Development of a birthweight standard and comparison with currently used standards. What is a 10th centile?

INTRODUCTION: Fetal growth charts are often used in clinical practice. It is important to understand the usefulness and the pitfalls associated with these tools. Without validation, it is difficult to ascertain if the cutoffs we intend are the ones we actually select. We developed a national standard for birthweight (BW) and compared it with other published reference values. STUDY DESIGN: Multicenter retrospective study. We collected data on live births, including first trimester ultrasound and pathology, from 23 to 42 weeks' gestational age (GA). We used a variation of the lambda (λ), mu (µ), and sigma (σ) method (LMS) to construct and smooth predicted centiles. GA data was plotted and modeled in days from 24 to 42 weeks. Resulting centiles were validated and compared with other published and widely used reference values. Data from both BW and estimated fetal weight was used to validate the model. RESULTS: Data on 661,338 births were collected from 22 institutions, including 71,515 cases with first trimester ultrasound. We excluded preterm cesarean section from analysis, because of a significant bias (up to 18%) on BW and used exclusively first trimester ultrasound dates from 34 to 42 weeks. The standard compares favorably with tables currently in use, both ultrasound and birthweight based. CONCLUSION: The use of first trimester ultrasound limits variability by minimizing some random error sources, such as data introduction and GA errors, while allowing better precision (GA in days). This results in a narrower range in the extreme centiles than other charts. Validation with estimates of fetal weight are sound in second and early third trimester fetuses, because that will be a "real world" usage of this standard. While there are similarities between our series and some international/foreign growth charts, other are unfit to characterize our population. This reinforces the need for validation of standards, and sound methodological practices when doing so.

Gestational age and fetal growth assessment among obstetricians.

OBJECTIVE: We aimed to characterize gestational age assessment and fetal growth evaluation among obstetricians. METHODS: Observational, cross-sectional study. We applied a questionnaire to obstetrics specialists and residents, during a national congress on obstetrics. RESULTS: Almost all 179 respondents correct gestational age in the first trimester by ultrasound, but 63% only if there is a difference of 2-9 days. Ultrasound at 11-13 weeks was considered more accurate than at 8-10 weeks by 81%, with a higher proportion of specialists choosing correctly the last answer (p = 0.05). One-third of the respondents did not correctly point the error associated with the ultrasound estimation of fetal weight (EFW). Of the 88% who use a growth table, only 32% were able to identify it by publication/author. Ninety-eight percent identify fetal growth restriction risk (FGR) with centiles (10th in 76%) and 73% of doctors diagnose FGR without other pathological findings (10th in 49%). 44% finds that a low EFW centile maintenance (4th to 3rd) is more worrisome than the crossing of two quartiles (75th to 24th). CONCLUSIONS: The role of ultrasound in gestational age assessment and use of EFW use for FGR classification was disparate among participants. EFW and respective centiles may be over relied upon.

Feasibility and reproducibility of transvaginal, transabdominal, and 3D volume reconstruction sonography for measurement of the corpus callosum at different gestational ages.

OBJECTIVE: To compare the feasibility and reproducibility of transvaginal and transabdominal approaches, and 3D volume reconstruction sonography for measurement of corpus callosum (CC) length at different gestational ages. METHODS: Forty-six normal fetuses were examined by 2D and 3D ultrasound at 23-25, 27-28 and 31-32 weeks of gestation. Direct mid-sagittal views were obtained by either a transabdominal and/or transvaginal approach. 3D reconstructed mid-sagittal views were obtained by 3D multiplanar manipulations and Volume Contrast Imaging in the C-plane technique (VCI-C) from volumes acquired in axial planes. RESULTS: The CC could be measured in 91% of transvaginal acquisitions, in 52% of transabdominal acquisitions, in 92% of multiplanar reconstructions, and in 86% of VCI-C reconstructions. The success rate was independent of gestational age for transvaginal acquisition and slightly dependent on gestational age for 3D reconstruction techniques. Transabdominal acquisition was dependent on gestational age and fetal presentation. Inter- and intra-observer agreement was slightly better for measurements obtained from direct mid-sagittal views with either transvaginal or transabdominal acquisition than in views obtained by volume reconstruction. The reproducibility of measurements taken in reconstructed mid-sagittal views decreased with gestational age. CONCLUSION: 3D volume reconstruction techniques allow visualization and measurement of the CC in a high percentage of cases, with good reproducibility.