A new sonographic weight formula for fetuses <or= 2500 g

PURPOSE

Birth weight is an important predictive parameter for neonatal morbidity and mortality in the small fetus. Accurate estimation of fetal weight is therefore a valuable tool for determining the further obstetric management. The majority of studies presenting new formulas have included relatively small samples with a narrow range of birth weights, mostly term fetuses. In a previous study, we evaluated several weight formulas over the whole range of birth weights and in defined subgroups. We were able to show that some regression formulas appeared to be favorable within these subgroups. Notably, the highest levels of inaccuracy were found in the group of infants with a birth weight of less than 2500 g. This led us to hypothesize that a formula based on the lower birth weight group might increase the accuracy of weight estimation. The aim of the present study was therefore to develop a new specific formula for estimating weight in fetuses less than or equal to 2500 g and to compare the new regression formula with commonly used weight equations.

MATERIALS AND METHODS

This study included 260 pregnancies. The inclusion criteria were a singleton pregnancy; birth weight equal to or less than 2500 g; an ultrasound examination with complete biometric parameters within 7 days prior to delivery; and an absence of structural or chromosomal malformations. The data for the first 130 newborns were used to develop a new formula. The remaining 130 infants were used to evaluate the new regression formula and to compare it to commonly used weight equations. Stepwise regression analysis was carried out with the birth weight as the dependent variable and biometric parameters as independent parameters to obtain the best-fit formula.

RESULTS

The mean absolute percentage error for the new formula was 7.71 %. Compared to the other formulas, it generated the highest intraclass correlation coefficient. By the limits of agreement, the new formula demonstrated only a slight tendency towards underestimating fetal weight, and it provided the smallest range of all weight equations.

CONCLUSION

With proper application, our new formula can improve the accuracy of fetal weight estimation.

Three-dimensional power Doppler sonography of the (sub)endometrium and angiogenic cytokine concentrations

The aim of this study was to determine the correlation between three-dimensional power Doppler sonography (3D-PDS) of the (sub)endometrium and concentrations of angiogenic cytokines in patients attending an IVF programme. A total of 42 patients was included in a prospective, non-randomized clinical study. 3D-PDS of the (sub)endometrium was performed on the day of oocyte aspiration, with and without contrast agent. Quantitative assessment included the following 3D Doppler parameters: vascularization index, flow intensity, and vascularization flow index. On the same day, concentrations of oestradiol (serum only), vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF) 1, IGF-binding protein 3 (IGFBP-3) and leptin were determined in the serum and in the follicular fluid. All 3D-PDS indices were significantly higher with contrast enhancement (P < 0.05). Follicular fluid concentrations of VEGF and IGFBP-3, as well as serum concentrations of leptin, showed significant P-values when correlated with (sub)endometrial Doppler indices. A weak linear dependency appeared between flow intensity and VEGF and leptin. Furthermore, weak dependencies were apparent between 3D Doppler parameters and high follicular fluid concentrations of VEGF and IGFBP-3. It is concluded that there is only little evidence for an association between (sub)endometrial Doppler indices as assessed by 3D-PDS and concentrations of angiogenic cytokines.

Weight estimation by three-dimensional ultrasound imaging in the small fetus

OBJECTIVES

To improve birth weight estimation in fetuses weighing <or= 1600 g at birth by deriving a new formula including measurements obtained using three-dimensional (3D) sonography.

METHODS

In a prospective cohort study, biometric data of 150 singleton fetuses weighing <or= 1600 g at birth were obtained by sonographic examination within 1 week before delivery. Exclusion criteria were multiple pregnancy, intrauterine death as well as major structural or chromosomal anomalies. A new formula was derived using our data, and was then compared with currently available equations for estimating weight in the preterm fetus.

RESULTS

Different statistical estimation strategies were pursued. Gradient boosting with component- wise smoothing splines achieved the best results. The resulting new formula (estimated fetal weight = 656.41 + 1.8321 x volABDO + 31.1981 x HC + 5.7787 x volFEM + 73.5214 x FL + 8.3009 x AC - 449.8863 x BPD + 32.5340 x BPD(2), where volABDO is abdominal volume determined by 3D volumetry, HC is head circumference, volFEM is thigh volume determined by 3D volumetry, FL is femur length and BPD is biparietal diameter) proved to be superior to established equations in terms of mean squared prediction errors, signed percentage errors and absolute percentage errors.

CONCLUSIONS

Our new formula is relatively easy to use and needs no adjustment to weight percentiles or to fetal lie. In fetuses weighing <or= 1600 g at birth it is superior to weight estimation by traditional formulae using two-dimensional measurements.

How good is fetal weight estimation using volumetric methods?

PURPOSE

Birth weight is an important predictive parameter for neonatal morbidity and mortality, and accurate estimation of fetal weight is therefore a valuable tool for determining the further obstetric management. Many sonographic weight formulas have been introduced. Most of these widely accepted formulas were derived from non-linear regression analysis. Only few formulas have been constructed using other methods, such as the physically based volumetric method based on routine two-dimensional biometric parameters in the fetus. The rationale for calculating fetal weight from volumetric measurements was that weight should to be directly proportional to fetal volume. In a recent review by Dudley, this method was considered to have some advantages in comparison with conventional regression formulas. However, to the best of our knowledge, none of the published volumetric formulas has ever been evaluated in a large population of fetuses. The aim of this study was to compare the volumetry-based formulas with widely accepted weight equations derived from regression analysis. We evaluated weight equations over the whole weight range and in specific weight groups in order to find out whether some equations were preferable in the groups tested.

MATERIALS AND METHODS

3975 pregnancies were included in order to evaluate four conventional formulas and four formulas based on volumetric models. The inclusion criteria were a singleton pregnancy, ultrasound examination with complete biometric parameters within 7 days before delivery, and an absence of structural or chromosomal malformations. The equations were compared over the whole weight range and in specific weight groups.

RESULTS

Over the whole weight range, no single formula was able to offer a substantial advantage. In the small fetus, the Hadlock formula was preferable due to its low level of systematic error. For mid-sized fetuses, the Schild formula should be considered. In macrosomic fetuses, all formulas tended to underestimate the actual birth weight. Here, the best accuracy was achieved using the Merz formula.

CONCLUSION

Neither a volumetric formula nor a conventional formula proved to be superior over the whole weight range. Within specific weight groups, some formulas showed improved accuracy. However, new approaches such as three-dimensional ultrasonography need to be pursued further in order to achieve better results in fetal weight estimation.

Fetal weight estimation by ultrasound: comparison of 11 different formulae and examiners with differing skill levels

PURPOSE

Fetal weight is an important predictive parameter of neonatal morbidity and mortality. Precise estimation of fetal weight is therefore a valuable item of information for further prenatal and obstetric management. Many regression formulae for sonographic fetal weight estimation have been published during the last 30 years, which, unfortunately, generally show poor rates of accuracy. The aim of this study was to compare commonly used formulae in different birth weight groups in order to assess whether any of the formulae are more or less favourable. The second purpose was to estimate the role of examiners on the accuracy of fetal weight estimation.

MATERIALS AND METHODS

11 different formulae were evaluated in a group of 1941 pregnancies. Each fetus underwent ultrasound examination with complete biometric parameters within seven days before delivery. The assessment was carried out by either experienced or inexperienced sonographers.

RESULTS

Over the whole weight range and in the subgroup of newborns with a birth weight less than 2500 g (n = 160), two Hadlock regression formulae (including abdominal circumference, femur length, head circumference, biparietal diameter, and abdominal circumference, femur length, biparietal diameter, respectively) showed the best levels of accuracy. Infants with a birth weight between 2500 and 3999 g (n = 1570) were best estimated using the gender-specific Schild formula. Macrosomic newborns (n = 211) were best evaluated using Merz's regression formula. The more skilled sonographers were able to achieve much higher intraclass correlation coefficients for all formulae.

CONCLUSION

Some regression formulae appear to be favourable within defined weight ranges. Accuracy of the formulae, however, is still unsatisfactory, and new formulae focusing on specific weight ranges (e. g., macrosomic fetuses) are needed. In addition, experience in obstetric ultrasound improves accuracy of fetal weight estimation.

Specific weight formula for fetuses with abdominal wall defects

OBJECTIVES

To develop and to evaluate a specific sonographic weight formula for fetuses with abdominal wall defects.

METHODS

For formula finding, 380 preterm singleton pregnancies without fetal anomalies were included. Ultrasound examinations with complete biometric parameters were performed within 7 days before delivery. Stepwise regression analysis was carried out with birth weight as the dependent variable and sonographic parameters (abdominal measurements not included) as independent variables to obtain the best-fit formula. The new equation was evaluated in a group of 97 fetuses with either gastroschisis or omphalocele.

RESULTS

In the evaluation group, the mean (SD) percentage error of the new equation was -0.84 (12.03), showing no systematic bias. The mean absolute percentage error was 9.29. The new specific method provided significantly greater accuracy than commonly used formulae.

CONCLUSIONS

This specific weight formula for fetuses with abdominal wall defects is an accurate method of estimating fetal weight.

[Eye disease and mode of delivery]

Many ophthalmologists and obstetricians recommend either an assisted vaginal delivery with forceps or vacuum extraction or a Caesarean section in cases of pre-existing eye diseases such as severe myopia, retinal detachment, diabetic retinopathy, or glaucoma. These recommendations, however, are not evidence-based. None of the published trials have reported any retinal changes after vaginal delivery. In general, eye disease is not an indication for an instrumental or operative delivery provided that regular eye examinations (once each trimester) have been performed.