Intraexaminer and Interexaminer Variability in 3D Fetal Volume Measurements During the Second and Third Trimesters of Pregnancy

The NICHD Fetal 3D Study: A Pregnancy Cohort Study of Fetal Body Composition and Volumes

There's a paucity of robust normal fractional limb and organ volume standards from a large and diverse ethnic population. The Fetal 3D Study was designed to develop research and clinical applications for fetal soft tissue and organ volume assessment. The NICHD Fetal Growth Studies (2009-2013) collected 2D and 3D fetal volumes. In the Fetal 3D Study (2015-2019), sonographers performed longitudinal 2D and 3D measurements for specific fetal anatomical structures in research ultrasounds of singletons and dichorionic twins. The primary aim was to establish standards for fetal body composition and organ volumes, overall and by maternal race/ethnicity, and determine whether these standards vary for twins versus singletons. We describe the study design, methods, and details about reviewer training. Basic characteristics of this cohort, with their corresponding distributions of fetal 3D measurements by anatomical structure, are summarized. This investigation is responsive to critical data gaps in understanding serial changes in fetal subcutaneous fat, lean body mass, and organ volume in association with pregnancy complications. In the future, this cohort can answer critical questions regarding the potential influence of maternal characteristics, lifestyle factors, nutrition, and biomarker and chemical data on longitudinal measures of fetal subcutaneous fat, lean body mass, and organ volumes.

Does a Caesarean Section Scar Affect Placental Volume, Vascularity and Localization?

Caesarean section is associated with an increased risk of abnormal placental implantation and adverse pregnancy outcomes in subsequent pregnancies. Besides the placenta accrete spectrum, only a few of the previous studies focused on other placental development alterations in the scarred uterus. We assessed placental development deviations in the uterus with a Caesarean section scar by evaluating placental volume (PV) and vascular flow indexes. From 1 January 2021 until 31 March 2022, placental volumes and vascularization indexes (VI, FI, VFI) were prospectively measured by 3D power Doppler and VOCAL techniques in 221 patients attending the first trimester screening program. We also calculated the placental quotient to standardize PV to the gestational age. No statistically significant differences in the values of placental volume, placental quotient and placental vascularization indexes were detected between women with previous Caesarean section delivery or women with vaginal delivery. FI was significantly lower in nulliparous in the first trimester. The results of our study suggest that 3D placental evaluation was not able to detect placental development alteration in the uterus with a Caesarean section scar. Future research needs to verify whether 3D power Doppler and Vocal techniques can provide more information if used in an earlier gestational age.

Soft tissue assessment for fetal growth restriction

Contemporary clinical practice heavily relies on interpretation of population-based birth weight standards to evaluate neonatal nutrition status. Obstetricians have adopted the use of estimated fetal weight in a similar manner to estimate fetal nutritional status. However, most fetal weight prediction models overemphasize skeletal parameters such as biparietal diameter, head circumference, and femur diaphysis length. Although most EFW calculations also include abdominal circumference, this 2D growth parameter is largely defined by liver size and a small rim of subcutaneous fat. Advances in 3D ultrasound imaging and the development of more robust image analysis tools have now made it possible to reliably add a soft tissue component for fetal nutritional assessment. This chapter explains why fetal soft tissue evaluation is clinically relevant, describes different techniques for evaluating these sonographic parameters, and outlines future directions for their practical utility in the care of malnourished fetuses.

Towards Automated Semantic Segmentation in Prenatal Volumetric Ultrasound

Volumetric ultrasound is rapidly emerging as a viable imaging modality for routine prenatal examinations. Biometrics obtained from the volumetric segmentation shed light on the reformation of precise maternal and fetal health monitoring. However, the poor image quality, low contrast, boundary ambiguity, and complex anatomy shapes conspire toward a great lack of efficient tools for the segmentation. It makes 3-D ultrasound difficult to interpret and hinders the widespread of 3-D ultrasound in obstetrics. In this paper, we are looking at the problem of semantic segmentation in prenatal ultrasound volumes. Our contribution is threefold: 1) we propose the first and fully automatic framework to simultaneously segment multiple anatomical structures with intensive clinical interest, including fetus, gestational sac, and placenta, which remains a rarely studied and arduous challenge; 2) we propose a composite architecture for dense labeling, in which a customized 3-D fully convolutional network explores spatial intensity concurrency for initial labeling, while a multi-directional recurrent neural network (RNN) encodes spatial sequentiality to combat boundary ambiguity for significant refinement; and 3) we introduce a hierarchical deep supervision mechanism to boost the information flow within RNN and fit the latent sequence hierarchy in fine scales, and further improve the segmentation results. Extensively verified on in-house large data sets, our method illustrates a superior segmentation performance, decent agreements with expert measurements and high reproducibilities against scanning variations, and thus is promising in advancing the prenatal ultrasound examinations.

A retrospective segmentation analysis of placental volume by magnetic resonance imaging from first trimester to term gestation

BACKGROUND

Abnormalities of the placenta affect 5-7% of pregnancies. Because disturbances in fetal growth are often preceded by dysfunction of the placenta or attenuation of its normal expansion, placental health warrants careful surveillance. There are limited normative data available for placental volume by MRI.

OBJECTIVE

To determine normative ranges of placental volume by MRI throughout gestation.

MATERIALS AND METHODS

In this cross-sectional retrospective analysis, we reviewed MRI examinations of pregnant females obtained between 2002 and 2017 at a single institution. We performed semi-automated segmentation of the placenta in images obtained in patients with no radiologic evidence of maternal or fetal pathology, using the Philips Intellispace Tumor Tracking Tool.

RESULTS

Placental segmentation was performed in 112 women and had a high degree of interrater reliability (single-measure intraclass correlation coefficient =0.978 with 95% confidence interval [CI] 0.956, 0.989; P<0.001). Normative data on placental volume by MRI increased nonlinearly from 6 weeks to 39 weeks of gestation, with wider variability of placental volume at higher gestational age (GA). We fit placental volumetric data to a polynomial curve of third order described as placental volume = -0.02*GA³ + 1.6*GA² - 13.3*GA + 8.3. Placental volume showed positive correlation with estimated fetal weight (P=0.03) and birth weight (P=0.05).

CONCLUSION

This study provides normative placental volume by MRI from early first trimester to term gestation. Deviations in placental volume from normal might prove to be an imaging biomarker of adverse fetal health and neonatal outcome, and further studies are needed to more fully understand this metric. Assessment of placental volume should be considered in all routine fetal MRI examinations.

Fractional fetal thigh volume in the prediction of normal and abnormal fetal growth during the third trimester of pregnancy

Background

Currently, 2-dimensional ultrasound estimation of fetal size rather than fetal growth is used to define fetal growth restriction, but single estimates in late pregnancy lack sensitivity and may identify small for gestational age rather than growth restriction. Single or longitudinal measures of 3-dimensional fractional thigh volume may address this problem.

Objective

We sought to derive normal values for 3-dimensional fractional thigh volume in the third trimester, determine if fractional thigh volume is superior to 2-dimensional ultrasound biometry alone for detecting fetal growth restriction, and determine whether individualized growth assessment parameters have the potential to identify fetal growth restriction remote from term delivery.

Study Design

This was a longitudinal prospective cohort study of 115 unselected pregnancies in a tertiary referral unit (St Mary’s Hospital, Manchester, United Kingdom). Standard 2-dimensional ultrasound biometry measurements were obtained, along with fractional thigh volume measurements (based on 50% of the femoral diaphysis length). Measurements were used to calculate estimated fetal weight (Hadlock). Individualized growth assessment parameters and percentage deviations in longitudinally measured biometrics were determined using a Web-based system (iGAP; http://iGAP.research.bcm.edu). Small for gestational age was defined <10th and fetal growth restriction <3rd customized birthweight centile. Logistic regression was used to compare estimated fetal weight (Hadlock), estimated fetal weight (biparietal diameter–abdominal circumference–fractional thigh volume), fractional thigh volume, and abdominal circumference for the prediction of small for gestational age or fetal growth restriction at birth. Screening performance was assessed using area under the receiver operating characteristic curve.

Results

There was a better correlation between fractional thigh volume and estimated fetal weight ((biparietal diameter–abdominal circumference–fractional thigh volume) obtained at 34-36 weeks with birthweight than between 2-dimensional biometry measures such as abdominal circumference and estimated fetal weight (Hadlock). There was also a modest improvement in the detection of both small for gestational age and fetal growth restriction using fractional thigh volume–derived measures compared to standard 2-dimensional measurements (area under receiver operating characteristic curve, 0.86; 95% confidence interval, 0.79–0.94, and area under receiver operating characteristic curve, 0.92; 95% confidence interval, 0.85–0.99, respectively).

Conclusion

Fractional thigh volume measurements offer some improvement over 2-dimensional biometry for the detection of late-onset fetal growth restriction at 34-36 weeks.