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. 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:. 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. 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. Accordingly, in creating recommendations and the associated summary table, single-point cutoffs were chosen based on expert review. 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—4. 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.
Experts recommend having your first scan when you are six weeks pregnant. TVS is the. Miscarriage is a common complication of pregnancy affecting up to one in four clinical pregnancies. Ultrasound is the diagnostic tool of choice.
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. 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. 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.
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. Congratulations on your pregnancy! Trying to Conceive Pregnant. Br J Obstet Gynaecol ; For example, for a day-5 embryo, the EDD would be days from the embryo replacement date. He could throw everything he's got on - is. Indeed, because a large window of the long bones.
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. Please understand that you are not alone and your doctor is always there to answer your queries. The first trimester scan is of utmost importance as it helps your doctor to understand a lot about your growing baby — if the little one is in the right position inside the uterus, if he is growing well or not, hear his heartbeat, calculate your due date etc. Generally, two scans are done during the first trimester — a dating and viability scan, between six and nine weeks and an early morphology scan NT scan between eleven and thirteen weeks.
However, sometimes it may be earlier and sometimes later as well. It is normal to be unable to detect a heartbeat until closer to 7 or 8 weeks. The list of scans to be done during pregnancy usually varies from person to person. A low-risk pregnancy may have four or five scans during the entire pregnancy. Here is a list of the routine scans:. Right from the time you conceive your baby till the time of delivery, your growing baby goes through several stages of development from a fertilized egg to a garlic bulb size baby in the womb before he or she is born.
The early scan can reveal some fantastic things about fetal development in the womb. This is the gestation sac.
The expert can identify the location of the sac to determine whether it is in your uterus or not. This is to make sure that there is no sign of an ectopic pregnancy. She may ask you to come back for another scan in one or two weeks. At this time, the head to bottom length of the embryo is measured to calculate your due date.
It will grow rapidly in the coming weeks. In the next few weeks,the doctor may advise you for an early morphology scan NT scan. The doctor will then take note of your entire health history and perform a full physical and pelvic exam. Usually at this time, your doctor may perform an ultrasound scan to confirm the pregnancy. The ultrasound scan is one of the routine tests conducted during pregnancy which determines the normal development of your baby and detects any fetal abnormalities as well.