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  1. Gestational age - Wikipedia
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  4. Methods for Estimating the Due Date

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.

Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11, 15— 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.

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Gestational age - Wikipedia

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.

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.


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  • Estimated date of delivery - Wikipedia.

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.

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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.

The estimated date of delivery EDD , also known as expected date of confinement [1] , and estimated due date or simply due date , is a term describing the estimated delivery date for a pregnant woman. Confinement is a traditional term referring to the period of pregnancy when an upper-class, noble, or royal woman would withdraw from society in medieval and tudor times be confined to their rooms with midwives, ladies-in-waiting and female family members only to attend them. Except in threatened pregnancies for example, in pre-eclampsia , "lying-in" or bedrest is no longer a part of antenatal care.

According to American Congress of Obstetricians and Gynecologists , the main methods to calculate gestational age are: Childbirth on average occurs at a gestational age of days 40 weeks , which is therefore often used as a standard estimation for individual pregnancies. There is in any case considerable variation among individual pregnancies. Given that these gestation lengths are only estimates of an average, it is helpful to consider gestation time as a range of dates rather than as a single "due date".

The median is merely a guideline for the day at which half of all births occur earlier, and half of all births occur later. Births rarely occur on a due date, but they are clustered around due dates. Naegele's rule is a standard way of calculating the due date for a pregnancy when assuming a gestational age of days at childbirth.

The rule estimates the expected date of delivery EDD by adding a year, subtracting three months, and adding seven days to the origin of gestational age. The result is approximately days 40 weeks from the start of the last menstrual period. Another method is by adding 9 months and 7 days to the first day of the last menstrual period. Naegele's rule is named after Franz Karl Naegele — , the German obstetrician who devised the rule.

Gestational age

In , Naegele became ordinary professor and director of the lying-in hospital in Heidelberg. Also, preexisting maternal medical conditions with genetic component, e. Parental ancestral background race also plays a role in pregnancy duration. Gestational age at birth is on average shortened by various pregnancy aspects: From Wikipedia, the free encyclopedia. Measure of the age of a pregnancy. By gestational sac diameter.

By crown-rump length CRL. Estimated date of delivery. A comparison between age assessed from oocyte retrieval, crown-rump length and biparietal diameter". Ultrasound in Obstetrics and Gynecology. An International Journal of Obstetrics and Gynaecology.

Methods for Estimating the Due Date

The Rule of Eights Hunter, L. J Obstet Gynecol Neonatal Nurs. Paediatric and Perinatal Epidemiology. Clinically Oriented Embryology , p. Clinical Management Guidelines for Obstetrcian-Gynecologists: Number 38, September Perinatal care at the threshold of viability". What are the chances that my baby will survive?. Journal of Child Neurology. Regional Differences and Measurement Issues". Population and Development Review. Perinatal statistics series no. Retrieved 4 July Archived from the original on 5 November The Journal of Pediatrics.


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