New charts for ultrasound dating of pregnancy and assessment of fetal growth

New charts for ultrasound dating of pregnancy and assessment of fetal growth: longitudinal data from a population‐based cohort study.
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Linear array image of the fetal femur. The femur length is measured between the arrows. Biologic variation may lead to inaccuracies of FL measurements in a manner similar to that of the other fetal growth parameters. In addition, several technical factors are potential sources of error in the measurement of the femur. Linear-array ultrasound imaging provides more accurate measurements of FL. In addition, FL measurements obtained in the axial plane parallel to the ultrasonic beam have less mean absolute error than those obtained in the lateral plane, perpendicular to the ultrasonic beam 1.

Artifactual bowing of the femur may also occur on ultrasound imaging and lead to a shortened FL measurement. The distal femoral epiphysis becomes echogenic in the third trimester and is separated from the distal end of the diaphysis, the osseous portion of the shaft.

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Inclusion of the distal epiphysis will falsely overestimate FL. Gestational age assessment by FL is particularly useful when head measurement is difficult to obtain due to fetal position.


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The accuracy of a single parameter is dependent on the gestational age at the time of ultrasound examination Table 9. Several methods have been employed to improve the accuracy of gestational age assessment compared with the use of a single parameter. Two of these methods, growth-adjusted sonographic age 79 and averaging multiple parameters 80 , 81 are discussed.

Several principles are important to remember when assessing gestational age by ultrasound:. Gestational age can be more accurately predicted by obtaining paired BPD measurements the first from 20 to 26 weeks' gestation and the second from 31 to 33 weeks' gestation and assigning gestational age by a method developed by Sabbagha and co-workers 79 known as growth-adjusted sonographic age GASA.

Paired BPD measurements obtained at different gestational ages allows categorization of the specific cephalic growth pattern. The first measurement should be obtained between 20 and 26 weeks' gestation, and the second measurement should be obtained between 30 and 33 weeks' gestation. The first BPD measurement will not distinguish the fetus with large, average, or small BPD growth, and, therefore, the fetus is assigned a mean gestational age based on an assumed average BPD growth pattern.

The second BPD measurement identifies the specific type of growth pattern. For example, in the fetus with average growth the second BPD measurement will fall between the 10th and 90th percentiles, confirming the gestational age assignment from the first BPD measurement. In contrast, BPD growth in the small-for-gestational age fetus will follow a slow growth pattern and the second BPD measurement will be less than or equal to the 10th percentile for the gestational age assigned by the first BPD. Since the first BPD measurement failed to recognize the small growth pattern and, therefore, underestimated gestational age, the second measurement allows the gestational age assessment to be adjusted based on the BPD growth pattern.

Assessment of Gestational Age by Ultrasound

Such a fetus with a slowed growth pattern would have the gestational age advanced by 1 week at the time of the second BPD measurement. Similarly, dates in the large-for-gestational age fetus may be adjusted by GASA at the time of the second BPD measurement, decreasing gestational age assignment by 1 week if the BPD measurement is greater than or equal to the 90th percentile Fig. Fetal growth patterns from second trimester BPD of 5.

The first BPD of 5. A second BPD measurement 10 weeks later will identify the fetus as large 90 th percentile , average between 10 th and 90 th percentiles , or small 10 th percentile and lead to a closer assessment of fetal age. Predictive of three fetal growth patterns leading to a closer assessment of gestational age and neonatal weight.

Am J Obstet Gynecol Reprinted with permission of C. The method of GASA has not been used when the first BPD measurement is obtained prior to 20 weeks' gestation; therefore, it is best to confine the use of GASA to pregnancies in which serial ultrasound studies are contemplated and the first measurement is obtained between 20 and 26 weeks' gestation. Multiple Fetal Growth Parameters Hadlock and co-workers 80 , 81 combined several measurements in an effort to increase the accuracy of gestational age assessment.


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  • Assessment of Gestational Age by Ultrasound | GLOWM.
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The rationale for employing multiple parameters for fetal dating is that when two or more parameters predict the same end point, the probability of correctly predicting that end point is increased. The use of multiple parameters improved the accuracy of gestational age assessment compared with any single parameter Table However, if gestational age estimates of the various parameters are quite different, averaging multiple parameters will decrease the accuracy of the best predictor s.

Averaging of fetal growth parameters should be avoided when certain conditions are suspected, such as fetal macrosomia, intrauterine growth retardation both symmetric and asymmetric , and congenital anomalies skeletal dysplasias, hydrocephalus, and others. Multiple Gestations The detection of multiple gestations is important since multiple gestations are at greater risk for many complications, particularly fetal growth retardation.

Fetal biometric data are available for twin gestations 81 , 82 , 83 , 84 , 85 ; however, triplet and quadruplet pregnancies have not been adequately studied owing to their infrequent occurrence. In general, ultrasound-derived fetal dating tables obtained for singleton pregnancies can be used accurately for twin pregnancies until approximately 30 weeks' gestation.

Grumbach and co-workers 86 have suggested that the femur continues to grow normally throughout pregnancy in twin gestations, while the head BPD and HC and abdominal AC growth rates decrease in the last 10 weeks of pregnancy. Although further studies are required to confirm these findings, this study suggests that FL measurement may be a more reliable parameter to use for gestational age assessment in twin gestations during the third trimester.

Gestational age estimations in twin pregnancies prior to 30 weeks' gestation should be performed in a similar manner to that for singleton pregnancies. A simple, but uniform approach to the evaluation of gestational age should be performed in all fetuses. The ultrasound assessment of fetal age is based on the earliest ultrasound study, provided the measurement is technically adequate.

Early in gestation fetal measurements have the least variability and, therefore, are most likely to predict fetal age. In the first trimester, the CRL measurement is used to estimate gestational age, whereas in the second and third trimesters fetal head BPD and HC , body AC , and extremity FL measurements are used to assess gestational age. The following guidelines are recommended for the assessment of gestational age:. Use of the multiple parameters method of assessing gestational age is valid when the gestational age estimates of the various ultrasound parameters are similar.

If the gestational age estimates of one or several parameters is greater than 2 weeks different than the estimates of the other parameters, either the abnormal ultrasound parameters should be excluded or a different method should be used to estimate gestational age. When the various ultrasound parameters predict different gestational ages the fetus should be further evaluated to explain these differences.

Methods for Estimating the Due Date

For example, an abnormally small FL measurement may suggest short-limb defects, a large BPD may be secondary to hydrocephalus, and an abnormally small or large AC measurement may suggest asymmetric intrauterine growth retardation or macrosomia, respectively. In the instance of an abnormal cephalic index, the HC should be used to estimate gestational age, rather than the BPD measurement. In conclusion, assessment of gestational age is fundamental to obstetric care and should be a carefully thought-out process. Assessment should depend on history and physical examination, as well as ultrasound evaluation.

Liquor amnii in the management of the pregnancy complicated by rhesus sensitization. Goldenberg RL, Nelson K: Iatrogenic respiratory distress syndrome. Neonatal respiratory distress following elective delivery: Routine ultrasound screening for the prediction of gestational age.

Assessment of fetal maturity and dysmaturity. Ultrasound in managing the high-risk pregnancy. In Spellacy WD ed: Management of the High-Risk Pregnancy, pp — Baltimore, University Park Press, Clinical estimation of gestational age: Rules for avoiding preterm delivery. Ultrasound scanning of ovaries to detect ovulation in women.

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Methods for Estimating the Due Date - ACOG

Variability of ovarian follicular growth in natural menstrual cycles. Growth and development of the human fetus prior to the twentieth week of gestation. Length and depth of the uterus and the diameter of the gestation sac in normal gravidas during early pregnancy. Acta Obstet Gynecol Scand 50 suppl: Br J Obstet Gynaecol The ultrasonic measurement of fetal crown-rump length as a method of assessing gestational age. Underestimation of gestational age by conventional crown-rump length growth curves.

The prediction of fetal maturity by ultrasonic measurement of the biparietal diameter.

What is Fetal Wellbeing Assessment?

J Obstet Gynaecol Br Commonw Sonar BPD and fetal age: Definition of the relationship. Campbell S, Newman GB: Growth of the fetal biparietal diameter during normal pregnancy. Sabbagha RE, Hughey M: Standardization of sonar cephalometry and gestational age. Analysis of percentile growth differences in two normal populations using same methodology. Hughey M, Sabbagha RE: Cephalometry by real time imaging: Am J Obstct Gynecol Analysis of biparietal diameter as an accurate indicator of gestational age.

J Clin Ultrasound 8: A critical reevaluation of the relation to menstrual age by means of realtime ultrasound.

Detailed screening for fetal anomalies and cardiac defects at the week scan. The Generation R Study: Determinants and consequences of discrepancies in menstrual and ultrasonographic gestational age estimates. Ethnic differences in prenatal growth and the association with maternal and fetal characteristics. Management of preterm infants with intrauterine growth restriction. Customized fetal growth standards: First trimester origins of fetal growth impairment.

Gordon C S Smith. 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.