Crown rump length pregnancy dating

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Methods for Estimating the Due Date

Conclusion Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. Fetal Imaging Workshop Invited Participants. A comparison of recalled date of last menstrual period with prospectively recorded dates. J Womens Health Larchmt ; Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol ; Last menstrual period versus ultrasound for pregnancy dating. Int J Gynaecol Obstet ; First trimester ultrasound screening is effective in reducing postterm labor induction rates: Ultrasound for fetal assessment in early pregnancy.

Cochrane Database of Systematic Reviews , Issue 7. Predicting delivery date by ultrasound and last menstrual period in early gestation. New charts for ultrasound dating of pregnancy and assessment of fetal growth: Ultrasound Obstet Gynecol ; First- and second-trimester ultrasound assessment of gestational age.

Assessment of Gestational Age by Ultrasound

First- vs second-trimester ultrasound: Br J Obstet Gynaecol ; Gestational age in pregnancies conceived after in vitro fertilization: Ultrasound dating at 12—14 weeks of gestation. A prospective cross-validation of established dating formulae in in-vitro fertilized pregnancies.

Methods for Estimating the Due Date - ACOG

Accuracy of gestational age estimation by means of fetal crown—rump length measurement. Estimation of gestational age by transvaginal sonographic measurement of greatest embryonic length in dated human embryos. Ultrasound Obstet Gynecol ;4: Underestimation of gestational age by conventional crown—rump length dating curves. New crown—rump length curve based on over pregnancies. Standardization of sonar cephalometry and gestational age.

Sonographic prediction of gestational age: Measurement of the AC is performed in the same manner as that of the HC, that is, by 1 tracing the outer perimeter of the AC by the trackball on the ultrasonic equipment or by digitizer or 2 the same equation as for HC using transverse and anteroposterior diameters of the fetal abdomen.

Biologic variation and technical factors may contribute to the inaccuracy of AC measurements in a manner similar to that previously described for bi-parietal diameters. Of particular note, the abdominal circumference is the growth parameter most commonly affected in pregnancies complicated by abnormal fetal growth patterns.

Variation in AC measurements in macrosomic and growth-retarded fetuses is due to differences in liver size and width of subcutaneous tissue in these two types of abnormal growth patterns. Thus, estimation of gestational age by AC will lead to inaccuracies in fetuses displaying either of these growth patterns. Transaxial image of the upper fetal abdomen. Ultrasound image with anteroposterior solid arrows and transverse open arrows diameter measurements. The abdominal circumference may be calculated using these diameters or measured directly. Diagram of the transaxial ultrasound image of the fetal abdomen at the level of the abdominal circumference measurement with fetal spine curved arrow , the umbilical portion of the left portal vein solid arrow , and fetal stomach open arrow.

All the fetal long bones can be adequately examined and measured by ultrasound; however, the femur is the largest of the long bones, least moveable, and easiest to image. The femur may be adequately visualized from 14 weeks' gestation until delivery. The femoral neck and both proximal and distal epiphyseal cartilages are excluded from the measurement. Femur length FL measurements may be used to accurately predict gestational age between 14 weeks' gestation and term Table 8. Although there is controversy regarding the accuracy of the FL prior to 26 weeks' gestation, 38 , 39 the accuracy of gestational age prediction based on FL is greatest in the second trimester and least near term.

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.

Crown-rump length

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. 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:.

Pregnancy dating by fetal crown-rump length: a systematic review of charts.

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. 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.

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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.

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.

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