Prenatal prediction of small-for-gestational age neonates using MR imaging: comparison with conventional 2D ultrasound

Timing of induction of labor in suspected macrosomia: retrospective cohort study, systematic review and meta-analysis

OBJECTIVES

Large-for-gestational age (LGA) is associated with several adverse maternal and neonatal outcomes. Although many studies have found that early induction of labor (IOL) in case of a LGA fetus reduces the incidence of shoulder dystocia, no current guidelines recommend this particular clinical strategy, owing to concerns about increased rates of Cesarean delivery (CD) and neonatal complications. The purpose of this study was to assess whether the timing of IOL in LGA fetuses affected maternal and neonatal outcomes in a single center, and to combine these results with evidence reported in the literature.

METHODS

This study comprised two parts. The first part was a retrospective cohort study that included consecutive patients with a singleton pregnancy and an estimated fetal weight ≥ 90th percentile on ultrasound between 35 + 0 and 39 + 0 weeks' gestation, who were eligible for normal vaginal delivery. The second part of the study was a systematic review of the literature and meta-analysis, including the results of our cohort study as well as those of previous studies that compared IOL with expectant management in patients with a LGA fetus. The perinatal outcomes of the study were CD, operative vaginal delivery, shoulder dystocia, brachial plexus palsy, anal sphincter injury, postpartum hemorrhage, Apgar score, umbilical artery pH, admission to the neonatal intensive care unit, use of continuous positive airway pressure, intracranial hemorrhage, need for phototherapy and bone fracture.

RESULTS

Of the 547 patients included in this retrospective cohort study, 329 (60.1%) underwent IOL and 218 (39.9%) experienced spontaneous labor. Following covariate balancing, the odds of CD were significantly higher in the IOL group compared with the spontaneous-labor group. This difference only became apparent beyond 40 weeks' gestation (hazard ratio, 1.90; P = 0.030). The difference between the IOL and spontaneous-labor groups for the rate of shoulder dystocia was not statistically significant (hazard ratio, 1.57; P = 0.200). Seventeen studies, in addition to our own results, were included in the systematic review and meta-analysis, giving a total population of 111 300 participants. Although there was no significant difference in the rate of CD between IOL and expectant management after pooling the results of included studies, the risk for shoulder dystocia was significantly lower in the IOL group (odds ratio (OR), 0.64 (95% CI, 0.42-0.98); I2 = 19% from 12 studies) when considering only IOL performed before 40 + 0 weeks. When the studies in which IOL was carried out exclusively before 40 + 0 weeks were removed from the analysis, the risk for CD in the remaining studies was significantly higher in the IOL group (OR, 1.46 (95% CI, 1.02-2.09); I2 = 56%). There were no statistically significant differences between the IOL and expectant-management groups for the remaining perinatal outcomes. Nulliparity, history of CD and low Bishop score, but not method of induction, were independent risk factors for intrapartum CD in patients that underwent IOL for LGA.

CONCLUSIONS

The timing of IOL in patients with suspected macrosomia significantly impacts on perinatal adverse outcomes. IOL has no impact on rates of shoulder dystocia but increases the odds of CD when considered irrespective of gestational age; in contrast, IOL may decrease the risk of shoulder dystocia without increasing the risk of other adverse maternal outcomes, in particular CD, when performed before 40 + 0 weeks (GRADE: low/very low). © 2024 International Society of Ultrasound in Obstetrics and Gynecology.

Reducing macrosomia-related birth complications in primigravid women: ultrasound- and magnetic resonance imaging-based models

BACKGROUND

Many complications increase with macrosomia, which is defined as birthweight of ≥4000 g. The ability to estimate when the fetus would exceed 4000 g could help to guide decisions surrounding the optimal timing of delivery. To the best of our knowledge, there is no available tool to perform this estimation independent of the currently available growth charts.

OBJECTIVE

This study aimed to develop ultrasound- and magnetic resonance imaging-based models to estimate at which gestational age the birthweight would exceed 4000 g, evaluate their predictive performance, and assess the effect of each model in reducing adverse outcomes in a prospectively collected cohort.

STUDY DESIGN

This study was a subgroup analysis of women who were recruited for the estimation of fetal weight by ultrasound and magnetic resonance imaging at 36 0/7 to 36 6/7 weeks of gestation. Primigravid women who were eligible for normal vaginal delivery were selected. Multiparous patients, patients with preeclampsia spectrum, patients with elective cesarean delivery, and patients with contraindications for normal vaginal delivery were excluded. Of note, 2 linear models were built for the magnetic resonance imaging- and ultrasound-based models to predict a birthweight of ≥4000 g. Moreover, 2 formulas were created to predict the gestational age at which birthweight will reach 4000 g (predicted gestational age); one was based on the magnetic resonance imaging model, and the second one was based on the ultrasound model. This study compared the adverse birth outcomes, such as intrapartum cesarean delivery, operative vaginal delivery, anal sphincter injury, postpartum hemorrhage, shoulder dystocia, brachial plexus injury, Apgar score of <7 at 5 minutes of life, neonatal intensive care unit admission, and intracranial hemorrhage in the group of patients who delivered after the predicted gestational age according to the magnetic resonance imaging-based or the ultrasound-based models with those who delivered before the predicted gestational age by each model, respectively.

RESULTS

Of 2378 patients, 732 (30.8%) were eligible for inclusion in the current study. The median gestational age at birth was 39.86 weeks of gestation (interquartile range, 39.00-40.57), the median birthweight was 3340 g (interquartile range, 3080-3650), and 63 patients (8.6%) had a birthweight of ≥4000 g. Prepregnancy body mass index, geographic origin, gestational age at birth, and fetal body volume were retained for the optimal magnetic resonance imaging-based model, whereas maternal age, gestational diabetes mellitus, diabetes mellitus type 1 or 2, geographic origin, fetal gender, gestational age at birth, and estimated fetal weight were retained for the optimal ultrasound-based model. The performance of the first model was significantly better than the second model (area under the curve: 0.98 vs 0.89, respectively; P<.001). The group of patients who delivered after the predicted gestational age by the first model (n=40) had a higher risk of cesarean delivery, postpartum hemorrhage, and shoulder dystocia (adjusted odds ratio: 3.15, 4.50, and 9.67, respectively) than the group who delivered before this limit. Similarly, the group who delivered after the predicted gestational age by the second model (n=25) had a higher risk of cesarean delivery and postpartum hemorrhage (adjusted odds ratio: 5.27 and 6.74, respectively) than the group who delivered before this limit.

CONCLUSION

The clinical use of magnetic resonance imaging- and ultrasound-based models, which predict a gestational age at which birthweight will exceed 4000 g, may reduce macrosomia-related adverse outcomes in a primigravid population. The magnetic resonance imaging-based model is better for the identification of the highest-risk patients.

Diagnostic performance of 32 vs 36 weeks ultrasound in predicting late-onset fetal growth restriction and small-for-gestational-age neonates: a systematic review and meta-analysis

OBJECTIVE

Fetal growth restriction is an independent risk factor for fetal death and adverse neonatal outcomes. The main aim of this study was to investigate the diagnostic performance of 32 vs 36 weeks ultrasound of fetal biometry in detecting late-onset fetal growth restriction and predicting small-for-gestational-age neonates.

DATA SOURCES

A systematic search was performed to identify relevant studies published until June 2022, using the databases PubMed, Web of Science, and Scopus.

STUDY ELIGIBILITY CRITERIA

Cohort studies in low-risk or unselected singleton pregnancies with screening ultrasound performed at ≥32 weeks of gestation were used.

METHODS

The estimated fetal weight and abdominal circumference were assessed as index tests for the prediction of small for gestational age (birthweight of <10th percentile) and detecting fetal growth restriction (estimated fetal weight of <10th percentile and/or abdominal circumference of <10th percentile). The 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 area under the receiver operating characteristic curves were constructed, and quantitative data synthesis was performed using random-effects models.

RESULTS

The analysis included 25 studies encompassing 73,981 low-risk pregnancies undergoing third-trimester ultrasound assessment for growth, of which 5380 neonates (7.3%) were small for gestational age at birth. The pooled sensitivities for estimated fetal weight of <10th percentile and abdominal circumference of <10th percentile in predicting small for gestational age were 36% (95% confidence interval, 27%-46%) and 37% (95% confidence interval, 19%-60%), respectively, at 32 weeks ultrasound and 48% (95% confidence interval, 41%-56%) and 50% (95% confidence interval, 25%-74%), respectively, at 36 weeks ultrasound. The pooled specificities for estimated fetal weight of <10th percentile and abdominal circumference of <10th percentile in detecting small for gestational age were 93% (95% confidence interval, 91%-95%) and 95% (95% confidence interval, 85%-98%), respectively, at 32 weeks ultrasound and 93% (95% confidence interval, 91%-95%) and 97% (95% confidence interval, 85%-98%), respectively, at 36 weeks ultrasound. The observed diagnostic odds ratios for an estimated fetal weight of <10th percentile and an abdominal circumference of <10th percentile in detecting small for gestational age were 8.8 (95% confidence interval, 5.4-14.4) and 11.6 (95% confidence interval, 6.2-21.6), respectively, at 32 weeks ultrasound and 13.3 (95% confidence interval, 10.4-16.9) and 36.0 (95% confidence interval, 4.9-260.0), respectively, at 36 weeks ultrasound. The pooled sensitivity, specificity, and diagnostic odds ratio in predicting fetal growth restriction were 71% (95% confidence interval, 52%-85%), 90% (95% confidence interval, 79%-95%), and 25.8 (95% confidence interval, 14.5-45.8), respectively, at 32 weeks ultrasound and 48% (95% confidence interval, 41%-55%), 94% (95% confidence interval, 93%-96%), and 16.9 (95% confidence interval, 10.8-26.6), respectively, at 36 weeks ultrasound. Abdominal circumference of <10th percentile seemed to have comparable sensitivity to estimated fetal weight of <10th percentile in predicting small-for-gestational-age neonates.

CONCLUSION

An ultrasound assessment of the fetal biometry at 36 weeks of gestation seemed to have better predictive accuracy for small-for-gestational-age neonates than an ultrasound assessment at 32 weeks of gestation. However, an opposite trend was noted when the outcome was fetal growth restriction. Fetal abdominal circumference had a similar predictive accuracy to that of estimated fetal weight in detecting small-for-gestational-age neonates.

Measuring intrauterine growth in healthy pregnancies using quantitative magnetic resonance imaging

OBJECTIVE

The aim of this study was to determine in utero fetal-placental growth patterns using in vivo three-dimensional (3D) quantitative magnetic resonance imaging (qMRI).

STUDY DESIGN

Healthy women with singleton pregnancies underwent fetal MRI to measure fetal body, placenta, and amniotic space volumes. The fetal-placental ratio (FPR) was derived using 3D fetal body and placental volumes (PV). Descriptive statistics were used to describe the association of each measurement with increasing gestational age (GA) at MRI.

RESULTS

Fifty-eight (58) women underwent fetal MRI between 16 and 38 completed weeks gestation (mean = 28.12 ± 6.33). PV and FPR varied linearly with GA at MRI (r_PV,GA = 0.83, r_FPR,GA = 0.89, p value < 0.001). Fetal volume varied non-linearly with GA (p value < 0.01).

CONCLUSIONS

We describe in-utero growth trajectories of fetal-placental volumes in healthy pregnancies using qMRI. Understanding healthy in utero development can establish normative benchmarks where departures from normal may identify early in utero placental failure prior to the onset of fetal harm.

Fetal magnetic resonance imaging at 36 weeks predicts neonatal macrosomia: the PREMACRO study

BACKGROUND

Large-for-gestational-age fetuses are at increased risk of perinatal morbidity and mortality. Magnetic resonance imaging seems to be more accurate than ultrasound in the prediction of macrosomia; however, there is no well-powered study comparing magnetic resonance imaging with ultrasound in routine pregnancies.

OBJECTIVE

This study aimed to prospectively compare estimates of fetal weight based on 2-dimensional ultrasound and magnetic resonance imaging with actual birthweights in routine pregnancies.

STUDY DESIGN

From May 2016 to February 2019, women received counseling at the 36-week clinic. Written informed consent was obtained for this Ethics Committee-approved study. In this prospective, single-center, blinded study, pregnant women with singleton pregnancies between 36 0/7 and 36 6/7 weeks' gestation underwent both standard evaluation of estimated fetal weight with ultrasound according to Hadlock et al and magnetic resonance imaging according to the formula developed by Baker et al, based on the measurement of the fetal body volume. Participants and clinicians were aware of the results of the ultrasound but blinded to the magnetic resonance imaging estimates. Birthweight percentile was considered as the gold standard for the ultrasound and magnetic resonance imaging-derived percentiles. The primary outcome was the area under the receiver operating characteristic curve for the prediction of large-for-gestation-age neonates with birthweights of ≥95th percentile. Secondary outcomes included the comparative prediction of large-for-gestation-age neonates with birthweights of ≥90th, 97th, and 99th percentiles and small-for-gestational-age neonates with birthweights of ≤10th, 5th, and 3rd percentiles for gestational age and maternal and perinatal complications.

RESULTS

Of 2914 women who were initially approached, results from 2378 were available for analysis. Total fetal body volume measurements were possible for all fetuses, and the time required to perform the planimetric measurements by magnetic resonance imaging was 3.0 minutes (range, 1.3-5.6). The area under the receiver operating characteristic curve for the prediction of a birthweight of ≥95th percentile was 0.985 using prenatal magnetic resonance imaging and 0.900 using ultrasound (difference=0.085, P<.001; standard error, 0.020). For a fixed false-positive rate of 5%, magnetic resonance imaging for the estimation of fetal weight detected 80.0% (71.1-87.2) of birthweight of ≥95th percentile, whereas ultrasound for the estimation of fetal weight detected 59.1% (49.0-68.5) of birthweight of ≥95th percentile. The positive predictive value was 42.6% (37.8-47.7) for the estimation of fetal weight using magnetic resonance imaging and 35.4% (30.1-41.1) for the estimation of fetal weight using ultrasound, and the negative predictive value was 99.0% (98.6-99.3) for the estimation of fetal weight using magnetic resonance imaging and 98.0% (97.6-98.4) for the estimation of fetal weight using ultrasound. For a fixed false-positive rate of 10%, magnetic resonance imaging for the estimation of fetal weight detected 92.4% (85.5-96.7) of birthweight of ≥95th percentile, whereas ultrasound for the estimation of fetal weight detected 76.2% (66.9-84.0) of birthweight of ≥95th percentile. The positive predictive value was 29.9% (27.2-32.8) for the estimation of fetal weight using magnetic resonance imaging and 26.2% (23.2-29.4) for the estimation of fetal weight using ultrasound, and the negative predictive value was 99.6 (99.2-99.8) for the estimation of fetal weight using magnetic resonance imaging and 98.8 (98.4-99.2) for the estimation of fetal weight using ultrasound. The area under the receiver operating characteristic curves for the prediction of large-for-gestational-age neonates with birthweights of ≥90th, 97th, and 99th percentiles and small-for-gestational-age neonates with birthweights of ≤10th, 5th, and 3rd percentiles was significantly larger in prenatal magnetic resonance imaging than in ultrasound (P<.05 for all).

CONCLUSION

At 36 weeks' gestation, magnetic resonance imaging for the estimation of fetal weight performed significantly better than ultrasound for the estimation of fetal weight in the prediction of large-for-gestational-age neonates with birthweights of ≥95th percentile for gestational age and all other recognized cutoffs for large-for-gestational-age and small-for-gestational-age neonates (P<.05 for all).

Fetal Growth Restriction Prediction: How to Move beyond

The actual burden and future burden of the small-for-gestational-age (SGA) babies turn their screening in pregnancy a question of major concern for clinicians and policymakers. Half of stillbirths are due to growth restriction in utero, and possibly, a quarter of livebirths of low- and middle-income countries are SGA. Growing body of evidence shows their higher risk of adverse outcomes at any period of life, including increased rates of neurologic delay, noncommunicable chronic diseases (central obesity and metabolic syndrome), and mortality. Although there is no consensus regarding its definition, birthweight centile threshold, or follow-up, we believe birthweight <10th centile is the most suitable cutoff for clinical and epidemiological purposes. Maternal clinical factors have modest predictive accuracy; being born SGA appears to be of transgenerational heredity. Addition of ultrasound parameters improves prediction models, especially using estimated fetal weight and abdominal circumference in the 3rd trimester of pregnancy. Placental growth factor levels are decreased in SGA pregnancies, and it is the most promising biomarker in differentiating angiogenesis-related SGA from other causes. Unfortunately, however, only few societies recommend universal screening. SGA evaluation is the first step of a multidimensional approach, which includes adequate management and long-term follow-up of these newborns. Apart from only meliorating perinatal outcomes, we hypothesize SGA screening is a key for socioeconomic progress.

The use of magnetic resonance imaging in the prediction of birthweight

Extremes of fetal growth can increase adverse pregnancy outcomes, and this is equally applicable to single and multiple gestations. Traditionally, these cases have been identified using simple two-dimensional ultrasound which is quite limited by its low precision. Magnetic resonance imaging (MRI) has now been used for many years in obstetrics, mainly as an adjunct to ultrasound for congenital abnormalities and increasingly as part of the post-mortem examination. However, MRI can also be used to accurately assess fetal weight as first demonstrated by Baker et al in 1994, using body volumes rather than standard biometric measurements. This publication was followed by several others, all of which confirmed the superiority of MRI; however, despite this initial promise, the technique has never been successfully integrated into clinical practice. In this review, we provide an overview of the literature, detail the various techniques and formulas currently available, discuss the applicability to specific high-risk groups and present our vision for the future of MRI within clinical obstetrics.

Two new models for the estimation of foetal weight more than a week before delivery: An MRI study

PURPOSE

To develop and evaluate new formulas to determine the magnetic resonance imaging (MRI)-based estimated foetal weight (EFW) more than a week before delivery.

METHODS

The study included 153 women with singleton pregnancies who gave birth to live, normal neonates within 15-21 days of the MRI examination for whom foetal body volume biometry data were available at term. All foetuses were randomly divided into a testing group (102) and a validation group (51). Regression analysis was used to determine the single volume or the combination of volume and MRI-to-delivery interval that determined the EFW. The accuracy of the two new models and the primary existing model developed by Baker et al. were evaluated in validation group.

RESULTS

The two new models had similar mean percentage errors (MPEs) (3.9% vs 3.9%) and proportions of pregnancies with an MPE < 10% (92.2% vs 90.2%); the model incorporating volume and MRI-to-delivery had relatively higher proportions of pregnancies with an MPE < 5% (72.5% vs 64.7%) and EFWs in agreement with the birth weights. The error in the Baker model was almost twice that in the new models.

CONCLUSION

The accuracy of foetal weight estimation more than one week before delivery using the model developed by Baker et al. was poor and was significantly improved by the new models. A combination of the foetal body volume and MRI-to-delivery interval will enable the more accurate determination of the EFWs.

Magnetic resonance imaging for prenatal estimation of birthweight in pregnancy: review of available data, techniques, and future perspectives

Fetuses at the extremes of growth abnormalities carry a risk of perinatal morbidity and death. Their identification traditionally is done by 2-dimensional ultrasound imaging, the performance of which is not always optimal. Magnetic resonance imaging superbly depicts fetal anatomy and anomalies and has contributed largely to the evaluation of high-risk pregnancies. In 1994, magnetic resonance imaging was introduced for the estimation of fetal weight, which is done by measuring the fetal body volume and converting it through a formula to fetal weight. Approximately 10 studies have shown that magnetic resonance imaging is more accurate than 2-dimensional ultrasound imaging in the estimation of fetal weight. Yet, despite its promise, the magnetic resonance imaging technique currently is not implemented clinically. Over the last 5 years, this technique has evolved quite rapidly. Here, we review the literature data, provide details of the various measurement techniques and formulas, consider the application of the magnetic resonance imaging technique in specific populations such as patients with diabetes mellitus and twin pregnancies, and conclude with what we believe could be the future perspectives and clinical application of this challenging technique. The estimation of fetal weight by ultrasound imaging is based mainly on an algorithm that takes into account the measurement of biparietal diameter, head circumference, abdominal circumference, and femur length. The estimation of fetal weight by magnetic resonance imaging is based on one of the 2 formulas: (1) magnetic resonance imaging-the estimation of fetal weight (in kilograms)=1.031×fetal body volume (in liters)+0.12 or (2) magnetic resonance imaging-the estimation of fetal weight (in grams)=1.2083×fetal body volume (in milliliters)ˆ0.9815. Comparison of these 2 formulas for the detection of large-for-gestational age neonates showed similar performance for preterm (P=.479) and for term fetuses (P=1.000). Literature data show that the estimation of fetal weight with magnetic resonance imaging carries a mean or median relative error of 2.6 up to 3.7% when measurements were performed at <1 week from delivery; whereas for the same fetuses, the relative error at 2-dimensional ultrasound imaging varied between 6.3% and 11.4%. Further, in a series of 270 fetuses who were evaluated within 48 hours from birth and for a fixed false-positive rate of 10%, magnetic resonance imaging detected 98% of large-for-gestational age neonates (≥95th percentile for gestation) compared with 67% with ultrasound imaging estimates. For the same series, magnetic resonance imaging applied to the detection of small-for-gestational age neonates ≤10th percentile for gestation, for a fixed 10% false-positive rate, reached a detection rate of 100%, compared with only 78% for ultrasound imaging. Planimetric measurement has been 1 of the main limitations of magnetic resonance imaging for the estimation of fetal weight. Software programs that allow semiautomatic segmentation of the fetus are available from imaging manufacturers or are self-developed. We have shown that all of them perform equally well for the prediction of large-for-gestational age neonates, with the advantage of the semiautomatic methods being less time-consuming. Although many challenges remain for this technique to be generalized, a 2-step strategy after the selection of a group who are at high risk of the extremes of growth abnormalities is the most likely scenario. Results of ongoing studies are awaited (ClinicalTrials.gov Identifier # NCT02713568).

Ultrasonographic estimation of fetal weight: development of new model and assessment of performance of previous models

OBJECTIVES

To develop a new formula for ultrasonographic estimation of fetal weight and evaluate the accuracy of this and all previous formulae in the prediction of birth weight.

METHODS

The study population consisted of 5163 singleton pregnancies with fetal biometry at 22-43 weeks' gestation and live birth of a phenotypically normal neonate within 2 days of the ultrasound examination. Multivariable fractional polynomial analysis was used to determine the combination of variables that provided the best-fitting models for estimated fetal weight (EFW). A systematic review was also carried out of articles reporting formulae for EFW and comparing EFW to actual birth weight. The accuracy of each model for EFW was assessed by comparing mean percentage error, absolute mean error (AE), proportion of pregnancies with AE ≤ 10% and Euclidean distance.

RESULTS

The most accurate models, with the lowest Euclidean distance and highest proportion of AE ≤ 10%, were provided by the formulae incorporating ≥ 3 rather than < 3 biometrical measurements. The systematic review identified 45 studies describing a total of 70 models for EFW by various combinations of measurements of fetal head circumference (HC), biparietal diameter, femur length (FL) and abdominal circumference (AC). The most accurate model with the lowest Euclidean distance and highest proportion of AE ≤ 10% was provided by the formula of Hadlock et al., published in 1985, which incorporated measurements of HC, AC and FL; there was a highly significant linear association between EFW and birth weight (r = 0.959; P < 0.0001), and EFW was within 10% of birth weight in 80% of cases. The performance of the best model developed in this study, utilizing HC, AC and FL, was very similar to that of Hadlock et al. CONCLUSION: Despite many efforts to develop new models for EFW, the one reported in 1985 by Hadlock et al., from measurements of HC, AC and FL, provides the most accurate prediction of birth weight and can be used for assessment of all babies, including those suspected to be either small or large. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.