This study was conducted over a 4-year period in a population of pregnant women undergoing routine second- or third-trimester ultrasound examination at 20–36 weeks' gestation as part of routine antenatal care in France.
ACTUAL FETUS SIZE BY WEEK FULL
The aims of this study were: (1) to establish French EFW reference charts and equations in full accordance with the recommended method of analysis 10, 11 and (2) to highlight the differences between EFW and birth-weight reference ranges constructed during the same study period, in the same health authority and using similar statistical methods. This highlights the need for specific reference ranges, which ideally should also be specific for gender 8 and ethnicity 9. Indeed, such a process may lead to an inaccurate assessment of fetal weight and inappropriate counseling and planned location for preterm delivery. However, in such cases, EFW should not be compared directly with the distribution of birth-weight measurements, as a large number of premature births are related to factors that affect fetal growth. It is a simple and straightforward indicator of global growth that is easy to use for doctors and easy to understand for patients. When EFW is calculated prior to delivery in order to help in decision-making, it can be compared to birth-weight reference charts and, in experienced hands, nearly 80% of EFWs are within 10% of the actual birth weight, with most of the remainder being within 20% of actual birth weight 7.ĮFW can also be used earlier in gestation to monitor fetal growth. It has an accuracy similar to that of clinical ultrasound examination for delivery at or beyond 37 weeks' gestation, whereas it is significantly superior to clinical estimates of weight for preterm birth 6. The measurement of fetal biometry in the second and third trimesters is an important part of these examinations and biometric measurements are combined routinely in order to calculate the estimated fetal weight (EFW) 5.ĮFW is a useful parameter with which to predict birth weight and outcome when it is calculated a few days before delivery.
ACTUAL FETUS SIZE BY WEEK SERIES
In a low-risk and unselected population, such screening is based mainly on a series of ultrasound examinations 1- 4. The screening and management of abnormal fetal growth, whether it be macrosomia or growth restriction, remain important objectives of prenatal care. We provide additional evidence that comparing EFW with birth-weight charts is misleading. However, before full term, birth-weight charts reflect a significant proportion of growth-restricted fetuses that deliver prematurely. EFW is computed throughout gestation based on measurements in healthy fetuses. We present new reference charts and equations for EFW. At 28–32 weeks' gestation, the 50 th centile for birth weight compared approximately with the 10 th centile for EFW. Comparison with the birth-weight chart showed that the EFW was noticeably larger at 25–36 weeks' gestation. New charts and equations for Z-score calculations at 20–36 weeks' gestation are reported. Resultsġ8 959 fetuses were included in the study. This chart was compared with that of birth weight at 25–36 weeks' gestation during the same study period and in the same health authority. We used a polynomial regression approach (mean and SD model) to compute a new reference chart for EFW. EFW was calculated based on Hadlock's formula. No data were excluded on the basis of abnormal biometry. Exclusion criteria were a known abnormal karyotype or congenital malformation and multiple pregnancy. Methodsīiometric data were obtained at 20–36 weeks' gestation from routine screening examinations spanning 4 years. To formulate reference charts and equations for estimated fetal weight (EFW) from a large sample of fetuses and to compare these charts and equations with those obtained for birth weight during the same study period and in the same single health authority.
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