Overestimation of fetal weight by ultrasound: does it influence the likelihood of cesarean delivery for labor arrest?

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

KEY POINTS

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

To know or not to know: Effect of third-trimester sonographic fetal weight estimation on outcomes of large-for-gestational age neonates

OBJECTIVE

The aim of the present study was to evaluate the impact of late third-trimester sonographic estimation of large for gestational age fetuses on pregnancy management and selected fetal and maternal adverse outcomes.

METHODS

A retrospective cohort study was conducted in a tertiary, university-affiliated medical center between 2015 and 2019. All singleton large-for-gestational-age neonates born during this period were included. The cohort was divided into two groups: neonates for whom fetal weight was estimated on late third trimester (<14 days before delivery) sonography and neonates with no recent fetal weight estimation. The groups were compared for pregnancy management strategies, rates of labor induction, cesarean deliveries, and maternal and neonatal outcomes.

RESULTS

A total of 1712 neonates were included in the study, among whom 791 (46.2%) had a late third-trimester fetal weight estimation (study group) and 921 (53.8%) did not (control group). Compared to the control group, the study group was characterized by higher rates of maternal primiparity (24.20% vs 19.20%, P = 0.013), higher maternal body mass index (26.0 ± 6.2 kg/m2 vs 24.7 ± 4.5 kg/m2, P = 0.002), more inductions of labor (29.84% vs 16.40%, P < 0.001) and cesarean deliveries (31.0% vs 19.97%, P < 0.001). There were no clinical differences in neonatal birth weight (4041 ± 256 g vs 3984 264 g, P < 0.001) and no significant differences between other neonatal outcomes, as rates of admission to the neonatal intensive care unit, jaundice, hypoglycemia, and shoulder dystocia.

CONCLUSION

Late third-trimester sonographic fetal weight estimation is associated with a higher rate of labor induction and planned and intrapartum cesarean deliveries. In this retrospective cohort study, those interventions did not lead to reduction in maternal or neonatal adverse outcomes.

Vaginal delivery rate by near delivery sonographic weight estimation and maternal stature among nulliparous women

BACKGROUND

We evaluated the risk for cesarean delivery among term nulliparous women, categorized by maternal stature and recent sonographic estimated fetal weight (EFW).

METHODS

A retrospective study including singleton deliveries of nulliparous women between 2011 and 2020, with sonographic EFW within 1 week of delivery. We categorized maternal height into five groups: ≤150, 151-155, 156-160, 161-165, and ≥166 cm. Fetal weight estimation was categorized into five groups as well: ≤2500 g, 2501-2999, 3000-3499, 3500-3999, and ≥4000 g.

RESULTS

Overall, 13 107 deliveries were included. The cesarean delivery rate was inversely correlated with maternal height, ranging from 41.0% in group 1 to 13.1% in group 5. The vaginal delivery rate ranged from 33.3% in maternal height group 1 with EFW of ≥4000 g to 85% in maternal height group 5 with EFW of ≤2500 g. In weight categories above 2500 g, maternal height correlated significantly with vaginal delivery rate, except in weight category ≥4000 g in which vaginal delivery rate ranged around 30% in maternal height categories 1-3 and increased significantly in groups 4-5 to 50-60%. In multivariable logistic regression analysis, EFW was independently associated with CD for EFW categories 3500-3999 and ≥4000 g [aOR 95% CI 1.49 (1.08-2.06) and 4.39 (2.97-6.50), respectively]. Maternal height was negatively associated with CD [aOR 95% CI 0.67 (0.64-0.70)] for each increase in maternal height group.

CONCLUSIONS

Cesarean delivery rate was inversely correlated with maternal height, ranging from 41.0% among women ≤150 cm to 13.1% among women ≥166 cm. Maternal height and EFW of ≥3500 g are independently associated with CD rates among term nulliparous women.

Influence of Sonographic Fetal Weight Estimation Inaccuracies in Macrosomia on Perinatal Outcome

OBJECTIVE

 To evaluate the influence of inaccurate sonographic fetal weight estimation in macrosomia on the mode of delivery and neonatal outcome (NO).

METHODS

 In 14 633 pregnancies between 2002 and 2016, this retrospective study evaluated the association between sonographic fetal weight estimation, true birth weight (BW), mode of delivery (primary cesarean section [pCS], secondary cesarean section, vaginal delivery, and operative vaginal delivery rates) and NO parameters (5-min Apgar < 7, pH < 7.1, neonatal intensive care unit [NICU] admission, shoulder dystocia). Singleton pregnancies > 37 + 0 weeks with ultrasound-estimated fetal weight (EFW) within 7 days before delivery were included. The study population was divided into four groups: Group 1 (false-negative): EFW < 4000 g/BW ≥ 4000 g; Group 2 (true-positive): EFW ≥ 4000 g/BW ≥ 4000 g; Group 3 (false-positive): EFW ≥ 4000 g/BW < 4000 g; and Group 4 (true-negative): EFW < 4000 g/BW < 4000 g.

RESULTS

 As expected, the highest secondary cesarean section (sCS) rate was found in Group 2 (true-positive) (30.62 %), compared with only 17.68 % in Group 4 (true-negative). The sCS rate in the false-positive Group 3 was significantly higher (28.48 %) in comparison with the false-negative Group 1 (21.22 %; OR 1.48; 95 % CI, 1.16 to 1.89; P = 0.002). In comparison with the true-negative Group 4, univariate analyses showed significantly higher rates for sCS in all other groups: odds ratio (OR) 2.06 for Group 2 (95 % CI, 1.74 to 2.42; P < 0.001), 1.85 for Group 3 (95 % CI, 1.54 to 2.22, P < 0.001), and 1.25 for Group 1 (95 % CI, 1.05 to 1.49; P < 0.01). No significant differences were found for NO between Groups 1 and 3 for the parameters 5-min Apgar < 7 (P = 0.75), pH < 7.1 (P = 0.28), or NICU admission (P = 0.54). However, there was a significantly higher chance for shoulder dystocia in Group 1 compared with Group 3 (OR 4.58; 95 % CI, 1.34 to 24.30; P = 0.008).

CONCLUSION

 Sonographic EFW inaccuracies in fetal macrosomia appear to have a greater impact on the mode of delivery than birth weight itself. Underestimation of fetal weight may be associated with a higher probability of shoulder dystocia.

A Maternal Serum Metabolite Ratio Predicts Large for Gestational Age Infants at Term: A Prospective Cohort Study

CONTEXT

Excessive birth weight is associated with maternal and neonatal complications. However, ultrasonically estimated large for gestational age (LGA; >90th percentile) predicts these complications poorly.

OBJECTIVE

To determine whether a maternal serum metabolite ratio developed for fetal growth restriction (FGR) is predictive of birth weight across the whole range, including LGA at birth.

METHODS

Metabolites were measured using ultrahigh performance liquid chromatography-tandem mass spectroscopy. The 4-metabolite ratio was previously derived from an analysis of FGR cases and a random subcohort from the Pregnancy Outcome Prediction study. Here, we evaluated its relationship at 36 weeks of gestational age (wkGA) with birth weight in the subcohort (n = 281). External validation in the Born in Bradford (BiB) study (n = 2366) used the metabolite ratio at 24 to 28 wkGA.

RESULTS

The inverse of the metabolite ratio at 36 wkGA predicted LGA at term [the area under the receiver operating characteristic curve (AUROCC) = 0.82, 95% CI 0.73 to 0.91, P = 6.7 × 10-5]. The ratio was also inversely associated with birth weight z score (linear regression, beta = -0.29 SD, P = 2.1 × 10-8). Analysis in the BiB cohort confirmed that the ratio at 24 to 28 wkGA predicted LGA (AUROCC = 0.60, 95% CI 0.54 to 0.67, P = 8.6 × 10-5) and was inversely associated with birth weight z score (beta = -0.12 SD, P = 1.3 × 10-9).

CONCLUSIONS

A metabolite ratio which is strongly predictive of FGR is equally predictive of LGA birth weight and is inversely associated with birth weight across the whole range.

Obstetric consequences of a false-positive diagnosis of large-for-gestational-age fetus

Objective

To compare delivery outcomes between true‐positive (TP) and false‐positive (FP) large‐for‐gestational‐age (LGA) fetuses, appropriate‐for‐gestational‐age (AGA) fetuses, and false‐negative (FN) LGA fetuses.

Methods

Retrospective cohort study of singleton pregnancies at risk for macrosomia without contraindication to vaginal delivery, receiving an ultrasound scan at 34–37 weeks of pregnancy.

Results

In all, 430 pregnancies were included: 155 TP LGA, 87 FP LGA, 177 AGA and 11 FN LGA newborns. Cesarean section rate during labor was significantly higher in FP LGA than in AGA (19% vs. 8.7%) but not significantly different between FP LGA and TP LGA (19% vs. 32.4%). Median birth weight z score was significantly higher in TP LGA (1.9) compared with the FP LGA and AGA (0.91 and 0.84, respectively), whereas no significant differences were found between FP LGA and AGA. Admission to a neonatal intensive care unit was significantly more frequent in TP LGA than AGA, whereas shoulder dystocia, postpartum hemorrhage, and third‐ to fourth‐degree perineal tears were similar between the different groups.

Conclusion

A false‐positive diagnosis of LGA fetus is associated with a significant increase of cesarean section during labor. Therefore, a suspicious ultrasound may result in reduction of the clinical threshold for the diagnosis of abnormal labor.

A false‐positive diagnosis of LGA fetus on ultrasound at 34–37 weeks is associated with a significant increase in cesarean section during labor.

Changes in placental elastography in the third trimester - Analysis using a linear mixed effect model

INTRODUCTION

Research into the role of ultrasound elastography to assess compromised placental tissue is ongoing. There is particular interest in evaluating its potential in the investigation of changes associated with uteroplacental dysfunction. To date, there is limited data on how different maternal and fetal considerations, such as advancing gestational age, amniotic fluid Index (AFI) and maternal body mass index (BMI) may influence shear wave velocity (SWV) measurements. This study aimed to evaluate longitudinal changes in SWV throughout gestation and model these changes with other developing fetal and maternal physiological and biological characteristics.

METHODS

The study utilised 238 singleton pregnancies and collected longitudinal data at repeated intervals in the 3rd trimester representing 629 individual data points. Linear mixed model regression analysis was used to identify significant predictors for SWV.

RESULTS

From a total of ten variables selected for modelling, only gestational age, AFI, BMI, and sample depth were found to be significant predictors of placental SWV, and gestational age and AFI were found to have only a minimal impact on SWV.

DISCUSSION

Sophisticated statistical modelling demonstrates that many of the expected maternal and fetal changes in the 3rd trimester have no or minimal impact on placental SWV. Understanding which factors influence placental SWV is essential to ascertain the technique's utility in managing pregnancies complicated by placental dysfunction in the future.

Adverse Outcomes among Low-Risk Pregnancies at 39 to 41 Weeks: Stratified by Birth Weight Percentile

OBJECTIVE

This study aimed to assess the risk of adverse outcomes among low-risk pregnancies at 39 to 41 weeks, stratified by birth weight percentile.

STUDY DESIGN

This retrospective cohort study utilized the U.S. vital statistics datasets (2013-2017) and evaluated low-risk women with nonanomalous cephalic singleton gestations who labored and delivered at 39 to 41 weeks, regardless of ultimate mode of delivery. Newborns were categorized as small (<10th percentile), large (>90th percentile), or appropriate (10-90th percentile) for gestational ages (SGA, LGA, and AGA, respectively). The primary outcome, composite neonatal adverse outcome (CNAO), included Apgar's score <5 at 5 minutes, assisted ventilation >6 hours, seizure, or neonatal death. The secondary outcome, composite maternal adverse outcome (CMAO), included intensive care unit admission, blood transfusion, uterine rupture, or unplanned hysterectomy. Multivariable Poisson's regression was used to estimate the association (using adjusted relative risk [aRR] and 95% confidence interval [CI]).

RESULTS

Of 19.8 million live births during the study interval, approximately 8.9 million (44.9%) met the inclusion criteria, with 9.9% being SGA, 9.2% being LGA, and 80.9% being AGA. SGA newborns delivered at 40 (aRR = 1.17; 95% CI: 1.12-1.23) and at 41 weeks (aRR = 1.55; 95% CI: 1.45-1.66) had a higher risk of CNAO than at 39 weeks. Similarly, LGA newborns delivered at 40 (aRR = 1.13; 95% CI: 1.07-1.19) and 41 weeks (aRR = 1.44; 95% CI: 1.35-1.54) and AGA newborns delivered at 40 (aRR = 1.24; 95% CI: 1.21-1.26) and 41 weeks (aRR = 1.57; 95% CI: 1.53-1.61) also had a higher risk of CNAO than at 39 weeks. CMAO was also significantly higher at 40 and 41 weeks than at 39 weeks, regardless of whether the mothers delivered SGA, LGA, or AGA newborns.

CONCLUSION

Among low-risk pregnancies, the risks of composite neonatal and maternal adverse outcomes increase from 39 through 41 weeks' gestation, irrespective of whether newborns are SGA, LGA, or AGA.

Current Resources for Evidence-Based Practice, May 2021

An extensive review of new resources to support the provision of evidence-based care for women and infants. The current column includes a discussion of the prenatal prediction of fetal macrosomia and commentaries on reviews focused on the effects of date palm and dill seed on labor outcomes and the current research available on SARS-CoV-2 and pregnancy outcomes.

Late Pregnancy Ultrasound to Screen for and Manage Potential Birth Complications in Nulliparous Women: A Cost-Effectiveness and Value of Information Analysis

BACKGROUND

Fetal growth restriction is a major risk factor for stillbirth. A routine late-pregnancy ultrasound scan could help detect this, allowing intervention to reduce the risk of stillbirth. Such a scan could also detect fetal presentation and predict macrosomia. A trial powered to detect stillbirth differences would be extremely large and expensive.

OBJECTIVES

It is therefore critical to know whether this would be a good investment of public research funds. The aim of this study is to estimate the cost-effectiveness of various late-pregnancy screening and management strategies based on current information and predict the return on investment from further research.

METHODS

Synthesis of current evidence structured into a decision model reporting expected costs, quality-adjusted life-years, and net benefit over 20 years and value-of-information analysis reporting predicted return on investment from future clinical trials.

RESULTS

Given a willingness to pay of £20 000 per quality-adjusted life-year gained, the most cost-effective strategy is a routine presentation-only scan for all women. Universal ultrasound screening for fetal size is unlikely to be cost-effective. Research exploring the cost implications of induction of labor has the greatest predicted return on investment. A randomized, controlled trial with an endpoint of stillbirth is extremely unlikely to be a value for money investment.

CONCLUSION

Given current value-for-money thresholds in the United Kingdom, the most cost-effective strategy is to offer all pregnant women a presentation-only scan in late pregnancy. A randomized, controlled trial of screening and intervention to reduce the risk of stillbirth following universal ultrasound to detect macrosomia or fetal growth restriction is unlikely to represent a value for money investment.

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.

The rates and medical necessity of cesarean delivery in China, 2012-2019: an inspiration from Jiangsu

BACKGROUND

The World Health Organization (WHO) in 2015 stated that every effort should be made to provide cesarean delivery (CD) for women in need. In China, the two-child policy largely prompts the number of advanced age childbirth, which raises the possibility of an increasing number of women who need a c-section. The aim of this study was to assess the trends in the overall and medical indication-classified CD rates in the era of the two-child policy in Jiangsu, China.

METHODS

A retrospective cross-sectional study of 291,448 women who delivered in 11 hospitals in Jiangsu province between 2012 and 2019 was conducted. Medical cesarean indication for each woman was ascertained by manually reviewing the medical records. The 291,448 women were divided into two subgroups according to the presence of the indications: the indicated group (7.80%) and the non-indicated group (92.20%). We then fitted joinpoint regression and log-binomial regression models to estimate trends in the CD rates across the study period.

RESULTS

The overall CD rate was observed with a declining trend from 52.51% in 2012-2015 to 49.76% in 2016-2019 (adjusted RR, 0.92; 95% CI, 0.91-0.93; P < 0.001), along with an annual percentage change (APC) to be - 1.0 (95% CI, - 2.1 to 0.0) across the period. The participants were then divided into two subgroups according to the presence of medical CD indications: the indicated group (7.80%) and the non-indicated group (92.20%).We found the declining trend was most pronounced in the non-indicated group, with the CD rates decreased from 50.02% in 2012-2015 to 46.27% in 2016-2019 (adjusted RR, 0.90; 95% CI, 0.89-0.90; P < 0.001). By contrast, we observed a steady trend in the CD rate of the indicated group, which maintained from 87.47% in 2012-2015 to 86.57% in 2016-2019 (P = 0.448). In the indicated group, a higher risk of adverse pregnancy outcomes was revealed for those women who delivered vaginally as compared with those who received c-section. We further investigated that women with following specific indications had a higher proportion of vaginal delivery, i.e., pregnancy complications, fetal macrosomia, and pregnancy complicated with tumor (34.70%, 10.84%, and 16.34%, respectively). Women with the above 3 indications were observed with a higher risk of adverse pregnancy outcomes if delivered vaginally. The incidence rates of the medical indications among the general population increased considerably over the 8-year period (P < 0.001).

CONCLUSIONS

Although the overall CD rate apparently decreased in the recent years, along with the decline of the unnecessary CD rate, a considerable proportion of indicated women were not provided with CD service in Jiangsu, China. Instead of targeting the overall CD rate, we need to take actions to reduce unnecessary CD rate and provide adequate c-section service for women with indications, particularly for those with underlying diseases and suspected fetal macrosomia.

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.

Cephalopelvic disproportion as primary diagnosis for cesarean section: Role of neonatal birthweight in relation to maternal height at a Hospital in Merida, Mexico

OBJECTIVE

To analyze the association between newborn and maternal characteristics and the risk for cesarean section (CS) due to cephalopelvic disproportion (CPD) and non-CPD causes compared to vaginal deliveries (VD) in a sample of infants and mothers from Merida, Yucatan, Mexico.

METHODS

The final sample consisted of 3453 single, live, and term infants born between January 2016 and May 2017 at the Maternal-Infant Hospital in Merida and their mothers (aged ≥19 years). The mode of delivery was established as the dependent variables: (a) VD, (b) CS due to CPD, and (c) non-CPD CS. Independent variables were maternal height and weight, the number of previous VD, newborn weight, and neonatal birthweight (BW) index/maternal height index. A multinomial regression model was used to analyze the association between newborn and maternal characteristics and outcome variable.

RESULTS

By mode of delivery, 2124 (62%) births corresponded to VD, 1042 (30%) to non-CPDCS, and 287 (8%) to CS due to CPD. Mothers who had CS due to CPD weighed more at the end of their pregnancy and were shorter. Maternal age and weight increased the risk for having CS due to CPD compared to VD and maternal height, and the number of previous VD reduces the risk for experiencing CS due to CPD compared to vaginal births. The relative risk ratio for higher neonatal BW/maternal height index was significant for CS due to CPD and non-CPD CS.

CONCLUSION

According to our results from a public hospital in Merida, Mexico, CPD is a result of the interrelation of maternal and fetal size, rather than an independent result of maternal height or BW.

Maternal and system characteristics, oxytocin administration practices, and cesarean birth rate

BACKGROUND

The cesarean birth rate in the United States is 32%, and there is discussion about the cause of high surgical birth rates. Our purpose was to determine whether mode of birth is influenced by maternal, nurse, and system factors.

METHODS

Secondary analysis of a data set of 163 women having postdates labor induction with oxytocin. Kaplan-Meier survival curves were calculated to compare the time for patients to reach an infusion rate of 6 mU/min, consistent with endogenous oxytocin levels in active labor. We used the log-rank test to evaluate survival curve differences. Multiple logistic regression and Cox proportional hazards models were conducted and included covariates that had statistically significant bivariate relationships with the time variable, or were clinically meaningful.

RESULTS

The mean time to reach 6 mU/min was longer for women who birthed by cesarean (172.5 minutes) than for women who had vaginal birth (125.0 minutes, P = .024). The mean time to reach 6 mU/min was also longer for women admitted on night shift (147.0 minutes) than day shift (110.2 minutes, P = .018). No maternal characteristics were significantly related to the time to reach a rate of 6 mU/min.

CONCLUSIONS

Even during the initial hours of labor induction, it is important that the oxytocin infusion is titrated appropriately to aid women in achieving timely vaginal birth. Intrapartum nurses should receive education about the pharmacokinetics of intravenous oxytocin to understand proper administration of this high-alert medication.

Does the Porter formula hold its promise? A weight estimation formula for macrosomic fetuses put to the test

Purpose

Estimating fetal weight using ultrasound measurements is an essential task in obstetrics departments. Most of the commonly used weight estimation formulas underestimate fetal weight when the actual birthweight exceeds 4000 g. Porter et al. published a specially designed formula in an attempt to improve detection rates for such macrosomic infants. In this study, we question the usefulness of the Porter formula in clinical practice and draw attention to some critical issues concerning the derivation of specialized formulas of this type.

Methods

A retrospective cohort study was carried out, including 4654 singleton pregnancies with a birthweight ≥ 3500 g, with ultrasound examinations performed within 14 days before delivery. Fetal weight estimations derived using the Porter and Hadlock formulas were compared.

Results

Of the macrosomic infants, 27.08% were identified by the Hadlock formula, with a false-positive rate of 4.60%. All macrosomic fetuses were detected using the Porter formula, with a false-positive rate of 100%; 99.96% of all weight estimations using the Porter formula fell within a range of 4300 g ± 10%. The Porter formula only provides macrosomic estimates.

Conclusions

The Porter formula does not succeed in distinguishing macrosomic from normal-weight fetuses. High-risk fetuses with a birthweight ≥ 4500 g in particular are not detected more precisely than with the Hadlock formula. For these reasons, we believe that the Porter formula should not be used in clinical practice. Newly derived weight estimation formulas for macrosomic fetuses must not be based solely on a macrosomic data set.

Electronic supplementary material

The online version of this article (10.1007/s00404-019-05410-7) contains supplementary material, which is available to authorized users.

Optimal Timing of Prenatal Ultrasound in Predicting Birth Weight in Diabetic Pregnancies

OBJECTIVE

This study sought to determine the optimal timing of ultrasound in the third trimester to predict birth weight accurately in diabetic women with a singleton pregnancy.

METHODS

A retrospective cohort study of all diabetic women with a singleton pregnancy treated in Halifax, Nova Scotia, was performed. Estimated fetal weight was derived from ultrasound measures using the Hadlock2 equation. The Mongelli equation was used to predict birth weight. The association between gestational age at ultrasound and accuracy of predicted birth weight was assessed, with accuracy as a continuous variable representing the difference between predicted and actual birth weight and as a categorical variable (with four gestational age categories) representing whether predicted birth weight was within, over, or under 250 g of actual birth weight RESULTS: The cohort of 943 women comprised 121 (12.8%) with type 1 diabetes, 111 (11.7%) with type 2 diabetes, and 711 (75.4%) with gestational diabetes. Ultrasound scans performed at term were the most accurate in predicting birth weight. At this gestational age, the mean difference between predicted and actual birth weight was -30 g (95% confidence interval -109 to -48). After adjusting for maternal body mass index, age, smoking, type of diabetes, and interval between ultrasound examination and delivery, accuracy improved as gestational age at ultrasound increased (P = 0.005). The odds of underpredicting or overpredicting birth weight were not significantly affected by the timing of the ultrasound examination.

CONCLUSION

Because the predictive accuracy of ultrasound prediction of birth weight improves with gestational age, fetal growth assessment at term is recommended to aid with delivery planning in women with diabetes.

Identifying fetal growth disorders using ultrasound in obese nulliparous women

OBJECTIVE

We evaluated the ability of third trimester ultrasound to diagnose fetal growth disorders among obese women.

METHODS

This is a retrospective cohort study of obese nulliparous women who delivered term singleton neonates who had an ultrasound within 5 weeks of delivery. We characterized the sensitivity, specificity, positive predictive value and negative predictive value of ultrasound to detect large-for-gestational age (LGA) and small-for-gestational age (SGA) infants. Antenatally, LGA and SGA were defined as an ultrasound estimated fetal weight >90% or <10% based on the Hadlock formula. Postnatally, LGA or SGA designation was based on gestational age-based birthweight percentiles. Test characteristics were analyzed for the total cohort and by class of obesity (class II, body mass index [BMI] = 35.0-39.9 kg/m² versus class III, BMI ≥ 40 kg/m²). We compared the area under the curve for receiver-operating characteristic (ROC) curves for different classes of obesity.

RESULTS

Of 690 women, 13 (1.9%) screened positive for SGA and 19 (2.8%) delivered an SGA neonate. In contrast, 158 (22.9%) screened positive for LGA and 97 (14.1%) delivered an LGA neonate. The sensitivity of ultrasound for SGA was 26.3% and the specificity was 98.8%. The sensitivity for LGA was 75.3% and the specificity was 85.7%. The ROC curves did not differ significantly for different classes of obesity (p = .69 for SGA, p = .75 for LGA).

CONCLUSION

Ultrasound in obese women who delivered term pregnancies has a high specificity but poor sensitivity for SGA and a low positive predictive value for LGA.

The cost-effectiveness of universal late-pregnancy screening for macrosomia in nulliparous women: a decision analysis

Objective

To identify the most cost‐effective policy for detection and management of fetal macrosomia in late‐stage pregnancy.

Design

Health economic simulation model.

Setting

All English NHS antenatal services.

Population

Nulliparous women in the third trimester treated within the UK NHS.

Methods

A health economic simulation model was used to compare long‐term maternal–fetal health and cost outcomes for two detection strategies (universal ultrasound scanning at approximately 36 weeks of gestation versus selective ultrasound scanning), combined with three management strategies (planned caesarean section versus induction of labour versus expectant management) of suspected fetal macrosomia. Probabilities, costs and health outcomes were taken from literature.

Main outcome measures

Expected costs to the NHS and quality‐adjusted life‐years (QALYs) gained from each strategy, calculation of net benefit and hence identification of most cost‐effective strategy.

Results

Compared with selective ultrasound, universal ultrasound increased QALYs by 0.0038 (95% CI 0.0012–0.0076), but also costs by £123.50 (95% CI 99.6–149.9). Overall, the health gains were too small to justify the cost increase given current UK thresholds cost‐effective policy was selective ultrasound coupled with induction of labour where macrosomia was suspected.

Conclusions

The most cost‐effective policy for detection and management of fetal macrosomia is selective ultrasound scanning coupled with induction of labour for all suspected cases of macrosomia. Universal ultrasound scanning for macrosomia in late‐stage pregnancy is not cost‐effective.

Tweetable abstract

Universal late‐pregnancy ultrasound screening for fetal macrosomia is not warranted.

Universal late‐pregnancy ultrasound screening for fetal macrosomia is not warranted.

Sonographic Estimated Fetal Weight and Cesarean Delivery among Nulliparous Women with Obesity

Objective  This study was aimed to examine the association between having an ultrasound estimate of fetal weight (US-EFW) and mode of delivery among obese women. Study Design  A retrospective cohort study of nulliparous women with a body mass index of ≥ 35 kg/m ² who delivered term singleton gestations. We examined whether having had an US-EFW within 35 days of delivery, or an US-EFW ≥ 90th percentile for gestational age, was associated with intrapartum cesarean delivery. Results  Of 2,826 women, 22.5% ( n  = 636) had an US-EFW within 35 days of delivery. Having an US-EFW was associated with increased frequency of cesarean (43.1% for those with an US-EFW versus 30.0% for those without, p  < 0.001); this finding persisted when controlling for confounders (adjusted odds ratio [aOR] 1.48, 95% confidence interval [CI] 1.21-1.81). Of the 636 women with an US-EFW, 22.5% ( n  = 143) had an US-EFW ≥ 90th percentile for gestational age, which was associated with increased frequency of an intrapartum cesarean (60.8% for those with an US-EFW ≥ 90th percentile vs. 37.9% for those with an US-EFW of < 90th percentile, p  < 0.001), even when accounting for confounders (aOR = 1.78, 95% CI: 1.10-2.87). Conclusion  The presence of an US-EFW among nulliparous obese women was associated with undergoing intrapartum cesarean delivery.

Does prenatal identification of fetal macrosomia change management and outcome?

PURPOSE

To assess whether there is an association between predicted fetal macrosomia and adverse outcomes in macrosomic newborns (> 4000 g), based on a sonographic evaluation up to 2 weeks prior to delivery.

METHODS

A retrospective cohort study of 3098 mothers of macrosomic babies who were delivered at our institution (2000-2015). We compared the management and outcomes of women with predicted fetal macrosomia with that of women with unknown fetal macrosomia. The primary outcomes were cesarean section (CS) rate and postpartum hemorrhage. Secondary outcomes were composite maternal and neonatal outcomes and birth injuries.

RESULTS

In 601 (19.4%) women fetal macrosomia was predicted, and in 2497 (80.6%) women, fetal macrosomia was unknown. CS rate was more than 3.5 times higher in the group of predicted macrosomia (47.2% vs. 12.7%, P < 0.001) than those with unpredicted macrosomia; not only due to non-progressive labor, but for non-reassuring heart rate as well. However, predicted fetal macrosomia reduced the risk of postpartum hemorrhage (aOR 0.5, 95% CI 0.2-1.0), maternal (aOR 0.3, 95% CI 0.2-0.5) and neonatal composite adverse outcomes (aOR 0.7 95% CI 0.6-0.9). It was also associated with increased risk for induction of labor, episiotomy, 3rd- or 4th-degree tears and a longer maternal hospitalization. Birth injuries and shoulder dystocia were not different between the groups.

CONCLUSIONS

Antepartum CS was found to be associated with predicted fetal macrosomia. Moreover, a planned CS due to macrosomia was associated with reduced risk for postpartum hemorrhage, maternal and neonatal outcome, even for babies with a mean birth weight < 4500 g.

Association between Sonographic Estimated Fetal Weight and the Risk of Cesarean Delivery among Nulliparous Women with Diabetes in Pregnancy

OBJECTIVE

The objective of this study was to examine the association between an ultrasound-estimated fetal weight (US-EFW) and mode of delivery among nulliparous diabetic women.

STUDY DESIGN

This is a retrospective cohort study of nulliparous women with medication-requiring gestational or pregestational diabetes who delivered term, singleton gestations following a trial of labor. We determined whether having had an US-EFW within 35 days of delivery was associated with cesarean delivery.

RESULTS

Of 304 women who met the eligibility criteria, 231 (76.0%) had an US-EFW within 35 days of delivery. An US-EFW was associated with increased likelihood of intrapartum cesarean (51.5% for those with an ultrasound vs. 27.4% for those without, p < 0.001); this finding persisted even when controlling for birth weight and other confounding factors (adjusted odds ratio: 2.23, 95% confidence interval: 1.16-4.28). Among women with a recent US-EFW, a diagnosis of a large-for-gestational-age (LGA) fetus was associated with overall intrapartum cesarean frequency (65.2% for women with an LGA fetus vs. 46.1% for those without, p = 0.009), but this association did not remain significant in multivariable models.

CONCLUSION

An US-EFW within 35 days of delivery among nulliparous women with medication-requiring diabetes was positively associated with intrapartum cesarean delivery.

Disadvantages of a weight estimation formula for macrosomic fetuses: the Hart formula from a clinical perspective

Purpose

Sonographic fetal weight (FW) estimation to detect macrosomic fetuses is an essential part of everyday routine work in obstetrics departments. Most of the commonly used weight estimation formulas underestimate FW when the actual birth weight (BW) exceeds 4000 g. One of the best-established weight estimation formulas is the Hadlock formula. In an effort to improve the detection rates of macrosomic infants, Hart et al. published a specially designed formula including maternal weight at booking. The usefulness of the Hart formula was tested.

Methods

Retrospective study of 3304 singleton pregnancies, birth weight ≥ 3500 g. The accuracy of the Hadlock and Hart formula were tested. A subgroup analysis examined the influence of the maternal weight. The Chi-squared test and one-way analysis of variation were carried out. For all analyses, p < 0.05 was considered statistically significant.

Results

The overall percentages of births falling within ± 5% and ± 10% of the BW using the Hadlock formula were 27% and 53%, respectively. Using the Hart formula, 24% and 54% were identified within these levels. With the Hart formula, 94% of all weight estimations fall within 4200 g ± 5% and nearly 100% fall within 4200 g ± 10%.

Conclusions

Applying the Hart formula results in an overestimation of fetal weight in neonates with a birth weight < 4000 g and fails to identify high-risk fetuses. We, therefore, do not consider Hart’s formula to be of clinical relevance.

Accuracy of sonographic estimated fetal weight in suspected macrosomia: the likelihood of overestimating and underestimating the true birthweight

Objective: Macrosomia has increased risk of serious adverse outcomes for both infants and their mothers. As such, many providers recommend induction of labor or cesarean delivery (CD) based on sonographic estimated fetal weight (sonoEFW) cutoffs. It is known that sonoEFW is a poor predictor of birthweight (BW), especially at the extremes of weight. It is not clear, however, whether sonoEFWs tend to underestimate or overestimate the true BW among fetuses with suspected macrosomia. The objective of this study was to compare rates of overestimation of BW among women with suspected macrosomia by sonoEFW.Methods: This was a retrospective cohort study of women who presented to a single maternal-fetal medicine ultrasound unit within 2 weeks prior to delivery from January 2011 to November 2017. We identified women who received a sonoEFW ≥4000 g. The study sample was divided into four sonoEFW categories: 4000-4249, 4250-4499, 4500-4749, and ≥4750 g. Accuracy of sonoEFW was compared across groups, with the primary outcome being overestimation of BW.Results: A total of 502 patients were included, of whom 301 (60.1%) had a sonoEFW 4000-4249 g, 135 (26.9%) had a sonoEFW 4250-4499 g, 45 (9.0%) had a sonoEFW 4500-4749 g, and 21 (4.2%) had a sonoEFW ≥4750 g. In each sonoEFW group, the risk of overestimating BW was greater than 50%, and the likelihood of overestimation of BW increased significantly across sonoEFW groups (69.4, 76.3, 80.0, 95.2%, p < .001). This held true after adjusting for differences in baseline characteristics, including diabetes and amniotic fluid index. BW ≥4500 g was not accurately predicted. Among women with sonoEFW 4500-4749 g, only 28.9% delivered a neonate with a BW >4500 g; for women with a sonoEFW ≥4750 g, only 47.6% had a BW >4500 g. One hundred sixty-one (32.1%) women underwent CD for suspected macrosomia. Of these CDs, 48 (29.8%) of neonates had a BW <4000 g and 134 (83.2%) had a BW <4500 g.Conclusion: In patients undergoing sonoEFW within 2 weeks of delivery, sonoEFWs ≥4000 g are significantly more likely to overestimate than underestimate the true BW. Obstetricians should be cautious about intervening based on sonoEFW alone, given the high risk that this value is an overestimation of the true weight.

Blinded ultrasound fetal biometry at 36 weeks and risk of emergency Cesarean delivery in a prospective cohort study of low-risk nulliparous women

OBJECTIVES

To compare the association between risk of emergency Cesarean delivery (CD) and non-customized vs customized ultrasound estimated fetal weight (EFW) at 36 weeks' gestation, determine whether addition of ultrasound EFW to a model based on maternal characteristics alone improved prediction of emergency CD, assess the screening performance of a multivariable model using both EFW and maternal characteristics to predict emergency CD, and determine whether women at high predicted risk of emergency CD based on this model had higher risk of maternal and perinatal morbidity compared with screen-negative women.

METHODS

We studied 3047 low-risk (no pre-existing medical conditions or acquired complications of pregnancy) nulliparous women from the prospective Pregnancy Outcome Prediction study (Cambridge, UK) cohort, who underwent ultrasound EFW at ∼36 weeks' gestation. Both the women and their clinicians were blinded to fetal biometry results. Emergency CD was defined as delivery by Cesarean section in pregnancies in which the date of delivery had not been prearranged. Additional candidate predictors of emergency CD evaluated were maternal age, height, body mass index (BMI), weight gain, fetal abdominal circumference growth velocity and fetal sex. External validation of the predictive model was performed using routinely collected data from 55 337 births in Scotland between 2003 and 2008. Women with an estimated risk of emergency CD ≥ 40% were defined as screen positive.

RESULTS

Blinded EFW was associated strongly with the risk of emergency CD (coefficient for increase of 1 SD in EFW, 0.39 (95% CI, 0.30-0.48); odds ratio (OR), 1.48 (95% CI, 1.35-1.62)). The coefficient for customized EFW was similar (0.42 (95% CI, 0.33-0.51); OR, 1.53 (95% CI, 1.39-1.67)); hence, for simplicity, non-customized EFW was employed subsequently. A multivariable logistic regression model combining maternal characteristics (age, height, BMI and weight gain between 12 and 36 weeks) was moderately predictive of emergency CD (area under the receiver-operating characteristics curve (AUC) = 0.68). Addition of blinded EFW to the model increased the AUC to 0.71 and improved prediction (likelihood-ratio test P < 0.0001). Based on this model, 189 (6.2%) women were screen positive and 48% of these delivered by CD. Screen-positive women had elevated risks of severe postpartum hemorrhage (relative risk (RR), 2.49; 95% CI, 1.83-3.38), any adverse neonatal outcome (RR, 1.86; 95% CI, 1.22-2.82) and severe adverse neonatal outcome (RR, 4.03; 95% CI, 1.35-12.03) compared with screen-negative women. The risks of these events were also higher compared with women who had a term CD for breech presentation. The model was similarly predictive of the risk of emergency CD and perinatal morbidity when evaluated using the dataset from Scotland.

CONCLUSIONS

Ultrasound EFW at 36 weeks, combined with maternal characteristics, can identify women who are at increased risk of subsequent emergency CD. These women are at increased risk of maternal and perinatal morbidity compared with women at low risk of emergency CD and those having CD for breech presentation at term. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Accuracy of immediate antepartum ultrasound estimated fetal weight and its impact on mode of delivery and outcome - a cohort analysis

Background

The aim of the study was to investigate the accuracy of ultrasound-derived estimated fetal weight (EFW) and to determine its impact on management and outcome of delivery.

Methods

In this single-center cohort analysis, women with a singleton term pregnancy in the beginning stages of labor were included. Women with immediately antepartum EFW (N = 492) were compared to women without ultrasound (N = 515).

Results

EFW was correct (deviation from birth weight ≤ 10%) in 72.2% (355/492) of patients with fetal biometry; 19.7% (97/492) were underestimated, and 8.1% (40/492) were overestimated. Newborns with a lower birth weight were more frequently overestimated, and newborns with higher birth weight were more frequently underestimated. The mean difference between EFW and real birth weight was − 114.5 g (standard deviation ±313 g, 95% confidence interval 87.1–142.0). The rate of non-reassuring fetal heart tracing (9.8% vs. 1.9%, P < 0.001) and of caesarean delivery (9.1% vs. 5.0%, P = 0.013) was higher in women with EFW. Overestimation was associated with an increased risk for delivery by caesarean section (odds ratio 2.80; 95% confidence interval 1.2–6.5, P = 0.017). After adjustment, EFW remained associated with increased non-reassuring fetal heart tracing (odds ratio 4.73; 95% confidence interval 2.3–9.6) and caesarean delivery (odds ratio 1.86; 95% confidence interval 1.1–3.1). The incidence of perineal tears of grade 3/4, shoulder dystocia, postnatal depression and neonatal acidosis did not differ between groups.

Conclusions

Antepartum ultrasound-derived EFW does not improve maternal and fetal outcome and is therefore not recommended.

Identifying Fetal Growth Disorders Using Ultrasonography in Women With Diabetes

OBJECTIVES

We evaluated the ability of third-trimester ultrasonography (US) to diagnose disorders of fetal growth among women with diabetes mellitus.

METHODS

This work was a retrospective cohort study of women with diabetes who delivered term singleton neonates at a single academic medical center and who had a US examination within 5 weeks of delivery. We characterized the sensitivity, specificity, positive predictive value, and negative predictive value of US to detect large-for-gestational age (LGA) and small-for-gestational age (SGA) infants. Large and small for gestational age were defined as a US estimated fetal weight of greater than 90% and less than 10%, respectively, based on the Hadlock formula (Radiology 1991; 181:129-133); US estimates of LGA or SGA were compared with postnatal findings of LGA or SGA based on gestational age-based weight percentiles. Test characteristics were analyzed for the total cohort and by the type of diabetes. We compared the areas under the curve for receiver operating characteristic curves for different types of diabetes.

RESULTS

Of 521 women, 3 (0.6%) screened positive for SGA, and 64 (12.3%) delivered an SGA neonate. In contrast, 129 (24.8%) screened positive for LGA, and 61 (11.7%) delivered an LGA neonate. The receiver operating characteristic curves did not differ significantly for different types of diabetes (P = .68).

CONCLUSIONS

Ultrasonography in women with diabetes and term or late preterm pregnancies has high specificity but poor sensitivity for SGA and a low positive predictive value for LGA. The diagnostic capability of US to detect fetal growth abnormalities did not differ significantly by the type of diabetes.

Sonographic large fetal head circumference and risk of cesarean delivery

BACKGROUND

Persistently high rates of cesarean deliveries are cause for concern for physicians, patients, and health systems. Prelabor assessment might be refined by identifying factors that help predict an individual patient's risk of cesarean delivery. Such factors may contribute to patient safety and satisfaction as well as health system planning and resource allocation. In an earlier study, neonatal head circumference was shown to be more strongly associated with delivery mode and other outcome measures than neonatal birthweight.

OBJECTIVE

In the present study we aimed to evaluate the association of sonographically measured fetal head circumference measured within 1 week of delivery with delivery mode.

STUDY DESIGN

This was a multicenter electronic medical record-based study of birth outcomes of primiparous women with term (37-42 weeks) singleton fetuses presenting for ultrasound with fetal biometry within 1 week of delivery. Fetal head circumference and estimated fetal weight were correlated with maternal background, obstetric, and neonatal outcome parameters. Elective cesarean deliveries were excluded. Multinomial regression analysis provided adjusted odds ratios for instrumental delivery and unplanned cesarean delivery when the fetal head circumference was ≥35 cm or estimated fetal weight ≥3900 g, while controlling for possible confounders.

RESULTS

In all, 11,500 cases were collected; 906 elective cesarean deliveries were excluded. A fetal head circumference ≥35 cm increased the risk for unplanned cesarean delivery: 174 fetuses with fetal head circumference ≥35 cm (32%) were delivered by cesarean, vs 1712 (17%) when fetal head circumference <35 cm (odds ratio, 2.49; 95% confidence interval, 2.04-3.03). A fetal head circumference ≥35 cm increased the risk of instrumental delivery (odds ratio, 1.48; 95% confidence interval, 1.16-1.88), while estimated fetal weight ≥3900 g tended to reduce it (nonsignificant). Multinomial regression analysis showed that fetal head circumference ≥35 cm increased the risk of unplanned cesarean delivery by an adjusted odds ratio of 1.75 (95% confidence interval, 1.4-2.18) controlling for gestational age, fetal gender, and epidural anesthesia. The rate of prolonged second stage of labor was significantly increased when either the fetal head circumference was ≥35 cm or the estimated fetal weight ≥3900 g, from 22.7% in the total cohort to 31.0%. A fetal head circumference ≥35 cm was associated with a higher rate of 5-minute Apgar score ≤7: 9 (1.7%) vs 63 (0.6%) of infants with fetal head circumference <35 cm (P = .01). The rate among fetuses with an estimated fetal weight ≥3900 g was not significantly increased. The rate of admission to the neonatal intensive care unit did not differ among the groups.

CONCLUSION

Sonographic fetal head circumference ≥35 cm, measured within 1 week of delivery, is an independent risk factor for unplanned cesarean delivery but not instrumental delivery. Both fetal head circumference ≥35 cm and estimated fetal weight ≥3900 g significantly increased the risk of a prolonged second stage of labor. Fetal head circumference measurement in the last days before delivery may be an important adjunct to estimated fetal weight in labor management.

Population-Based Risk Factors for Shoulder Dystocia

OBJECTIVE

To re-examine the risk factors for shoulder dystocia given the increasing rates of obesity and diabetes in pregnant women.

DESIGN

Retrospective observational study.

SETTING

Five hospitals located in Wisconsin, Florida, Maryland, Michigan, and Alabama.

PARTICIPANTS

We evaluated 19,236 births that occurred between April 1, 2011, and July 25, 2013.

METHODS

Data were collected from electronic medical records and used to evaluate the risk of shoulder dystocia. Data were analyzed using a generalized linear mixed model, which controlled for clustering due to site.

RESULTS

When insulin was prescribed, gestational diabetes was associated with an increased risk of shoulder dystocia (odds ratio = 2.10, 95% confidence interval [1.01, 4.37]); however, no similar association was found with regard to gestational diabetes treated with glycemic agents or through diet. Use of epidural anesthesia was associated with an increased risk for shoulder dystocia (odds ratio = 3.47, 95% confidence interval [2.72, 4.42]). Being Black or Hispanic, being covered by Medicaid or having no insurance, infant gestational age of 41 weeks or greater, and chronic diabetes were other significant risk factors.

CONCLUSION

With the changing characteristics of pregnant women, labor and birth clinicians care for more pregnant women who have an increased risk for shoulder dystocia. Our findings may help prospectively identify women with the greatest risk.

Practice Bulletin No. 173: Fetal Macrosomia

Suspected fetal macrosomia is encountered commonly in obstetric practice. As birth weight increases, the likelihood of labor abnormalities, shoulder dystocia, birth trauma, and permanent injury to the neonate increases. The purpose of this document is to quantify those risks, address the accuracy and limitations of methods for estimating fetal weight, and suggest clinical management for a pregnancy with suspected fetal macrosomia.

Association of Recorded Estimated Fetal Weight and Cesarean Delivery in Attempted Vaginal Delivery at Term

OBJECTIVE

To evaluate the association between documentation of estimated fetal weight, and its value, with cesarean delivery.

METHODS

This was a secondary analysis of a multicenter observational cohort of 115,502 deliveries from 2008 to 2011. Data were abstracted by trained and certified study personnel. We included women at 37 weeks of gestation or greater attempting vaginal delivery with live, nonanomalous, singleton, vertex fetuses and no history of cesarean delivery. Rates and odds ratios (ORs) were calculated for women with ultrasonography or clinical estimated fetal weight compared with women without documentation of estimated fetal weight. Further subgroup analyses were performed for estimated fetal weight categories (less than 3,500, 3,500-3,999, and 4,000 g or greater) stratified by diabetic status. Multivariable analyses were performed to adjust for important potential confounding variables.

RESULTS

We included 64,030 women. Cesarean delivery rates were 18.5% in the ultrasound estimated fetal weight group, 13.4% in the clinical estimated fetal weight group, and 11.7% in the no documented estimated fetal weight group (P<.001). After adjustment (including for birth weight), the adjusted OR of cesarean delivery was 1.44 (95% confidence interval [CI] 1.31-1.58, P<.001) for women with ultrasound estimated fetal weight and 1.08 for clinical estimated fetal weight (95% CI 1.01-1.15, P=.017) compared with women with no documented estimated fetal weight (referent). The highest estimates of fetal weight conveyed the greatest odds of cesarean delivery. When ultrasound estimated fetal weight was 4,000 g or greater, the adjusted OR was 2.15 (95% CI 1.55-2.98, P<.001) in women without diabetes and 9.00 (95% CI 3.65-22.17, P<.001) in women with diabetes compared to those with estimated fetal weight less than 3,500 g.

CONCLUSION

In this contemporary cohort of women attempting vaginal delivery at term, documentation of estimated fetal weight (obtained clinically or, particularly, by ultrasonography) was associated with increased odds of cesarean delivery. This relationship was strongest at higher fetal weight estimates, even after controlling for the effects of birth weight and other factors associated with increased cesarean delivery risk.

Labor and Delivery Experiences of Mothers with Suspected Large Babies

OBJECTIVE

To characterize the prevalence of and factors associated with clinicians' prenatal suspicion of a large baby; and to determine whether communicating fetal size concerns to patients was associated with labor and delivery interventions and outcomes.

METHODS

We examined data from women without a prior cesarean who responded to Listening to Mothers III, a nationally representative survey of women who had given birth between July 2011 and June 2012 (n = 1960). We estimated the effect of having a suspected large baby (SLB) on the odds of six labor and delivery outcomes.

RESULTS

Nearly one-third (31.2%) of women were told by their maternity care providers that their babies might be getting "quite large"; however, only 9.9% delivered a baby weighing ≥4000 g (19.7% among mothers with SLBs, 5.5% without). Women with SLBs had increased adjusted odds of medically-induced labor (AOR 1.9; 95% CI 1.4-2.6), attempted self-induced labor (AOR 1.9; 95% CI 1.4-2.7), and use of epidural analgesics (AOR 2.0; 95% CI 1.4-2.9). No differences were noted for overall cesarean rates, although women with SLBs were more likely to ask for (AOR 4.6; 95% CI 2.8-7.6) and have planned (AOR 1.8; 95% CI 1.0-4.5) cesarean deliveries. These associations were not affected by adjustment for gestational age and birthweight.

CONCLUSIONS FOR PRACTICE

Only one in five US women who were told that their babies might be getting quite large actually delivered infants weighing ≥4000 g. However, the suspicion of a large baby was associated with an increase in perinatal interventions, regardless of actual fetal size.

Comparison of 2- and 3-Dimensional Sonography for Estimation of Birth Weight and Neonatal Adiposity in the Setting of Suspected Fetal Macrosomia

OBJECTIVES

To compare the accuracy of 2-dimensional (2D) and 3-dimensional (3D) fetal measurements for prediction of birth weight Z score and neonatal adiposity (percent body fat) in the setting of suspected fetal macrosomia.

METHODS

We conducted a prospective observational study of term singleton pregnancies with suspected macrosomia. Patients were enrolled on admission to labor and delivery and underwent sonographic examinations. Within 48 hours of delivery, neonatal anthropometric measurements were obtained.

RESULTS

Thirty-four neonates were included in the analysis. Mothers were very obese (mean body mass index ± SD, 39.1 ± 7.8 kg/m(2)); 56.5% were white; and 39.1% had diabetes. Neonates were 38% female and had a mean birth weight of 3940.0 ± 496.8 g, percent body fat of 18.5% ± 4.0%, and Ponderal index of 2.8 ± 0.3 g/cm(3). Mean 2D estimated fetal weight was 3973 ± 443 g; mean 3D estimated fetal weight was 3803 ± 528 g; and mean thigh volume was 102.5 ± 19.6 cm(3). Both 2D and 3D measurements accounted for about half the variance in predicted birth weight (R(2) for 2D = 0.53, 71% within 10% of birth weight; R(2) for 3D = 0.47, 65% within 10% of birth weight). Thigh volume Z score was the prenatal parameter most highly correlated with both birth weight Z score (R(2) = 0.52; r = 0.72; 95% confidence interval, 0.54-0.84; P < .001) and percent body fat (R(2) = 0.22; r = 0.47; 95% confidence interval, 0.17-0.69; P = .04).

CONCLUSIONS

In our population of fetuses with suspected macrosomia, fractional thigh volume was the best sonographic estimate of neonatal percent body fat and birth weight Z score. Future research on prediction of neonatal weight and adiposity in macrosomic fetuses should include an estimate of fetal soft tissue given the generalized increase in body fat of these fetuses.

Relationship Between Third-Trimester Sonographic Estimate of Fetal Weight and Mode of Delivery

OBJECTIVES

Some have suggested, based on limited data, that knowledge of an estimated fetal weight from a sonogram in a low-risk population, particularly in the setting of a larger fetus, is associated with increased risk of cesarean delivery. We aimed to investigate, among women delivering neonates weighing greater than 3500 g, whether having had a sonographically estimated fetal weight in temporal proximity to delivery was associated with the risk of cesarean delivery.

METHODS

We conducted a retrospective cohort study of term nulliparous women delivering live-born, cephalic, singleton, nonanomalous fetuses with birth weights of greater than 3500 g. The study was powered to detect a 30% change in cesarean delivery frequency with the presence of a sonographic examination after 36 weeks' gestation.

RESULTS

Of the 2099 women meeting inclusion criteria, 419 (20%) had a sonographic examination after 36 weeks' gestation. Women were similar with respect to demographic and obstetric characteristics regardless of whether they underwent sonography. There were no differences in rates of cesarean delivery regardless of whether women had or did not undergo sonography after 36 weeks (33.2% versus 29.4%, respectively; P = .13). There also were no differences in rates of chorioamnionitis, postpartum hemorrhage, episiotomy, third- or fourth-degree perineal laceration, or neonatal adverse outcomes based on sonographic status. Findings were similar in a multivariable analysis, as well as when the study population was restricted to those with birth weights of greater than 4000 and 4500 g.

CONCLUSIONS

In this population of neonates weighing greater than 3500 g, the presence of a sonographic examination was not associated with the frequency of cesarean delivery.

The Suspected Macrosomic Fetus at Term: A Clinical Dilemma

Estimation of fetal weight is an important component of antenatal and intrapartum management of pregnant women. While many clinicians use ultrasound estimates of fetal weight to assess fetal growth, there are inherent challenges in both the diagnosis and management of suspected fetal macrosomia. Given the inaccuracy in estimating fetal weight, and the risks that accompany cesarean birth or induction of labor, the management of suspected fetal macrosomia requires open communication and shared decision making between the woman and her health care providers. This case study and literature review highlight the current management and recommendations for suspected fetal macrosomia.

Ultrasound Fetal Weight Estimation: How Accurate Are We Now Under Emergency Conditions?

The primary aim of this study was to evaluate the accuracy of sonographic estimation of fetal weight when performed at due date by first-line sonographers. This was a prospective study including 500 singleton pregnancies. Ultrasound examinations were performed by residents on delivery day. Estimated fetal weights (EFWs) were calculated and compared with the corresponding birth weights. The median absolute difference between EFW and birth weight was 200 g (100-330). This difference was within ±10% in 75.2% of the cases. The median absolute percentage error was 5.53% (2.70%-10.03%). Linear regression analysis revealed a good correlation between EFW and birth weight (r = 0.79, p < 0.0001). According to Bland-Altman analysis, bias was -85.06 g (95% limits of agreement: -663.33 to 494.21). In conclusion, EFWs calculated by residents were as accurate as those calculated by experienced sonographers. Nevertheless, predictive performance remains limited, with a low sensitivity in the diagnosis of macrosomia.

Does induction of labor for constitutionally large-for-gestational-age fetuses identified in utero reduce maternal morbidity?

BACKGROUND

The number of infants with a birth weight > 97th percentile for gestational age has increased over the years. Although some studies have examined the interest of inducing labor for fetuses with macrosomia suspected in utero, only a few have analyzed this suspected macrosomia according to estimated weight at each gestational age. Most studies have focused principally on neonatal rather than on maternal (and still less on perineal) outcomes. The principal aim of this study was to assess whether a policy of induction of labor for women with a constitutionally large-for-gestational-age fetus might reduce the occurrence of severe perineal tears; the secondary aims of this work were to assess whether this policy would reduce either recourse to cesarean delivery during labor or neonatal complications.

METHODS

This historical cohort study (n = 3077) analyzed records from a French perinatal database. Women without diabetes and with a cephalic singleton term pregnancy were eligible for the study. We excluded medically indicated terminations of pregnancy and in utero fetal deaths. Among the pregnancies with fetuses suspected, before birth, of being large-for-gestational-age, we compared those for whom labor was induced from ≥ 37 weeks to ≤ 38 weeks+ 6 days (n = 199) to those with expectant obstetrical management (n = 2878). In this intention-to-treat analysis, results were expressed as crude and adjusted relative risks.

RESULTS

The mean birth weight was 4012 g ± 421 g. The rate of perineal lesions did not differ between the two groups in either primiparas (aRR: 1.06; 95% CI: 0.86-1.31) or multiparas (aRR: 0.94; 95% CI: 0.84-1.05). Similarly, neither the cesarean rate (aRR: 1.11; 95% CI: 0.82-1.50) nor the risks of resuscitation in the delivery room or of death in the delivery room or in the immediate postpartum or of neonatal transfer to the NICU (aRR = 0.94; 95% CI: 0.59-1.50) differed between the two groups.

CONCLUSIONS

A policy of induction of labor for women with a constitutionally large-for-gestational-age fetus among women without diabetes does not reduce maternal morbidity.

Estimated fetal weight by ultrasound: a modifiable risk factor for cesarean delivery?

OBJECTIVE

The purpose of this study was to investigate whether knowledge of ultrasound-obtained estimated fetal weight (US-EFW) is a risk factor for cesarean delivery (CD).

STUDY DESIGN

Retrospective cohort from a single center in 2009-2010 of singleton, term live births. CD rates were compared for women with and without US-EFW within 1 month of delivery and adjusted for potential confounders.

RESULTS

Of the 2329 women in our cohort, 50.2% had US-EFW within 1 month of delivery. CD was significantly more common for women with US-EFW (15.7% vs 10.2%; P < .001); after we controlled for confounders, US-EFW remained an independent risk factor for CD (odds ratio, 1.44; 95% confidence interval, 1.1-1.9). The risk increased when US-EFW was >3500 g (odds ratio, 1.8; 95% confidence interval, 1.3-2.7).

CONCLUSION

Knowledge of US-EFW, above and beyond the impact of fetal size itself, increases the risk of CD. Acquisition of US-EFW near term appears to be an independent and potentially modifiable risk factor for CD.

Utilization of antenatal ultrasound scan and implications for caesarean section: a cross-sectional study in rural Eastern China

Background

Antenatal ultrasound scan is a widely accepted component of antenatal care. Studies have looked at the relationship between ultrasound scanning and caesarean section (CS) in certain groups of women in China. However, there are limited data on the utilization of antenatal ultrasound scanning in the general population, including its association with CS. The purpose of this study is to describe the utilization of antenatal ultrasound screening in rural Eastern China and to explore the association between antenatal ultrasound scan and uptake of CS.

Methods

Based on a cluster randomized sample, a total of 2326 women with childbirth participated in the study. A household survey was conducted to collect socio-economic information, obstetric history and utilization of maternal health services.

Results

Coverage of antenatal care was 96.8% (2251/2326). During antenatal care, 96.1% (2164/2251) women received ultrasound screening and the reported average number was 2.55. 46.8% women received at least 3 ultrasound scans and the maximum number reached 11. The CS rate was found to be 54.8% (1275/2326). After adjusting for socio-demographic and clinical variables, it showed a statistically significant association between antenatal ultrasound scans and uptake of CS by multivariate logistic regression model. High husband education level, high maternal age, having previous adverse pregnant outcome and pregnancy complications during the index pregnancy were also found to be risk factors of choosing a CS.

Conclusions

A high use of antenatal ultrasound scan in rural Eastern China is found and is influenced by socio-demographic and clinical factors. Evidence-based guidelines for antenatal ultrasound scans need to be developed and disseminated to clinicians including physicians, nurses and sonographers. Guidance about the appropriate use of ultrasound scans should also be shared with women in order to discourage unreasonable expectations and demands. It is important to monitor the use of antenatal ultrasound scan as well as the indications for caesarean section in rural China.