Lactate detection in the brain of growth-restricted fetuses with magnetic resonance spectroscopy

The Association between Infant Birth Weight, Head Circumference, and Neurodevelopmental Outcomes

OBJECTIVE

 The aim of this study was to evaluate whether being small for gestational age (SGA) or large for gestational age (LGA) or having a small or large head circumference (HC) at birth is associated with adverse neurodevelopmental outcomes.

STUDY DESIGN

 This is a secondary analysis of a multicenter negative randomized trial of thyroxine therapy for subclinical hypothyroid disorders in pregnancy. The primary outcome was child intelligence quotient (IQ) at 5 years of age. Secondary outcomes included several neurodevelopmental measures. Associations between the outcomes in children with SGA (<10th percentile) or LGA (>90th percentile) birth weights, using ethnicity- and sex-specific population nomogram as well as nomograms from the National Fetal Growth (NFG) study, were compared with the referent of those with appropriate for gestational age (AGA) birth weight. Similar analyses were performed for HC.

RESULTS

 Using the population nomogram, 90 (8.2%) were SGA and 112 (10.2%) were LGA. SGA neonates were more likely to be born preterm to mothers who were younger, smoked, and were less likely to have less than a high school education, whereas LGA neonates were more likely to be born to mothers who were older and have higher body mass index, compared with AGA neonates. SGA at birth was associated with a decrease in the child IQ at 5 years of age by 3.34 (95% confidence interval [CI], 0.54-6.14) points, and an increase in odds of child with an IQ < 85 (adjusted odds ratio [aOR], 1.9; 95% CI, 1.1-3.2). There was no association between SGA and other secondary outcomes, or between LGA and the primary or secondary outcomes. Using the NFG standards, SGA at birth remained associated with a decrease in the child IQ at 5 years of age by 3.14 (95% CI, 0.22-6.05) points and higher odds of an IQ < 85 (aOR, 2.3; 95% CI, 1.3-4.1), but none of the other secondary outcomes. HC was not associated with the primary outcome, and there were no consistent associations of these standards with the secondary outcomes.

CONCLUSION

 In this cohort of pregnant individuals with hypothyroid disorders, SGA birth weight was associated with a decrease in child IQ and greater odds of child IQ < 85 at 5 years of age. Using a fetal growth standard did not appear to improve the detection of newborns at risk of adverse neurodevelopment.

T2* weighted fetal MRI and the correlation with placental dysfunction

INTRODUCTION

Transverse relaxation time (T2*) is related to tissue oxygenation and morphology. We aimed to describe T2* weighted MRI in selected fetal organs in normal pregnancies, and to investigate the correlation between fetal organ T2* and placental T2*, birthweight (BW) deviation, and redistribution of fetal blood flow.

METHODS

T2*-weighted MRI was performed in 126 singleton pregnancies between 23+6- and 41+3-weeks' gestation. The T2* value was obtained from the placenta and fetal organs (brain, lungs, heart, liver, kidneys, and spleen). In normal BW pregnancies (BW > 10th centile), the correlation between the T2* value and gestational age (GA) at MRI was estimated by linear regression. The correlation between fetal organ Z-score and BW group was demonstrated by boxplots and investigated by analysis of variance (ANOVA) for each organ.

RESULTS

In normal BW pregnancies fetal organ T2* was negatively correlated with GA. We found a significant correlation between BW group and fetal organ T2* z-score in the fetal heart, kidney, lung and spleen. A positive linear correlation was demonstrated between fetal organ T2* and outcomes related to placental function such as BW deviation and placenta T2* in all investigated fetal organs except for the fetal liver. In the fetal heart, kidneys, and spleen the T2* value showed a significant correlation with fetal redistribution of blood flow (Middle cerebral artery Pulsatility Index) before delivery.

DISCUSSION

Fetal T2* is correlated with BW, placental function, and redistribution of fetal blood flow, suggesting that fetal organ T2* reflects fetal oxygenation and morphological changes related to placental dysfunction.

Magnetic resonance spectroscopy brain metabolites at term and 3-year neurodevelopmental outcomes in very preterm infants

BACKGROUND

Noninvasive advanced neuroimaging and neurochemical assessment can identify subtle abnormalities and predict neurodevelopmental impairments. Our objective was to quantify white matter metabolite levels and evaluate their relationship with neurodevelopmental outcomes at age 3 years.

METHODS

Our study evaluated a longitudinal prospective cohort of very premature infants (<32 weeks gestational age) with single-voxel proton magnetic resonance spectroscopy from the centrum semiovale performed at term-equivalent age and standardized cognitive, verbal, and motor assessments at 3 years corrected age. We separately examined metabolite ratios in the left and right centrum semiovale. We also conducted an exploratory interaction analysis for high/low socioeconomic status (SES) to evaluate the relationship between metabolites and neurodevelopmental outcomes, after adjusting for confounders.

RESULTS

We found significant relationships between choline/creatine levels in the left and right centrum semiovale and motor development scores. Exploratory interaction analyses revealed that, for infants with low SES, there was a negative association between choline/creatine in the left centrum semiovale and motor assessment scores at age 3 years.

CONCLUSIONS

Brain metabolites from the centrum semiovale at term-equivalent age were associated with motor outcomes for very preterm infants at 3 years corrected age. This effect may be most pronounced for infants with low SES.

IMPACT

Motor development at 3 years corrected age for very preterm infants is inversely associated with choline neurochemistry within the centrum semiovale on magnetic resonance spectroscopy at term-equivalent age, especially in infants with low socioeconomic status. No prior studies have studied metabolites in the centrum semiovale to predict neurodevelopmental outcomes at 3 years corrected age based on high/low socioeconomic status. For very preterm infants with lower socioeconomic status, higher choline-to-creatine ratio in central white matter is associated with worse neurodevelopmental outcomes.

Brain-Derived Neurotrophic Factor Levels in Cord Blood from Growth Restricted Fetuses with Doppler Alteration Compared to Adequate for Gestational Age Fetuses

Background and Objectives: Fetal growth restriction (FGR) is a severe obstetric disease characterized by a low fetal size entailing a set of undesired consequences. For instance, previous studies have noticed a worrisome association between FGR with an abnormal neurodevelopment. However, the precise link between FGR and neurodevelopmental alterations are not yet fully understood yet. Brain-derived neurotrophic factor (BDNF) is a critical neurotrophin strongly implicated in neurodevelopmental and other neurological processes. In addition, serum levels of BDNF appears to be an interesting indicator of pathological pregnancies, being correlated with the neonatal brain levels. Therefore, the aim of this study is to analyze the blood levels of BDNF in the cord blood from fetuses with FGR in comparison to those with weight appropriate for gestational age (AGA). Materials and Methods: In this study, 130 subjects were recruited: 91 in group A (AGA fetuses); 39 in group B (16 FGR fetuses with exclusively middle cerebral artery (MCA) pulsatility index (PI) < 5th percentile and 23 with umbilical artery (UA) PI > 95th percentile). Serum levels of BDNF were determined through ELISA reactions in these groups. Results: Our results show a significant decrease in cord blood levels of BDNF in FGR and more prominently in those with UA PI >95th percentile in comparison to AGA. FGR fetuses with exclusively decreased MCA PI below the 5th percentile also show reduced levels of BDNF than AGA, although this difference was not statistically significant. Conclusions: Overall, our study reports a potential pathophysiological link between reduced levels of BDNF and neurodevelopmental alterations in fetuses with FGR. However, further studies should be conducted in those FGR subjects with MCA PI < 5th percentile in order to understand the possible implications of BDNF in this group.

An integrated approach based on advanced CTG parameters and Doppler measurements for late growth restriction management

Background

The clinical diagnosis of late Fetal Growth Restriction (FGR) involves the integration of Doppler ultrasound data and Fetal Heart Rate (FHR) monitoring through computer assisted computerized cardiotocography (cCTG). The aim of the study was to evaluate the diagnostic power of combined Doppler and cCTG parameters by contrasting late FGR –and healthy controls.

Methods

The study was conducted from January 2018 to May 2020. Only pregnant women who had the last Doppler measurement obtained within 1 week before delivery and cCTG performed within 24 h before delivery were included in the study. Two hundred forty-nine pregnant women fulfilling the inclusion criteria were enrolled in the study; 95 were confirmed as late FGR and 154 were included in the control group.

Results

Among the extracted cCTG parameters, Delta Index, Short Term Variability (STV), Long Term Variability (LTV), Acceleration and Deceleration Phase Rectified Slope (APRS, DPRS) values were lower in the late FGR participants compared to the control group. In the FGR cohort, Delta, STV, APRS, and DPRS were found different when stratifying by MCA_PI (MCA_PI <5th centile or > 5th centile). STV and DPRS were the only parameters to be found different when stratifying by (UA_PI >95th centile or UA_PI <95th centile). Additionally, we measured the predictive power of cCTG parameters toward the identification of associated Doppler measures using figures of merit extracted from ROC curves.

The AUC of ROC curves were accurate for STV (0,70), Delta (0,68), APRS (0,65) and DPRS (0,71) when UA_PI values were > 95th centile while, the accuracy attributable to the prediction of MCA_PI was 0.76, 0.77, 0.73, and 0.76 for STV, Delta, APRS, and DPRS, respectively.

An association of UA_PI>95th centile and MCA_PI<5th centile with higher risk for NICU admission, was observed, while CPR < 5th centile resulted not associated with any perinatal outcome. Values of STV, Delta, APRS, DPRS were significantly lower for FGR neonates admitted to NICU, compared with the uncomplicated FGR cohort.

Conclusions

The results of this study show the contribution of advanced cCTG parameters and fetal Doppler to the identification of late FGR and the association of those parameters with the risk for NICU admission.

Trial registration

Retrospectively registered.

Influence of Cerebral Vasodilation on Blood Reelin Levels in Growth Restricted Fetuses

Fetal growth restriction (FGR) is one of the most important obstetric pathologies. It is frequently caused by placental insufficiency. Previous studies have shown a relationship between FGR and impaired new-born neurodevelopment, although the molecular mechanisms involved in this association have not yet been completely clarified. Reelin is an extracellular matrix glycoprotein involved in development of neocortex, hippocampus, cerebellum and spinal cord. Reelin has been demonstrated to play a key role in regulating perinatal neurodevelopment and to contribute to the emergence and development of various psychiatric pathologies, and its levels are highly influenced by pathological conditions of hypoxia. The purpose of this article is to study whether reelin levels in new-borns vary as a function of severity of fetal growth restriction by gestational age and sex. We sub-grouped fetuses in: normal weight group (Group 1, n = 17), FGR group with normal umbilical artery Doppler and cerebral redistribution at middle cerebral artery Doppler (Group 2, n = 9), and FGR with abnormal umbilical artery Doppler (Group 3, n = 8). Our results show a significant association of elevated Reelin levels in FGR fetuses with cerebral blood redistribution compared to the normal weight group and the FGR with abnormal umbilical artery group. Future research should focus on further expanding the knowledge of the relationship of reelin and its regulated products with neurodevelopment impairment in new-borns with FGR and should include larger and more homogeneous samples and the combined use of different in vivo techniques in neonates with impaired growth during their different adaptive phases.

The application of in utero magnetic resonance imaging in the study of the metabolic and cardiovascular consequences of the developmental origins of health and disease

Observing fetal development in utero is vital to further the understanding of later-life diseases. Magnetic resonance imaging (MRI) offers a tool for obtaining a wealth of information about fetal growth, development, and programming not previously available using other methods. This review provides an overview of MRI techniques used to investigate the metabolic and cardiovascular consequences of the developmental origins of health and disease (DOHaD) hypothesis. These methods add to the understanding of the developing fetus by examining fetal growth and organ development, adipose tissue and body composition, fetal oximetry, placental microstructure, diffusion, perfusion, flow, and metabolism. MRI assessment of fetal growth, organ development, metabolism, and the amount of fetal adipose tissue could give early indicators of abnormal fetal development. Noninvasive fetal oximetry can accurately measure placental and fetal oxygenation, which improves current knowledge on placental function. Additionally, measuring deficiencies in the placenta’s transport of nutrients and oxygen is critical for optimizing treatment. Overall, the detailed structural and functional information provided by MRI is valuable in guiding future investigations of DOHaD.

Fetal Oxygen and Glucose Consumption in Human Pregnancy Complicated by Fetal Growth Restriction

In healthy pregnancy, glucose and oxygen availability are essential for fetal growth and well being. However, how substrate delivery and fetal uptake are affected in human pregnancy complicated by fetal growth restriction (FGR) is still unknown. Here, we show that the human FGR fetus has a strikingly reduced umbilical uptake of both oxygen and glucose. In 30 healthy term and 32 FGR human pregnancies, umbilical volume flow (Qumb) and parallel umbilical vein (uv) and artery (ua) blood samples were obtained at elective Cesarean section to calculate fetal glucose and oxygen uptake as Qumb · Δ (uv-ua) differences. Umbilical blood flow was significantly lower in FGR pregnancy (-63%; P<0.001) but not when normalized for fetal body weight. FGR pregnancy had significantly lower umbilical oxygen delivery and uptake, both as absolute values (delivery: -78%; uptake: -78%) and normalized (delivery: -50%; uptake: -48%) for fetal body weight (all P<0.001). Umbilical glucose absolute delivery and uptake were significantly reduced (delivery: -68%; uptake: -72%) but only glucose uptake was decreased when normalized for fetal body weight (-30%; P<0.05). The glucose/oxygen quotient was significantly increased (+100%; P<0.05) while glucose clearance was significantly decreased (71%; P<0.001) in FGR pregnancy (both P<0.05). The human fetus in FGR pregnancy triggers compensatory mechanisms to reduce its metabolic rate, matching the proportion of substrate consumption relative to oxygen delivery as a survival strategy during complicated pregnancy.

Clinical course of a fetus with hypoplastic left heart syndrome and premature ductal constriction

Premature ductal constriction was diagnosed in a 30-week gestation fetus with hypoplastic left heart syndrome. The fetus developed right ventricular hypertrophy and mild tricuspid regurgitation. Foetal neuroimaging showed slowed growth of the brain and increased lactate. We describe the imaging and clinical findings. Fetuses with critical CHD and in utero ductal constriction are at increased risk of morbidity and mortality, and require appropriate counselling.

Fetal and neonatal neuroimaging

Magnetic resonance imaging (MRI) can provide detail of the soft tissues of the fetal and neonatal brain that cannot be obtained by any other imaging modality. Conventional T1 and T2 weighted sequences provide anatomic detail of the normally developing brain and can demonstrate lesions, including those associated with preterm birth, hypoxic ischemic encephalopathy, perinatal arterial stroke, infections, and congenital malformations. Specialized imaging techniques can be used to assess cerebral vasculature (magnetic resonance angiography and venography), cerebral metabolism (magnetic resonance spectroscopy), cerebral perfusion (arterial spin labeling), and function (functional MRI). A wealth of quantitative tools, most of which were originally developed for the adult brain, can be applied to study the developing brain in utero and postnatally including measures of tissue microstructure obtained from diffusion MRI, morphometric studies to measure whole brain and regional tissue volumes, and automated approaches to study cortical folding. In this chapter, we aim to describe different imaging approaches for the fetal and neonatal brain, and to discuss their use in a range of clinical applications.

Quantitative susceptibility mapping in the human fetus to measure blood oxygenation in the superior sagittal sinus

OBJECTIVES

To present the feasibility of performing quantitative susceptibility mapping (QSM) in the human fetus to evaluate the oxygenation (S_vO₂) of cerebral venous blood in vivo.

METHODS

Susceptibility weighted imaging (SWI) data were acquired from healthy pregnant subjects (n = 21, median = 31.3 weeks, interquartile range = 8.8 weeks). The susceptibility maps were generated from the SWI-phase images using a modified QSM processing pipeline, optimised for fetal applications. The processing pipeline is as follows: (1) mild high-pass filtering followed by quadratic fitting of the phase images to eliminate background phase variations; (2) manual creation of a fetal brain mask that includes the superior sagittal sinus (SSS); (3) inverse filtering of the resultant masked phase images using a truncated k-space approach with geometric constraint. Further, the magnetic susceptibility, ∆χ_v and corresponding putative S_vO₂ of the SSS were quantified from the generated susceptibility maps. Systematic error in the measured S_vO₂ due to the modified pipeline was also studied through simulations.

RESULTS

Simulations showed that the systematic error in S_vO₂ when using a mask that includes a minimum of 5 voxels around the SSS and five slices remains < 3% for different orientations of the vessel relative to the main magnetic field. The average ∆χ_v in the SSS quantified across all gestations was 0.42 ± 0.03 ppm. Based on ∆χ_v, the average putative S_vO₂ in the SSS across all fetuses was 67% ± 7%, which is in good agreement with published studies.

CONCLUSIONS

This in vivo study demonstrates the feasibility of using QSM in the human fetal brain to estimate ∆χ_v and S_vO₂.

KEY POINTS

• A modified quantitative susceptibility mapping (QSM) processing pipeline is tested and presented for the human fetus. • QSM is feasible in the human fetus for measuring magnetic susceptibility and oxygenation of venous blood in vivo. • Blood magnetic susceptibility values from MR susceptometry and QSM agree with each other in the human fetus.

Fetal neuroimaging: an update on technical advances and clinical findings

This paper is based on a literature review from 2011 to 2016. The paper is divided into two main sections. The first section relates to technical advances in fetal imaging techniques, including fetal motion compensation, imaging at 3.0 T, 3-D T2-weighted MRI, susceptibility-weighted imaging, computed tomography, morphometric analysis, diffusion tensor imaging, spectroscopy and fetal behavioral assessment. The second section relates to clinical updates, including cerebral lamination, migrational anomalies, midline anomalies, neural tube defects, posterior fossa anomalies, sulcation/gyration and hypoxic-ischemic insults.

Imaging putative foetal cerebral blood oxygenation using susceptibility weighted imaging (SWI)

OBJECTIVE

To evaluate the magnetic susceptibility, ∆χ _v , as a surrogate marker of venous blood oxygen saturation, S _v O ₂, in second- and third-trimester normal human foetuses.

METHODS

Thirty-six pregnant women, having a mean gestational age (GA) of 31 2/7 weeks, underwent magnetic resonance imaging (MRI). Susceptibility-weighted imaging (SWI) data from the foetal brain were acquired. ∆χ _v of the superior sagittal sinus (SSS) was quantified using MR susceptometry from the intra-vascular phase measurements. Assuming the magnetic property of foetal blood, ∆χ _do , is the same as that of adult blood, S _v O ₂ was derived from the measured Δχ _v . The variation of ∆χ _v and S _v O ₂, as a function of GA, was statistically evaluated.

RESULTS

The mean ∆χ _v in the SSS in the second-trimester (n = 8) and third-trimester foetuses (n = 28) was found to be 0.34± 0.06 ppm and 0.49 ±0.05 ppm, respectively. Correspondingly, the derived S _v O ₂ values were 69.4% ±3.27% and 62.6% ±3.25%. Although not statistically significant, an increasing trend (p = 0.08) in Δχ _v and a decreasing trend (p = 0.22) in S _v O ₂ with respect to advancing gestation was observed.

CONCLUSION

We report cerebral venous blood magnetic susceptibility and putative oxygen saturation in healthy human foetuses. Cerebral oxygen saturation in healthy human foetuses, despite a slight decreasing trend, does not change significantly with advancing gestation.

KEY POINTS

• Cerebral venous magnetic susceptibility and oxygenation in human foetuses can be quantified. • Cerebral venous oxygenation was not different between second- and third-trimester foetuses. • Foetal cerebral venous oxygenation does not change significantly with advancing gestation.

Does 3T Fetal MRI Improve Image Resolution of Normal Brain Structures between 20 and 24 Weeks' Gestational Age?

BACKGROUND AND PURPOSE

Stronger magnetic fields have the potential to improve fetal image resolution. Our objective was to detect whether there was better anatomic resolution of brain structures in fetuses imaged with a 3T magnet compared with a 1.5T magnet.

MATERIALS AND METHODS

Multiple cerebral and facial anatomic structures were retrospectively assessed in 28 fetal MR imaging scans with normal findings (12 at 3T and 16 at 1.5T) with a 0-3 grading score. Fetuses were assessed during the second trimesters (gestational age, 20-24 weeks). The association between the quality ratings and magnetic field strengths (1.5T versus 3T) was evaluated by a linear mixed-effects model. A quantitative assessment of the signal intensity was also performed in the different layers of the developing brain. Comparative log-ratios were calculated across the different layers of the fetal brain.

RESULTS

There was a statistically significant interaction between location and magnetic field strength (P < .001). The cerebral structures of the cerebellum, pons, venous system, semicircular canal, and cochlea showed statistically significant higher values on the 3T magnet. Similarly, statistical significance was also obtained on the quantitative assessment of the multilayer appearance of the brain; the 3T magnet had a median factor of 8.38 higher than the 1.5T magnet (95% CI, 4.73-14.82). Other anatomic structures assessed in the supratentorial compartment of the brain showed higher values on the 3T magnet with no statistical significance.

CONCLUSIONS

Both magnets depict cerebral and facial normal anatomic structures; however, our data indicates better anatomic detail on the 3T than on the 1.5T magnet.

Contemporary Modalities to Image the Fetal Brain

Fetal brain ultrasound remains as the mainstay for screening fetal intracranial anatomy. One of its main advantages is the availability of 3 dimensional and other ultrasound modalities for a better understanding of fetal neurodevelopment. Neurosonography is performed when findings, suggestive of an abnormality, are present on a screening ultrasound or if a high-risk situation of brain injury is present. This technique offers the use of complementary imaging planes, axial, coronal and sagittal, and the ability to image intracranial anatomy from the transabdominal and transvaginal approaches. Fetal brain magnetic resonance imaging is more sensitive than ultrasound. As an adjunctive imaging modality, magnetic resonance imaging offers additional sequences to complete the information on neurodevelopment from different perspectives, such as brain metabolism, microstructure, and connectivity.

The predictive value of lactate peak detected by the magnetic resonance spectroscopy in the brain of growth-restricted fetuses for adverse perinatal outcomes

OBJECTIVE

To compare perinatal outcomes between patients with and without abnormal Doppler findings and lactate peak in the fetal brain detected by magnetic resonance spectroscopy ((1)HMRS) and to assess the feasibility of fetal brain lactate in the prediction of adverse obstetric outcomes in growth-restricted fetuses.

METHODS

Pregnancies with FGR fetuses underwent Doppler ultrasonography and 3 Tesla (1)HMRS for the presence of lactate peak prior to the delivery. Patients were assigned into the following groups; normal Doppler, no lactate peak (Group 1), normal Doppler, lactate peak (+) (Group II), abnormal Doppler, no lactate peak (Group III), abnormal Doppler, lactate peak (+) (Group IV).

RESULTS

Five perinatal deaths, all in Group IV, were encountered (p < 0.001). Perinatal death rate was higher in patients with Doppler flow abnormality ((5/12 (41.7%)) than in patients without Doppler abnormality (0/23) (p < 0.001) and was significantly higher in the presence (5/18 (27.8%)) than in the absence of lactate peak (0/17) (p = 0.019).

CONCLUSIONS

Fetuses with brain lactate peak detected by (1)HMRS in addition to altered Doppler findings are more likely to develop short-term morbidities and perinatal death. Fetal brain lactate detected by (1)HMRS may represent a clinical marker of altered brain metabolism and further perinatal complications.

Impact of cerebral redistribution on neurodevelopmental outcome in small-for-gestational-age or growth-restricted babies: a systematic review

OBJECTIVES

To review systematically the evidence on impact of cerebral redistribution, as assessed by fetal middle cerebral artery (MCA) Doppler, on neurological outcomes in small-for-gestational-age (SGA) or growth-restricted fetuses.

METHODS

For this systematic review, MEDLINE was searched for all controlled studies reporting neurological outcomes in SGA or growth-restricted babies with cerebral redistribution based on MCA Doppler indices, from inception to September 2013. We used relative risk or odds ratios, with 95% CI, to identify the association of cerebral redistribution with neurological outcomes.

RESULTS

The search yielded 1180 possible citations, of which nine studies were included in the review, with a total of 1198 fetuses. Definitions of SGA and cerebral redistribution were variable, as was study quality. Data could not be synthesized in meta-analyses because of heterogeneity in outcome reporting. Cerebral redistribution was not associated with increased risk of intraventricular hemorrhage in neonates (five studies; n = 806). When present in preterm fetuses, cerebral redistribution was associated with normal Neonatal Behavioral Assessment Scale (NBAS) scores at 40 weeks (one study; n = 62) but abnormal psychomotor development at 1 year of age on the Bayley scale (one study; n = 172). When present in term SGA fetuses, cerebral redistribution was associated with increased risk of motor and state organizational problems on NBAS (two studies; n = 158), and lower mean percentile scores in communication and problem solving at 2 years of age on the Ages and Stages Questionnaire (one study; n = 125).

CONCLUSIONS

SGA fetuses with cerebral redistribution may be at higher risk of neurodevelopmental problems. More data are needed from adequately controlled studies with long-term follow-up before conclusions can be drawn. If these findings are true, there is a need to re-evaluate timing of delivery in the management of SGA fetuses, particularly when cerebral redistribution is found at term gestation.

MR imaging of the fetal brain at 1.5T and 3.0T field strengths: comparing specific absorption rate (SAR) and image quality

OBJECTIVES

Our two objectives were to evaluate the feasibility of fetal brain magnetic resonance imaging (MRI) using a fast spin echo sequence at 3.0T field strength with low radio frequency (rf) energy deposition (as measured by specific absorption rate: SAR) and to compare image quality, tissue contrast and conspicuity between 1.5T and 3.0T MRI.

METHODS

T2 weighted images of the fetal brain at 1.5T were compared to similar data obtained in the same fetus using a modified sequence at 3.0T. Quantitative whole-body SAR and normalized image signal to noise ratio (SNR), a nominal scoring scheme based evaluation of diagnostic image quality, and tissue contrast and conspicuity for specific anatomical structures in the brain were compared between 1.5T and 3.0T.

RESULTS

Twelve pregnant women underwent both 1.5T and 3.0T MRI examinations. The image SNR was significantly higher (P=0.03) and whole-body SAR was significantly lower (P<0.0001) for images obtained at 3.0T compared to 1.5T. All cases at both field strengths were scored as having diagnostic image quality. Images from 3.0T MRI (compared to 1.5T) were equal (57%; 21/37) or superior (35%; 13/37) for tissue contrast and equal (61%; 20/33) or superior (33%, 11/33) for conspicuity.

CONCLUSIONS

It is possible to obtain fetal brain images with higher resolution and better SNR at 3.0T with simultaneous reduction in SAR compared to 1.5T. Images of the fetal brain obtained at 3.0T demonstrated superior tissue contrast and conspicuity compared to 1.5T.

Fetal MRI: A Technical Update with Educational Aspirations

Fetal magnetic resonance imaging (MRI) examinations have become well-established procedures at many institutions and can serve as useful adjuncts to ultrasound (US) exams when diagnostic doubts remain after US. Due to fetal motion, however, fetal MRI exams are challenging and require the MR scanner to be used in a somewhat different mode than that employed for more routine clinical studies. Herein we review the techniques most commonly used, and those that are available, for fetal MRI with an emphasis on the physics of the techniques and how to deploy them to improve success rates for fetal MRI exams. By far the most common technique employed is single-shot T2-weighted imaging due to its excellent tissue contrast and relative immunity to fetal motion. Despite the significant challenges involved, however, many of the other techniques commonly employed in conventional neuro- and body MRI such as T1 and T2*-weighted imaging, diffusion and perfusion weighted imaging, as well as spectroscopic methods remain of interest for fetal MR applications. An effort to understand the strengths and limitations of these basic methods within the context of fetal MRI is made in order to optimize their use and facilitate implementation of technical improvements for the further development of fetal MR imaging, both in acquisition and post-processing strategies.

Quantitative magnetic resonance imaging of the fetal brain in utero: Methods and applications

Application of modern magnetic resonance imaging (MRI) techniques to the live fetus in utero is a relatively recent endeavor. The relative advantages and disadvantages of clinical MRI relative to the widely used and accepted ultrasonographic approach are the subject of a continuing debate; however the focus of this review is on the even younger field of quantitative MRI as applied to non-invasive studies of fetal brain development. The techniques covered under this header include structural MRI when followed by quantitative (e.g., volumetric) analysis, as well as quantitative analyses of diffusion weighted imaging, diffusion tensor imaging, magnetic resonance spectroscopy and functional MRI. The majority of the published work reviewed here reflects information gathered from normal fetuses scanned during the 3^rd trimester, with relatively smaller number of studies of pathological samples including common congenital pathologies such as ventriculomegaly and viral infection.

Proton Magnetic Resonance Spectroscopy Assessment of Fetal Brain Metabolism in Late-Onset ‘Small for Gestational Age' versus ‘Intrauterine Growth Restriction' Fetuses

Objectives: We used magnetic resonance spectroscopy (MRS) to evaluate brain metabolic differences in small fetuses near term as compared to appropriate for gestational age (AGA) fetuses. Study Design: 71 term small fetuses (estimated fetal weight <10th centile for gestational age with normal umbilical artery Doppler sonography) were subclassified as late intrauterine growth restriction (IUGR) (n = 50) or small for gestational age (SGA) (n = 21), and compared with 65 AGA fetuses. IUGR was defined by either abnormal middle cerebral artery, abnormal uterine artery Doppler sonography or estimated fetal weight <3rd centile. All participants underwent brain magnetic resonance imaging at 37 weeks of gestation, and single-voxel magnetic resonance spectra were obtained from the frontal lobe on a 3-tesla scanner. N-acetylaspartate (NAA)/choline (Cho), NAA/creatine (Cr) and Cho/Cr ratios were calculated and compared between cases and controls. The association of the metabolic ratios with the study groups was tested. Results: After MRS processing and applying quality control criteria, 31 spectra from late-onset IUGR, 11 from SGA and 30 from AGA fetuses were selected for further analysis. Both SGA and late-onset IUGR fetuses showed significantly reduced NAA/Cho levels when compared to AGA fetuses. This decrease followed a linear trend across the three clinical groups that were considered. Conclusions: Both SGA and late-onset IUGR fetuses showed differences in MRS brain metabolic ratios. The findings suggest that despite near-normal perinatal outcomes, SGA fetuses are not constitutionally small and may represent a form of growth disorder that needs to be clarified.

Placental mitochondrial content and function in intrauterine growth restriction and preeclampsia

Intrauterine growth restriction (IUGR) and pregnancy hypertensive disorders such as preeclampsia (PE) associated with IUGR share a common placental phenotype called "placental insufficiency", originating in early gestation when high availability of energy is required. Here, we assess mitochondrial content and the expression and activity of respiratory chain complexes (RCC) in placental cells of these pathologies. We measured mitochondrial (mt)DNA and nuclear respiratory factor 1 (NRF1) expression in placental tissue and cytotrophoblast cells, gene and protein expressions of RCC (real-time PCR and Western blotting) and their oxygen consumption, using the innovative technique of high-resolution respirometry. We analyzed eight IUGR, six PE, and eight uncomplicated human pregnancies delivered by elective cesarean section. We found lower mRNA levels of complex II, III, and IV in IUGR cytotrophoblast cells but no differences at the protein level, suggesting a posttranscriptional compensatory regulation. mtDNA was increased in IUGR placentas. Both mtDNA and NRF1 expression were instead significantly lower in their isolated cytotrophoblast cells. Finally, cytotrophoblast RCC activity was significantly increased in placentas of IUGR fetuses. No significant differences were found in PE placentas. This study provides genuine new data into the complex physiology of placental oxygenation in IUGR fetuses. The higher mitochondrial content in IUGR placental tissue is reversed in cytotrophoblast cells, which instead present higher mitochondrial functionality. This suggests different mitochondrial content and activity depending on the placental cell lineage. Increased placental oxygen consumption might represent a limiting step in fetal growth restriction, preventing adequate oxygen delivery to the fetus.

Novel use of proton magnetic resonance spectroscopy (1HMRS) to non-invasively assess placental metabolism

Background

Placental insufficiency is a major cause of antepartum stillbirth and fetal growth restriction (FGR). In affected pregnancies, delivery is expedited when the risks of ongoing pregnancy outweigh those of prematurity. Current tests are unable to assess placental function and determine optimal timing for delivery. An accurate, non-invasive test that clearly defines the failing placenta would address a major unmet clinical need. Proton magnetic resonance spectroscopy (¹H MRS) can be used to assess the metabolic profile of tissue in-vivo. In FGR pregnancies, a reduction in N-acetylaspartate (NAA)/choline ratio and detection of lactate methyl are emerging as biomarkers of impaired neuronal metabolism and fetal hypoxia, respectively. However, fetal brain hypoxia is a late and sometimes fatal event in placental compromise, limiting clinical utility of brain ¹H MRS to prevent stillbirth. We hypothesised that abnormal placental ¹H MRS may be an earlier biomarker of intrauterine hypoxia, affording the opportunity to optimise timing of delivery in at-risk fetuses.

Methods and Findings

We recruited three women with severe placental insufficiency/FGR and three matched controls. Using a 3T MR system and a combination of phased-array coils, a 20×20×40 mm¹H MRS voxel was selected along the ‘long-axis’ of the placenta with saturation bands placed around the voxel to prevent contaminant signals. A significant choline peak (choline/lipid ratio 1.35–1.79) was detected in all healthy placentae. In contrast, in pregnancies complicated by FGR, the choline/lipid ratio was ≤0.02 in all placentae, despite preservation of the lipid peak (p<0.001).

Conclusions

This novel proof-of-concept study suggests that in severe placental insufficiency/FGR, the observed 60-fold reduction in the choline/lipid ratio by ¹H MRS may represent an early biomarker of critical placental insufficiency. Further studies will determine performance of this test and the potential role of 1H-MRS in the in-vivo assessment of placental function to inform timing of delivery.