Predictive value of a single early fetal weight estimate in normal pregnancies

Multivariable prediction models for fetal macrosomia and large for gestational age: A systematic review

BACKGROUND

The identification of large for gestational age (LGA) and macrosomic fetuses is essential for counselling and managing these pregnancies.

OBJECTIVES

To systematically review the literature for multivariable prediction models for LGA and macrosomia, assessing the performance, quality and applicability of the included model in clinical practice.

SEARCH STRATEGY

MEDLINE, EMBASE and Cochrane Library were searched until June 2022.

SELECTION CRITERIA

We included observational and experimental studies reporting the development and/or validation of any multivariable prediction model for fetal macrosomia and/or LGA. We excluded studies that used a single variable or did not evaluate model performance.

DATA COLLECTION AND ANALYSIS

Data were extracted using the Checklist for critical appraisal and data extraction for systematic reviews of prediction modelling studies checklist. The model performance measures discrimination, calibration and validation were extracted. The quality and completion of reporting within each study was assessed by its adherence to the TRIPOD (Transparent Reporting of a multivariable prediction model for Individual Prognosis Or Diagnosis) checklist. The risk of bias and applicability were measured using PROBAST (Prediction model Risk Of Bias Assessment Tool).

MAIN RESULTS

A total of 8442 citations were identified, with 58 included in the analysis: 32/58 (55.2%) developed, 21/58 (36.2%) developed and internally validated and 2/58 (3.4%) developed and externally validated a model. Only three studies externally validated pre-existing models. Macrosomia and LGA were differentially defined by many studies. In total, 111 multivariable prediction models were developed using 112 different variables. Model discrimination was wide ranging area under the receiver operating characteristics curve (AUROC 0.56-0.96) and few studies reported calibration (11/58, 19.0%). Only 5/58 (8.6%) studies had a low risk of bias.

CONCLUSIONS

There are currently no multivariable prediction models for macrosomia/LGA that are ready for clinical implementation.

Evaluation of sonographic and clinical measures in early versus late third trimester for birth weight prediction

OBJECTIVE

To evaluate the optimal timing for fetal weight estimation during the third trimester.

METHODS

This retrospective cohort study involved fetal weight estimations from both early (28+0-36+6 weeks) and late (37+0 weeks and beyond) third trimester. These estimations were converted to predicted birth weights using the gestation-adjusted projection formula. Birth weight predictions were compared with actual birth weights, to identify the most effective timing for weight prediction.

RESULTS

The study included 3549 cases, revealing mean percentage errors (MPE) of -3.69% for early sonographic assessments, -2.5% for late sonographic assessments, and -1.9% for late clinical assessments. A significant difference was found between early and late sonographic estimations (P < 0.001), whereas late sonographic and clinical assessments did not differ significantly (P = 0.771). Weight predictions for fetuses below the 10th and above the 90th centiles were less accurate than for those within the 10th-90th centiles (P < 0.001). In women with obesity, late clinical estimations were less precise (MPE of -5.85) compared with non-obese women (MPE of -1.66, P < 0.001). For women with diabetes, early sonographic estimations were more accurate (MPE of -1.31) compared with non-diabetic patients (MPE of -3.94, P < 0.001) though this difference did not persist later in pregnancy.

CONCLUSION

Sonographic and clinical weight predictions in the late third trimester were more accurate than earlier third-trimester sonographic assessments, hence continuous follow up and assessments closer to term are important. In women with diabetes, no adjustments in weight prediction methods are necessary. Accurately predicting birth weights for abnormally small or large fetuses remains challenging, indicating the need for improved screening and diagnostic strategies.

Comparison of a Two (32/38 Weeks) versus One (36 Weeks) Ultrasound Protocol for the Detection of Decreased Fetal Growth and Adverse Perinatal Outcome

Third-trimester ultrasound has low sensitivity to small for gestational age (SGA) and adverse perinatal outcomes (APOs). The objective of this study was to compare, in terms of cost-effectiveness, two routine third-trimester surveillance protocols for the detection of SGA and evaluate the added value of a Doppler study for the prediction of APO. This was a retrospective observational study of low-risk pregnancies that were followed by a two growth scans protocol (P2) at 32 and 38 weeks or by a single growth scan at 36 weeks (P1). Ultrasound scans included an estimated fetal weight (EFW) in all cases and a Doppler evaluation in most cases. A total of 1011 pregnancies were collected, 528 with the P2 protocol and 483 with the P1 protocol. While the two models presented no differences for the detection of SGA in terms of sensitivity (47.89% vs. 50% p = 0.85) or specificity (94.97 vs. 95.86% p = 0.63), routine performance of two growth scans (P2) led to a 35% cost increase. The accuracy of EFW for the detection of SGA showed a noteworthy improvement when reducing the interval to labor, and the only parameter with predictive capacity of APO was the cerebroplacental ratio at 38 weeks. In low-risk pregnancies, the higher costs of a two-scan growth surveillance protocol at the third trimester are not justified by an increase in diagnostic effectivity.

Additional single third trimester ultrasound scan in detection of large for gestational age fetuses

PURPOSE OF REVIEW

To evaluate the accuracy of growth scans in the third trimester. To evaluate the accuracy of universal third trimester ultrasound scans in the detection of large for gestational age (LGA) fetuses. To investigate how universal ultrasound scans affect the delivery and outcomes.

RECENT FINDINGS

Universal third trimester screening for LGA recorded a 22% positive predictive value (PPV), and 96% negative predicted value (NPV). The sensitivity in most studies reaches around 70% or more, of all the LGA fetuses delivered, there are different studies for and against universal ultrasonic screening of LGA. Estimated fetal weight (>4 kg/90th centile) and abdominal circumference are the best predictors of LGA with nearly 70% sensitivity. One study reported that an antenatal ultrasonic diagnosis of LGA in a low risk population has a weak association with the incidence of shoulder dystocia or poor neonatal outcomes. Universal screening in the third trimester for LGAs is not cost effective.

SUMMARY

Low risk pregnancies constitute the majority of the pregnancy population. All low risk pregnancy women will only receive two routine scans throughout the whole pregnancy. There is no evidence at present that conclusively demonstrates that an additional scan at 36 weeks improves maternal and neonatal outcomes and is cost effective.

Discriminatory Capacity of Prenatal Ultrasound Measures for Large-for-Gestational-Age Birth: A Bayesian Approach to ROC Analysis Using Placement Values

Predicting large fetuses at birth is of great interest to obstetricians. Using an NICHD Scandinavian Study that collected longitudinal ultrasound examination data during pregnancy, we estimate diagnostic accuracy parameters of estimated fetal weight (EFW) at various times during pregnancy in predicting large-for-gestational-age. We adopt a placement value based Bayesian regression model with random effects to estimate ROC curves. The use of placement values allows us to model covariate effects directly on the ROC curves and the adoption of a Bayesian approach accommodates the a priori constraint that an ROC curve of EFW near delivery should dominate another further away. The proposed methodology is shown to perform better than some alternative approaches in simulations and its application to the Scandinavian Study data suggests that diagnostic accuracy of EFW can improve about 65% from week 17 to 37 of gestation.

Universal late pregnancy ultrasound screening to predict adverse outcomes in nulliparous women: a systematic review and cost-effectiveness analysis

BACKGROUND

Currently, pregnant women are screened using ultrasound to perform gestational aging, typically at around 12 weeks' gestation, and around the middle of pregnancy. Ultrasound scans thereafter are performed for clinical indications only.

OBJECTIVES

We sought to assess the case for offering universal late pregnancy ultrasound to all nulliparous women in the UK. The main questions addressed were the diagnostic effectiveness of universal late pregnancy ultrasound to predict adverse outcomes and the cost-effectiveness of either implementing universal ultrasound or conducting further research in this area.

DESIGN

We performed diagnostic test accuracy reviews of five ultrasonic measurements in late pregnancy. We conducted cost-effectiveness and value-of-information analyses of screening for fetal presentation, screening for small for gestational age fetuses and screening for large for gestational age fetuses. Finally, we conducted a survey and a focus group to determine the willingness of women to participate in a future randomised controlled trial.

DATA SOURCES

We searched MEDLINE, EMBASE and the Cochrane Library from inception to June 2019.

REVIEW METHODS

The protocol for the review was designed a priori and registered. Eligible studies were identified using keywords, with no restrictions for language or location. The risk of bias in studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. Health economic modelling employed a decision tree analysed via Monte Carlo simulation. Health outcomes were from the fetal perspective and presented as quality-adjusted life-years. Costs were from the perspective of the public sector, defined as NHS England, and the costs of special educational needs. All costs and quality-adjusted life-years were discounted by 3.5% per annum and the reference case time horizon was 20 years.

RESULTS

Umbilical artery Doppler flow velocimetry, cerebroplacental ratio, severe oligohydramnios and borderline oligohydramnios were all either non-predictive or weakly predictive of the risk of neonatal morbidity (summary positive likelihood ratios between 1 and 2) and were all weakly predictive of the risk of delivering a small for gestational age infant (summary positive likelihood ratios between 2 and 4). Suspicion of fetal macrosomia is strongly predictive of the risk of delivering a large infant, but it is only weakly, albeit statistically significantly, predictive of the risk of shoulder dystocia. Very few studies blinded the result of the ultrasound scan and most studies were rated as being at a high risk of bias as a result of treatment paradox, ascertainment bias or iatrogenic harm. Health economic analysis indicated that universal ultrasound for fetal presentation only may be both clinically and economically justified on the basis of existing evidence. Universal ultrasound including fetal biometry was of borderline cost-effectiveness and was sensitive to assumptions. Value-of-information analysis indicated that the parameter that had the largest impact on decision uncertainty was the net difference in cost between an induced delivery and expectant management.

LIMITATIONS

The primary literature on the diagnostic effectiveness of ultrasound in late pregnancy is weak. Value-of-information analysis may have underestimated the uncertainty in the literature as it was focused on the internal validity of parameters, which is quantified, whereas the greatest uncertainty may be in the external validity to the research question, which is unquantified.

CONCLUSIONS

Universal screening for presentation at term may be justified on the basis of current knowledge. The current literature does not support universal ultrasonic screening for fetal growth disorders.

FUTURE WORK

We describe proof-of-principle randomised controlled trials that could better inform the case for screening using ultrasound in late pregnancy.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42017064093.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 15. See the NIHR Journals Library website for further project information.

Universal third-trimester ultrasonic screening using fetal macrosomia in the prediction of adverse perinatal outcome: A systematic review and meta-analysis of diagnostic test accuracy

BACKGROUND

The effectiveness of screening for macrosomia is not well established. One of the critical elements of an effective screening program is the diagnostic accuracy of a test at predicting the condition. The objective of this study is to investigate the diagnostic effectiveness of universal ultrasonic fetal biometry in predicting the delivery of a macrosomic infant, shoulder dystocia, and associated neonatal morbidity in low- and mixed-risk populations.

METHODS AND FINDINGS

We conducted a predefined literature search in Medline, Excerpta Medica database (EMBASE), the Cochrane library and ClinicalTrials.gov from inception to May 2020. No language restrictions were applied. We included studies where the ultrasound was performed as part of universal screening and those that included low- and mixed-risk pregnancies and excluded studies confined to high risk pregnancies. We used the estimated fetal weight (EFW) (multiple formulas and thresholds) and the abdominal circumference (AC) to define suspected large for gestational age (LGA). Adverse perinatal outcomes included macrosomia (multiple thresholds), shoulder dystocia, and other markers of neonatal morbidity. The risk of bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. Meta-analysis was carried out using the hierarchical summary receiver operating characteristic (ROC) and the bivariate logit-normal (Reitsma) models. We identified 41 studies that met our inclusion criteria involving 112,034 patients in total. These included 11 prospective cohort studies (N = 9986), one randomized controlled trial (RCT) (N = 367), and 29 retrospective cohort studies (N = 101,681). The quality of the studies was variable, and only three studies blinded the ultrasound findings to the clinicians. Both EFW >4,000 g (or 90th centile for the gestational age) and AC >36 cm (or 90th centile) had >50% sensitivity for predicting macrosomia (birthweight above 4,000 g or 90th centile) at birth with positive likelihood ratios (LRs) of 8.74 (95% confidence interval [CI] 6.84-11.17) and 7.56 (95% CI 5.85-9.77), respectively. There was significant heterogeneity at predicting macrosomia, which could reflect the different study designs, the characteristics of the included populations, and differences in the formulas used. An EFW >4,000 g (or 90th centile) had 22% sensitivity at predicting shoulder dystocia with a positive likelihood ratio of 2.12 (95% CI 1.34-3.35). There was insufficient data to analyze other markers of neonatal morbidity.

CONCLUSIONS

In this study, we found that suspected LGA is strongly predictive of the risk of delivering a large infant in low- and mixed-risk populations. However, it is only weakly (albeit statistically significantly) predictive of the risk of shoulder dystocia. There was insufficient data to analyze other markers of neonatal morbidity.

THIRD TRIMESTER ULTRASOUND SCAN COMBINED WITH A CLINICAL METHOD FOR ACCURATE BIRTHWEIGHT PREDICTION AT TERM: A COHORT STUDY IN SPAIN

OBJECTIVE

To develop and assess an equation based on maternal clinical parameters and third trimester ultrasound biometry (combined method), and compare it with ultrasound-estimated foetal weight (EFW) calculated using the Hadlock 2 formula.

METHODS

Cohort study. A total of 1,224 women with singleton pregnancies who had undergone foetal ultrasound scanning (USS) at 34 weeks were recruited. The study was conducted at a reference center in Valencia (Spain) between January and December 2016. A gestation-adjusted projection (GAP) method was applied to estimated foetal-weight-for-gestational-age by foetal gender at delivery (EFWa). A multivariate regression was created to estimate foetal weight at term (EFWmr) using anthropometric, demographic, ultrasonographic and obstetric-neonatal variables. EFWa and EFWmr were calculated and compared with actual birthweight.

RESULTS

The proportion for EFWmr within <10% of actual birthweight was greater than EFWa (82% vs. 65%, p<0.001). The mean relative error in foetal-weight predictions by using EFWmr was reduced from 6.7% to 0.9% (difference 5.7% 95% CI: 5.4 to 6.0) paired t-test p<0.001, significantly improving the accuracy attainable with USS. The EFWmr outperformed the GAP method in predicting birthweight, within 1% relative error. For new- borns <2,500 g, the proportion of estimates within <10% of the actual birthweight for the EFWmr was greater than that of the EFWa (20.4 vs. 16.3%, p=0.005). For babies with normal birthweight (2,500-3,999 g), EFWmr was a better predictor of birthweight than EFWa (84.5 vs. 65.7%, p<0.001).

CONCLUSIONS

Mathematical modelling to predict birthweight improves third trimester routine ultrasound measurement to estimate neonatal weight at term.

Fetal front-abdominal wall thickness in the second trimester as a predictor of abnormal fetal growth

Objectives: Worldwide, approximately 9% of infants have a birth weight ≥4000 g, who are defined as fetal macrosomia, with wide variations between countries. Another form of abnormal fetal growth is fetal growth restriction. Infants with low birth weight (LBW) for their gestational age are primarily categorized as either small for gestational age (SGA) or fetal (intrauterine) growth restriction (FGR). All forms of abnormal fetal growth have high morbidity rates of neonatal. Therefore, diagnosis of abnormal fetal growth as early as possible is crucial for optimal clinical care. The measurement of fetal front-abdominal wall thickness (FAWT) is an easy examination. We conducted this study, wondering whether FAWT can predict birth weight or can determine LGA/macrosomia and/or LBW infants in advance.Methods: This longitudinal cohort study was done in a tertiary center between September 2016 and September 2019. In total, 768 pregnant women with who attended our clinic for oral glucose tolerance test (OGTT) screening between the 26th and 28th weeks of gestation were included in this study. A total of 768 patients were evaluated in the present study. However, 186 of them were excluded in the follow-up of the study because they met the exclusion criteria or they gave birth in another hospital. Eventually, 582 pregnant women were included, with 57 in the LBW group, 461 in the AGA group, and 64 in the LGA group. In addition, 55 fetuses in the LGA group were determined to be macrosomic (birth weight > 4000 g). The FAWT and classic fetal biometric measurements, such as BPD, AC, FL, and EFW, were compared between the AGA group and the macrosomic infants. Statistical analysis was performed to compare the AGA group and the macrosomic infants group. There were no macrosomic infants in the AGA group, so this was used as the control group.Results: There were no significant differences between the groups for maternal age, gravidity, parity, gestational age on the day of the examination, and gestational age at birth. The mean FAWT was significantly thinner in the SGA group than in the appropriate for gestational age (AGA) group (3.4 versus 3.9 mm, respectively, p < .001), while it was significantly thicker in the LGA group than in the AGA group (4.1 versus 3.9 mm, respectively, p < .001).Conclusion: FAWT measurement can provide more information and may be more sensitive toward fetal nutrition and growth than the AC value during the second trimester. Some benefits can be gained through the measurement of FAWT at the end of the second trimester. FAWT measurements can be used in obstetrical practice with a similar performance in predicting the LGA and macrosomic infant like AC and EFW.

Accuracy of clinical suspicion of growth restriction at term despite a normal growth ultrasound: A retrospective cohort study

BACKGROUND

Small for gestational age (SGA) is a major determinant of poor perinatal outcome. Detecting SGA at term using ultrasound is challenging and we often plan birth based on clinical assessment.

AIMS

To determine the incidence of SGA infants with birthweight <10th centile among women undergoing planned birth at term for suspected SGA despite a normal estimated fetal weight (EFW) on ultrasound at 35-37 weeks.

MATERIALS AND METHODS

We performed a retrospective study including all women with a fetal growth ultrasound at ≥35 weeks reporting an EFW ≥ 10th centile (appropriate for gestational age, AGA) who subsequently had an induction of labour or caesarean birth at ≥37 weeks due to ongoing clinical suspicion of SGA between 2012-2014. The primary outcome was the incidence of SGA newborns using customised centiles.

RESULTS

There were 532 women who had a planned birth for clinical suspicion of SGA during the study period. Of these, 205 (38.5%) had an AGA fetus on ultrasound ≥35 weeks but were subsequently delivered because of a persisting clinical suspicion of SGA on abdominal assessment. Sixty-eight percent (n = 139/205) delivered an SGA infant. Furthermore, almost half of these SGA infants (47.5%) had a birthweight <3rd centile. Neonatal outcomes were worse for the SGA infants, with 15.1% (n = 21/205) requiring special care nursery compared to 1.5% (n = 1/205) of those AGA at birth.

CONCLUSIONS

A reassuring ultrasound with EFW ≥10th centile in the late third trimester should not override clinical concerns of impaired fetal growth at term.

Biochemical tests of placental function versus ultrasound assessment of fetal size for stillbirth and small-for-gestational-age infants

BACKGROUND

Stillbirth affects 2.6 million pregnancies worldwide each year. Whilst the majority of cases occur in low- and middle-income countries, stillbirth remains an important clinical issue for high-income countries (HICs) - with both the UK and the USA reporting rates above the mean for HICs. In HICs, the most frequently reported association with stillbirth is placental dysfunction. Placental dysfunction may be evident clinically as fetal growth restriction (FGR) and small-for-dates infants. It can be caused by placental abruption or hypertensive disorders of pregnancy and many other disorders and factorsPlacental abnormalities are noted in 11% to 65% of stillbirths. Identification of FGA is difficult in utero. Small-for-gestational age (SGA), as assessed after birth, is the most commonly used surrogate measure for this outcome. The degree of SGA is associated with the likelihood of FGR; 30% of infants with a birthweight < 10th centile are thought to be FGR, while 70% of infants with a birthweight < 3rd centile are thought to be FGR. Critically, SGA is the most significant antenatal risk factor for a stillborn infant. Correct identification of SGA infants is associated with a reduction in the perinatal mortality rate. However, currently used tests, such as measurement of symphysis-fundal height, have a low reported sensitivity and specificity for the identification of SGA infants.

OBJECTIVES

The primary objective was to assess and compare the diagnostic accuracy of ultrasound assessment of fetal growth by estimated fetal weight (EFW) and placental biomarkers alone and in any combination used after 24 weeks of pregnancy in the identification of placental dysfunction as evidenced by either stillbirth, or birth of a SGA infant. Secondary objectives were to investigate the effect of clinical and methodological factors on test performance.

SEARCH METHODS

We developed full search strategies with no language or date restrictions. The following sources were searched: MEDLINE, MEDLINE In Process and Embase via Ovid, Cochrane (Wiley) CENTRAL, Science Citation Index (Web of Science), CINAHL (EBSCO) with search strategies adapted for each database as required; ISRCTN Registry, UK Clinical Trials Gateway, WHO International Clinical Trials Portal and ClinicalTrials.gov for ongoing studies; specialist abstract and conference proceeding resources (British Library's ZETOC and Web of Science Conference Proceedings Citation Index). Search last conducted in Ocober 2016.

SELECTION CRITERIA

We included studies of pregnant women of any age with a gestation of at least 24 weeks if relevant outcomes of pregnancy (live birth/stillbirth; SGA infant) were assessed. Studies were included irrespective of whether pregnant women were deemed to be low or high risk for complications or were of mixed populations (low and high risk). Pregnancies complicated by fetal abnormalities and multi-fetal pregnancies were excluded as they have a higher risk of stillbirth from non-placental causes. With regard to biochemical tests, we included assays performed using any technique and at any threshold used to determine test positivity.

DATA COLLECTION AND ANALYSIS

We extracted the numbers of true positive, false positive, false negative, and true negative test results from each study. We assessed risk of bias and applicability using the QUADAS-2 tool. Meta-analyses were performed using the hierarchical summary ROC model to estimate and compare test accuracy.

MAIN RESULTS

We included 91 studies that evaluated seven tests - blood tests for human placental lactogen (hPL), oestriol, placental growth factor (PlGF) and uric acid, ultrasound EFW and placental grading and urinary oestriol - in a total of 175,426 pregnant women, in which 15,471 pregnancies ended in the birth of a small baby and 740 pregnancies which ended in stillbirth. The quality of included studies was variable with most domains at low risk of bias although 59% of studies were deemed to be of unclear risk of bias for the reference standard domain. Fifty-three per cent of studies were of high concern for applicability due to inclusion of only high- or low-risk women.Using all available data for SGA (86 studies; 159,490 pregnancies involving 15,471 SGA infants), there was evidence of a difference in accuracy (P < 0.0001) between the seven tests for detecting pregnancies that are SGA at birth. Ultrasound EFW was the most accurate test for detecting SGA at birth with a diagnostic odds ratio (DOR) of 21.3 (95% CI 13.1 to 34.6); hPL was the most accurate biochemical test with a DOR of 4.78 (95% CI 3.21 to 7.13). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.88 and median prevalence of 19%, EFW, hPL, oestriol, urinary oestriol, uric acid, PlGF and placental grading will miss 50 (95% CI 32 to 68), 116 (97 to 133), 124 (108 to 137), 127 (95 to 152), 139 (118 to 154), 144 (118 to 161), and 144 (122 to 161) SGA infants, respectively. For the detection of pregnancies ending in stillbirth (21 studies; 100,687 pregnancies involving 740 stillbirths), in an indirect comparison of the four biochemical tests, PlGF was the most accurate test with a DOR of 49.2 (95% CI 12.7 to 191). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.78 and median prevalence of 1.7%, PlGF, hPL, urinary oestriol and uric acid will miss 2 (95% CI 0 to 4), 4 (2 to 8), 6 (6 to 7) and 8 (3 to 13) stillbirths, respectively. No studies assessed the accuracy of ultrasound EFW for detection of pregnancy ending in stillbirth.

AUTHORS' CONCLUSIONS

Biochemical markers of placental dysfunction used alone have insufficient accuracy to identify pregnancies ending in SGA or stillbirth. Studies combining U and placental biomarkers are needed to determine whether this approach improves diagnostic accuracy over the use of ultrasound estimation of fetal size or biochemical markers of placental dysfunction used alone. Many of the studies included in this review were carried out between 1974 and 2016. Studies of placental substances were mostly carried out before 1991 and after 2013; earlier studies may not reflect developments in test technology.

Diagnostic performance of third-trimester ultrasound for the prediction of late-onset fetal growth restriction: a systematic review and meta-analysis

OBJECTIVE

The objective of the study was to establish the diagnostic performance of ultrasound screening for predicting late smallness for gestational age and/or fetal growth restriction.

DATA SOURCES

A systematic search was performed to identify relevant studies published since 2007 in English, Spanish, French, Italian, or German, using the databases PubMed, ISI Web of Science, and SCOPUS.

STUDY ELIGIBILITY CRITERIA

We used rrospective and retrospective cohort studies in low-risk or nonselected singleton pregnancies with screening ultrasound performed at ≥32 weeks of gestation.

STUDY APPRAISAL AND SYNTHESIS METHODS

The estimated fetal weight and fetal abdominal circumference were assessed as index tests for the prediction of birthweight <10th (i.e. smallness for gestational age), less than the fifth, and less than the third centile and fetal growth restriction (estimated fetal weight less than the third or estimated fetal weight <10th plus Doppler signs). Quality of the included studies was independently assessed by 2 reviewers, using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. For the meta-analysis, hierarchical summary receiver-operating characteristic curves were constructed, and quantitative data synthesis was performed using random-effects models. The sensitivity of the abdominal circumference <10th centile and estimated fetal weight <10th centile for a fixed 10% false-positive rate was derived from the corresponding hierarchical summary receiver-operating characteristic curves. Heterogeneity between studies was visually assessed using Galbraith plots, and publication bias was assessed by funnel plots and quantified by Deeks' method.

RESULTS

A total of 21 studies were included. Observed pooled sensitivities of abdominal circumference and estimated fetal weight <10th centile for birthweight <10th centile were 35% (95% confidence interval, 20-52%) and 38% (95% confidence interval, 31-46%), respectively. Observed pooled specificities were 97% (95% confidence interval, 95-98%) and 95% (95% confidence interval, 93-97%), respectively. Modeled sensitivities of abdominal circumference and estimated fetal weight <10th centile for 10% false-positive rate were 78% (95% confidence interval, 61-95%) and 54% (95% confidence interval, 46-52%), respectively. The sensitivity of estimated fetal weight <10th centile was better when aimed to fetal growth restriction than to smallness for gestational age. Meta-regression analysis showed a significant increase in sensitivity when ultrasound evaluation was performed later in pregnancy (P = .001).

CONCLUSION

Third-trimester abdominal circumference and estimated fetal weight perform similar in predicting smallness for gestational age. However, for a fixed 10% false-positive rate extrapolated sensitivity is higher for abdominal circumference. There is evidence of better performance when the scan is performed near term and when fetal growth restriction is the targeted condition.

Analysis of the effectiveness of ultrasound and clinical examination methods in fetal weight estimation for term pregnancies

Objective:

To compare the accuracy of clinical and ultrasonographic (USG) estimation of fetal weight in non-complicated, term pregnancies.

Materials and Methods:

Two hundred term pregnant women were included in the study. We used three formulae for the estimation of fetal weight at term; the Hadlock formula for the USG method, and two different formulas for clinical methods, maternal symphysis-fundal height and abdominal circumference at the level of umbilicus. Accuracy was determined by mean percentage error, mean absolute percentage error and proportion of estimates within 10% of actual birth weight (birth weight ±10%). Patients were divided into two groups according to actual birth weight, the normal birth weight group (2500-3999 g) and high birth weight group (≥4000 g).

Results:

All three methods statistically overestimated birth weight for the high and normal birth weight groups (p<0.001, p=1.000, p=0.233) (p=0.037, p<0.001, and p<0.001). For both groups, the mean absolute percentage errors of USG were smaller than for the other two clinical methods and the number of estimates were within 10% of actual birth weight for USG was greater than for the clinical methods; the differences were statistically significant (p<0.001). No statistically significant difference of accuracy was observed for all three methods for the high birth weight group (p=0.365, p=0.768, and p=0.540). However, USG systematically underestimated birth weight in this group.

Conclusion:

For estimation of fetal birth weight in term pregnancies, ultrasonography is better than clinical methods. In the suspicion of macrosomia, it must be remembered that no method is better than any other. In addition, if ultrasonography is used, careful management is recommended because ultrasonography overestimates in this group.

Sonographic fetal weight estimation in normal and overweight/obese healthy term pregnant women by gestation-adjusted projection (GAP) method

PURPOSE

The objective of this study is to assess the ultrasound accuracy in fetal weight estimation related to the time distance between the actual weight recorded at delivery and the period of sonography among normal and overweight/obese pregnant women within 3 weeks prior birth at term.

METHODS

Four-hundred and ninety patients with healthy pregnancy were studied in a cohort study. The absolute percent error in estimation was achieved by gestation-adjusted projection method from Hadlock model for weight calculation as measure of accuracy. The mean percentage error variation over the weeks was correlated to maternal body mass index (BMI, Kg/m(2)) at ultrasound. The relationship between BMI and ultrasound performance was assessed by linear regression.

RESULTS

The overall proportion of supposed sonographic estimated fetal weight at birth within ±10 % of the birth weight significantly declines over the weeks (P = .016). The trend toward a progressive deterioration in ultrasound accuracy is not statistically significant for normal weight women (P = .272) but it is for over-weight/obese (P = .044). On univariate analysis, the absolute percent error and absolute error are positively related to BMI.

CONCLUSIONS

Accuracy is related to the week at ultrasound scan with a gradual deterioration over the time and it worsens with increasing distance in days between the date of ultrasounds and delivery. The deterioration is greater for BMI ≥ 25.

Diagnostic accuracy of placental growth factor and ultrasound parameters to predict the small-for-gestational-age infant in women presenting with reduced symphysis-fundus height

OBJECTIVES

To assess the diagnostic accuracy of placental growth factor (PlGF) and ultrasound parameters to predict delivery of a small-for-gestational-age (SGA) infant in women presenting with reduced symphysis-fundus height (SFH).

METHODS

This was a multicenter prospective observational study recruiting 601 women with a singleton pregnancy and reduced SFH between 24 and 37 weeks' gestation across 11 sites in the UK and Canada. Plasma PlGF concentration < 5(th) centile, estimated fetal weight (EFW) < 10(th) centile, umbilical artery Doppler pulsatility index > 95(th) centile and oligohydramnios (amniotic fluid index < 5 cm) were compared as predictors for a SGA infant < 3(rd) customized birth-weight centile and adverse perinatal outcome. Test performance statistics were calculated for all parameters in isolation and in combination.

RESULTS

Of the 601 women recruited, 592 were analyzed. For predicting delivery of SGA < 3(rd) centile (n = 78), EFW < 10(th) centile had 58% sensitivity (95% CI, 46-69%) and 93% negative predictive value (NPV) (95% CI, 90-95%), PlGF had 37% sensitivity (95% CI, 27-49%) and 90% NPV (95% CI, 87-93%); in combination, PlGF and EFW < 10(th) centile had 69% sensitivity (95% CI, 55-81%) and 93% NPV (95% CI, 89-96%). The equivalent receiver-operating characteristics (ROC) curve areas were 0.79 (95% CI, 0.74-0.84) for EFW < 10(th) centile, 0.70 (95% CI, 0.63-0.77) for low PlGF and 0.82 (95% CI, 0.77-0.86) in combination.

CONCLUSIONS

For women presenting with reduced SFH, ultrasound parameters had modest test performance for predicting delivery of SGA < 3(rd) centile. PlGF performed no better than EFW < 10(th) centile in determining delivery of a SGA infant.

Customised versus population-based growth charts as a screening tool for detecting small for gestational age infants in low-risk pregnant women

BACKGROUND

Fetal growth restriction is defined as failure to reach growth potential and considered one of the major complications of pregnancy. These infants are often, although not universally, small for gestational age (SGA). SGA is defined as a weight less than a specified percentile (usually the 10th percentile). Identification of SGA infants is important because these infants are at increased risk of perinatal morbidity and mortality. Screening for SGA is a challenge for all maternity care providers and current methods of clinical assessment fail to detect many infants who are SGA. Large observational studies suggest that customised growth charts may be better able to differentiate between constitutional and pathologic smallness. Customised charts adjust for physiological variables such as maternal weight and height, ethnicity and parity.

OBJECTIVES

To assess the benefits and harms of using population-based growth charts compared with customised growth charts as a screening tool for detection of fetal growth in pregnant women.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (12 March 2014), reviewed published guidelines and searched the reference lists of review articles.

SELECTION CRITERIA

Randomised, quasi-randomised or cluster-randomised clinical trials comparing customised versus population-based growth charts used as a screening tool for detection of fetal growth in pregnant women.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion.

MAIN RESULTS

No randomised trials met the inclusion criteria.

AUTHORS' CONCLUSIONS

There is no randomised trial evidence currently available. Further randomised trials are required to accurately assess whether the improvement in detection shown is secondary to customised charts alone or an effect of the policy change. Future research in large trials is needed to investigate the benefits and harms (including perinatal mortality) of using customised growth charts in different settings and for both fundal height and ultrasound measurements.

Tracking of fetal growth characteristics during different trimesters and the risks of adverse birth outcomes

BACKGROUND

Fetal growth characteristics are used to identify influences of several maternal characteristics and to identify individuals at increased risk of adverse outcomes. The extent to which fetal growth characteristics track in different trimesters is not known.

METHODS

In a population-based prospective cohort study among 8636 pregnant women, we examined the extent to which fetal growth characteristics track, are influenced by maternal socio-demographic and lifestyle related determinants and are associated with birth outcomes. Fetal growth was assessed in each trimester and at birth.

RESULTS

Correlation coefficient between first-trimester crown-rump length and birthweight was r = 0.12 (P-value < 0.05). Correlation coefficients for fetal-head circumference, (femur) length and (estimated) fetal weight ranged from r = 0.16 to r = 0.30 (all P-values < 0.05) between second trimester and birth and from r = 0.36 to r = 0.58 (all P-values < 0.05) between third trimester and birth, and were highest for (estimated) fetal weight. Correlation coefficients for (estimated) fetal weight tended to be lower among overweight mothers, as compared with normal weight mothers, but were not influenced by other maternal characteristics. First, second and third-trimester fetal growth characteristics were associated with risks of preterm birth and small size for gestational age at birth,with the strongest associations present in third trimester.

CONCLUSION

Fetal growth characteristics track moderately throughout gestation, with stronger tracking coefficients present in later pregnancy. Tracking coefficients were not materially influenced by maternal socio-demographic and lifestyle characteristics. First, second and third trimester fetal growth characteristics were associated with the risk of adverse birth outcomes.

Predicting risk for large-for-gestational age neonates at term: a population-based Bayesian theorem study

OBJECTIVES

To evaluate the prediction of large-for-gestational age (LGA) term neonates using the routine third-trimester ultrasound examination and to investigate whether the prediction could be further improved by adding information on maternal characteristics.

METHODS

Information on 56,792 singleton term pregnancies with a routine ultrasound examination at 32-34 weeks' gestation was retrieved from a population-based perinatal register. Estimated fetal weights (FW) were expressed as gestational age-specific standard deviation scores (Z-scores). The prediction of LGA was assessed by receiver-operating characteristics (ROC) curves, with LGA defined as birth weight Z-score > + 2. The data set with complete clinical information (n = 48,809) was divided into a development and a validation set. Using the development set, multiple logistic regression analysis was performed to identify maternal characteristics associated with LGA. The odds ratios obtained were converted into likelihood ratios. These were then applied to the validation set and the probability for LGA for each infant was estimated using the Bayesian theorem.

RESULTS

The FW Z-score showed a high predictive ability for LGA (area under the ROC curve (AUC) 0.89 (95% CI, 0.89-0.90)). Prediction was further improved by using the model that included both FW Z-scores and maternal variables (AUC 0.91 (95% CI, 0.90-0.92)) (P for difference < 10(-6) ). The corresponding AUC for a model including maternal characteristics only was 0.74 (95% CI, 0.73-0.76).

CONCLUSIONS

Routine third-trimester ultrasound FW estimation is effective in the prediction of LGA neonates at term. The prediction of LGA might be further improved by using a model including maternal characteristics.

Predicting large fetuses at birth: do multiple ultrasound examinations and longitudinal statistical modelling improve prediction?

Predicting large fetuses at birth has long been a challenge in obstetric practice. We examined whether ultrasound examinations at multiple times during pregnancy improve the accuracy of prediction using repeated, longitudinal statistical modelling, and whether adding maternal characteristics improves the accuracy of prediction. We used data from a previous study conducted in Norway and Sweden from 1986 to 1989 in which each pregnant woman had four ultrasound examinations at around 17, 25, 33 and 37 weeks of gestation. At birth, infant size was classified as large-for-gestational age (LGA, >90th centile) and macrosomia (>4000 g) or not. We used a longitudinal random effects model with quadratic fixed and random effects to predict term LGA and macrosomia at birth. Receiver-operator curves and mean-squared error were used to measure accuracy of the prediction. Ultrasound examination around 37 weeks had the best accuracy in predicting LGA and macrosomia at birth. Adding multiple ultrasound examinations at earlier gestations did not improve the accuracy. Adjusting for maternal characteristics had limited impact on the accuracy of prediction. Thus, a single ultrasound examination at late gestation close to birth is the simplest method currently available to predict LGA and macrosomia.

Customised versus population-based growth charts as a screening tool for detecting small for gestational age infants in low-risk pregnant women

BACKGROUND

Fetal growth restriction is defined as failure to reach growth potential and considered one of the major complications of pregnancy. These infants are often, although not universally, small for gestational age (SGA). SGA is defined as a weight less than a specified percentile (usually the 10th percentile). Identification of SGA infants is important because these infants are at increased risk of perinatal morbidity and mortality. Screening for SGA is a challenge for all maternity care providers and current methods of clinical assessment fail to detect many infants that are SGA. Large observational studies suggest that customised growth charts may be better able to differentiate between constitutional and pathologic smallness. Customised charts adjust for physiological variables such as maternal weight and height, ethnicity and parity.

OBJECTIVES

To assess the benefits and harms of using population-based growth charts compared with customised growth charts as a screening tool for detection of fetal growth in pregnant women.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 September 2011), reviewed published guidelines and searched the reference lists of review articles.

SELECTION CRITERIA

Randomised, quasi-randomised or cluster randomised clinical trials comparing customised versus population-based growth charts used as a screening tool for detection of fetal growth in pregnant women.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion.

MAIN RESULTS

No randomised trials met the inclusion criteria.

AUTHORS' CONCLUSIONS

There is no randomised trial evidence currently available. Further randomised trials are required to accurately assess whether the improvement in detection shown is secondary to customised charts alone or an effect of the policy change. Future research in large trials is needed to investigate the benefits and harms (including perinatal mortality) of using customised growth charts in different settings and for both fundal height and ultrasound measurements.

Prediction of newborn birth weight based on the estimation at 20-24 weeks of gestation

OBJECTIVE

The aim of this study was to develop a mathematical equation to predict the birth weight during the second trimester at 20-24 weeks of gestation.

MATERIALS AND METHODS

In a university hospital, 110 healthy pregnant women were eligible for inclusion at 20-24 weeks of gestation. We recorded the maternal weight (pre-pregnancy, mid-pregnancy, and at delivery) and body mass index (BMI), newborn birth weight, time period from ultrasound examination to term delivery, and also the fetal biometrics sonographically at 20-24 weeks of gestation. Pearson's correlation was used to verify the extent of the relationship between all the above measurements and the newborn birth weight. Multiple regressions with the stepwise method were used to analyze maternal weight factors, fetal biometrical factors, and pregnancy interval. An equation for term birth weight estimation during the second trimester was determined.

RESULTS

Maternal BMI at mid-pregnancy, time interval from mid-pregnancy to term, and abdominal circumference had the highest correlation with newborn birth weight (r = 0.388, 0.341, and 0.315, respectively, p < 0.05). Using the stepwise regression analysis, an optimal formula with variance of 0.303 was derived: estimated birth weight = -700 + 49.766 × (mid-pregnancy BMI [kg/m2]) + 13.362 × (time interval from mid-pregnancy to term delivery [days]) + 68.696 × (abdominal circumference [cm]).

CONCLUSION

We propose an accurate, simple, and easy formula to better assess the newborn birth weight at mid-pregnancy for the Asian population. Mid-pregnancy BMI was a more significant factor for birth weight estimation than other maternal weight factors in this study.

Value of a single early third trimester fetal biometry for the prediction of birth weight deviations in a low risk population

OBJECTIVE

To analyze the value of a single ultrasound biometry examination at the onset of the third trimester of pregnancy for the detection of small-for-gestational-age (SGA) and large-for-gestational-age (LGA) at birth in a low risk population. The aim of this study was to develop a simple and useful method for the detection of growth deviations during pregnancy in primary care (midwife or general practitioner) practices.

SETTING

A Dutch primary care midwifery practice.

STUDY DESIGN

In an earlier study, we developed parity and sex specific fetal growth charts of abdominal circumference (AC) and head circumference (HC) on the basis of ultrasound data of a low-risk midwifery population in the Netherlands. In the present study, we calculated sensitivity, specificity and predictive values at different cut-off points of AC and HC for the prediction of growth deviations at birth. Patients booked for perinatal care between 1 January 1993 and 31 December 2003 (n=3449) were used for the identification of cut-off points (derivation cohort) and those admitted between 1 January 2004 and 31 December 2005 (n=725) were used to evaluate the performance of these cut-offs in an independent population (validation cohort). For the determination of SGA and macrosomia at birth, we used the recently published Dutch birth weight percentiles.

RESULTS

Most promising cut-offs were AC <or=25(th) percentile for the prediction of SGA (birth weight <or=10(th) percentile) and AC >or=75(th) percentile for the prediction of macrosomia (birth weight >or=90(th) percentile). Within the validation cohort these cut-offs performed slightly better than in the derivation cohort. For the prediction of SGA, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 53% (95% CI 49-58%), 81% (95% CI 80-83%), 26% (95% CI 23-29%), and 93% (95% CI 93-94%), respectively. The false positive rate was 74%. For the prediction of macrosomia, the values of these parameters were 64% (95% CI 59-69%), 80% (95% CI 78-81%), 23% (95% CI 20-26%), and 96% (95% CI 95-97%), respectively. Here, false positive rate was 77%. No cut-offs were found that predicted extreme birth weight deviations (<or=2.3 percentile; >or=97.7 percentile) sufficiently well.

CONCLUSIONS

In a low risk population, we could predict future growth deviations with a higher sensitivity and in a significant earlier stage (at the onset of the third trimester of pregnancy) than with the use of conventional screening methods (i.e., palpation of the uterus only and fundus-symphysis measurement). Sonographic measurement of fetal abdominal circumference enables to detect more than half of cases of SGA at birth and more than two-thirds of cases of macrosomia with acceptable false-positive rates. We suggest that fetuses with biometry results below the 25(th) percentile or above the 75(th) percentile at the onset of the third trimester of pregnancy should be more intensively investigated in order to distinguish between pathology (e.g., IUGR or macrosomia) and physiology and to decide about the appropriate level of further perinatal care.

Use of the amniotic fluid index combined with estimated fetal weight within 10 days of delivery for prediction of macrosomia at birth

OBJECTIVE

The purpose of this study was to assess the value of combining the sonographically estimated fetal weight (EFW) and amniotic fluid index (AFI) measured within 10 days of term delivery for prediction of macrosomia at birth.

METHODS

Prospective sonographic fetal biometric measurements and delivery ward data of a single center, uploaded separately over a 4-year period, were retrospectively linked to yield an unselected sample of nondiabetic pregnancies with live-born term neonates.

RESULTS

Of the 1925 pregnancies evaluated, 140 (7.2%) were macrosomic (birth weight > or =4000 g). The AFI was significantly higher in the macrosomic group (P < .001). On receiver operating characteristic curve analysis, the area under the curve was larger for predictions based on the EFW alone than on the AFI. An EFW of 4000 g or higher had a positive predictive value of 46.6% for macrosomia at birth. Use of the previously suggested combined EFW and AFI cutoffs of 3689 g and 119 mm, respectively, yielded a positive predictive value of 30.3%.

CONCLUSIONS

Combined use of the EFW and AFI rather than the EFW alone does not improve prediction of macrosomia at birth.

Accuracy of a single fetal weight estimation at 29-34 weeks in diabetic pregnancies: can it predict large-for-gestational-age infants at term?

OBJECTIVES

This study was undertaken to evaluate the accuracy of a single sonographic estimated fetal weight at 29-34 weeks' gestation with respect to birthweight determination in diabetic pregnancies.

STUDY DESIGN

A retrospective cohort study of 423 diabetic pregnancies with detailed fetal measurements at 29-34 weeks' gestation. Multivariate regression analysis was used to predict the birthweight. The percentiles of the estimated fetal weight and the calculated birthweight were compared with the actual birthweight percentile.

RESULTS

The mean birthweight percentile at term was significantly higher than the estimated fetal weight percentile at 29-34 weeks' gestation in the women with poor glycemic control, but not the women with good control. On multivariate analysis, the estimated fetal weight, interval from ultrasound to delivery, hemoglobin A1C level, gestational age at ultrasound, and classification of glycemic control were independently associated with the birthweight. Both the estimated fetal weight and the calculated birthweight had a low sensitivity and a low positive predictive value for predicting large-for-gestational-age infants.

CONCLUSION

Accelerated fetal growth is evident primarily in diabetic women with poor glycemic control. These fetuses cannot be identified by a single ultrasound examination at 29-34 weeks' gestation.