Dating ultrasound vs lmp

We used ultrasound to scan 17, nonselected singleton pregnancies at completed weeks. The last menstrual period LMP was considered certain in 13, and uncertain in cases. The duration of pregnancy from the scan to the day of spontaneous delivery was predicted by crown-rump length, biparietal diameter BPD , and femur length FL using linear regression models, and the results were compared with estimates based on LMP. At all gestational ages, ultrasound was superior to certain LMP in predicting the day of delivery by at least 1.


  1. Methods for Estimating the Due Date - ACOG.
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Just wondering what other people's thoughts and experiences are. This means I'm now 13w3 days instead of in the 12 week so that makes me happy if it's true lol. I guess yours was very confident. Your baby will most likely be fine and just as healthy. I'm sure if you wanted see what presents itself closer to your due date you can even push a scheduled c out a few days esp if this is your first. Dating scans are more accurate since you can ovulate early or later. Based off of LMP with my daughter I would have been due February 12th dating scan changed it to February 5th a week before.

I ended up delivering at 41 weeks and it was definitely correct she was 8lbs and 20inches long and she also passed merconium I trust technology more than a day that I try to remember. Most doctors will let you go overdue for a week or two anyway. With this one I will go early or on my due date because of the fact that my daughter passed merconium and we are going to try and avoid that this time. Based off my LMP I should be 14w1d, but when I had my dating scan, the measured the baby an entire week back.

My DR did change my due date so I went from the 6th to 13th.

Ultrasound VS Lmp dating

He also threw in there that the baby could have a growth spurt though and it's really not a big deal. With my first 3 pregnancies my baby's measured right on track with my lmp at 12 and 20 week ultrasound. I'm now on my 4 pregnancy and I had a ultrasound on Friday when I thought I was 12 weeks and 2 days. My baby measured at 13 weeks and 3 days so my dr changed my due date.


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  • 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. 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.

    Dating your Pregnancy | The MotHERS Program™

    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.

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    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.