Prediction of birth weight by ultrasound in Turkish population. Which formula should be used in Turkey to estimate fetal weight?

Evaluation of the accuracy of ultrasonography fetal weight estimation models; assessing regression formulae in a Turkish population

In this study, we aimed to evaluate the accuracy of fetal weight prediction, to investigate the validity of sonographic fetal anthropometric parameters in a Turkish population and to assess the most commonly used sonographic formulas for estimation of fetal birth weight. Our retrospective, cross-sectional study included 126 singleton deliveries between June 2010 and January 2011, at the Department of Obstetrics and Gynecology of the GATA Haydarpaşa Training Hospital. Ultrasonography measurement results were applied to nine different fetal weight estimation formulas. Mean error, mean absolute error, mean percentage error and mean absolute percentage error rates were calculated. Under- or overestimation rates and correlation coefficients were also calculated. Fetal biparietal diameter (BPD) and abdominal circumference (AC) were significantly correlated with the actual birth weight and the power analysis for both parameters was calculated as 81%. The highest correlation coefficients in our general population were those of the F1 (Hadlock 1) and F2 (Hadlock 2) models. The highest mean percentage error was detected on F8 (Merz 2) model. Fetal weight estimation modalities were observed to give the best results in a weight range of 3,000 and 3,500 g. Regression formulae used in our population, in general, tended to underestimate, however Hadlock 1 and 2 formulations provided the most accurate results. The Hadlock 1 formula estimated the closest to the actual birth weight in fetuses expected to be born under 3,000 g or over 3,500 g.

Does the level of amniotic fluid have an effect on the accuracy of sonographic estimated fetal weight at term?

OBJECTIVE

Controversy exists concerning the impact of amniotic fluid index (AFI) on the accuracy of sonographic estimation of fetal weight (EFW). Thus, we aimed to evaluate whether differences in AFI has an influence on the accuracy of sonographic EFW.

METHODS

All term, singleton pregnancies which underwent a sonographic EFW and measurement of AFI within a week from delivery were included. Cases were stratified into three categories according to AFI: (1) Normal AFI (51-249 mm), (2) Oligohydramnios (AFI ≤ 50 mm) and (3) Polyhydramnios (AFI ≥ 250 mm). Inaccurate EFW was defined if there was more than 15% difference between sonographic EFW and actual birthweight.

RESULTS

Overall, 1746 pregnancies were identified (1096 with normal AFI, 455 with oligohydramnios and 195 with polyhydramnios). Mean AFI was 115.8 ± 60 mm, 28.1 ± 13 mm and 293 ± 35 mm, p < 0.001, and mean sonographic EFW was 3182.5 ± 573 g, 3118.8 ± 517 g and 3713.2 ± 461 g, p < 0.001, respectively. Demographic data and gestational age at delivery were similar. Mean birthweight was 3221.7 ± 535 g, 3132.5 ± 505 g and 3654.1 ± 480 g, p < 0.001, respectively. The rate of inaccurate EFW was similar between the groups (8.4%, 8.7% and 9.7%, p = 0.19, respectively). On multivariate analysis, AFI was not associated with EFW inaccuracy (OR 1.01, 95% C.I 0.67-1.54, p = 0.93).

CONCLUSION

AFI has limited impact on the percentage of errors in sonographic fetal weight estimation a week prior delivery.

Macrosomia, top of the iceberg: the charm of underlying factors

BACKGROUND

Macrosomia is associated with childhood obesity. Gestational diabetes mellitus (GDM) is a risk factor for macrosomia. The aim of this large-scale investigation was to determine the incidence, risk factors, characteristic features, and perinatal outcome of macrosomic infants.

METHODS

This prospective study was carried out on 6385 newborns. Demographic data included maternal age, paternal age, type of delivery, sex, parity and gestational age at delivery. Anthropometric measurements were recorded. ABO/Rh typing was performed and GDM was diagnosed.

RESULTS

Out of 6385 term deliveries, 477 infants (7.47%) were macrosomic. Incidence of GDM was 0.6% and 4.8% in the control group and in macrosomic births, respectively. Incidence of GDM(+) cases was 4% among macrosomic infants weighing 4000-4500 g. GDM(+) cases were densely populated (11%) in macrosomic infants weighing ≥ 4500 g (P ≤ 0.05). Male/female ratio was significantly higher in macrosomic infants weighing ≥ 4500 g than those weighing 4000-4500 g (P ≤ 0.05). High parental age was the risk factor for GDM. Blood group A was the most frequently observed type among mothers with macrosomic infants, however, blood group O was dominant in cases with GDM. In multivariate logistic regression analysis, the male infant was the most striking infant characteristic and GDM was the most striking maternal characteristic that were significantly associated with increased odds of macrosomic birth.

CONCLUSIONS

This research reports the association between blood group system and macrosomia as well as parental age and GDM simultaneously. Our study reports a prevalence of GDM in both infants with normal birth weight and macrosomic newborns at the same time.

Sonographic fetal weight estimation: which model should be used?

OBJECTIVE

The purpose of this study was to compare the accuracy of different sonographic models for fetal weight estimation.

METHODS

We evaluated 26 different models using 3705 sonographic weight estimations performed less than 3 days before delivery. Models were ranked on the basis of systematic and random errors and were grouped according to the combination of biometric indices in each model. Cluster analysis was used to compare the accuracy of the different model groups.

RESULTS

A considerable variation in the accuracy of the different models was found. For birth weights (BWs) in the range of 1000 to 4500 g, models based on 3 or 4 fetal biometric indices were significantly more accurate than models that incorporated only 1 or 2 indices. The accuracy of weight estimation decreased at the extremes of BWs, leading to overestimation in low-BW categories as opposed to underestimation when the BW exceeded 4000 g. The precision of most models was lowest in the low-BW groups.

CONCLUSIONS

To improve the accuracy of fetal weight estimation, sonographic models that are based on 3 or 4 fetal biometric indices should be preferred. Recognizing the accuracy and the tendency for underestimation or overestimation of each of the available models is important for the judicious interpretation of fetal weight estimations, especially at the extremes of fetal weight.

New regression formulas for sonographic weight estimation within 10, 7, and 3 days of delivery

OBJECTIVES

The purpose of this study was to develop new regression formulas based on large numbers of sonographic examinations performed within 10, 7, and 3 days of delivery.

METHODS

Sonographic fetal biometric measurements and delivery ward data for an unselected population were analyzed. Multivariate linear regression models were fitted to the sonographic data to predict the actual birth weight (BW) within 10, 7, and 3 days.

RESULTS

The analyses included 6289, 5449, and 4007 patients who underwent sonographic examinations within 10, 7, and 3 days of delivery, respectively. All models yielded very high correlation coefficients (r = 0.927-0.958; R(2) = 0.859-0.918), low mean deviations between the calculated and actual BWs (6.4%-6.6% +/- 1 SD of 5.5%-5.9%), and high percentages of the calculated BW within 10% of the actual BW (78.5%-80.4%). Estimated fetal weight analyses made within 3 days of delivery yielded slightly better results than within 7 and 10 days.

CONCLUSIONS

The new regression formulas yielded overall similar results, with a small advantage for estimates calculated within 3 days of delivery. Further prospective studies are needed to compare the accuracy of these formulas with those used to date.

Sonographic estimation of fetal weight: comparison of bias, precision and consistency using 12 different formulae

OBJECTIVES

To determine the major sources of error in ultrasonographic assessment of fetal weight and whether they have changed over the last decade.

METHODS

We performed a prospective observational study in 1991 and again in 2000 of a mixed-risk pregnancy population, estimating fetal weight within 7 days of delivery. In 1991, the Rose and McCallum formula was used for 72 deliveries. Inter- and intraobserver agreement was assessed within this group. Bland-Altman measures of agreement from log data were calculated as ratios. We repeated the study in 2000 in 208 consecutive deliveries, comparing predicted and actual weights for 12 published equations using Bland-Altman and percentage error methods. We compared bias (mean percentage error), precision (SD percentage error), and their consistency across the weight ranges.

RESULTS

95% limits of agreement ranged from - 4.4% to + 3.3% for inter- and intraobserver estimates, but were - 18.0% to 24.0% for estimated and actual birth weight. There was no improvement in accuracy between 1991 and 2000. In 2000 only six of the 12 published formulae had overall bias within 7% and precision within 15%. There was greater bias and poorer precision in nearly all equations if the birth weight was < 1,000 g.

CONCLUSIONS

Observer error is a relatively minor component of the error in estimating fetal weight; error due to the equation is a larger source of error. Improvements in ultrasound technology have not improved the accuracy of estimating fetal weight. Comparison of methods of estimating fetal weight requires statistical methods that can separate out bias, precision and consistency. Estimating fetal weight in the very low birth weight infant is subject to much greater error than it is in larger babies.