Specific weight formula for fetuses with abdominal wall defects

Estimating fetal weight in gastroschisis: A 10 year audit of outcomes at the National Maternity Hospital

OBJECTIVE

To identify whether conventional methods of estimating fetal growth (Hadlock's formula), which relies heavily on abdominal circumference measurements, are accurate in fetuses with gastroschisis.

METHODS

A retrospective cohort study was performed between the period January 1, 2011 and December 31, 2021 in a tertiary referral maternity hospital identifying all pregnancies with a diagnosis of gastroschisis. Projected fetal weight was obtained using the formula (EFW [Hadlock's formula] + 185 g × [X/7]) where X was the number of days to delivery.

RESULTS

During the study period 41 cases were identified. The median maternal age was 25. The median BMI was 25 and 63% were primiparous women (n = 26). Median gestation at diagnosis was 21 weeks. Median gestation at delivery was 36 weeks. A total of 4.8% of mothers had a history of drug use (n = 2). The rate of maternal tobacco use was 21.9% (n = 9). A total of 4.8% of fetuses had additional congenital anomalies including amniotic band syndrome and myelomeningocele (n = 2). Estimated fetal weight (EFW) and birth weight data were available for 34 cases. A Wilcoxon signed-rank test showed projected EFW using Hadlock's formula did not result in a statistically significant different birth weight (Z = -1.3, P = 0.169). Median projected weight and actual birth weight were 2241.35 and 2415 g respectively. Median difference was 0.64 g (95% CI: -148 to -28.5).

CONCLUSION

Our data showed accuracy using standard formulae for EFW in fetuses with gastroschisis.

Prediction of Neonatal Growth Restriction in Fetuses With Gastroschisis by Early Third Trimester Ultrasonography Utilizing Contemporary Birth Weight Percentiles

OBJECTIVE

To identify the estimated fetal weight (EFW) formula and threshold for the optimal prediction of fetal growth restriction (FGR) at 26-34 weeks' in fetuses with gastroschisis.

METHODS

Late second and third trimester ultrasound data were used to calculate the EFW utilizing eight different formulas: Hadlock I-IV, Honarvar, Shepard, Siemer, and Warsof. EFW and birth weight percentiles were assigned from US population growth curves. FGR and small for gestational age (SGA) were defined as EFW and birth weight less than the tenth percentile for gestational age; Receiver operating characteristic (ROC) curves were used to compare formula performance for FGR diagnosis at 26-34 weeks' to identify an SGA birth weight.

RESULTS

There were 170 newborns with gastroschisis; 46 (27%) were SGA. The mean gestational age at the time of ultrasound was 30.8 ± 1.7 weeks. The mean gestational age at birth was 36.3 ± 1.7 weeks. ROC curve analysis found the Hadlock III formula had the largest area under the curve (AUC) of 0.813 closely followed by Hadlock IV (AUC = 0.811) and Hadlock II (AUC = 0.808) for diagnosis of FGR correlating to neonatal SGA diagnosis. Hadlock II, Hadlock III, and Hadlock IV had the highest diagnostic accuracies when compared to the other EFW formulas.

CONCLUSIONS

The Hadlock II, Hadlock III, and Hadlock IV formulas have comparable predictive performance in the optimal identification of FGR in fetuses with gastroschisis at 26-34 weeks'. A threshold of an EFW less than the 25.2th percentile is suggested.

Correlation between estimated fetal weight and weight at birth in infants with gastroschisis and omphalocele

BACKGROUND

An accurate estimated fetal weight (EFW) calculated with traditional formulae in cases of abdominal wall defects (AWDs) can be challenging. As a result of reduced abdominal circumference, fetal weight may be underestimated, which could affect prenatal management. Siemer et al. proposed a formula without the use of abdominal circumference, but it is not used in our protocols yet.

OBJECTIVES

Our aim was to evaluate the correlation of EFW and birth weight in fetuses with AWD by using Hadlock 1, Hadlock 2, and Siemer et al.'s formulae. Our secondary goal was to evaluate how often fetuses classified as small for gestational age (SGA) were in fact SGA at birth.

STUDY DESIGN

This was a retrospective cohort study of gestations complicated by gastroschisis and omphalocele at two tertiary-care centers in Brazil and Italy during an 8-year period. Of a total of 114 cases, 85 (44 cases of gastroschisis and 41 cases of omphalocele) met our criteria.

RESULTS

The last prenatal scan was performed 5.2 (±4.1) days before birth. The mean gestational age at birth was 37.2 (±1.8) weeks. Correlation of EFW with birth weight was calculated with the three formulae with and without adjustment for weight gain between scan and birth, with the use of the Spearman coefficient. The correlation between EFW and weight at birth was positive according to all three formulae for the infants with gastroschisis. This finding was not confirmed in the infants with omphalocele. All formulae overestimated the number of SGA cases: although only 17.6% of fetuses were actually SGA at birth, the Hadlock formulae had classified nearly 35% of them as SGA, and Siemer et al.'s formula, 15.3%.

CONCLUSION

All three formulae yielded a good correlation between EFW in the last scan and birth weight in the infants with gastroschisis but not for those with omphalocele. Cases of SGA were overestimated.

Ductus venosus reversed flow in omphalocele: Could it be a prognostic factor for long-term neurological impairment?

Omphalocele (exomphalos) represents one of the most frequent congenital abdominal wall defects. It presents as a defect of inconstant size and is located on the midline, at the base of the umbilical cord, the skin, fascia, and abdominal muscles being absent at this level. Omphaloceles are classified as liver-containing or non-liver-containing, the latter containing primarily bowel loops. We present the case of a 37-year-old pregnant woman with an early diagnosis of liver-containing omphalocele associating ductus venosus reversed flow, with the aim to highlight the importance of the first-trimester morphology scan and to develop a pilot study regarding the neurological development of infants after surgical repair of giant omphaloceles. The particularity of this case consists of a fetus with a positive diagnosis of a giant liver-containing omphalocele but with a small abdominal wall defect during the first-trimester morphology scan at 13 weeks and 3 days of gestation which associated ductus venosus reversed flow, presenting a normal karyotype postabortum. With a small defect, we can speculate the risk of strangling besides the mechanical traction exercised on the ductus venosus generating fetal distress, specifically fetal hypoxia at an early gestational age. In conclusion, the main issue, in this case, was if the fetal omphalocele and ductus venosus reversed flow indicated fetal hypoxia, what was the obstruction effect on the oxygenated blood pathway caused by the abdominal defect, and which were the long-term effects on infants with this complex pathology with an unknown outcome.

Accuracy of Ultrasound to Predict Neonatal Birth Weight Among Fetuses With Gastroschisis: Impact on Timing of Delivery

OBJECTIVES

To determine the accuracy of ultrasound estimation of fetal weight among fetuses with gastroschisis and how the diagnosis of fetal growth restriction (FGR) affects the timing of delivery.

METHODS

This was a retrospective cohort study including all fetuses with a diagnosis of gastroschisis at our institution from November 2012 through October 2017. We excluded multiple gestations, pregnancies with major structural or chromosomal abnormalities, and those for which prenatal and postnatal follow-up were unavailable. Performance characteristics of ultrasound to predict being small for gestational age (SGA) were calculated for the first and last ultrasound estimations of fetal weight.

RESULTS

Our cohort included 75 cases of gastroschisis. At the initial ultrasound estimation, 15 of 58 (25.9%) fetuses met criteria for FGR; 48 of 70 (68.6%) met criteria at the time of the last ultrasound estimation (median, 34.7 weeks). Cesarean delivery was performed for 37 of 75 (49.3%), with FGR and concern for fetal distress as the indication for delivery in 17 of 37 (45.9%). Only 6 of 17 (35.3%) of the neonates born by cesarean delivery for an indication of FGR and fetal distress were SGA. The initial ultrasound designation of FGR corresponded to SGA at birth in 8 of 15 (53.3%), whereas the last ultrasound estimation corresponded to SGA in 17 of 48 (35.4%). The initial ultrasound estimation agreed with the last ultrasound estimation before delivery with the diagnosis of FGR in 13 of 15 (86.7%).

CONCLUSIONS

Ultrasound in the third trimester was sensitive but had a low positive predictive value and low accuracy for the diagnosis of SGA at birth for fetuses with gastroschisis. A large proportion of fetuses were born by cesarean delivery with indications related to FGR or fetal concerns.

Accuracy of estimated fetal weight assessment in fetuses with abdominal wall defects

BACKGROUND

Gastroschisis and omphalocele are congenital abdominal wall defects in which the bowel and other abdominal contents extrude from the fetal abdominal cavity. Standard formulas for estimated fetal weight using ultrasound include fetal abdominal circumference measurement and have a range of error of approximately 10%. It is unknown whether the accuracy of estimated fetal weight assessment is compromised in fetuses with abdominal wall defects because of the extrusion of abdominal contents.

OBJECTIVE

This study aimed to assess the accuracy of standard estimated fetal weight assessment in fetuses with abdominal wall defects by comparing prenatal assessment of fetal weight with actual birthweight.

STUDY DESIGN

A retrospective cohort study of fetuses diagnosed with gastroschisis or omphalocele was performed at a single center from 2012 to 2018. Fetuses with additional anomalies or confirmed chromosome abnormalities were excluded. Estimated fetal weight was calculated using the Hadlock formula. Published estimates of fetal growth rate were used to establish a projected estimated fetal weight at birth from the final growth ultrasound, and the percent difference between projected estimated fetal weight at birth and actual birthweight was calculated. The Wilcoxon rank-sum test was used to examine the difference between projected estimated fetal weight and actual birthweight.

RESULTS

We had complete data for 112 fetuses with abdominal wall defects, including 85 with gastroschisis and 27 with omphalocele. The median (interquartile range) projected estimated fetal weight was similar to median birthweight, at 2283 g (interquartile range, 2000-2810) and 2306 g (interquartile range, 1991-264), respectively, which did not represent a statistically significant difference between projected estimated fetal weight and actual birthweight (P=.32). The median percent error was 6.8 (3.1-12.8). In addition, we did not find any statistical difference between projected estimated fetal weight and actual birthweight in patients with gastroschisis (P=.52) or omphalocele (P=.35) individually. Estimated fetal weight was underestimated in most cases (n=68 [60.7%]).

CONCLUSION

In fetuses with abdominal wall defects, standard measurement of fetal weight shows an accuracy that is at least comparable with previously established margins of error for ultrasound assessment of fetal weight. Standard estimated fetal weight assessment remains an appropriate method of estimating fetal weight in these fetuses.

Abdominal Wall Defects-Current Treatments

Gastroschisis and omphalocele reflect the two most common abdominal wall defects in newborns. First postnatal care consists of defect coverage, avoidance of fluid and heat loss, fluid administration and gastric decompression. Definitive treatment is achieved by defect reduction and abdominal wall closure. Different techniques and timings are used depending on type and size of defect, the abdominal domain and comorbidities of the child. The present review aims to provide an overview of current treatments.

Accuracy of sonographic estimation of weight in fetuses with abdominal wall defects

BACKGROUND

Accurate estimation of fetal weight is essential in guiding management of fetuses with abdominal wall defects (AWDs), as growth restriction is an important predictor of perinatal morbidity and mortality. Several sonographic formulae are available involving multiple biometric parameters, but abdominal circumference measurements may underestimate weight in fetuses with AWDs. No formula has yet shown superior accuracy.

AIMS

The objectives of this study were to evaluate, in fetuses with gastroschisis and omphalocoele, the accuracy of a sonographic estimated fetal weight (EFW) formula proposed by Siemer and colleagues, specifically for use in fetuses with AWDs compared to the commonly used Hadlock IV formula in estimating fetal weight, and detecting small for gestational age (SGA) fetuses.

MATERIALS AND METHODS

A retrospective cohort of 113 fetuses with AWDs was identified from an Australian teaching hospital over 13 years. Pregnancy data and sonographic fetal biometry parameters were obtained. The accuracy of each formula in predicting birthweight was compared using Bland-Altman limits of agreement, and the intraclass correlation coefficient between EFW and actual birthweight. Performance of each formula in detecting SGA fetuses was determined.

RESULTS

The Siemer and Hadlock formulae have similar accuracies for predicting birthweight in fetuses with AWDs. The Hadlock formula has a higher detection rate for SGA < 10^th centile and < 3^rd centile compared to the Seimer formula (84% vs 68% and 83% vs 67% respectively), albeit with a higher false-positive rate.

CONCLUSION

There is no clear clinical advantage in using the Siemer formula, which is specifically designed for fetuses with AWDs, over the Hadlock formula to estimate weight in fetuses with AWDs.

Fetal abdominal wall defects in an Australian tertiary setting: contemporary characteristics, ultrasound accuracy, and outcome

PURPOSE

In this study, we aimed to comprehensively evaluate risk factors, ultrasound estimation of fetal weight, prenatal management, and pregnancy outcomes of gastroschisis and omphalocele at a metropolitan Australian hospital.

MATERIAL AND METHODS

This was a retrospective single-center cohort study from 2006 to 2014 at a tertiary hospital with colocated neonatal surgical facilities. Demographic, pregnancy, ultrasound, birth and neonatal data were compared between gastroschisis and omphalocele. Correlation between routine (Hadlock 1 &2) and specific (Siemer) estimated fetal weight (EFW) estimation formulae with birth weight (BW) was made for those 50 gastroschisis cases with ≥2 third trimester scans and last scan ≤2 weeks prior to birth.

RESULTS

There were 126 abdominal wall defects: 83 gastroschisis and 43 omphalocele. Consistent with international literature, the average maternal age was lower for gastroschisis and rates of smoking higher, while there were more intrauterine deaths and pregnancy terminations in omphalocele. Gastroschisis mothers were more likely living outside Sydney, had more infections in pregnancy and were followed with a larger number of antenatal visits, with a shorter period from the last visit to birth. In omphalocele pregnancies, amniocentesis was more likely performed, with more abnormal results than in gastroschisis fetuses. All EFW formulae had a good correlation between Z score for the last US and actual BW (ICC 0.693-0.815), with Hadlock 2 being the best. Siemer formula had the best correlation from first to the last scan. Gastroschisis newborns were born earlier (36.8 versus 38.2 wks p = .001), with smaller birthweight (2.52 versus 3.03 kg, p < .001), a longer request of intensive care (central line, parenteral nutrition, intubation) and second surgery, along with more multisystem complications (average 1.5 versus 0.7, p = .004) and a longer hospital stay (58.8 versus 36.8 d, p < .001).

CONCLUSION

Demographic, antenatal, and pregnancy outcome data for abdominal wall defects correlated well with the international literature. Hadlock 1-2 gave the most consistent EFW estimate, with all formulae showing good correlation.

Fetal growth standards in gastroschisis: Reference values for ultrasound measurements

OBJECTIVES

The objectives of this study were to create growth curves based on ultrasonography biometric parameters of fetuses with gastroschisis, comparing them with normal growth standards, and to analyze umbilical artery (UA) Doppler velocimetry patterns.

METHODS

A cohort study of 72 fetuses with gastroschisis, at gestational ages between 14 and 39 weeks was designed. Mean and standard deviation were calculated, with the 5th, 10th, 50th, 90th, and 95th centiles being established for biometric parameters according to gestational age. Curves were obtained, comparing with normal reference via the Mann-Whitney test. UA Doppler velocimetry patterns were obtained.

RESULTS

A total of 434 examinations were performed, and centiles were established for biparietal diameter, head circumference, abdominal circumference, femur length, and estimated fetal weight. A significant difference was observed between the gastroschisis measurements when compared to control, with all curves shifted downwards. Abdominal circumference was the parameter presenting the largest difference. Estimated fetal weight was also lower, with mean difference of 256.3 ± 166.8 g for the 50th centile (P < .0001). UA Doppler velocimetry was normal in 97.5%.

CONCLUSIONS

Fetuses with gastroschisis show symmetrical growth deficits in the second and third trimesters, with normal UA Doppler velocimetry. These results reinforce the hypothesis that they are constitutionally smaller, yet not restricted because of placental insufficiency.

Predicting birth weight in fetuses with gastroschisis

OBJECTIVE

To determine the accuracy of commonly utilized ultrasound formulas for estimating birth weight (BW) in fetuses with gastroschisis.

STUDY DESIGN

A retrospective review was conducted of all inborn pregnancies with gastroschisis within the five institutions of the University of California Fetal Consortium (UCfC) between 2007 and 2012. Infants delivered at ⩾28 weeks who had an ultrasound within 21 days before delivery were included. Prediction of BW was evaluated for each of the five ultrasound formulas: Hadlock 1 (abdominal circumference (AC), biparietal diameter (BPD), femur length (FL) and head circumference (HC)) and Hadlock 2 (AC, BPD and FL), Shepard (AC and BPD), Honarvar (FL) and Siemer (BPD, occipitofrontal diameter (OFD), and FL) using Pearson's correlation, mean difference and percent error and Bland-Altman analysis. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the ultrasound diagnosis of intrauterine growth restriction (IUGR) were assessed.

RESULTS

We identified 191 neonates born with gastroschisis within the UCfC, with 111 neonates meeting the inclusion criteria. The mean gestational age at delivery was 36.3±1.7 weeks and the mean BW was 2448±460 g. Hadlock (1) formula was found to have the best correlation (r=0.81), the lowest mean difference (8±306 g) and the lowest mean percent error (1.4±13%). The Honarvar and Siemer formulas performed significantly worse when compared with Hadlock 1, with a 13.7% (P<0.001) and 3.9% (P=0.03) difference, respectively, between estimated and actual BW. This was supported by Bland-Altman plots. For Hadlock 1 and 2, sensitivity was 80% with a NPV of 91%.

CONCLUSION

The widely used Hadlock (1) and (2) formulas provided the best estimated BW in infants with gastroschisis despite its inclusion of abdominal circumference. Furthermore, this formula performs well with diagnosis of IUGR.

Gastroschisis: A Review of Management and Outcomes

We performed an evidence-based review of the obstetrical management of gastroschisis. Gastroschisis is an abdominal wall defect, which has increased in frequency in recent decades. There is variation of prevalence by ethnicity and several known maternal risk factors. Herniated intestinal loops lacking a covering membrane can be identified with prenatal ultrasonography, and maternal serum α-fetoprotein level is commonly elevated. Because of the increased risk for growth restriction, amniotic fluid abnormalities, and fetal demise, antenatal testing is generally recommended. While many studies have aimed to identify antenatal predictors of neonatal outcome, accurate prognosis remains challenging. Delivery by 37 weeks appears reasonable, with cesarean delivery reserved for obstetric indications. Postnatal surgical management includes primary surgical closure, staged reduction with silo, or sutureless umbilical closure. Overall prognosis is good with low long-term morbidity in the majority of cases, but approximately 15% of cases are very complex with complicated hospital course, extensive intestinal loss, and early childhood death.

A New Sonographic Weight Estimation Formula for Small-for-Gestational-Age Fetuses

OBJECTIVES

The purpose of this study was to develop a new specific weight estimation formula for small-for-gestational-age (SGA) fetuses that differentiated between symmetric and asymmetric growth patterns.

METHODS

A statistical estimation technique known as component-wise gradient boosting was applied to a group of 898 SGA fetuses (symmetric, n = 750; asymmetric, n = 148). A new formula was derived from the data obtained and was then compared to other commonly used equations.

RESULTS

The new formula derived is as follows: estimated fetal weight = e^[1.3734627 + 0.0057133 × biparietal diameter + 0.0011282 × head circumference + 0.0201147 × abdominal circumference + 0.0183081 × femur length - 0.0000177 × biparietal diameter(2) - 0.0000018 × head circumference(2) - 0.0000297 × abdominal circumference(2) -0.0001007 × femur length(2) + 0.0397563 × I(sex = male) + 0.0064505 × gestational age (days) + 0.0096528 × I(SGA = asymmetric)], where the function I denotes an indicator function, which is 1 if the expression is fulfilled (sex = male; SGA type = asymmetric) and otherwise 0. In the whole study group and the 2 subgroups, the new formula showed the lowest median absolute percentage error, mean percentage error, and random error and the best distribution of absolute percentage errors within prespecified error bounds.

CONCLUSIONS

The new formula substantially improves weight estimation in SGA fetuses.

Gastroschisis--what should be told to parents?

Gastroschisis is a common congenital abdominal wall defect. It is almost always diagnosed prenatally thanks to routine maternal serum screening and ultrasound screening programs. In the majority of cases, the condition is isolated (i.e. not associated with chromosomal or other anatomical anomalies). Prenatal diagnosis allows for planning the timing, mode and location of delivery. Controversies persist concerning the optimal antenatal monitoring strategy. Compelling evidence supports elective delivery at 37  weeks' gestation in a tertiary pediatric center. Cesarean section should be reserved for routine obstetrical indications. Prognosis of infants with gastroschisis is primarily determined by the degree of bowel injury, which is difficult to assess antenatally. Prenatal counseling usually addresses gastroschisis issues. However, parental concerns are mainly focused on long-term postnatal outcomes including gastrointestinal function and neurodevelopment. Although infants born with gastroschisis often endure a difficult neonatal course, they experience few long-term complications. This manuscript, which is structured around common parental questions and concerns, reviews the evidence pertaining to the antenatal, neonatal and long-term implications of a fetal gastroschisis diagnosis and is aimed at helping healthcare professionals counsel expecting parents.

Accuracy of sonography to predict estimated weight in fetuses with gastroschisis

OBJECTIVES

The purpose of this study was to determine whether sonographic formulas for estimating fetal weight are as accurate for fetuses affected with gastroschisis as they are for healthy fetuses. We hypothesized that because the most commonly used Hadlock formulas rely on the abdominal circumference as a biometric variable, estimates of birth weight are less reliable in fetuses with gastroschisis than in healthy fetuses.

METHODS

We performed a chart review of all fetuses with a prenatal diagnosis of gastroschisis at 3 tertiary care institutions from 1990 to 2008. Charts were reviewed for clinical and sonographic data. The estimated fetal weight at the prenatal sonogram closest to delivery was compared to the birth weight. Published Hadlock formulas using 4 biometric parameters were used to calculate the estimated fetal weight. Data analysis was performed using the Student t test and χ(2) test for continuous and categorical variables, respectively.

RESULTS

One hundred eleven patients with gastroschisis were identified. Sixty-six patients had a prenatal sonogram with a calculated estimated fetal weight within 7 days of delivery; 88 patients had a sonogram within 14 days. The mean birth weights ± SD were 2292 ± 559 and 2477 ± 531 g in the 0- to 7- and 8- to 14-day groups, respectively. Sonographic biometric measurements underestimated the birth weight by an average of 5.6%. Intrauterine growth restriction was predicted in 72% of all pregnancies but was only present in 52%.

CONCLUSIONS

Our study shows a systematic error of birth weight underestimation when using the Hadlock formulas in fetuses affected with gastroschisis.

Does gastric dilation predict adverse perinatal or surgical outcome in fetuses with gastroschisis?

OBJECTIVE

To compare perinatal and infant surgical outcomes in fetuses with gastroschisis with and without gastric dilation in a single-center cohort.

METHODS

This was a retrospective study of all singleton pregnancies with a prenatal diagnosis of gastroschisis managed at University of Toronto perinatal centers between January 2001 and February 2010. Digital prenatal ultrasound images were reviewed to determine fetal gastric size within 2 weeks of delivery. Perinatal and surgical outcomes were compared in fetuses with and without gastric dilation including: gestational age at delivery, mode of delivery, indication for Cesarean section, meconium-stained amniotic fluid, birth weight percentile, Apgar scores at 1 and 5 min, umbilical artery pH, time to full enteral feeding, length of hospital stay, bowel atresia or necrosis and need for bowel resection.

RESULTS

Ninety-eight fetuses with prenatally diagnosed gastroschisis managed at our center were included in the study, of which 32 (32.7%) were found to have gastric dilation. Gastric dilation predicted meconium-stained amniotic fluid at delivery (53% vs. 24%; P = 0.017), but no other adverse perinatal outcome. Surgical morbidity rates (bowel atresia, bowel necrosis, perforation diagnosed postnatally, need for bowel resection, total time to full enteral feeding and length of hospital stay) were unaffected by gastric dilation.

CONCLUSIONS

In gastroschisis, fetal gastric dilation is associated with meconium-stained amniotic fluid at delivery, but is not predictive of any serious perinatal or postnatal complications. Fetal growth and well-being should be serially evaluated on ultrasound using biophysical and Doppler assessment to decide on the optimal timing and mode of delivery.

Ultrasound prediction of birthweight and growth restriction in fetal gastroschisis

OBJECTIVE

Most ultrasound estimated fetal weight (EFW) formulas incorporate abdominal circumference, which may overstimate growth restriction in fetal gastroschisis. The aim of this study was to determine the optimal ultrasound formula for prediction of birthweight and fetal growth restriction (FGR) in gastroschisis.

STUDY DESIGN

We conducted a retrospective cohort analysis of singleton fetuses with gastroschisis. Percentage of error between ultrasound EFW (performed within 2 weeks of delivery) and birthweight was calculated. Agreement between EFW by ultrasound formulas and birthweight was determined by Bland-Altman limits of agreement; concordance between ultrasound and birthweight diagnosis of FGR was evaluated with McNemar's test.

RESULTS

Birthweight was best predicted by the formulas of Shepard et al and Siemer et al. Only these formulas demonstrated significant agreement with birthweight for prediction of FGR at the 5th and 10th percentiles.

CONCLUSION

The formulas of Shepard et al and Siemer et al best estimate birthweight, and their use has the potential to reduce rates of overdiagnosis of FGR.

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.

Incorporation of femur length leads to underestimation of fetal weight in asymmetric preterm growth restriction

OBJECTIVE

To review the performance of a variety of biometry formulae for estimated fetal weight (EFW) in the management of severely growth restricted fetuses with abnormal umbilical artery Doppler at a single perinatal institution.

METHODS

Forty-three pregnancies were retrospectively reviewed. Inclusion criteria were: chromosomally/ structurally normal fetus; complete ultrasound biometry at < or = 7 days from delivery; EFW < 10(th) centile; absent/reversed end-diastolic flow in the umbilical arteries; and delivery at < 32 + 6 weeks. EFW accuracy and precision were compared among nine formulae utilizing combinations of head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL) measurements.

RESULTS

Twenty-six (60.5%) fetuses showed asymmetric growth (HC/AC ratio > 95(th) centile). Analysis of the systematic and random errors associated with each formula showed that the birth weight of asymmetrically-grown fetuses was most closely approximated by the Hadlock equation that utilized BPD and AC measurements only. The birth weight of symmetrically-grown fetuses was most closely approximated by EFW derived from Hadlock equations that utilized > or = three biometry measurements, including FL. Incorporation of FL into Hadlock formulae led to significant underestimation of birth weight in the fetuses with asymmetric growth (mean percentage error +/- SD: EFW(FL-AC), -13.3 +/- 9.8%; EFW(BPD-FL-AC), -10.8 +/- 9.8%; EFW(HC-FL-AC), -11.8 +/- 9.3%; EFW(BPD-HC-FL-AC), -11.7 +/- 9.5%; P < 0.001). The same equations were accurate in fetuses with symmetric growth (EFW(FL-AC), 3.1 +/- 10.0%; EFW(BPD-FL-AC), 1.0 +/- 8.9%; EFW(HC-FL-AC), 0.3 +/- 8.7%; EFW(BPD-HC-FL-AC), 0.4 +/- 15.5%). Use of the best performing equation (Hadlock 3), which does not include FL, to estimate weight in asymmetrically-grown fetuses over 28 weeks' gestation, would have reduced the proportion of those with an underestimation of fetal weight of > 100 g from nine (50.0%) to three (16.7%).

CONCLUSIONS

Biometry methods that exclude FL should be considered in asymmetric intrauterine growth restriction associated with abnormal umbilical artery Doppler waveforms.