Ultrasonic estimation of fetal weight at term: An evaluation of eight formulae

Comparing Fetal Ultrasound Biometric Measurements to Neonatal Anthropometry at the Extremes of Birthweight

OBJECTIVE

 Error in birthweight prediction by sonographic estimated fetal weight (EFW) has clinical implications, such as avoidable cesarean or misclassification of fetal risk in labor. We aimed to evaluate optimal timing of ultrasound and which fetal measurements contribute to error in fetal ultrasound estimations of birth size at the extremes of birthweight.

STUDY DESIGN

 We compared differences in head circumference (HC), abdominal circumference (AC), femur length, and EFW between ultrasound and corresponding birth measurements within 14 (n = 1,290) and 7 (n = 617) days of birth for small- (SGA, <10th percentile), appropriate- (AGA, 10th-90th), and large-for-gestational age (LGA, >90th) newborns.

RESULTS

 Average differences between EFW and birthweight for SGA neonates were: -40.2 g (confidence interval [CI]: -82.1, 1.6) at 14 days versus 13.6 g (CI: -52.4, 79.7) at 7 days; for AGA, -122.4 g (-139.6, -105.1) at 14 days versus -27.2 g (-50.4, -4.0) at 7 days; and for LGA, -242.8 g (-306.5, -179.1) at 14 days versus -72.1 g (-152.0, 7.9) at 7 days. Differences between fetal and neonatal HC were larger at 14 versus 7 days, and similar to patterns for EFW and birthweight, differences were the largest for LGA at both intervals. In contrast, differences between fetal and neonatal AC were larger at 7 versus 14 days, suggesting larger error in AC estimation closer to birth.

CONCLUSION

 Using a standardized ultrasound protocol, SGA neonates had ultrasound measurements closer to actual birth measurements compared with AGA or LGA neonates. LGA neonates had the largest differences between fetal and neonatal size, with measurements 14 days from delivery showing 3- to 4-fold greater differences from birthweight. Differences in EFW and birthweight may not be explained by a single fetal measurement; whether estimation may be improved by incorporation of other knowable factors should be evaluated in future research.

KEY POINTS

· Ultrasound measurements may be inadequate to predict neonatal size at birth.. · Birthweight estimation error is higher for neonates >90th percentile.. · There is higher error in AC closer to birth..

Accuracy of Estimated Fetal Weight by Ultrasound Versus Leopold Maneuver

ABSTRACT

Estimated fetal weight (EFW) is frequently used for clinical decision-making in obstetrics. The goals of this study were to determine the accuracy of EFW assessments by Leopold and ultrasound and to investigate any associations with maternal characteristics. Postgraduate years 1 and 2 obstetrics and gynecology resident physicians from Harbor-UCLA Medical Center from 2014 to 2020 performed EFW assessments on 10 preterm (<37 weeks' gestational age) fetuses by ultrasound biometry and 10 full-term (≥37 weeks' gestational age) fetuses by ultrasound biometry and Leopold maneuver. Assessments were included if the patients delivered within 2 weeks of the assessments. One thousand six hundred ninety-seven EFW assessments on 1183 patients performed by 33 residents were analyzed; 72.6% of sonographic full-term EFWs, 69% of Leopold full-term EFWs, and 61.5% of sonographic preterm EFWs were within 10% of the neonatal birth weight (BW). The lowest estimation error in our study occurred when actual BW was 3600 to 3700 g. After adjusting for BW, residents were found to have lower accuracy when the mother had a higher body mass index (BMI) for full-term estimation methods (Leopold and ultrasound, β = 0.13 and 0.12, P = 0.001 and 0.002, respectively). Maternal BMI was not related to estimation error for preterm fetuses ( β = 0.01, P = 0.75). Clinical and sonographic EFW assessments performed by obstetrics and gynecology junior residents are within 10% of neonatal BW much of the time. In our cohort, they tended to overestimate EFWs of lower-BW infants and underestimate EFWs of higher-BW infants. Accuracy of full-term EFW assessments seems to decrease with increasing maternal BMI.

The choice of reference chart affects the strength of the association between malaria in pregnancy and small for gestational age: an individual participant data meta-analysis comparing the Intergrowth-21 with a Tanzanian birthweight chart

BACKGROUND

The prevalence of small for gestational age (SGA) may vary depending on the chosen weight-for-gestational-age reference chart. An individual participant data meta-analysis was conducted to assess the implications of using a local reference (STOPPAM) instead of a universal reference (Intergrowth-21) on the association between malaria in pregnancy and SGA.

METHODS

Individual participant data of 6,236 newborns were pooled from seven conveniently identified studies conducted in Tanzania and Malawi from 2003-2018 with data on malaria in pregnancy, birthweight, and ultrasound estimated gestational age. Mixed-effects regression models were used to compare the association between malaria in pregnancy and SGA when using the STOPPAM and the Intergrowth-21 references, respectively.

RESULTS

The 10th percentile for birthweights-for-gestational age was lower for STOPPAM than for Intergrowth-21, leading to a prevalence of SGA_STOPPAM of 14.2% and SGA_IG21 of 18.0%, p < 0.001. The association between malaria in pregnancy and SGA was stronger for STOPPAM (adjusted odds ratio (aOR) 1.30 [1.09-1.56], p < 0.01) than for Intergrowth-21 (aOR 1.19 [1.00-1.40], p = 0.04), particularly among paucigravidae (SGA_STOPPAM aOR 1.36 [1.09-1.71], p < 0.01 vs SGA_IG21 aOR 1.21 [0.97-1.50], p = 0.08).

CONCLUSIONS

The prevalence of SGA may be overestimated and the impact of malaria in pregnancy underestimated when using Intergrowth-21. Comparing local reference charts to global references when assessing and interpreting the impact of malaria in pregnancy may be appropriate.

Effective Macrosomia Prediction Using Random Forest Algorithm

(1) Background: Macrosomia is prevalent in China and worldwide. The current method of predicting macrosomia is ultrasonography. We aimed to develop new predictive models for recognizing macrosomia using a random forest model to improve the sensitivity and specificity of macrosomia prediction; (2) Methods: Based on the Shandong Multi-Center Healthcare Big Data Platform, we collected the prenatal examination and delivery data from June 2017 to May 2018 in Jinan, including the macrosomia and normal-weight newborns. We constructed a random forest model and a logistic regression model for predicting macrosomia. We compared the validity and predictive value of these two methods and the traditional method; (3) Results: 405 macrosomia cases and 3855 normal-weight newborns fit the selection criteria and 405 pairs of macrosomia and control cases were brought into the random forest model and logistic regression model. On the basis of the average decrease of the Gini coefficient, the order of influencing factors was: interspinal diameter, transverse outlet, intercristal diameter, sacral external diameter, pre-pregnancy body mass index, age, the number of pregnancies, and the parity. The sensitivity, specificity, and area under curve were 91.7%, 91.7%, and 95.3% for the random forest model, and 56.2%, 82.6%, and 72.0% for logistic regression model, respectively; the sensitivity and specificity were 29.6% and 97.5% for the ultrasound; (4) Conclusions: A random forest model based on the maternal information can be used to predict macrosomia accurately during pregnancy, which provides a scientific basis for developing rapid screening and diagnosis tools for macrosomia.

The effect of fetal weight on the accuracy of sonographic weight estimation among women with diabetes

Objective: The assessment of sonographic estimated fetal weight (EFW) enables identification of fetuses in the extremes of weight, thus aiding in the planning and management of peripartum care. There are conflicting reports regarding the accuracy of EFW in diabetic mothers. We aimed to study the factors associated with the accuracy of EFW at term, specifically the role of gestational and pre-gestational diabetes in this setting.Methods: A retrospective study including all women carrying singleton term gestations who delivered within a week following a sonographic fetal weight estimation between 2011 and 2019. Accurate EFW was defined as within 10% of the actual birthweight. We allocated the study cohort into two groups: (1) Accurate EFW (2) inaccurate EFW. Both groups were compared in order to identify factors associated with the inaccuracy of EFW.Results: Overall, 41,263 deliveries were available for evaluation, including 412 (1.0%) deliveries among women with pre-gestational diabetes and 4,735 (11.5%) among women with gestational diabetes. Of them, 7,280 (17.6%) had inaccurate EFW. Inaccurate EFW was associated with nulliparity, OR 0.82 [95% CI] (0.78-0.87), oligohydramnios, OR 0.81 [95% CI] (0.71-0.93), pregestational diabetes, OR [95% CI] 0.61 (0.50-0.79), and extremity of fetal weight; <2,500 grams-OR [95% CI] 0.37 (0.33-0.41) and >4,000 grams OR [95% CI] 0.52 (0.48-0.57). On multiple regression analysis, the following factors were independently associated with inaccurate EFW: pregestational diabetes, OR [95% CI] 0.58 (0.46-0.73), p < .001, nulliparity, OR [95% CI] 0.86 (0.82-0.91), p < .001 and higher fetal weight (for each 500 grams), OR [95% CI [1.25 (1.21-1.30), p < .001. On analysis of different weight categories, pregestational diabetes was associated with inaccurate EFW only in those with birthweight >3,500 grams, OR [95% CI] 0.37 (0.24-0.56) (p < .001).Conclusion: Among pregestational diabetic women, the accuracy of sonographic EFW when assessed to be >3,500 grams is questionable. This should be taken into consideration when consulting women and planning delivery management.Synopsis: Among pregestational diabetic women, the accuracy of estimated sonographic fetal weight higher than 3,500 grams is of limited accuracy.

Ensemble Learning to Improve the Prediction of Fetal Macrosomia and Large-for-Gestational Age

Background: The objective of this study was to investigate the use of ensemble methods to improve the prediction of fetal macrosomia and large for gestational age from prenatal ultrasound imaging measurements. Methods: We evaluated and compared the prediction accuracies of nonlinear and quadratic mixed-effects models coupled with 26 different empirical formulas for estimating fetal weights in predicting large fetuses at birth. The data for the investigation were taken from the Successive Small-for-Gestational-Age-Births study. Ensemble methods, a class of machine learning techniques, were used to improve the prediction accuracies by combining the individual models and empirical formulas. Results: The prediction accuracy of individual statistical models and empirical formulas varied considerably in predicting macrosomia but varied less in predicting large for gestational age. Two ensemble methods, voting and stacking, with model selection, can combine the strengths of individual models and formulas and can improve the prediction accuracy. Conclusions: Ensemble learning can improve the prediction of fetal macrosomia and large for gestational age and have the potential to assist obstetricians in clinical decisions.

Estimation of fetal weight using Hadlock's formulas: Is head circumference an essential parameter?

OBJECTIVES

To test the equivalence of two fetal weight estimation formulas generated by Hadlock, a formula that includes head circumference parameter (H1), and another (H2) which excludes this parameter. A secondary aim was to identify the patients in which H2 formula is less reliable to use.

STUDY DESIGN

This retrospective cohort study included a total of 1220 sonographic fetal weight estimations performed within seven days of delivery and recorded at a single medical center from January 2014 to December 2016. Estimated fetal weight was calculated using H1 and H2 formulas. Their accuracies were compared using percentage error, the proportion of weight estimations falling within ±15% error interval and by Bland-Altman analysis. Multivariate regression was performed to evaluate factors affecting weight estimation by H2 formula.

RESULTS

The mean birth weight was 3288.92 ± 641.27gr. The H2 formula presented with statistically significant higher value of systemic mean percent error comparing to H1 (3.19% vs. 1.87%, p < 0.001 respectively). H2 formula had a lower accuracy compared to H1 in predicting fetal weight within ±15% of birth weight (90.49% vs. 93.44%, p < 0.01 respectively). Using Bland-Altman analysis, the 95% limits of agreement between both formulas were (-142.03) to 231.79gr with a mean of 44.88gr. Factors found to influence significantly on H2 formula were long femur length (OR 1.144, p < 0.0001) and low maternal age (OR 0.947, p < 0.01).

CONCLUSIONS

H1formula was more accurate than H2 formula in predicting fetal weight at term. However, the accuracy difference was found to be small. Therefore, if ultrasonographic evaluation of HC is technically difficult, Hadlock formula that excludes head circumference can be used with confidence. Caution should be paid with higher values of femur length and lower maternal age.

Gestational diabetes and ultrasound-assessed fetal growth in South Asian and White European women: findings from a prospective pregnancy cohort

BACKGROUND

Maternal gestational diabetes (GDM) is an established risk factor for large size at birth, but its influence on intrauterine fetal growth in different ethnic populations is less well understood. Here, we examine the joint associations of GDM and ethnicity with longitudinal fetal growth in South Asian and White European origin women.

METHODS

This study included 10,705 singletons (4747 White European and 5958 South Asian) from a prospective cohort of women attending an antenatal clinic in Bradford, in the North of England. All women completed a 75-g oral glucose tolerance test at 26-28 weeks' gestation. Ultrasound measurements of fetal head circumference (HC), femur length (FL) abdominal circumference (AC), and estimated fetal weight (EFW), and corresponding anthropometric measurements at birth were used to derive fetal growth trajectories. Associations of GDM and ethnicity with these trajectories were assessed using multilevel fractional polynomial models.

RESULTS

Eight hundred thirty-two pregnancies (7.8%) were affected by GDM: 10.4% of South Asians and 4.4% of White Europeans. GDM was associated with a smaller fetal size in early pregnancy [differences (95% CI) in mean HC at 12 weeks and mean AC and EFW at 16 weeks comparing fetuses exposed to GDM to fetuses unexposed (reference) = - 1.8 mm (- 2.6; - 1.0), - 1.7 mm (- 2.5; - 0.9), and - 6 g (- 10; - 2)] and a greater fetal size from 24 weeks' gestation through to term [differences (95% CI) in mean HC, AC, and EFW comparing fetuses exposed to GDM to those unexposed = 0.9 mm (0.3; 1.4), 0.9 mm (0.2; 1.7), and 7 g (0; 13) at 24 weeks]. Associations of GDM with fetal growth were of similar magnitude in both ethnic groups. Growth trajectories, however, differed by ethnicity with South Asians being smaller than White Europeans irrespective of GDM status. Consequently, South Asian fetuses exposed to GDM were smaller across gestation than fetuses of White Europeans without GDM.

CONCLUSIONS

In both ethnic groups, GDM is associated with early fetal size deviations prior to GDM diagnosis, highlighting the need for novel strategies to diagnose pregnancy hyperglycemia earlier than current methods. Our findings also suggest that ethnic-specific fetal growth criteria are important in identifying hyperglycemia-associated pathological effects.

The accuracy of ultrasound estimation of fetal weight in comparison to birth weight: A systematic review

Ultrasound estimation of fetal weight is a highly influential factor in antenatal management, guiding both the timing and mode of delivery of a pregnancy. Although substantial research has investigated the most accurate ultrasound formula for calculating estimated fetal weight, current evidence indicates significant error levels. The aim of this systematic review was to identify the most accurate method, whilst identifying sources of inaccuracy in order to facilitate recommendations for future practice. Seven studies met the inclusion criteria and 11 different formulae were assessed; ultrasound calculation of fetal weight was most commonly overestimated. The Hadlock A formula produced the most accurate results, with the lowest levels of random error. Methods incorporating just two measurement parameters were inconsistent, producing large random errors across multiple studies. Key sources of inaccuracy included difficulties obtaining accurate fetal measurements in late gestation; the remainder were operator dependent, including lack of experience and insufficient training and audit. The accuracy of ultrasound estimated fetal weight has improved in the last decade, though a lack of consistency remains evident. National implementation of a rigorous audit programme would likely improve accuracy further, and increase the confidence and clinical value of the method.

Early Second-Trimester Fetal Growth Restriction and Adverse Perinatal Outcomes

OBJECTIVE

To estimate the risk of adverse perinatal outcomes among women with isolated fetal growth restriction from 17 to 22 weeks of gestation.

METHODS

This was a retrospective cohort study of all singleton, nonanomalous pregnancies undergoing ultrasonography to assess fetal anatomy between 17 and 22 weeks of gestation at a single center from 2010 to 2014. After excluding patients with fetal structural malformations, chromosomal abnormalities, or identified infectious etiologies, we compared perinatal outcomes between pregnancies with and without fetal growth restriction, defined as estimated fetal weight less than the 10th percentile for gestational age. Our primary outcome was small for gestational age (SGA) at birth, defined as birth weight less than the 10th percentile. Secondary outcomes included preterm delivery at less than 37 and less than 28 weeks of gestation, preeclampsia, abruption, stillbirth, neonatal death, neonatal intensive care unit admission, intraventricular hemorrhage, need for respiratory support, and necrotizing enterocolitis.

RESULTS

Of 12,783 eligible patients, 355 (2.8%) had early second-trimester fetal growth restriction. Risk factors for growth restriction were African American race and tobacco use. Early second-trimester growth restriction was associated with a more than fivefold increase in risk of SGA at birth (36.9% compared with 9.1%, adjusted odds ratio [OR] 5.5, 95% CI 4.3-7.0), stillbirth (2.5% compared with 0.4%, OR 6.2, 95% CI 2.7-12.8), and neonatal death (1.4% compared with 0.3%, OR 5.2, 95% CI 1.6-13.5). Rates of indicated preterm birth at less than 37 weeks of gestation (7.3% compared with 3.3%, OR 2.3, 95% CI 1.5-3.5) and less than 28 weeks of gestation (2.5% compared with 0.2%, OR 10.8, 95% CI 4.5-23.4), neonatal need for respiratory support (16.9% compared with 7.8%, adjusted OR 1.6, 95% CI 1.1-2.2), and necrotizing enterocolitis (1.4% compared with 0.2%, OR 7.7, 95% CI 2.3-20.9) were also significantly higher for those with growth restriction. Rates of preeclampsia, abruption, and other neonatal outcomes were not significantly different.

CONCLUSION

Although fetal growth restriction in the early second trimester occurred in less than 3% of our cohort and most of those with isolated growth restriction did not have adverse outcomes, it is a strong risk factor for SGA, stillbirth, neonatal death, and indicated preterm birth.

Association between sonographic measurement of fetal head circumference and labor outcome

OBJECTIVE

To evaluate the association between sonographically measured head circumference (HC) and labor outcome.

METHODS

In a retrospective study at a tertiary medical center in Israel, data were reviewed for all term singleton deliveries between July 2007 and December 2012 with HC measurements up to 7days before delivery. HC was compared between women with operative vaginal delivery (OVD) or cesarean delivery for prolonged second stage and those with normal vaginal delivery. The impact of HC above the 75th percentile on pregnancy outcome was analyzed.

RESULTS

The study included 2351 women, of whom 2045 (87.0%) had a normal vaginal delivery, 259 (11.0%) underwent OVD, and 47 (2.0%) cesarean. Each 10mm increase in HC was associated with increased risk for obstetric intervention because of a prolonged second stage (adjusted odds ratio [aOR] 1.26; 95% confidence interval [CI] 1.08-1.46). HC above the 75th percentile was independently associated with increased odds of OVD (aOR 1.77; 95% CI 1.30-2.41), 1-minute Apgar score less than 7 (aOR 2.91; 95% CI 1.50-5.66), and neonatal asphyxia (aOR 2.19; 95% CI 1.02-4.71).

CONCLUSION

Term HC above the 75th percentile was associated with increased rates of obstetric interventions because of a prolonged second stage and might be associated with neonatal asphyxia.

Modelling foetal growth in a bi-ethnic sample: results from the Born in Bradford (BiB) birth cohort

BACKGROUND

Attempts to explain the increased risk for metabolic disorders observed in South Asians have focused on the "South Asian" phenotype at birth and subsequent post-natal growth, with little research on pre-natal growth.

AIM

To identify whether divergent growth patterns exist for foetal weight, head (HC) and abdominal circumferences (AC) in a sample of Pakistani and White British foetuses.

SUBJECTS AND METHODS

Models were based on 5553 (weight), 5154 (HC) and 5099 (AC) foetuses from the Born in Bradford birth cohort. Fractional polynomials and mixed effects models were employed to determine growth patterns from ~15 weeks of gestation-birth.

RESULTS

Pakistani foetuses were significantly smaller and lighter as early as 20 weeks. However, there was no ethnic difference in the growth patterns of weight and HC. For AC, Pakistani foetuses displayed a trend for reduced growth in the final trimester.

CONCLUSION

As the pattern of weight and HC growth was not significantly different during the period under investigation, the mechanism culminating in the reduced Pakistani size at birth may act earlier in gestation. Reduced AC growth in Pakistanis may represent reduced growth of the visceral organs, with consequences for post-natal liver metabolism and renal function.

Malaria and fetal growth alterations in the 3(rd) trimester of pregnancy: a longitudinal ultrasound study

Background

Pregnancy associated malaria is associated with decreased birth weight, but in-utero evaluation of fetal growth alterations is rarely performed. The objective of this study was to investigate malaria induced changes in fetal growth during the 3^rd trimester using trans-abdominal ultrasound.

Methods

An observational study of 876 pregnant women (398 primi- and secundigravidae and 478 multigravidae) was conducted in Tanzania. Fetal growth was monitored with ultrasound and screening for malaria was performed regularly. Birth weight and fetal weight were converted to z-scores, and fetal growth evaluated as fetal weight gain from the 26th week of pregnancy.

Results

Malaria infection only affected birth weight and fetal growth among primi- and secundigravid women. Forty-eight of the 398 primi- and secundigravid women had malaria during pregnancy causing a reduction in the newborns z-score of −0.50 (95% CI: −0.86, −0.13, P = 0.008, multiple linear regression). Fifty-eight percent (28/48) of the primi- and secundigravidae had malaria in the first half of pregnancy, but an effect on fetal growth was observed in the 3^rd trimester with an OR of 4.89 for the fetal growth rate belonging to the lowest 25% in the population (95%CI: 2.03–11.79, P<0.001, multiple logistic regression). At an individual level, among the primi- and secundigravidae, 27% experienced alterations of fetal growth immediately after exposure but only for a short interval, 27% only late in pregnancy, 16.2% persistently from exposure until the end of pregnancy, and 29.7% had no alterations of fetal growth.

Conclusions

The effect of malaria infections was observed during the 3^rd trimester, despite infections occurring much earlier in pregnancy, and different mechanisms might operate leading to different patterns of growth alterations. This study highlights the need for protection against malaria throughout pregnancy and the recognition that observed changes in fetal growth might be a consequence of an infection much earlier in pregnancy.

Development of a fetal weight chart using serial trans-abdominal ultrasound in an East African population: a longitudinal observational study

Objective

To produce a fetal weight chart representative of a Tanzanian population, and compare it to weight charts from Sub-Saharan Africa and the developed world.

Methods

A longitudinal observational study in Northeastern Tanzania. Pregnant women were followed throughout pregnancy with serial trans-abdominal ultrasound. All pregnancies with pathology were excluded and a chart representing the optimal growth potential was developed using fetal weights and birth weights. The weight chart was compared to a chart from Congo, a chart representing a white population, and a chart representing a white population but adapted to the study population. The prevalence of SGA was assessed using all four charts.

Results

A total of 2193 weight measurements from 583 fetuses/newborns were included in the fetal weight chart. Our chart had lower percentiles than all the other charts. Most importantly, in the end of pregnancy, the 10^th percentiles deviated substantially causing an overestimation of the true prevalence of SGA newborns if our chart had not been used.

Conclusions

We developed a weight chart representative for a Tanzanian population and provide evidence for the necessity of developing regional specific weight charts for correct identification of SGA. Our weight chart is an important tool that can be used for clinical risk assessments of newborns and for evaluating the effect of intrauterine exposures on fetal and newborn weight.

Birth weight- and fetal weight-growth restriction: impact on neurodevelopment

BACKGROUND

The newborn classified as growth-restricted on fetal weight curves, but not on birth weight curves, is classified prenatally as small for gestational age (SGA), but postnatally as appropriate for gestational age (AGA).

AIMS

To see (1) to what extent the neurodevelopmental outcomes at 24 months corrected age differed among three groups of infants (those identified as SGA based on birth weight curves (B-SGA), those identified as SGA based on fetal weight curves only (F-SGA), and the referent group of infants considered AGA, (2) if girls and boys were equally affected by growth restriction, and (3) to what extent neurosensory limitations influenced what we found.

STUDY DESIGN

Observational cohort of births before the 28th week of gestation.

OUTCOME MEASURES

Mental Development Index (MDI) and Psychomotor Development Index (PDI) of the Bayley Scales of Infant Development II.

RESULTS

B-SGA, but not F-SGA girls were at an increased risk of a PDI<70 (OR=2.8; 95% CI: 1.5, 5.3) compared to AGA girls. B-SGA and F-SGA boys were not at greater risk of low developmental indices than AGA boys. Neurosensory limitations diminished associations among girls of B-SGA with low MDI, and among boys B-SGA and F-SGA with PDI<70.

CONCLUSIONS

Only girls with the most severe growth restriction were at increased risk of neurodevelopmental impairment at 24 months corrected age in the total sample. Neurosensory limitations appear to interfere with assessing growth restriction effects in both girls and boys born preterm.

Accuracy of Fetal Weight Estimation in Women with Diet Controlled Gestational Diabetes

Purpose: To evaluate whether ultrasound accuracy of estimated fetal weight (EFW) differs in women with diet controlled gestational diabetes mellitus (GDM) compared to nondiabetic pregnant women. Material and Methods: We included 363 patients, 121 patients with diet controlled GDM and 242 patients with a normal oral glucose tolerance test (oGTT). Each case of diet controlled GDM was matched with 2 unaffected controls. All patients were screened/diagnosed for GDM by means of an oGTT. Both groups received ultrasound examination including fetal biometry, using Hadlock's Formula, within 7 days to delivery. After birth, gestational age, birthweight and Apgar scores were collected from each newborn. Results: There was a good correlation between EFW and birth weight (coefficient = 0.747, p < 0.001 by Pearson correlation, even after adjustment for glucose status). Regression analyses, including noGDM/GDM, maternal age, maternal body mass index, birth weight and time interval between ultrasound and delivery revealed that only fetal birth weight significantly influences weight difference between ultrasound EFW and actual birth weight at term. Conclusion: Our data suggests that ultrasound accuracy of EFW using Hadlock's Formula at term does not differ in women with diet controlled GDM compared to women with normal glucose tolerance.

Estimation of fetal weight in fetuses with abdominal wall defects: comparison of 2 recent sonographic formulas to the Hadlock formula

OBJECTIVE

Estimation of fetal weight is particularly challenging in fetuses with abdominal wall defects (AWDs). We sought to compare the accuracy and screening efficiency for intrauterine growth restriction (IUGR) of 2 recent sonographic formulas to those of the Hadlock formula (Am J Obstet Gynecol 1985; 151:333-337) in fetuses with AWDs.

METHODS

This was a retrospective cohort study of fetuses with AWDs. Fetuses with sonographically estimated fetal weights (EFWs) within 14 days before delivery were included. Using the individual biometric measurements, EFWs were calculated using the Honarvar (Int J Gynaecol Obstet 2001; 73:15-20; femur length [FL]), Siemer (Ultrasound Obstet Gynecol 2008; 31:397-400; FL, biparietal diameter [BPD], and occipitofrontal diameter), and Hadlock (BPD, head circumference, abdominal circumference, and FL) formulas. The calculated EFWs were adjusted for interval growth between the dates of sonography and delivery using published sonographic fetal growth velocity standards. Accuracy and screening efficiency for IUGR were compared.

RESULTS

Seventy-six fetuses were included: 53 with gastroschisis and 23 with omphalocele. The median gestational age at delivery was 36.6 weeks (range, 25.0 to 39.0 weeks). The Siemer formula had the lowest mean percentage error (-2.5% [95% confidence interval (CI), -6.2% to +1.2%]) without systematic bias (P = .182). The Hadlock formula had the highest precision (random error, 11.4%), sensitivity (91%), and accuracy for predicting IUGR (85% [95% CI, 77% to 94%]).

CONCLUSIONS

None of the 3 sonographic formulas is ideal for estimating fetal weight in fetuses with AWDs. The Siemer formula should be used when accuracy in the absolute EFW is the goal. For the purpose of making the more clinically relevant diagnosis of IUGR, use of the Hadlock formula is justified.

Clinical and ultrasound work-up and follow-up of preeclampsia

Hypertensive disorders are frequent during pregnancy and are related with an important morbidity and mortality worldwide. In this review we aim to provide the reader with a comprehensive overview of the clinical aspects of and the diagnostic tools used in the primary assessment and the (long term) follow-up of preeclampsia. The focus in this review will lay on the clinical follow-up of both the mother and the fetus aiming at the prevention of severe maternal complications as well as preventing growth restriction and prematurity in the child.

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.

Predictive factors and short-term fetal outcomes of breech presentation: a case-control study

OBJECTIVE

This study evaluated the predictive factors and short-term fetal outcomes of breech presentation by comparing breech and cephalic pregnancies of >or=36 weeks gestation.

MATERIALS AND METHODS

Two hundred and one breech and 149 cephalic pregnancies of >or=36 weeks gestation, with no other maternal or fetal problems, were compared with regard to placental localization, fetal heart rate variability, smoking, body mass index, maternal weight gain, placental weight, birth weight, sex, Apgar scores, and umbilical cord length.

RESULTS

Maternal weight gain, body mass index at term, smoking and hemoglobin values were significantly higher in breech presentation than in cephalic pregnancies. The placenta was located in the cornu-fundal region in 63.2% of breech presentations and 26.8% of cephalic presentations (p<0.001). Placental weights were 657 g and 597 g, respectively (p<0.001). Umbilical cord length was shorter in breech than cephalic pregnancies (p<0.001). Although breech pregnancies had significantly reduced fetal heart rate variability (p<0.001), Apgar scores were much higher in breech fetuses than in cephalic fetuses. Ninety-five percent of breech pregnancies underwent cesarean sections.

CONCLUSION

Cornu-fundal localization of the placenta, smoking, greater maternal weight gain, higher body mass index at term, greater placental weight, shorter umbilical cord, and lower estimated fetal weight may be predictive of persistent breech presentation. Reduced fetal heart rate variability did not have an adverse effect on Apgar scores after cesarean delivery in breech fetuses with no other problems at term.

Estimation of fetal weight by measurement of fetal thigh soft-tissue thickness in the late third trimester

OBJECTIVE

The accuracy of current formulae for the sonographic estimation of fetal weight (EFW) is compromised by significant intra- and interobserver variability of biometrical measurements, particularly circumferences. The aim of this study was to assess the reliability of the linear measurement of mid-thigh soft-tissue thickness (STT) and to derive a novel formula for EFW.

METHODS

This was a prospective study involving 388 singleton uncomplicated pregnancies. There were three consecutive phases: (1) to verify the relationship between STT and birth weight, (2) to derive a novel formula for EFW using femur length and STT only, and (3) to test the accuracy of the new equation. Only the 290 patients who delivered within 48 h of measurement were considered for the analysis. A comparison with other formulae was performed.

RESULTS

STT was significantly correlated with both abdominal circumference and birth weight (r(2) = 0.36 and 0.46, respectively; P < 0.001). Both intra- and interobserver variability were satisfactory (0.44 +/- 0.27 and 0.57 +/- 0.35 mm, respectively). The equation for EFW was developed using multiple stepwise regression analysis (EFW = - 1687.47 + (54.1 x femur length) + (76.68 x STT)) and tested prospectively on 69 patients. The new formula yielded results (r = 0.79) that were slightly better in accuracy than two other published equations, and had an absolute mean error of < 15% in 97% of cases.

CONCLUSIONS

Our findings confirm the potential of the linear measurement of mid-thigh STT as a valuable parameter for the sonographic assessment of fetal growth and EFW. Our new equation is apparently at least as reliable as the most widely used formulae for EFW.

Estimation of birth weight by two-dimensional ultrasonography: a critical appraisal of its accuracy

OBJECTIVE

To assess the accuracy and characterize two-dimensional ultrasonographic formulas for the estimation of birth weight according to the type of fetal biometric parameters these formulas rely on to make fetal weight predictions.

METHODS

A prospective recruitment of 589 pregnant women was carried out for this cross-sectional study. Different biometric parameters were taken ultrasonographically to estimate birth weight using 35 different formulas. Only those patients who delivered within 48 hours were considered for the analysis (n=441). Differences between the estimated and actual birth weight were assessed by percentage error, accuracy in predictions within +/-10% and +/-15% of error, and use of the Bland-Altman method. All formulas were assessed individually and clustered on the basis of the type of fetal biometric information that they incorporate.

RESULTS

Twenty-nine formulas provided an overall mean absolute percentage error less than or equal to 10%, with overall predictions within +/-10% and +/-15% of the actual birth weight (69.2% and 86.5%, respectively). Twenty formulas showed a good accuracy (bias 0.50 or less) and low variability (mean standard deviation 1.2). Among the categorized algorithms, formulas based on head-abdomen-femur measurements showed the lowest mean absolute percentage error. Upon stratification for birth weight, the group of formulas that rely on abdomen and femur measurements performed best for fetuses weighing more than 3,500 g (P<.01).

CONCLUSION

Our findings show that most formulas are relatively accurate at predicting birth weight up to 3,500 g, and all algorithms tend to underestimate large fetuses.

LEVEL OF EVIDENCE

III.

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.