Sonographic Fetal Weight Estimation Research Articles

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.

Identification of Newborns With Birth Weight of 4,500 Grams or More: The Impact of Obesity [16O

INTRODUCTION: Obesity is a known risk factor for fetal macrosomia (birth weight [BW] greater than or equal to 4,500g), but prior studies examining its effect on sonographic estimated fetal weight (SEFW) have been equivocal. Our objective was to determine the impact of obesity on sonographic detection of macrosomia. METHODS: We performed a multicenter retrospective cohort study of all non-anomalous singletons with SEFW greater than or equal to 4,000g. All SEFWs were performed by Registered Diagnostic Medical Sonographers within 14 days of delivery and were calculated using a Hadlock equation. Patients were grouped according to body mass index (kg/m2) at delivery (&lt;30.0 [non-obese], 30.0–39.9 [obese], and ≥ 40.0 [morbidly obese]). The primary outcome was the detection rate (DR) of macrosomic newborns. Secondary outcomes were false positive rate (FPR) and area under the receiver operator curve (AUC). RESULTS: Of the 330 women included, 83 (25.2%) were non-obese, 145 (43.9%) were obese, and 102 (30.9%) were morbidly obese. Overall there were 51 (15.5%) macrosomic newborns and its prevalence varied: 8.4% among non-obese, 14.5% among obese, and 22.5% among morbidly obese women. There were no significant differences in DR (42.9%, 52.4%, 60.9%; P=.67), FPR (7.9%, 9.7%, 10.1%; P=.87), or AUC (0.79, 0.77, 0.86; P=.51) for BW greater than or equal to 4,500 g between non-obese, obese, and morbidly obese women, respectively. CONCLUSION: Maternal obesity does not influence sonographic detection of newborns with BW of at least 4,500 g. Clinicians should not consider maternal obesity to be a limitation for identification of macrosomic newborns.

Identification of newborns with birthweight ≥ 4,500g: Ultrasound within one- vs. two weeks of delivery

ObjectiveOur objective was to compare the diagnostic characteristics of sonographic estimated fetal weight (SEFW) done within 7 versus 8−14 days before delivery for detection of fetal macrosomia (birthweight ≥ 4500 g). Study DesignWe performed a multicenter, retrospective cohort study of all non-anomalous singletons with SEFW ≥ 4000 g by Registered Diagnostic Medical Sonographers conducted within 14 days of delivery. Cohorts were grouped by time interval between ultrasound and delivery: 0−7 days versus 8−14 days. The detection rate (DR) and false positive rate (FPR) for detection of birthweight (BW) ≥ 4500 g were compared between groups with subgroup analysis for diabetic women. Area under the receiver operator curve (AUC) was calculated to analyze all possible SEFW cutoffs within our cohort. ResultsA total of 330 patients met inclusion criteria with 250 (75.8 %) having SEFW within 7 days and 80 (24.2 %) with SEFW 8−14 days prior to delivery. The rate of macrosomia was 15.1 % (N = 51). The DR for macrosomia was significantly higher when SEFW was performed within 7 days of delivery compared to 8−14 days among non-diabetic (73.0 % vs 7.1 %; p < 0.001) and diabetic women (76.5 % vs 16.7 %; p = 0.02). There was no significant change in FPR in either group. The AUC for detection of macrosomia was significantly higher when SEFW was performed within 7 days versus 8−14 days (0.89 vs 0.63; p < 0.01). ConclusionWith SEFW ≥ 4000 g, the detection of BW ≥ 4500 g is significantly higher when the sonographic examination is within 7 days of birth irrespective of maternal diabetes.

The Effect of Maternal Obesity on Sonographic Fetal Weight Estimation

ABSTRACT Background: Obesity is one of the most serious public health challenges of the 21st century. Obesity has reached epidemic proportions worldwide. Objective: To detect the possible effect of maternal obesity on the accuracy of sonographically estimated fetal weight (EFW) in the third-trimester shortly before labor and to compare the accuracy of the estimation between normal weight, overweight, and class I, class II and class III obese groups. Subjects and Methods: This was a prospective study of singleton pregnancies with sonographic fetal weight estimation prior to scheduled delivery. Women were classified according to current body mass index (BMI) into five categories: normal (BMI 18.5–24.9 kg/m2, n = 30), overweight (BMI 25.0–29.9 kg/m2, n = 30), obese class I (BMI 30.0–34.9kg/m2, n = 30), obese class II (BMI, 35.0–39.9 kg/m2, n = 30) and obese class III (BMI ≥ 40.0 kg/m2, n = 30).The EFW was compared with the actual birth weight(ABW), and the difference between them was recorded. Results: There was a statistically significant difference between US EFW by (g) and birth weight by (g) versus body mass index in obesity class II and III. Conclusion: Maternal obesity decreased the accuracy of sonographic fetal weight estimation. Clinicians should be aware of the limitations of sonographic fetal weight estimation, especially in obese patients.

1090: Identification of macrosomic newborns: One versus two-step approach

Limitations of Hadlock’s equations in identifying macrosomic fetuses (birthweight [BW] ≥ 4000g or ≥ 4500g) are known. Our objective was to evaluate a two-step screening method for detection of macrosomia utilizing Hadlock I to preselect at-risk women prior to application of a second regression equation. We performed a multicenter, retrospective review of all non-anomalous singletons who had ultrasound, by RDMS, within two weeks of delivery between 2013-2019. Our study group included all women with a Hadlock I calculated sonographic estimated fetal weight (SEFW) ≥ 4000g; additionally, to account for true and false negatives, we added an equal number of women with SEFW 3500-3999g. We then applied one of 43 published fetal weight regression equations to establish the “second step” SEFW. Area under the receiver operator curve (AUC), detection rate (DR), false positive rate (FPR), and accuracy (ACC) were calculated for all equations using our two-step method, and for Hadlock I alone, for detection of BW ≥ 4000g and 4500g. A paired analysis was performed to evaluate performance of each equation in the two-step approach versus Hadlock I as the reference. Of the 615 women who met inclusion criteria, 247 (40.2%) had BW ≥ 4000g and 56 (9.1%) had BW ≥ 4500g. There was no significant improvement for detection of BW ≥ 4000g with a two-step method compared to Hadlock I alone; however, the FPR was significantly decreased for detection of BW ≥ 4500g by applying equations by Ott or Hammami without a significant change in the detection rate (Table 1). Hadlock I remains relevant in a contemporary population for detection of BW ≥ 4000g. To identify newborns with BW ≥ 4500g, a two-step approach utilizing Hadlock I followed by Ott or Hammani significantly decreases the FPR, without compromising detection rate, and may be useful in clinical practice.

739: Comparison of sonographic fetal weight estimation formulas in patients with preterm premature rupture of membranes

739: Comparison of sonographic fetal weight estimation formulas in patients with preterm premature rupture of membranes

Evaluating the accuracy and precision of sonographic fetal weight estimation models in extremely early-onset fetal growth restriction.

Birthweight is a critical predictor of survival in extremely early-onset fetal growth restriction (diagnosed pre-28weeks' gestation, with abnormal umbilical/uterine artery Doppler waveforms), therefore accurate fetal weight estimation is a crucial component of antenatal management. Currently available sonographic fetal weight estimation models were predominantly developed in populations of mixed gestational age and varying fetal weights, but not specifically tested within the context of extremely early-onset fetal growth restriction. This study aimed to determine the accuracy and precision of fetal weight estimation in this population and investigate whether model performance is affected by other factors. Cases where a growth scan was performed within 48hours of delivery (n=65) were identified from a cohort of extremely early-onset fetal growth-restricted pregnancies at a single tertiary maternity center (n=159). Fetal biometry measurements were used to calculate estimated fetal weight using 21 previously published models. Systematic and random errors were calculated for each model and used to identify the best performing model, which in turn was used to explore the relationship between error and gestation, estimated fetal weight, fetal presentation, fetal asymmetry and amniotic fluid volume. Both systematic (median 8.2%; range -44.1 to 49.5%) and random error (median 11.6%; range 9.7-23.8%) varied widely across models. The best performing model was Hadlock head circumference-abdominal circumference-femur length (HC-AC-FL), regardless of gestational age, fetal size, fetal presentation or asymmetry, with an overall systematic error of 1.5% and random error of 9.7%. Despite this, it only calculated the estimated fetal weight within 10% of birthweight in 64.6% of cases. There was a weak negative relation between mean percentage error with Hadlock HC-AC-FL and amniotic fluid volume, suggesting fetal weight is overestimated at lower liquor volumes and underestimated at higher liquor volumes (P=0.002, adjusted R2 =0.08). Hadlock HC-AC-FL is the most accurate model currently available to estimate fetal weight in extremely early-onset fetal growth restriction independent of gestation or fetal size, asymmetry or presentation. However, for 35.4% of cases in this study, estimated fetal weight calculated using this model deviates by more than 10% from birthweight, highlighting a need for an improved model.

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

ObjectivesTo 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 designThis 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. ResultsThe 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). ConclusionsH1formula 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.

Estimation of fetal weight: a comparison of clinical and sonographic methods

Fetal weight estimation is important in the management of labour and delivery. This study aimed to compare the accuracy of the clinical and ultrasound methods of fetal weight estimation. This was a prospective study involving 110 term cephalic singleton pregnancies delivered within 24 hours of clinical fetal weight estimation using Johnson’s and Dare’s formulae and ultrasound estimation at a Tertiary hospital in Abakaliki, Nigeria. The data were analysed with Stata 11 software. The sonographic estimation within 10% of the actual birth weight (ABW) of 68.2% was significantly greater than the accuracy of Johnson’s (23.6%), Dare’s (26.4%), and the combined clinical formulae (27.1%). The clinical methods overestimated the fetal weight. Both methods showed a positive correlation with the ABW. In conclusion, the sonographic method had a better accuracy than the clinical methods. However, fetal weight overestimation by clinical methods warrants their usefulness in resource-poor settings such that the clinical determination of a normal weight foetus will exclude fear of complications from macrosomia. Impact statement What is already known on this subject? An accurate estimation of fetal weight is important in the management of labour and delivery. However, there is limited evidence that any of the available methods of fetal weight estimation is more accurate than the others. What do the results of this study add? This study showed that the clinical methods using Johnson’s and Dare’s formulae had a significantly higher mean percentage and absolute mean percentage error compared to the sonographic estimation of fetal weight. The sonographic estimation within 10% of actual birth weight (ABW) of 68.2% was significantly greater than that of Johnson’s and Dare’s formulae with 23.6% and 26.4%, respectively. All of the methods showed a positive correlation with the ABW. What are the implications of these findings for clinical practice and/or further research? This implies that the sonographic method has a better accuracy than the clinical methods in estimating the fetal weight. However, the overestimation of fetal weight by the clinical methods warrants their usefulness in resource-poor settings such that the clinical determination of a normal weight foetus will exclude the fear of complications from macrosomia.

Differences in fetal growth patterns between twins and singletons*

Objective: Twin fetus growth is delayed during the third trimester compared to singletons. Whether this phenomenon should be considered a normal physiologic characteristic of twins or a pathologic process inherent to twin pregnancies is currently unclear. Information on the growth rate of the individual fetal biometric indices may provide more insight into the mechanisms underlying these differences between twins and singletons. Our aim was to compare fetal growth pattern between twin and singleton fetuses.Methods: This was a retrospective study of women with an uncomplicated twin pregnancy who underwent sonographic fetal weight estimation between 16 and 38 weeks’ gestation in a single referral center. Twins-specific regression models were generated for biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL) and fetal weight as a function of gestational age and were compared to published singletons-based curves.Results: Overall 543 women were eligible for the study and underwent a total of 3401 sonographic weight estimations. Estimated weight of twin fetus emerged as lower than that of singletons starting at 26 weeks of gestation, and these differences increased with gestational age, reaching a mean difference of 300–350 g or of ∼10% at term. The growth of all four biometric indices was slower in twins compared to singletons, but the differences were most pronounced for AC which had the largest relative contribution to the lower fetal weight in twins (51.7 ± 7.3%), while the relative contribution of FL, HC, and BPD was smaller (26.4 ± 10.7, 15.5 ± 3.0, and 6.4%±5.7%, respectively). This was also reflected by a higher HC/AC ratio in twins compared with singletons starting at 22 weeks of gestation. The likelihood of a twin fetus being diagnosed as small for gestational age (fetal weight <10th percentile) was significantly lower when the newly developed twins-based curves (rather than singletons-based curves) were used (OR: 0.39, 95%-CI: 0.34–0.44).Conclusion: Twin fetus experience slowing of growth beginning at ∼26 weeks of gestation and a greater degree of asymmetric growth pattern compared with singletons. These findings suggest that the slower growth of twins may reflect a state of “relative growth restriction” compared with singleton gestations.

Influence of maternal obesity on the accuracy of ultrasonography birth weight prediction

Objective: The aim of the study was to investigate whether the accuracy of ultrasound estimates of fetal weight (EFW) was dependent on maternal obesity.Study design: A prospective cross-sectional study of 1064 singleton pregnant women classified according to body mass index (BMI) into two categories: normal (BMI < 25 kg/m2, n = 863) and obese (BMI ≥ 35 kg/m2, n = 201) was conducted. EFW were calculated using Hadlock’s formula, and the difference between EFW and the actual birthweight (absolute percent error) was analyzed in both groups. Spearman’s correlation was used to assess the relationship between ultrasound performance (absolute error), maternal BMI, and actual birth weight.Results: Median absolute error of sonographic EFW was 5.90 and 6.47% for the normal and obese groups, respectively (p .38). A correlation between EFW and birth weight (BW) was found in both groups, r = 0.755 (p < .001) and r = 0.753 (p < .001), respectively. The correlation between absolute error, maternal BMI, and fetal birth weight was poor.Conclusions: Maternal obesity is unrelated to the accuracy of sonographic EFW, and regardless of maternal or fetal size, ultrasound is currently an accurate method of prediction for both obese and normal weight pregnant women.

Accuracy of sonographic fetal weight estimation in full-term singleton pregnant women.

Objectives:To investigate the factors which might influence the sonographic fetal weight estimation (SFWE) accuracy.Methods:This prospective study was conducted among 949 singleton term pregnant women who delivered at a tertiary center, from January 2017 to December 2017. All participants’ maternal (i.e. parity, age, body mass index and gestational weight gain during pregnancy), fetal sonographic (i.e. fetal presentation, amniotic fluid index, localization of placenta and estimated fetal weight) and neonatal (birth weight and gender) characteristics were recorded. A p<0.05 was considered significant.Results:The mean absolute percent error (APE) values of SFWE was 8.2±6.5 percent, and overall failure ratio (APE >10%) was 33%. In failure group, primiparous woman and cephalic presentation fetus were significantly more common compared to accuracy group (55.9% vs.44.8%; p=0.001 and 98% vs. 95.2%; p=0.03, respectively). In contrast, the mean neonatal birth weight (NBW) value was significantly lower in failure group compared to success group (3250±565 gr vs. 3404±410 gr; p=0.001). The correlation between SFWE and NBW was linear, however negative, and significant (p=0.001). Logistic regression analysis revealed that primiparous woman, cephalic presentation fetus and <3300 gr NBW were independent risk factors for the SFWE failure (relative risks were 1.6, 2.8 and 2.4 respectively, p<0.05).Conclusion:SFWE has a high correlation with NBW, however it’s accuracy is still unsatisfactory, and depend on many unpredictable and inconsistent factors.

Factors influencing the accuracy of sonographic fetal weight estimation: a review

It's an essential part of delivery management for obstetricians to estimate fetal weight accurately. Nowadays, the two-dimensional ultrasonography is a main method to estimate fetal weight, but the sonographic estimated fetal weight (SEFW) is not accurate enough. Therefore, assessing the influencing factors in the accuracy of SEFW, decreasing the error of SEFW, and promoting the accuracy of SEFW, are important aspects for delivery decisions. In this article, papers on factors affecting the SEFW accuracy were reviewed. Our study shows that formulae containing three to four parameters were more accurate than those of one parameter or two. Ethnics, regions, the time interval between ultrasonic examination and delivery, birth weight, fetal gender and seniority of sonographers are influencing factors on SEFW. However, whether fetal position, the volume of amniotic fluid, maternal body mass index, and maternal diabetes have influence on SEFW, are controversial. Key words: Ultrasonography, prenatal; Fetal weight; Root cause analysis

P04.07: Effect of selected factors on accuracy of sonographic fetal weight estimation

P04.07: Effect of selected factors on accuracy of sonographic fetal weight estimation

EP05.11: Accuracy of sonographic fetal weight estimation in El‐Obeid, Sudan

EP05.11: Accuracy of sonographic fetal weight estimation in El‐Obeid, Sudan

Sonographic Versus Clinical Fetal Weight Estimation Accuracy

Background: Sonographic fetal weight estimation is an important component of antenatal care. It was found to be more reliable method to establish fetal weight at term and more consistent in various period of gestations. Aim of study: to compare clinical and sonographic methods for assessment of fetal weight regarding sensitivity, specificity and accuracy. Subjects and Methods: The study recruited 100 women scheduled for delivery from ante-natal care clinic with 38 weeks or more of gestation. Fetal weight was assed clinically and by ultrasound. Both techniques were compared and analyzed. Results: Ultrasound assessment of fetal weight showed better performance than the clinical method regarding absolute errors and error percentages. Ultrasound assessment showed better sensitivity and specificity in detecting fetal weight &gt; 3500 gm. Moreover, it showed less bias on Bland–Altman plot analysis. Conclusions: Ultrasound assessment of fetal weight is safe, reliable and sensitive method of fetal weight estimation.

Sonographic Estimated Fetal Weight among Diabetics at ≥ 34 Weeks and Composite Neonatal Morbidity.

Objectives The objective was to assess the composite neonatal morbidity (CNM) among diabetic women with sonographic estimated fetal weight (SEFW) at 10 to 90th versus >90th percentile for gestational age (GA). Study Design The inclusion criteria for this retrospective study were singleton pregnancies at 34 to 41 weeks, complicated by diabetes, and that had SEFW within 4 weeks of delivery. Odds ratios (ORs) with 95% confidence intervals (CI) were calculated. Results Among the 140 cohorts that met the inclusion criteria, 72% had SEFW at 10th to 90th percentile for GA, and 28% at >90th percentile. Compared with women with diabetes with last SEFW at 10th to 90th percentile, those with estimate > 90th percentile for GA had a significantly higher rate of CNM (13 vs. 28%; OR, 2.65; 95% CI, 1.07–6.59). Among 109 diabetic women who labored, the rate of shoulder dystocia was significantly higher with SEFW at >90th percentile for GA than those at 10th to 90th percentile (25 vs. 2%; p = 0.002); the corresponding rate of CNM was 29 versus 10% ( p = 0.02). Conclusion Among diabetic women with SEFW > 90th percentile for GA, CNM was significantly higher than in women with estimate at 10 to 90th percentile. Despite the increased risk of CNM, these newborns did not have long-term morbid sequela.

Reliability of sonographic fetal weight estimation in triplet pregnancies: a retrospective cohort study

PurposeTo review our experience in ultrasound fetal weight estimation in our large population of triplet pregnancies.MethodsNinety-seven triplet pregnancies were retrospectively included between January 2003 and January 2017. Sonographic fetal weight estimation using Hadlock’s and Schild’s formulas was compared to actual birth weight in a tertiary-care center in Vienna, Austria. Statistical analyses were performed using a stepwise linear regression model and crosstabs.ResultsThe median discrepancy between the sonographically estimated fetal weight by Hadlock’s formula and the actual birth weight was 106 g (IQR 56–190). The percentage error and its standard deviation were − 2.5 ± 12.1%, and the median percentage error was − 3.6%. Concerning the use of Hadlock’s formula, estimated fetal weight was the most important factor predictive of actual birth weight with an estimate of 0.920 (p < 0.001). Female neonates had been overestimated by a mean of 50.473 g per fetus. The sonographic prediction of small-for-gestational-age neonates was significantly reliable (p < 0.001), with positive and negative predictive values ranging from 81.3 to 100.0%. Similar results were obtained for Schild’s formula.ConclusionEven if sonographically estimated fetal weight in triplet pregnancies has a high overall accuracy of fetal weight estimation, there are some limitations in prediction of intrauterine growth restrictions, especially in female fetuses.

Fetal growth velocity and body proportion in the assessment of growth.

Fetal growth restriction implies failure of a fetus to meet its growth potential and is associated with increased perinatal mortality and morbidity. Therefore, antenatal detection of fetal growth restriction is of major importance in an attempt to deliver improved clinical outcomes. The most commonly used approach towards screening for fetal growth restriction is by means of sonographic fetal weight estimation, to detect fetuses small for gestational age, defined by an estimated fetal weight <10th percentile for gestational age. However, the predictive accuracy of this approach is limited both by suboptimal detection rate (as it may overlook non-small-for-gestational-age growth-restricted fetuses) and by a high false-positive rate (as most small-for-gestational-age fetuses are not growth restricted). Here, we review 2 strategies that may improve the diagnostic accuracy of sonographic fetal biometry for fetal growth restriction. The first strategy involves serial ultrasound evaluations of fetal biometry. The information obtained through these serial assessments can be interpreted using several different approaches including fetal growth velocity, conditional percentiles, projection-based methods, and individualized growth assessment that can be viewed as mathematical techniques to quantify any decrease in estimated fetal weight percentile, a phenomenon that many care providers assess and monitor routinely in a qualitative manner. This strategy appears promising in high-risk pregnancies where it seems to improve the detection of growth-restricted fetuses at increased risk of adverse perinatal outcomes and, at the same time, decrease the risk of falsely diagnosing healthy constitutionally small-for-gestational-age fetuses as growth restricted. Further studies are needed to determine the utility of this strategy in low-risk pregnancies as well as to optimize its performance by determining the optimal timing and interval between exams. The second strategy refers to the use of fetal body proportions to classify fetuses as either symmetric or asymmetric using 1 of several ratios; these include the head circumference to abdominal circumference ratio, transverse cerebellar diameter to abdominal circumference ratio, and femur length to abdominal circumference ratio. Although these ratios are associated with small for gestational age at birth and with adverse perinatal outcomes, their predictive accuracy is too low for clinical practice. Furthermore, these associations become questionable when other, potentially more specific measures such as umbilical artery Doppler are being used. Furthermore, these ratios are of limited use in determining the etiology underlying fetal smallness. It is possible that the use of the 2 gestational-age-independent ratios (transverse cerebellar diameter to abdominal circumference and femur length to abdominal circumference) may have a role in the detection of mild-moderate fetal growth restriction in pregnancies without adequate dating. In addition, despite their limited predictive accuracy, these ratios may become abnormal early in the course of fetal growth restriction and may therefore identify pregnancies that may benefit from closer monitoring of fetal growth.

Effect of Maternal Body Mass Index and Amniotic Fluid Index on the Accuracy of Sonographic Estimation of Fetal Weight in Late Gestation.

The objective of this study was to determine the effect, if any, of maternal body mass index (BMI) and amniotic fluid index (AFI) on the accuracy of sonographic estimated fetal weight (EFW) at 40 to 42 weeks' gestation. This was a retrospective cohort study of singleton gestations with ultrasound performed at 40 to 42 weeks from 2010 to 2013. In this study, patients with documented BMI and sonographic EFW and AFI, concurrently, within 7 days of delivery were included. Chronic medical conditions and fetal anomalies were excluded from this study. The primary variable of interest was the rate of substantial error in EFW, defined as absolute percentage error (APE) >10%. A total of 1,000 pregnancies were included. Overall, the APE was 6.0 ± 4.5% and the rate of substantial error was 17.4% (n = 174). There was no significant difference in APE or rate of substantial error between BMI groups. In the final multivariable logistic regression model, the rate of substantial error was increased in women with oligohydramnios (OR 1.79; 95% CI: 1.10-2.92). Furthermore, oligohydramnios was significantly more likely to overestimate EFW while polyhydramnios was more likely to underestimate EFW. Maternal BMI did not affect the accuracy of sonographic EFW. Sonographic EFW may be affected by extremes of AFI in the postdates period. Maternal BMI does not affect EFW accuracy at 40 to 42 weeks.