from 7 weeks but at this time due dates are not totally accurate as it is very early stages. We always recommend mums get a definitive dating scan closer to 12 weeks as this will be much more accurate.”

WoW babies confirms that it’s worth the wait for the 12 week scan.

“Definitely agree that dates from early scans are not accurate. Just half a millimetre at such an early stage can change your date by a week. Your 12-week scan will be far more accurate.

"I fell over at ‘7’ weeks by my last menstrual period (EDD 18 March) and was sent for an early scan. The sonographer then said that I was only about 4.5 weeks [EDD 2 April]. Then at the 12-week scan I got an EDD of 15 march, so that early scan was completely out.

"From then on he was smack bang on average size for babies EDD on 15 March. I wouldn’t take an early scan as read, as it’s not your official dating scan anyway.”

Does it get more accurate as you get more pregnant?

Well, you'd think so, wouldn't you. And yet, bizarrely, after your dating scan at 12 weeks, your due date can get less accurate the more pregnant you get.

Sonographer Jan Steward explains, “As your baby gets bigger all of the usual differentials start to happen between big and small babies so it’s much harder to be accurate. At around 12 weeks you can get more accurate measurements.”

What can you do if you believe your scan dates are wrong?

“If your dates are wildly out then it may mean there is an issue with your baby’s growth so you should certainly talk to your midwife or doctor,” says Jan Steward.

“You will be offered another scan if the sonographer feels there is an issue. By talking to the health care professionals you should get a clearer picture as to what is happening.”

Read more...

Can your pregnancy scan get your baby's sex wrong?
What does the size of your bump mean?
All you need to know about 3D and 4D scans

3D printers and scanners

Toggle Nav

Back

January 22, 2020

Previously, 3D printers seemed like a toy: the technology is interesting, but low accuracy and errors made it possible to produce only indicative product view. Modern 3D printers are others - such equipment is used in medicine, industry, aerospace, defense, aviation and other industries where high precision and quality parts are required. This are no longer household appliances to get acquainted with 3D printing technology, but high-grade industrial equipment of high precision. nine0003

3D scanners

3D scanner allows you to quickly examine a real object, digitize and create an accurate 3D computer model. The equipment is suitable for scanning small and complex parts, cases, medium-sized products, large objects. Scanners are distinguished by a high degree of detail, repeat in digital model surface parameters of any complexity.

The main tasks that a 3D scanner solves:

Reverse engineering. The project is created based on the finished details. The computer model can be used to development of new mechanisms, reproduce in unchanged form, refine, modernize.
Making accurate measurements. The digitized object can measure and analyze by software methods.
Quality control. 3D scanners check compliance parameters of parts to specified requirements, detect and calculate the magnitude of the deviations. In industry, volumetric scanning can be used as a replacement for the classical coordinate measuring machine. nine0020
Get ready-made drawings of a complex part without laborious parameter measurement process.
Creation of digital archives. Scanners are used for digitization of any three-dimensional objects, including jewelry ornaments, sculptures, archaeological finds.

Norgau 3D scanners

Portable hand models. Devices for fast scanning of objects without fine tuning and adjustment parameters. The technique provides high precision, can used to scan parts of any size. nine0003

Compact desktop scanners. Suitable for digitizing small objects with complex surfaces. Devices with powerful cameras work on the technology of optical triangulation with phase shift – fix the smallest details and accurately transfer them to digital model.

Stationary scanners and measuring instruments. Participate in a complex technical process, apply quality control of products on production lines, in measuring laboratories. For research uses optical and laser technologies. nine0003

Models with optical tracker. Equipment used for analysis of large-sized objects with a surface of any difficulties. The optical tracker tracks the movements of the scanner in space, takes into account movement when creating a three-dimensional model.

3D printers

3D printing is widely used in design work, designing, creating prototypes and finished parts during many industries. Depending on technology, 3D The printer layer-by-layer forms the "body" of the new part with a laser beam. The device prints flat sections of the model: liquid material or powdery material hardens at the right points, on it a new layer is applied - the product "grows". nine0059 Laser technology is used for industrial production. stereolithography (SLA, layer-by-layer curing of a liquid material) or selective laser melting (SLM, processing metal powder with an ytterbium laser).

Tasks that a 3D printer solves:

Faster development of new products. On the printer can quickly print prototypes, check parameters and test before starting serial production. nine0020
Reducing the cost of staff training. Technique completely automated, does not require staff to work with highly qualified.
Creation of finished parts in piece production. Type one part on a 3D printer faster and cheaper than develop a technical process for the production of classical methods.

Norgau 3D printers

SLA printers. Technology suitable for working with photopolymers Magna L90, Formula L1, Robusta G, Magna W120, Polypropylene-Like, Clara A, Formula W, Magna L100, Robusta LR. Photopolymers are selected according to requirements for strength, color, parameters of the finished product. AT list of offers several options for industrial SLA printers with different dimensions of the working area. The kit can order a UV oven, automatic material feeders and other equipment.

SLM printers. Alloys in powder form: stainless (17-4PH, AISI 410, AISI 304L, AISI 316L, AISI 904L), instrumental (1.2343, 1.2367, 1.2709), cobalt (CoCr), copper (CuSn6), nickel (INCONEL 625, INCONEL 718), aluminum alloys (AlSi12), titanium (Ti6Al4V, Ti6Al7Nb). Oxidation molten metal is prevented by protective gas (argon), which is fed into the working chamber. Possible additional equipment: stations for cooling and screening material, gas generator, compressor, filter cleaning system.

How to choose and buy a 3D scanner and 3D printer

Universal equipment - on one device you can produce an unlimited number of parts of different shapes and difficulties. The devices are used in industry for production of prototypes and finished products, production prototypes, piece parts, products of high complexity. 3D printing technology allows you to perform tasks that impossible to replicate on classic hardware. When choosing a technique, the average dimensions of future products are taken into account, necessary material, requirements for accuracy and speed of printing. nine0059 If you need help, call or send a request to our technical specialists [email protected] and receive detailed information about technologies, use cases. Experts will help you choose a model, talk about the differences, restrictions, methods of payment, delivery and launch of equipment.

Artec Studio 13

Creating accurate 3D models has never been easier

Autopilot has been implemented in Artec Studio. This is an advanced mode of operation that guides the user through all the steps of 3D scanning and data processing in a few simple steps. Answer a few simple questions about the object you are scanning and Artec's powerful 3D data manipulation software will select the most efficient algorithms for your data and create a highly accurate model ready for your professional applications.

Key Features:

High Accuracy - Whether you choose Autopilot or manual processing, you can be sure that the accuracy of the model will be very high.
Additional advanced settings for advanced users. Artec Studio has a set of advanced settings that provide advanced users with full control over processing processes and extensive editing options
Powerful technology to process data in seconds. nine0020
Automated functions to save time.
Ability to scan and process all data on a tablet with a portable battery.
Fully compatible with CAD, the ability to directly export the 3D model to Design X and SOLIDWORKS.
Create and process large datasets - Artec Studio is so powerful that you can process datasets up to 500 million polygons. This is ideal for large objects, as well as for creating 3D models with maximum detail. nine0020
Scanning with 3D sensors. Ideal for exploring the world of 3D scanning, Artec Studio Ultimate is also compatible with 3D sensors such as Kinect for Windows, allowing you to get professional 3D scanning skills without purchasing expensive 3D scanners.

Even new users can 3D scan black or shiny surfaces

Artec Studio 13 can now analyze the surface of your object and automatically adjust the scanner sensitivity to optimally digitize even difficult places. As a result, even inexperienced users can scan black, shiny objects or hair with ease! nine0003

Easy 3D scanning in Artec Studio

Powerful 3D creation software is essential for easy and convenient 3D scanning. The program literally controls how the scanner captures data and with what degree of accuracy. Artec Studio uses the most advanced 3D data processing algorithms that provide highly accurate results and at the same time make 3D scanning intuitive and user-friendly.

Scanning in Artec Studio is very easy thanks to the new 3D Radar mode. Artec Studio will show you that you are holding the scanner at the optimal distance by rendering real-time 3D data in green. If you move the scanner too close to the object, the image turns red, if you move it too far back, the image turns blue. Keep your data color green when scanning to make sure you get the best results.