Fractional limb volume--a soft tissue parameter of fetal body composition: validation, technical considerations and normal ranges during pregnancy. Three-dimensional ultrasonography (3DUS) allows evaluation of the soft tissue of fetal limbs, a parameter that has been described for the evaluation of fetal nutritional status. The fractional limb volume addresses the technical limitations of fetal weight estimation and growth assessment. Our group aimed at providing normal reference ranges for fractional limb volume as a new index of the fetal nutritional status. We also assessed the reproducibility of fractional fetal limb volume measurements during the second and third trimesters of pregnancy. A prospective, cross-sectional study of 387 gravid women between 18.0 and 42.1 weeks of gestation was conducted. Slices were traced manually to obtain fractional arm (AVol) or fractional thigh (TVol) volume and reference charts were established. No gender differences were found in these soft tissue measurements. Intra-observer mean bias for fractional limb volumes were: 2.2 4.2% for AVol and 2.0 4.2% for TVol. Inter-observer bias and agreement were -1.9 4.9% for AVol and -2.0 5.4% for TVol. Fractional limb volume assessment may improve the detection and monitoring of malnourished fetuses because this soft tissue parameter can be obtained quickly and reproducibly during mid to late pregnancy. Fetal growth parameters and birth weight: their relationship to neonatal body composition. Air displacement plethysmography is a non-invasive technique that uses total body volume and mass to derive body composition, including percentage body fat (%BF) and lean body mass (%LBM). This technology has recently been applied to assess neonatal and infant body composition. Since a major goal of prenatal assessment is to identify fetuses with abnormal intrauterine growth, air displacement plethysmography may offer important insight into which fetal growth parameters closely reflect the generalized nutritional state of neonates. Investigators at the PRB studied prospectively the relationship between standard fetal biometry and soft tissue parameters with birth weight in third-trimester pregnancies using three-dimensional ultrasonography (3DUS). Growth parameters included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), mid-thigh circumference and femoral diaphysis length (FDL). Soft tissue parameters included fractional arm volume (AVol) and fractional thigh volume (TVol). The TVol had the greatest correlation with newborn %BF of all single-parameter models. This parameter alone explained 46.1% of the variability in %BF. Birth weight similarly explained 44.7% of the variation in %BF. AC and estimated fetal weight (EFW) accounted for only 24.8% and 30.4% of the variance in %BF, respectively. Growth parameters, such as FDL (14.2%), HC (7.9%) and BPD (4.0%), contributed the least towards explaining the variance in %BF. TVol accounts for a large proportion of the variance in neonatal percentage body fat compared with traditional parameters measured during routine sonography such as abdominal circumference or estimated fetal weight. Downward percentile crossing as an indicator of an adverse prenatal environment. Postnatal health sequelae of low birth weight have been attributed to poor fetal growth secondary to adverse prenatal environments, and identification of prenatal growth-restricting events is essential to clarify pathways and mechanisms of fetal growth. A previous study from our group demonstrated that patients with an episode of increased uterine contractility that subsided and who deliver at term are at risk for delivering a small-for-gestational age neonate, suggesting that an episode of false preterm labor is not a benign condition. The Branch conducted a study to examine whether an episode of preterm labor was associated with compromised fetal growth. Fetal size at the end of the second trimester and birth were compared among women with normal pregnancies and those who experienced an episode of preterm labor (<37 weeks) and subsequently delivered at term (37 weeks). Longitudinal estimated fetal weight and changes in weight standard scores across the third trimester were studied. Neonates delivered at term after an episode of preterm labor were smaller at birth relative to their peers than at the end of the second trimester, and were 47% more likely to have experienced clinically significant downward centile crossing than their peers. We concluded that an episode of preterm labor may represent evidence of an adverse prenatal environment. However, such insult is not sufficient to cause irreversible preterm labor and delivery. Growth perturbations in a phenotype with rapid fetal growth preceding preterm labor and term birth. The Branch conducted a retrospective analysis of fetal biometry assessed by serial ultrasound in a prospective cohort of pregnant women to study fetal growth patterns predating an episode of preterm labor. Fetal growth patterns among uncomplicated pregnancies and those with an episode of preterm labor followed by term delivery were examined across the time intervals 16-22 weeks, 22-28 weeks, and 28-34 weeks using multilevel mixed-effects regression analysis. Fetal weight growth rate was faster at 16 weeks among pregnancies with an episode of preterm labor, declined across midgestation (22-28 weeks), and rebounded between 28 and 34 weeks. This was associated with changes in abdominal circumference growth and proportionately larger biparietal diameter from 22 weeks, greater femur, biparietal diameter and head circumference dimensions relative to abdominal circumference across midgestation (22-28 weeks), followed by proportionately smaller femur diaphyseal length and biparietal diameter subsequently. A distinctive rapid growth phenotype characterized fetal growth preceding an episode of preterm labor among patients who delivered at term. Perturbations in abdominal circumference growth and patterns of proportionality suggest that altered fetal growth pre-dates an episode of preterm labor. Early rapid growth, early birth: accelerated fetal growth and spontaneous late preterm birth. The past two decades in the United States have seen a 24% rise in spontaneous late preterm delivery (34.0 to 36.9 weeks) of unknown etiology. This study was conducted to compare fetal growth between patients with spontaneous late preterm birth and those who delivered at term in a cohort of pregnancies followed longitudinally. Preterm-delivered fetuses were significantly larger than their term-delivered peers by mid-second trimester in estimated fetal weight, head, limb, and abdominal dimensions, and they followed different growth trajectories. Piecewise regression assessed time-specific differences in growth rates at 4-week intervals from 16 weeks. Estimated fetal weight and abdominal circumference growth rates slowed at 20 weeks among the preterm-delivered, only to match and/or exceed their term-delivered peers at 24-28 weeks. Growth rates predicted birth timing: one standard score of estimated fetal weight increased the odds ratio for late preterm birth from 2.8 prior to 23 weeks, to 3.6 between 23 and 27 weeks. After 27 weeks, increasing size was protective. This study reports, for the first time, that a distinctive fetal growth pattern across gestation precedes spontaneous late preterm birth and stresses the importance of mid-gestation for the generation of fetal growth disorders.
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