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. TABLE Obstet Gynecol in press. Reprinted with permission of American College of Obstetricians and Gynecologists.
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.
Reprinted with permission of C. Mosby, St. 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.
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.
Radiology , 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:. If menstrual dates are unknown, or the difference between menstrual dates and the mean gestational age predicted by single or multiple parameters is greater than the range of error of these measurements, fetal age should be established using the best ultrasound predictors either single or multiple parameters or GASA method.
In the third trimester, gestational age assessment is particularly problematic. In the pregnancy with unknown menstrual dates or a discrepancy between menstrual dates and mean gestational age predicted by multiple parameters of more than 3 weeks, fetal age should be estimated by the multiple parameters method.
However, the potential error of this method in the third trimester of pregnancy may not be acceptable. Obstetric management must appreciate this potential for error. 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. 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.
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Statistical analysis. Research conduct, Manuscript writing. Correspondence to Laura Detti. The original online version of this Article was revised: The original version of this Article contained an error in the spelling of the author Patricia J.
Goedecke which was incorrectly given as Patricia J. Reprints and Permissions. Early pregnancy ultrasound measurements and prediction of first trimester pregnancy loss: A logistic model. Sci Rep 10, Download citation. Received : 19 August Accepted : 10 January Published : 31 January Anyone you share the following link with will be able to read this content:.
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Advanced search. Skip to main content Thank you for visiting nature. Download PDF. Subjects Computational biology and bioinformatics Outcomes research. This article has been updated. Abstract Our objective was to prospectively validate the use of gestational sac GS , yolk sac YS diameter, crown-rump length CRL , and embryonal heart rate HR dimensions to identify early pregnancy loss.
Materials and Methods This was a prospective cohort study. Figure 1. Full size image. Table 1 Demographics of the patient population divided by pregnancies that resulted in a first trimester loss and those that progressed beyond the first trimester continuing pregnancy.
Full size table. Results Of the pregnancies included in this study, Figure 2.
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