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Estimation of fetal weight by ultrasound
Insights
Estimating fetal birth weight (BW) using fetal measurements like head circumference (HC) and abdominal circumference (AC) can be done with various regression equations. The most accurate BW estimates with the least error come from using both HC and AC.
Area of Science:
- Obstetrics and Gynecology
- Fetal Medicine
- Biometry
Background:
- Accurate estimation of fetal birth weight (BW) is crucial for perinatal care and management.
- Existing methods for BW estimation rely on various fetal anthropometric measurements.
- Understanding the accuracy and limitations of different estimation methods is essential.
Purpose of the Study:
- To develop and compare multiple regression equations for estimating fetal BW and log10 BW.
- To evaluate the accuracy of BW estimates derived from different combinations of fetal measurements.
- To assess the influence of fetal anthropometry on the precision of BW estimation.
Main Methods:
- Linear, multilinear, parabolic, and polynomial regression analyses were performed.
- Equations were generated using abdominal circumference (AC) alone, and in combination with head circumference (HC) and biparietal diameter (BPD).
- Accuracy was assessed by comparing estimated BW with measured BW, analyzing mean percentage deviations and variance.
Main Results:
- Multiple regression equations were generated for BW and log10 BW estimation.
- Several equations provided BW estimates with comparable mean percentage deviations.
- The smallest variance in deviations was observed when using HC and AC, particularly with multilinear regression or separate brain/somatic weight estimates.
- Head circumference (HC) was identified as a superior modulus for brain size compared to biparietal diameter (BPD).
Conclusions:
- Fetal anthropometric measurements, especially HC and AC, can accurately estimate BW using appropriate regression models.
- Multilinear regression incorporating HC and AC offers precise BW estimation with minimal error variance.
- HC is a more reliable indicator of brain size than BPD, mitigating underestimation errors in specific fetal head shapes.
- Differences in ponderal growth exist between American and South African fetal populations across the gestational range.
Abstract:
Birth weight (BW) and log10 birth weight (LBW) are expressed as linear, multilinear, parabolic, and polynomial regression functions of the abdominal circumference (AC), and combinations of fetal index measurements, namely, AC and head circumference (HC); biparietal diameter (BPD) and AC; and BPD, HC, and AC. The relationship of somatic weight and log10 somatic weight to AC was similarly determined. The analysis generated 20 equations whose accuracy in providing BW estimates is compared. Several equations provide BW estimates whose mean percentage deviations from measured BWs do not differ significantly. The deviations, however, have the smallest variance when BW is estimated from the HC and AC either by using a multilinear regression equation or by deriving separate estimates of brain and somatic weights from these index measurements. The role of individual and population differences in fetal anthropometry as causes of error in estimating BW by different methods is discussed. Because HC is a function of both BPD and occipito-frontal diameter (OFD), it is a better brain-size modulus than the commonly used BPD and avoids the errors of underestimation which occur when the BPD is unusually small in cases of dolichocephaly. A comparison of ponderal growth in American and South African fetal populations shows differences throughout most of the gestational range (26-40 wk) analyzed in this study.