The development of the fetal thymus: an in utero sonographic evaluation

Enlarged cavum septum pellucidum and small thymus as markers for 22q11.2 deletion syndrome

BACKGROUND

Enlarged cavum septum pellucidum (CSP) and hypoplastic thymus are proposed extra-cardiac fetal markers for 22q11.2 deletion syndrome. We sought to determine if they were part of the fetal phenotype of our cohort of fetuses with 22q11.2 deletion syndrome.

METHODS

Case-control study of fetuses evaluated from 2016 to 2022. The study group included fetuses with laboratory confirmation of 22q11.2 deletion syndrome. The control group included pregnancies with conotruncal cardiac anomalies with normal microarray as well as structurally normal fetuses with normal microarray. The CSP and thymus were routinely measured during anatomical ultrasound in all patients at their initial visit at 27.1 ± 4.7 weeks. The CSP and thymus measurements were classified as abnormal if they were >95% or <5% for gestational age, respectively. The groups were compared using analysis of variance or Kruskal-Wallis for continuous variables and Fisher's exact test for categorical variables. Logistic regression was performed, and a Receiver Operating Characteristic (ROC) curve was constructed.

RESULTS

We identified 47 fetuses with 22q11.2 deletion syndrome and compared them to 47 fetuses with conotruncal anomalies and normal microarray and 47 structurally normal fetuses with normal microarray. 51% (24/47) of fetuses with 22q11.2 deletion syndrome had an enlarged CSP compared to 6% (3/47) of fetuses with a conotruncal anomaly and normal microarray and none of the structurally normal fetuses (p < 0.001). Of the fetuses with 22q11.2 deletion syndrome, 83% (39/47) had a hypoplastic or absent thymus compared to 9% (4/47) of the fetuses with a conotruncal anomaly and normal microarray and none of the structurally normal fetuses (p < 0.001). 87% (41/47) of the fetuses with 22q11.2 deletion syndrome had conotruncal cardiac anomalies. Logistic regression revealed that both enlarged CSP and hypoplastic/absent thymus were associated with 22q11.2 deletion syndrome. The area under the ROC curve for the two markers was 0.94.

CONCLUSION

An enlarged CSP and hypoplastic/absent thymus appear to be part of the fetal phenotype of 22q11.2 deletion syndrome. These markers are associated with conotruncal anomalies in the setting of 22q11.2 deletion syndrome but not in normal controls or fetuses with conotruncal defects and normal microarrays.

Decreased fetal thymus size in pregnancies after assisted reproductive technologies

OBJECTIVE

To compare the size of the fetal thymus, using both fetal thymic-thoracic ratio and fetal thymus transverse diameter values in Assisted reproductive technologies (ART) or naturally conceived pregnancies.

METHODS

In this retrospective study, fetal thymic-thoracic ratio and fetal thymus transverse diameter were evaluated in 204 pregnant women. Patients were examined in two groups. The study included 58 Intracytoplasmic sperm injection (ICSI) patients (study group) and 146 healthy pregnant women (control group).

RESULTS

Fetal thymic-thoracic ratio in ART pregnancies were found to be statistically significantly lower than that of the control group (p = .001). Also, the fetal thymus transverse diameter value was found to be statistically significantly lower in ART pregnancies compared to that of the control group (p = .001).

CONCLUSIONS

The size of the fetal thymus, manifested with a decrease in both fetal thymic-thoracic ratio and thymus transverse diameter values, decreased in ART pregnancies.

Assessment of fetal thymus size in pregnant women with rheumatic diseases: A case-control study

PURPOSE

To investigate the fetal thymic-thoracic ratio (TT-ratio) in pregnancies diagnosed with rheumatoid arthritis (RA) and ankylosing spondylitis (AS).

METHODS

Thirty-two pregnant women with rheumatic disease and 96 low-risk pregnant women between 20 and 37 weeks were included in the study. Three control patients were randomly selected for each study patient. TT-ratio was calculated by measuring the anterior-posterior diameter of the thymus and the intrathoracic mediastinal diameter. Data were compared between the study group, including RA and AS, and the control group.

RESULTS

Thirty-two pregnant women with arthritis, 19 diagnosed with RA and 13 with AS, were evaluated. The mean value of the study group TT-ratio was 0.33; control group, 0.36; a statistically significant difference was found (p < 0.001). Perinatal outcomes were not different when compared with control patients. There was a negative correlation between disease duration, maternal C-reactive protein, erythrocyte sedimentation rate, and TT-ratio.

CONCLUSION

This is the first study to prospectively evaluate the fetal TT-ratio in patients with RA and AS. Systemic inflammation appears to affect fetal thymus size. Appropriate management of maternal rheumatic diseases is essential for developing the thymus, a vital immune system component.

Fetal Thymus Size at 19-22 Weeks of Gestation: A Possible Marker for the Prediction of Low Birth Weight?

INTRODUCTION

The purpose was to compare thymus size measured during second trimester screening of fetuses who were subsequently small for gestational age at birth (weight below 10th percentile, SGA group) with fetuses with normal birth weight (control group). We hypothesized that measuring the fetal thymic-thoracic ratio (TT-ratio) might help predict low birth weight.

METHODS

Using three-vessel view echocardiograms from our archives, we measured the anteroposterior thymus size and the intrathoracic mediastinal diameter to derive TT-ratios in the SGA (n = 105) and control groups (n = 533) between 19+0 and 21+6 weeks of gestation. We analyzed the association between TT-ratio and SGA adjusted to the week of gestation using logistic regression. Finally, we determined the possible TT-ratio cut-off point for discrimination between SGA and control groups by means of receiver operating characteristics (ROC) curve analysis.

RESULTS

The TT-ratio was significantly higher in the SGA group than in the control group (p < 0.001). An increase of the TT-ratio by 0.1 was associated with a 3.1-fold increase in the odds of diagnosing SGA. We determined that a possible discrimination cut-off point between SGA and healthy controls was achieved using a TT-ratio of 0.390 (area under the ROC curve 0.695).

CONCLUSION

An increased TT-ratio may represent an additional prenatal screening parameter that improves the prediction of birth weight below the 10th percentile. Prospective studies are now needed to evaluate the use of fetal thymus size as predictive parameter for adverse fetal outcome.

Prenatal Sonographic Three-dimensional Virtual Organ Computer-assisted Analysis Thymic Volume Calculation May Predict Intrauterine Growth Restriction

Background

Intrauterine growth restriction (IUGR) refers to fetuses that are small for their gestational age. There is no effective test to predict this disease. The aim of our study is whether fetal three-dimensional (3D) ultrasonography (USG)-assisted thymus volume (TV) measurement predicts IUGR cases.

Methods

Fetal 3D USG thymus measurement between 15 and 24 weeks of gestation was performed in a total of 100 women of reproductive age. Fetal TV was measured using the virtual organ computer-assisted analysis system program. All cases were followed up in terms of pregnancy complications until delivery.

Results

IUGR was developed in six cases in total. In cases with IUGR, mean fetal TV was found to be statistically significantly lower than in healthy cases without it. When the fetal TV was taken as 0.1645, the sensitivity was calculated as 89.5% and the specificity as 50% for predicting IUGR. The use of low fetal volume parameters is a significant and good indicator for predicting IUGR according to the binary logistic regression analysis result.

Conclusion

According to the results of this study, 3D fetal TV measurement may be used in routine second-trimester sonographic anomaly screening to predict the development of fetal IUGR. In this way, fetal mortality and morbidity caused by IUGR may be reduced.

Fetal thymus in growth-restricted fetuses due to placental insufficiency

OBJECTIVE

The aim of this study was to assess fetal thymus size by ultrasound in growth-restricted fetuses due to placental insufficiency and compare to high-risk and low-risk pregnancy fetuses with normal placental function.

METHODS

This is a nested case-control study of pregnant women followed up at a university hospital (July 2012 to July 2013). In all, 30 pregnant women presenting small fetuses for gestational age (estimated fetal weight <p10) due to placental insufficiency (umbilical artery Doppler >p95) were compared to 30 high-risk and 30 low-risk pregnancies presenting normal Doppler indices. The thymus transverse diameter and perimeter were converted into zeta score according to the normal values for gestational age. Head circumference and femur length were used to calculate ratios.

RESULTS

Fetal thymus were significantly lower in pregnancies with placental insufficiency when compared to high-risk and low-risk pregnancies presenting, respectively, transverse diameter zeta score (-0.69±0.83 vs. 0.49±1.13 vs. 0.83±0.85, p<0.001) and P zeta score (-0.73±0.68 vs. 0.45±0.96 vs. 0.26±0.89, p<0.001). There was also a significant difference (p<0.05) in the ratios among the groups: pregnancies with placental insufficiency (TD/HC=0.10, P/FL=1.32, and P/HC=0.26), high-risk pregnancies (TD/HC=0.11, P/FL=1.40, and P/HC=0.30), and control group (DT/HC=0.11, P/FL=1.45, and P/HC=0.31).

CONCLUSION

Fetal thymus size is reduced in growth-restricted fetuses due to placental insufficiency, suggesting fetal response as a consequence of the adverse environment.

An enlarged fetal thymus may be the initial response to intrauterine inflammation in pregnant women at risk for preterm birth

OBJECTIVE

Fetal thymus involvement in prematurity has been studied, and this study aimed to evaluate its relationship with short cervix and amniotic fluid sludge in the second trimester of pregnancy.

METHODS

In this prospective cross-sectional study, 79 pregnant women (19+0 to 24+6 weeks) were included, and cervical length and the presence or absence of amniotic fluid sludge were evaluated. In the three-vessel view of the fetal thorax, the thymus was identified, and its perimeter and transverse diameter were measured and transformed to a zeta score based on gestational age.

RESULTS

Data from 22 women with short cervix (<25 mm) and 57 patients with normal cervix (≥25 mm) were analyzed. The transverse diameter of the fetal thymus was significantly greater in the short cervix group compared to that of the normal cervix group (z-score 2.708 vs. -0.043, p=0.003). There were no significant differences in the perimeter (z-score -0.039 vs. -0.071, p=0.890) or the transverse diameter (z-score 1.297 vs. -0.004, p=0.091) of the fetal thymus associated with the presence (n=21) or absence of sludge (n=58).

CONCLUSION

A short cervix is associated with an increased transverse diameter of the fetal thymus during the second trimester of gestation.

Finding the best method for screening for gestational diabetes mellitus: fetal thymic-thoracic ratio or fetal thymus transverse diameter

OBJECTIVE

The aim of this study was to compare the efficiency of fetal thymic-thoracic ratio and fetal thymus transverse diameter measurements in gestational diabetes mellitus.

METHODS

Fetal thymic-thoracic ratio and fetal thymus transverse diameter were assessed in 360 pregnant women. Patients were examined in two groups: 180 gestational diabetes mellitus (study group) and 180 healthy pregnant women (control group).

RESULTS

There were no statistically significant differences between the cases with gestational diabetes mellitus and the control group in terms of fetal thymus transverse diameter; however, the fetal thymic-thoracic ratio was found to be significantly lower in cases with gestational diabetes mellitus compared to that in the control group (p<0.001).

CONCLUSION

The fetal thymic-thoracic ratio is superior to the fetal thymus transverse diameter in evaluating the fetal thymus size.

Antenatal diagnosis of chorioamnionitis: A review of the potential role of fetal and placental imaging

Chorioamnionitis is present in up to 70% of spontaneous preterm births. It is defined as an acute inflammation of the chorion, with or without involvement of the amnion, and is evidence of a maternal immunological response to infection. A fetal inflammatory response can coexist and is diagnosed on placental histopathology postnatally. Fetal inflammatory response syndrome (FIRS) is associated with poorer fetal and neonatal outcomes. The only antenatal diagnostic test is amniocentesis which carries risks of miscarriage or preterm birth. Imaging of the fetal immune system, in particular the thymus and the spleen, and the placenta may give valuable information antenatally regarding the diagnosis of fetal inflammatory response. While ultrasound is largely limited to structural information, MRI can complement this with functional information that may provide insight into the metabolic activities of the fetal immune system and placenta. This review discusses fetal and placental imaging in pregnancies complicated by chorioamnionitis and their potential future use in achieving non-invasive antenatal diagnosis. This article is protected by copyright. All rights reserved.

Second trimester fetal thymus size in association to preterm birth

OBJECTIVES

The aim of this study was to compare the second trimester thymus-thorax-ratio (TTR) between fetuses born preterm (study group) and those born after 37 weeks of gestation were completed (control group).

METHODS

This study was conducted as a retrospective evaluation of the ultrasound images of 492 fetuses in the three vessel view. The TTR was defined as the quotient of a.p. thymus diameter and a.p. thoracic diameter.

RESULTS

Fetuses that were preterm showed larger TTR (p<0.001) the second trimester than those born after 37 weeks of gestation were completed. The sensitivity of a binary classifier based on TTR for predicting preterm birth (PTB) was 0.792 and the specificity 0.552.

CONCLUSIONS

In our study, fetuses affected by PTB showed enlarged thymus size. These findings led us to hypothesize, that inflammation and immunomodulatory processes are altered early in pregnancies affected by PTB. However, TTR alone is not able to predict PTB.

Ultrasonographic evaluation of the fetal thymic-thoracic ratio and its association with conotruncal heart defects

OBJECTIVE

To evaluate the thymic-thoracic ratio (TT ratio) on fetal ultrasound and its association with conotruncal heart defects.

METHODS

A case control study was carried out to retrospectively assess the TT ratio on fetal echocardiograms performed between 19 and 39 weeks of gestation, showing congenital heart defects, from January to December 2018. The control group was comprised of fetuses with no echocardiogram evidence of congenital cardiac malformations. Cases of multiple pregnancies and patients where the TT ratio could not be established have been excluded.

RESULTS

A total of 338 pregnancies have been analysed. Fifty-two pregnancies were diagnosed with fetal heart defects (15%), 17 of which showed conotruncal heart defects (32.7%). The TT ratio in normal fetuses (286 pregnancies) increased with gestational age, and had an average of 0.43 ± 0.06. Compared to the control group (normal fetuses), fetuses with conotruncal heart defects had significantly lower mean TT ratio (0.33 ± 0.07). Those that were diagnosed with nonconotruncal heart defects did not show any statistically significant difference in the TT ratios compared with the control group (0.40 ± 0.09 vs. 0.43 ± 0.06, respectively).

CONCLUSION

The TT ratio was significantly lower in fetuses with conotruncal heart defects compared with both the control group (normal fetuses) and the fetuses with nonconotruncal heart defects.

Assessment of the fetal thymus gland: Comparing MRI-acquired thymus volumes with 2D ultrasound measurements

OBJECTIVES

The fetal thymus gland has been shown to involute in response to intrauterine infection, and therefore could be used as a non-invasive marker of fetal compartment infection. The objective of this study was to evaluate how accurately 2D ultrasound-derived measurements of the fetal thymus reflect the 3D volume of the gland derived from motion corrected MRI images.

STUDY DESIGN

A retrospective study was performed using paired ultrasound and MRI datasets from the iFIND project (http://www.ifindproject.com). To obtain 3D volumetry of the thymus gland, T2-weighted single shot turbo spin echo (ssTSE) sequences of the fetal thorax were acquired. Thymus volumes were manually segmented from deformable slice-to-volume reconstructed images. To obtain 2D ultrasound measurements, previously stored fetal cine loops were used and measurements obtained at the 3-vessel-view (3VV) and 3-vessel-trachea view (3VT): anterior-posterior diameter (APD), intrathoracic diameter (ITD), transverse diameter (TD), perimeter and 3-vessel-edge (3VE). Inter-observer and intra-observer reliability (ICC) was calculated for both MRI and ultrasound measurements. Pearson correlation coefficients (PCC) were used to compare 2D-parameters with acceptable ICC to TV.

RESULTS

38 participants were identified. Adequate visualisation was possible on 37 MRI scans and 31 ultrasound scans. Of the 30 datasets where both MRI and ultrasound data were available, MRI had good interobserver reliability (ICC 0.964) and all ultrasound 3VV 2D-parameters and 3VT 3VE had acceptable ICC (>0.75). Four 2D parameters were reflective of the 3D thymus volume: 3VV TD r = 0.540 (P = 0.002); 3VV perimeter r = 0.446 (P = 0.013); 3VV APD r = 0.435 (P = 0.110) and 3VT TD r = 0.544 (P = 0.002).

CONCLUSIONS

MRI appeared superior to ultrasound for visualization of the thymus gland and reproducibility of measurements. Three 2D US parameters, 3VV TD, perimeter and 3VT APD, correlated well with TV. Therefore, these represent a more accurate reflection of the true size of the gland than other 2D measurements, where MRI is not available.

Correlation of first-trimester thymus size with chromosomal anomalies

OBJECTIVES

The aim of this study was to investigate the correlation between fetal thymus size measured during first-trimester screening and chromosomal anomalies.

METHODS

This study is a retrospective evaluation, in which the anterior-posterior diameter of the thymus in a midsagittal plane was measured in first-trimester ultrasound between 11⁺⁰ and 13⁺⁶ weeks of gestation in 168 fetuses with chromosomal anomalies (study group) and 593 healthy fetuses (control group). The included cases were subdivided into six groups: (1) trisomy 21, (2) trisomy 18, (3) trisomy 13, (4) Turner syndrome, (5) triploidy and (6) normal controls. Thymus size measurements were adjusted to the week of gestation, which was determined by ultrasound using crown-rump-length (CRL), by calculating a ratio between CRL and thymus size (CRL-thymus-ratio). Each study group was compared with the control group separately.

RESULTS

Thymus size in fetuses affected by trisomy 18 or trisomy 13 was noticeably smaller compared to the control group (1.4 mm [1.3, 1.5] and 1.3 mm [1.2, 1.4] vs. 1.8 mm [1.6, 2.1]; all p<0.001; respectively). The thymus size of fetuses with trisomy 21 and Turner syndrome did not differ from healthy fetuses. Between the CRL-thymus-ratios of the separate study groups no statistically noticeable differences could be found.

CONCLUSIONS

Fetal thymus size appeared to be smaller in pregnancies affected by trisomy 18 and trisomy 13. The predictive value of fetal thymus size in first-trimester screening should be evaluated prospectively.

Ultrasound Monitoring of Thymus Involution in Septic Mice

Thymus involution is characterized by a progressive regression of thymus size and contributes to immunosuppression in sepsis. High-frequency ultrasonography is a non-invasive monitoring system in multiple organs, including the thymus, in mice. However, thymus involution has not been studied using ultrasonography in septic mice. This study reports ultrasound approaches to monitoring septic thymus involution in mice. Sepsis was induced by cecum ligation and puncture (CLP). Mice were euthanized at three time points: baseline and days 3 and 10 after CLP. Thymus areas and volumes were measured using 2-D and 3-D ultrasound approaches. Thymus weights were measured ex vivo. Compared with values at baseline, both thymus area and volume decreased significantly at days 3 and 10. In addition, thymus areas and volumes correlated positively with thymus weights. In conclusion, ultrasonography provides reliable thymus measurements and is an optimal technique for monitoring thymus involution in septic mice.

Fetal thymus in the middle and late trimesters: Morphometry and development using post-mortem 3.0T MRI

The present study aimed to investigate the anatomical microstructure, features and signals of the fetal thymus by 3.0T FS-T2 weighted turbo spin echo sequences, which could provide imaging evidence for the evaluation of early-stage development of fetal thymus. In addition, the T2-weighted three-dimensional (3D) sequences and the 3D processing may contribute to the establishment of reference ranges for the fetal thymus. A total of 64 specimens obtained from the fetuses of 16-39 weeks of gestational age (GA) were scanned by 3.0T MRI. Morphological changes and quantitative measurements of the fetal thymus were assessed, including the anteroposterior diameter, width, height, surface area and volume. The shape of fetal thymus varied and the majority were X-shaped, with a narrow top and wide bottom. Morphology measurements demonstrated gradual growth with increasing GA. There were high linear correlations between width, height, surface area and volume and GA. No significant differences were observed between the sexes. Post-mortem 3.0T MRI clearly demonstrated changes in external contours and internal structure with GA. The images and data obtained reflect normal development of the fetal thymus and enrich the imaging data of fetal morphometry.

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on the Growth and Composition of Fetal Organs

BACKGROUND

The growth of fetal organs is a dynamic process involving considerable changes in the anatomical and physiological parameters that can alter fetal exposure to xenobiotics in utero. Physiologically based pharmacokinetic models can be used to predict the fetal exposure as time-varying parameters can easily be incorporated.

OBJECTIVE

The objective of this study was to collate, analyse and integrate the available time-varying parameters needed for the physiologically based pharmacokinetic modelling of xenobiotic kinetics in a fetal population.

METHODS

We performed a comprehensive literature search on the physiological development of fetal organs. Data were carefully assessed, integrated and a meta-analysis was performed to establish growth trends with fetal age and weight. Algorithms and models were generated to describe the growth of these parameter values as functions of age and/or weight.

RESULTS

Fetal physiologically based pharmacokinetic parameters, including the size of the heart, liver, brain, kidneys, lungs, spleen, muscles, pancreas, skin, bones, adrenal and thyroid glands, thymus, gut and gonads were quantified as a function of fetal age and weight. Variability around the means of these parameters at different fetal ages was also reported. The growth of the investigated parameters was not consistent (with respect to direction and monotonicity).

CONCLUSION

Despite the limitations identified in the availability of some values, the data presented in this article provide a unique resource for age-dependent organ size and composition parameters needed for fetal physiologically based pharmacokinetic modelling. This will facilitate the application of physiologically based pharmacokinetic models during drug development and in the risk assessment of environmental chemicals and following maternally administered drugs or unintended exposure to environmental toxicants in this population.

Antenatal corticosteroid administration is associated with decreased growth of the fetal thymus: a prospective cohort study

OBJECTIVE

To examine the effect of antenatal corticosteroid administration (ACS) on fetal thymus growth in women who received ACS compared with gestational-age-matched controls.

STUDY DESIGN

Fetal thymus size and growth were measured in women at risk for preterm delivery who received ACS and compared with a matched cohort of women who were at low risk for preterm delivery and did not receive ACS. Fetal thymus perimeter and diameter were measured by 2-D ultrasound at baseline and every 2 weeks until delivery.

RESULTS

After adjusting for confounders, ACS exposure was associated with a significant reduction in thymus perimeter size (-0.70; 95% CI: -1.33, -0.07; P = 0.03). For every additional week of exposure, thymus growth trajectory was significantly decreased in ACS-exposed fetuses (P = 0.04).

CONCLUSION

The association between ACS and reduced fetal thymus growth should be further examined to establish the impact of ACS on childhood thymus development and immune programming.

Fetal MRI findings in a retrospective cohort of 26 cases of prenatally diagnosed CHARGE syndrome individuals

"CHARGE syndrome" (CS) is a multifaceted syndrome associated with a poor prognosis. The prenatal diagnosis remains challenging especially as the fetal anomalies that may evoke suspicion of CS are not comprehensively described.

OBJECTIVE

This study aims to identify the anomalies in MRI with suspected CHARGE syndrome and to propose a possible standardization in the image-based prenatal diagnosis of CS.

METHODS

This was a retrospective study of 26 fetuses who underwent MRI and had a confirmed diagnosis of CS, as proven by histopathological and/or neonatal examinations and/or the presence of the CHD7 gene mutation.

RESULTS

The three most frequent MRI anomalies confirmed at histopathological and/or neonatal examinations were arhinencephaly in 100% (26 of 26), dysplasia of the semicircular canals agenesis (SCA) in 100% (24 of 24), and posterior fossa anomalies in 100% (22 of 22). Our study also revealed short petrous bones with a particular triangular shape in 24 of 24 cases of SCA. Other relevant findings included external ear anomalies in 36% (9 of 25), cleft lip and palate (9 of 9), ventriculomegaly (VMG) (6 of 6), short corpus callosum (3 of 3), and ocular asymmetry in 36.6% (4 of 11).

CONCLUSION

Our study emphasizes the interest of fetal MRI in the diagnosis of CS with an adapted knowledge of semiology.

Measuring fetal thymus size: a new method for diabetes screening in pregnancy

Objective: To investigate the correlation between fetal thymus size and diabetes in pregnancy.Method: Fetal thymus size was assessed in 160 pregnant women with gestational age of 19-39 weeks. They included 80 diabetic (investigation group) and 80 nondiabetic (control group) women. Fetal thymus size was measured by thymic-thoracic ratio. We did this with dividing the thymus' anteroposterior diameter by anteroposterior of mediastinum.Results: Thymic-thoracic ratio was significantly smaller in fetuses of diabetic mothers compared to the nondiabetic group (p = .001). It remained significant after subgrouping diabetic mothers into overt diabetes, insulin-dependent gestational diabetes, and noninsulin-dependent gestational diabetes.Conclusion: Although thymus size was smaller in fetuses of diabetic pregnant women compared to nondiabetic pregnant women, it seems that thymic-thoracic ratio can be a predictor of diabetes and its other related adverse effects during pregnancy.

Foetal thymus size in pregnancies after assisted reproductive technologies

PURPOSE

The aim of our study was to compare thymus sizes in foetuses conceived using assisted reproductive technologies (ART) to those conceived naturally (control group).

METHODS

Sonographic foetal thymus size was assessed retrospectively in 162 pregnancies conceived using ART and in 774 pregnancies conceived naturally. The anteroposterior thymic and the intrathoracic mediastinal diameter were measured to calculate the thymic-thoracic ratio (TT-ratio). The ART cases were subdivided into two groups: (1) intracytoplasmic sperm injection (ICSI; n = 109) and (2) in vitro fertilisation (IVF; n = 53).

RESULTS

The TT-ratio was smaller in pregnancies conceived using ART (p < 0.001). In both ART subgroups (ICSI and IVF), the TT-ratio was lower compared to the control group (p < 0.001). However, no difference between the two subgroups could be detected (p = 0.203).

CONCLUSIONS

Our data show reduced thymus size in foetuses conceived using ART compared to controls. These findings indicate that the use of ART may lead to certain deviations in organogenesis.

Correlation Between the Thymic-Thoracic Ratio and Cardiac Axis in Healthy Fetuses

OBJECTIVES

The aim of this study was to assess the correlation between the thymic-thoracic ratio and cardiac axis in healthy fetuses.

METHODS

The fetal thymic-thoracic ratio and cardiac axis were measured in 220 healthy fetuses. The normal ranges of the fetal thymic-thoracic ratio and cardiac axis for each gestational week were established. The Pearson correlation coefficient was calculated to analyze the relationship between the thymic-thoracic ratio and cardiac axis.

RESULTS

The mean fetal thymic-thoracic ratio increased slightly throughout the pregnancy, from 0.33 at 17 weeks' gestation to 0.37 at 37 weeks. No statistically significant correlation was found between the thymic-thoracic ratio and cardiac axis in healthy fetuses.

CONCLUSIONS

In healthy fetuses, the thymus occupies an increasingly larger portion of the upper mediastinum when the pregnancy advances. The cardiac axis is not affected by the thymic-thoracic ratio in healthy fetuses.

Small fetal thymus and adverse obstetrical outcome: a systematic review and a meta-analysis

INTRODUCTION

The aim of this study was to explore the association between small fetal thymus on ultrasound and adverse obstetrical outcome.

MATERIAL AND METHODS

Medline, Embase, Cochrane and Web of Science databases were searched. Primary outcome was the risk of preterm birth before 37 and 34 weeks of gestation in fetuses with, compared to those without, a small thymus on ultrasound.

SECONDARY OUTCOMES

occurrence of chorioamnionitis, intrauterine growth restriction, neonatal sepsis, gestational age at birth, birthweight, neonatal morbidity and preeclampsia.

RESULTS

Twelve studies including 1744 fetuses who had ultrasound assessment of thymus during pregnancy were included. Women with preterm premature rupture of the membranes or with preterm labor were at higher risk of preterm birth before 37 weeks (p = 0.01), or before 34 weeks (p < 0.001) for fetuses with a small fetal thymus compared to those without a small thymus, and the risk of chorioamnionitis was higher when the thymus was small (p < 0.001). Fetuses with small thymus were not at higher risk of intrauterine growth restriction (p = 0.3). A small thymus increased the risk of neonatal sepsis (p = 0.007) and morbidity (p = 0.003), but not the risk of preeclampsia (p = 0.9).

CONCLUSIONS

A small fetal thymus is associated with a higher risk of preterm birth, chorioamnionitis, neonatal sepsis and morbidity, but not with intrauterine growth restriction and preeclampsia.

Fetal thymus size in pregnant women with diabetic diseases

AIM

The aim of our study was to assess fetal thymus size in diabetic pregnancies compared with normal pregnancies.

METHODS

Sonographic fetal thymus size was retrospectively assessed in 161 pregnancies with maternal diabetes and in 161 uncomplicated pregnancies matched by gestational age. The anteroposterior thymic and the intrathoracic mediastinal diameter were measured and the quotient was calculated [thymic-thoracic ratio (TT-ratio)]. In addition, we defined the quotient of the anteroposterior thymic diameter and the head circumference as thymus-head ratio (TH-ratio). The maternal diabetes cases were subdivided into three groups: (1) diet-controlled gestational diabetes, (2) insulin-dependent gestational diabetes and (3) preexisting maternal diabetes.

RESULTS

TT-ratio and TH-ratio were smaller in pregnancies with maternal diabetes (P<0.001 and P<0.001, respectively). In all three maternal diabetes subgroups, the TT-ratio and the TH-ratio were lower compared with the control group (P<0.001 for each group).

CONCLUSIONS

Reduced fetal thymus size seems to be associated with diabetic pregnancy. We introduce fetal thymus size as a new potential prognostic parameter for maternal diabetes.

Sonographic measurement of the fetal thymus: Relationship with maternal obesity

BACKGROUND

The purpose of this study was to evaluate the influence of maternal obesity on the size of the fetal thymus.

METHODS

The study population consisted of 138 pregnant women who were divided into two groups based on their body mass index (BMI): Normal-weight group (n = 97; BMI: 18-25 kg/m² ) and obese group (n = 41; BMI: ≥ 30 kg/m² ). All participants underwent routine second-trimester prenatal ultrasound (US) screening at 20-25 weeks of gestation. Differences in US measurement of fetal thymus, fetal anthropometric measurements, subcutaneous adipose tissue thickness, fetal weight, gestational age, white blood cell count, and C-reactive protein (CRP) values between groups were compared.

RESULTS

The mean thymus size was 18.7 ± 2.9 mm for normal-weight group, and 21.6 ± 3.7 mm for the obese group (p < 0.001). CRP values were also significantly different between groups (6.8 ± 4.4 mg/dl for normal-weight group, 14.8 ± 1.8 mg/dl for obese group, p < 0.001).

CONCLUSIONS

Fetal thymus size was increased in obese women, and this increase may indicate immunologic abnormalities in fetuses. However, future large-scale studies are necessary to support this association. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:277-281, 2017.

Cardio-STIC Based Reference Ranges of Fetal Thymus Size in Singleton Pregnancies

OBJECTIVES

To establish the reference ranges of the fetal thymus size among Thai fetuses.

METHODS

The database of spatio-temporal image correlation (cardio-STIC) was assessed to obtain the volume data sets for offline analysis. The volume data sets acquired at 16 to 38 weeks were measured for the thymus transverse diameter (TD) and the thymus/thoracic (TT) ratio at the three-vessel view. The measured values were regressed to identify the best-fitted model.

RESULTS

A total of 622 volumes were successfully measured and the reference ranges of TD and TT ratio were established. Although TT was relatively constant or increased minimally with gestational age (GA), TD was significantly increased with gestational age. The predicted mean TD (mm) =  -31.206 + 2.854 × GA - 0.028 × GA² (r = 0.891; P < .001) and predicted standard deviation (SD) of TD (mm) = 0.837 + 0.073 × GA (r = 0.038; P < .001). Centile charts for predicting TD and equations for z-score calculation were also provided. Interobserver variability in TD measurement was better than that in TT ratio and thymic perimeter measurement.

CONCLUSIONS

Reference ranges of fetal TD and TT ratio have been provided. These normative data may be a useful tool in the assessment of thymus-associated conditions. For clinical purposes, we recommend measurements of the TD rather than TT ratio or perimeter because of its reproducibility and simplicity.

Sonographic measurement of fetal thymus size in uncomplicated singleton pregnancies

PURPOSE

To establish sonographic reference ranges of the normal fetal thymus size between 17 and 38 weeks of gestational age (GA).

METHODS

The study was conducted between April 1 and December 31, 2013. Low-risk singleton pregnancies without obstetrical and medical complications at the GAs between 17 and 38 weeks were recruited for thymus measurement. The fetal thymus was identified on transabdominal sonography at the three-vessel view. Maximal transverse diameter, perimeter, and thymus/thoracic ratio were measured. The best-fit models in predicting thymic dimensions as a function of GA and biparietal diameter (BPD) were determined using regression analysis, and percentile charts for predicting thymic dimensions were constructed.

RESULTS

A total of 296 singleton pregnancies were recruited in this study. Maximal transverse diameter, perimeter, and thymus/thoracic ratio increased throughout pregnancy. The regression equation for maximal transverse diameter of the thymus as a function of GA was as follows: Predicted mean thymus diameter (mm) = -25.904 + 2.476 × GA - 0.019 × GA² (r = 0.915; p < 0.001) with predicted standard deviations of thymus diameter (mm) = 1.428 + 0.044 × GA (r = 0.017; p < 0.001).

CONCLUSIONS

Sonographic reference ranges of the normal fetal thymic dimensions between 17 and 38 weeks of GA have been established. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:150-159, 2017.

Ultrasonographic approach to diagnosis of fetal inflammatory response syndrome: a tool for at-risk fetuses?

Preterm parturition is a syndrome that may result from many underlying mechanisms. Infection and inflammation are the prominent ones. Intrauterine infection and inflammation have an effect akin to sepsis, and that is similar to systemic inflammatory response in adults. Indeed, there is evidence to support the association of a fetal inflammatory response syndrome (FIRS) to systemic infection and inflammation. The utilization of invasive procedures for the prenatal diagnosis of FIRS is associated with a risk for complications resulting from the invasive method. The progress in the imaging quality of obstetrical ultrasound and the development of novel methods for functional anatomical assessment of the fetal organs may help to identify, noninvasively, fetuses at risk for FIRS in patients presenting with preterm labor. We review the studies describing advanced sonographic modalities and the imaging findings in the heart, thymus, kidney, adrenal glands, and spleen of these fetuses.

Prognostic Value of Fetal Thymus Size in Intrauterine Growth Restriction

OBJECTIVES

Our aim was to evaluate the size of the fetal thymus by sonography in pregnancies with intrauterine growth restriction (IUGR) and to search for a possible relationship between a small fetal thymus and adverse perinatal outcomes.

METHODS

The transverse diameter of the fetal thymus was prospectively measured in 150 healthy and 143 IUGR fetuses between 24 and 40 weeks' gestation. The fetuses with IUGR were further divided according to normal or abnormal Doppler assessment of the umbilical and middle cerebral arteries and ductus venosus. Measurements were compared with reference ranges from controls. To determine which perinatal outcomes were independently associated with a small fetal thymus, a multivariate logistic regression analysis was performed.

RESULTS

Thymus size was significantly lower in IUGR fetuses compared to controls (P < .05). Among IUGR fetuses, thymus size was significantly smaller in IUGR fetuses with abnormal Doppler flow compared to normal flow (P < .05). A small thymus in IUGR fetuses was independently associated with early delivery (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.05-1.49; P= .023), respiratory distress syndrome (OR, 1.36; 95% CI, 1.09-1.78; P= .005), early neonatal sepsis (OR, 1.65; 95% CI, 1.11-2.42; P= .001), and a longer stay in the neonatal intensive care unit (OR, 1.33; 95% CI, 1.08-1.71; P = .017).

CONCLUSIONS

Intrauterine growth restriction is associated with fetal thymic involution, and a small fetal thymus is an early indicator of adverse perinatal outcomes in pregnancies complicated by IUGR.

The use of imaging technology in the assessment of the fetal inflammatory response syndrome-imaging of the fetal thymus

The fetal inflammatory response syndrome (FIRS) describes a state of extensive fetal multi organ involvement during chorioamnionitis, and is associated with grave implications on perinatal outcome. The syndrome has been linked to the preterm parturition syndrome and is associated with inflammation/infection processes in most of the fetal organs. The fetal thymus, a major organ in the developing immune system involutes during severe neonatal disease and has been shown to be smaller in fetuses with FIRS. Various methods for imaging of the fetal thymus and measurement are described. Currently the only method to diagnose FIRS prenatally is through amniocentesis. We suggest that women who are admitted with preterm labor with intact membranes and those with PPROM should have a detailed sonographic examination of the fetal thymus as a surrogate marker of fetal involvement in intrauterine infection/inflammation processes.

Sonographic Evaluation of the Fetal Thymus Using the Thy-Box Technique Between 13 and 16 Weeks' Gestation

OBJECTIVES

The purposes of this study were to assess the feasibility of fetal thymus measurement between 13 and 16 weeks' gestation, to evaluate the potential difference using color Doppler sonography with the thy-box technique, and to construct normal percentile ranges.

METHODS

This retrospective study included 287 healthy singleton pregnancies. The fetal thymus was shown in an axial plane of the upper mediastinum. Color Doppler imaging was applied to outline the thy-box: ie, the area between the brachiocephalic artery posteriorly and internal mammary arteries laterally. Measurements of the lateral and anteroposterior diameters of the thymus with and without color Doppler imaging were compared.

RESULTS

The thymus was shown in 95% of the cases (273 of 287) between 13 and 16 weeks' gestation. The mean lateral thymus diameter ± SD with color Doppler imaging (5.30 ± 0.7 mm) was significantly longer in comparison to the measurement without color Doppler imaging (5.06 ± 0.8 mm; P < .001), whereas the anteroposterior diameter was significantly shorter (3.19 ± 0.9 versus 3.26 ± 0.8 mm; P = .044). Normal percentiles of thymus measurements for gestational age were constructed.

CONCLUSIONS

The fetal thymus can be clearly and accurately shown as early as 13 weeks' gestation by using the thy-box. Measurements with color Doppler imaging were significantly different from those without and hence are preferable, as color Doppler imaging can delineate the thymus borders more accurately.

Fetal thymus: visualization rate and volume by integrating 2D- and 3D-ultrasound during 2nd trimester echocardiography

OBJECTIVE

To assess the visualization rate and transverse diameter of fetal thymus by two-dimensional ultrasound (2DUS) as well as the fetal thymus volume by three-dimensional ultrasound (3DUS) during the 2nd trimester echocardiography.

METHODS

A prospective cross-sectional study involving 100 normal fetuses between 18w0d and 23w6d was performed. The identification of fetal thymus and peri-thymic vessels was realized at level of three vessels and trachea (3VT). The transverse diameter was obtained placing a line cursor perpendicular to the line connecting the sternum and the spine. The fetal thymus volume was obtained by virtual organ computer-aided analysis (VOCAL) with 30° of rotation. We used the percentage of visualization rate of 2D structures and means and 95% confidence intervals (CI) for fetal thymus transverse diameter and volume.

RESULTS

The visualization rate of fetal thymus by 2DUS was of 100% in all gestational ages using the 3VT view. Addition of color Doppler ultrasound facilitates identification of the thy-box and enhanced the calculation of both fetal thymus transverse diameter and volume. The mean fetal thymus transverse diameter by 2DUS ranged from 11 mm at 18 weeks to 19 mm at 23 weeks of gestation. The mean fetal thymus volume by 3DUS ranged from 1.25 cm(3) at 18 weeks to 2.61 cm(3) at 23 weeks of gestation.

CONCLUSION

We demonstrated a high visualization rate of fetal thymus and peri-thymic vessels by 2DUS during the 2nd trimester echocardiography. The measurements of transverse diameter by 2DUS and the volume by 3DUS also showed a high success rate.

[Absent or hypoplastic thymus: A marker for 22q11.2 microdeletion syndrome in case of polyhydramnios]

OBJECTIVES

In prenatal diagnosis of 22q11.2 microdeletion syndrome, without cardiac malformation or multiple associated congenital anomalies, we study the presence of polyhydramnios and its association with thymic dysgenesis.

MATERIALS AND METHODS

This was a multicenter retrospective observational study. It was performed in two multidisciplinary centers for prenatal diagnosis in the south of France between January 1, 2010 and June 30, 2013. Inclusion criteria were prenatal diagnosis of 22q11.2 deletion syndrome. We excluded from the study any fetus with cardiac malformation or multiple associated congenital anomalies.

RESULTS

During the inclusion period, eleven antenatal diagnoses of 22q11.2 microdeletion syndrome have been made. Six cases were excluded: 5 fetuses with cardiac malformation and one with multiple associated congenital anomalies. Therefore, five cases of isolated polyhydramnios were included. All 5 fetuses had a thymic dysgenesis: 3 had a thymic agenesis and 1 thymic hypoplasia diagnosed by sonography and 1 had a thymic agenesis diagnosed by retrospective reading of fetal MRI.

CONCLUSION

When faced with a polyhydramnios, the presence of a thymic dysgenesis should be search for by ultrasound screening and would alert to the possibility of a 22q11.2 microdeletion syndrome. The confirmation of this is diagnosis by amniocentesis would enable improved antenatal support for parents and would enable early implementation of the multidisciplinary neonatal care that is required to avoid serious complications of this syndrome.

Fetal thymus volume estimation by virtual organ computer-aided analysis in normal pregnancies

OBJECTIVES

The thymus has a pyramidal shape, which is best shown in coronal planes. The aim of this study was to evaluate the potential of virtual organ computer-aided analysis to estimate fetal thymus volume in normal pregnancies.

METHODS

Three-dimensional volume data sets from the axial upper mediastinal section were acquired from 37 normal pregnancies between 12 and 35 weeks' gestation. Thymus volume was calculated by virtual organ computer-aided analysis by 2 separate examiners. In 12 cases, volumes were also acquired with 4-dimensional sonography and spatiotemporal image correlation software to assess the variability in thymus size between the systolic and diastolic periods of fetal heart motion. Linear regression analysis was used to assess the relationship between the fetal thymus volume and gestational age. Paired Student t tests were used to evaluate both the level of agreement for interobserver and intraobserver variability and the difference between diastolic and systolic thymus volumes.

RESULTS

Identification of the borders of the thymus and calculation of its volume were successful in 28 patients (77.7%). Statistically significant linear growth of the thymus during pregnancy, from 12 to 35 weeks, was found. The growth coefficient for each gestational age was 0.43 (95% confidence interval, 0.355 to 0.504; P < .001). The difference in thymus size between systole and diastole was minor (0.0798 cm(3); 95% confidence interval, -0.044 to 0.203 cm(3)). Interobserver and intraobserver variability was not statistically significant.

CONCLUSIONS

Although the thymus has a complex shape, it was possible to determine its borders and to calculate its volume by virtual organ computer-aided analysis in 77.7% of cases. Linear growth during pregnancy was found, and the minor changes during systole and diastole could be explained by condensation of the soft tissue of the thymus secondary to cardiac activity.

The thy-box for sonographic assessment of the fetal thymus: nomogram and review of the literature

OBJECTIVES

To assess the feasibility and reproducibility of fetal thy-box visualization and to set normative data for the fetal thymus using this technique.

METHODS

We performed a cross-sectional observational study in pregnant women in their second trimester of pregnancy who attended the fetal medicine unit of the Hospital Gregorio Marañón from March 2011 to March 2013. Using thy-box sonography, which sets boundaries within the thymus, we assessed the feasibility of the thy-box and analyzed the factors related to its visualization. Measurements of the thy-box anteroposterior and transverse diameters were performed in healthy fetuses. Interobserver agreement was studied for both items. We set normative data for the thy-box diameters in singleton and twin pregnancies.

RESULTS

A total of 337 patients from 15 to 37 weeks were recruited after exclusion criteria. Thy-box feasibility was 74.2% (250 of 337). Nonfeasible cases were related to the fetal anterior spine and advanced gestational age. Assessment of the thy-box anteroposterior and transverse diameters was achievable in 250 fetuses. Interobserver agreement was good for feasibility and measurements (κ = 0.80). Linear growth of the thy-box in both diameters was observed in relation to gestational age during the second half of pregnancy. Thy-box diameters did not show significant differences according to the type of gestation, fetal sex, or chorionicity.

CONCLUSIONS

Thy-box diameters are achievable and reproducible by sonography in normal singleton and twin pregnancies during the second trimester; however, although feasible, the thy-box transverse diameter measurement is not reliable beyond 28 weeks. Further studies are needed to evaluate thy-box diameters in pathologic cases, especially conotruncal anomalies.

Monitoring fetal immune development in human pregnancies: current concepts and future goals

The vast majority of the current knowledge on immune development in the fetal period has been gained from animal studies, particularly from mouse models. This has led to a great improvement in our current understanding of immune ontogeny. However, it has also become clear that in many ways the mouse model of pregnancy differs from the situation in human pregnancy, such as the degree and importance of trophoblast invasion, the kind of MHC class repertoire of the extravillous trophoblast cells, and differences concerning the development and regulation of T-cells. It will be of paramount importance to develop non-invasive screening methods to assess fetal immune development in humans. The focus of this mini-review is to discuss how prenatal ultrasound evaluation can be used as a tool to monitor fetal immune development in human pregnancies. To identify the fetuses at risk of immune disorders could be the first step to developing prevention strategies in the future.

Variety of prenatally diagnosed congenital heart disease in 22q11.2 deletion syndrome

Objective

To analyze the spectrum of prenatally diagnosed congenital heart disease in a Korean population with 22q11.2 deletion syndrome, and to provide guidelines for screening 22q11.2 deletion prenatally.

Methods

This retrospective study evaluated 1,137 consecutive fetuses that had prenatal genetic testing for 22q11.2 deletion because of suspected congenital heart disease between September 2002 and December 2012, at Asan Medical Center, Seoul, Korea.

Results

Main cardiovascular diseases in the 53 fetuses with confirmed 22q11.2 deletions were tetralogy of Fallot (n = 24, 45%), interrupted aortic arch (n = 10, 19%), ventricular septal defect (n = 5, 9%), double outlet right ventricle (n = 4, 8%), and coarctation of the aorta (n = 4, 8%). Other cardiac defects were rarely associated with 22q11.2 deletion. One fetus had persistent truncus arteriosus, one had aortic stenosis, and one had hypoplastic right heart syndrome. Two fetuses had normal intracardiac anatomy with an isolated right aortic arch, and one had an isolated bilateral superior vena cava.

Conclusion

A variety of congenital heart diseases were seen during the prenatal period. Conotruncal cardiac defects except transposition of great arteries were strongly associated with 22q11.2 deletion. When such anomalies are diagnosed by fetal echocardiography, genetic testing for 22q11.2 deletion should be offered. Even if less frequent deletion-related cardiac defects are detected, other related anomalies, such as thymic hypoplasia or aplasia, should be evaluated to rule out a 22q11.2 deletion.

Reliability of fetal thymus measurement in prediction of 22q11.2 deletion: a retrospective study using four-dimensional spatiotemporal image correlation volumes

OBJECTIVES

To evaluate the thymic-thoracic ratio (TT-ratio) method in assessment of the fetal thymus in normal fetuses and in those with cardiac abnormalities, in the presence or absence of 22q11.2 deletion.

METHOD

Database records were reviewed for cases of conotruncal and arch abnormalities found on fetal echocardiography between January 2007 and September 2011. The 22q11.2 deletion status was retrieved and cases in which this was not known were excluded from the analysis, as were fetuses with aneuploidy or other genetic disorders. An additional 55 normal fetuses were analyzed as a control group. The TT-ratio was measured retrospectively using stored spatiotemporal image correlation (STIC) volume datasets.

RESULTS

Sixty-nine fetuses with relevant cardiac diagnoses were identified and, of these, 18 (26%) had 22q11.2 deletion. The mean gestational age at diagnosis was 22 weeks. Significant pairwise differences, but also overlap, were observed between all three groups (i.e. fetuses with heart defects with and without the 22q11.2 deletion and controls). The mean TT-ratio was 0.44 in our normal control group and was significantly smaller in fetuses with 22q11.2 deletion, corresponding to previously published data. However, the mean TT-ratio in the group with conotruncal anomalies but without the 22q11.2 deletion was also smaller than that in controls, in contrast to previously published data. The TT-ratio was above the normal mean, regardless of fetal karyotype, in all cases of interrupted aortic arch.

CONCLUSION

The TT-ratio method is a feasible and potentially useful tool during detailed fetal heart assessment. However, the absolute measurement is not reliable for prediction of 22q11.2 deletion and the obtained results should therefore be interpreted with caution. Fetal karyotyping should be recommended in cases with conotruncal heart abnormalities, irrespective of the TT-ratio.

Thymic-thoracic ratio in fetuses with trisomy 21, 18 or 13

OBJECTIVES

To assess thymic size expressed as the thymic-thoracic ratio (TT-ratio) in fetuses with trisomy 21, 18 or 13.

METHODS

The TT-ratio, the quotient of the anteroposterior thymic and the intrathoracic mediastinal diameter, was measured in 65 trisomic fetuses between 15 and 36 weeks' gestation, including 30 cases with trisomy 21, 19 with trisomy 18 and 16 with trisomy 13. In addition these 65 fetuses were divided into two groups, according to whether they showed growth that was appropriate-for-gestational age (AGA) (n = 39) or intrauterine growth restriction (IUGR) (n = 26). Measurements were compared with reference ranges from 302 normal fetuses.

RESULTS

The TT-ratio was low in 27.7% (n = 18) of the 65 fetuses with aneuploidy. In comparison to normal fetuses (mean TT-ratio, 0.44), those with trisomy 18 or 21 had a significantly smaller TT-ratio (mean, 0.38 (P < 0.001) and 0.40 (P < 0.05), respectively), while those with trisomy 13 did not (mean, 0.43). These values were not as low as those observed previously in fetuses with del.22q11, suggesting a mechanism involving accelerated thymic involution rather than primary thymic hypoplasia. Furthermore, the TT-ratio was significantly lower than normal in both AGA (P < 0.05) and IUGR (P < 0.001) fetuses.

CONCLUSION

Fetuses with trisomy 18 or 21, but not trisomy 13, have a small thymus, suggesting accelerated thymic involution in utero. IUGR may contribute to the reduced thymic size in trisomy 18 fetuses. Trisomy 21 fetuses seem to have additional factors leading to a small thymus which could be a possible confirmation of the reduced immune response observed in fetuses and neonates with Down syndrome.

Thymic volume in healthy, small for gestational age and growth restricted fetuses

OBJECTIVE

The aim of this study was to verify the hypothesis that a difference in thymic size exists between small for gestational age (SGA) fetuses, likely constitutional, and intrauterine growth restricted (IUGR) fetuses because of placental causes.

METHODS

We studied 27 SGA and 36 control fetuses. SGA was defined as fetal abdominal circumference (AC) and birthweight <10th percentile for gestational age. We defined as constitutional SGA those with normal uterine and umbilical artery Doppler flow velocity waveforms (FVW), and as IUGR those with abnormal uterine FVW. IUGR were further divided based on normal or abnormal umbilical FVW. Fetal thymic volume (TV) was acquired by three-dimensional ultrasound and reconstructed with virtual organ computer-aided analysis. To correct for the influence of fetal size on thymic dimension, TV/AC ratio was calculated.

RESULTS

Controls presented a higher TV/AC compared with each group of SGA (p < 0.001). TV/AC was significantly lower in IUGR with abnormal umbilical FVW compared with both constitutional SGA (p = 0.01) and IUGR with normal umbilical FVW (p = 0.01).

CONCLUSIONS

The differences in TV/AC between constitutional SGA and IUGR with abnormal umbilical FVW suggest that, in the latter, a specific 'trigger' might compromise trophoblastic invasion and thymic development; however, some kind of alteration of the immune system might occur in all SGA fetuses.

Impaired fetal thymic growth precedes clinical preeclampsia: a case-control study

In preeclampsia the maternal adaptive immune system undergoes specific changes, which are different from the physiological processes associated with healthy pregnancy. Whether preeclampsia also affects the fetal immune system is difficult to investigate, due to limited access to the fetus. We hypothesized that if preeclampsia affects the fetal adaptive immune system this might be associated with early changes in thymic growth. In this case-control study, 53 preeclamptic and 120 healthy control pregnancies were matched for maternal age, gestational age and smoking. Fetal thymus diameter was measured as the greatest width perpendicular to a line connecting sternum and spine based on ultrasound images taken at 17-21 weeks gestation. Independent of fetal and maternal anthropometric measures, thymuses were found to be smaller in preeclamptic pregnancies than healthy controls (16.2 mm versus 18.3 mm, respectively, mean difference=2.1 mm, 95% CI: 0.8-3.3, p<0.001), and the odds of developing preeclampsia was estimated to be 0.72 (95% CI: 0.60-0.86, p<0.001) lower for each 1 mm increase in thymus diameter. There was no correlation between the onset of preeclampsia and fetal thymus size. This is the first study to suggest that fetal thymus growth is reduced before the clinical onset of preeclampsia and precedes any described fetal anomalies or maternal immunological changes associated with preeclampsia. We propose that the fetal adaptive immune system is either passively affected by maternal processes preceding clinical preeclampsia or is actively involved in initiating preeclampsia in later pregnancy.

Foetal volumetry using magnetic resonance imaging in intrauterine growth restriction

OBJECTIVES

We used magnetic resonance imaging (MRI) to perform volumetry of foetuses with and without growth restriction, and identify deviations in organ growth.

STUDY DESIGN

20 growth restricted and 19 normal foetuses were scanned once during pregnancy at gestational age 20.53-36.57 weeks. MRI scans were performed on a 1.5T system using ssFSE sequences. Manual segmentation of whole body, brain, heart, lung, liver, thymus and kidney volume was performed. Data on the severity of foetal growth restriction and pregnancy outcome was collected.

RESULTS

There was a significant reduction in foetal whole body volume and volume of all internal organs except the brain in growth restricted foetuses. A brain:liver ratio above 3.0 was associated with a 3.3 fold increase in risk of perinatal mortality (95% CI=1.68-6.47).

CONCLUSION

MRI provides an accurate assessment of foetal organ growth. It may have a role to play in monitoring disease severity and the effect of future interventions.

Comparison of measurements of the transverse diameter and perimeter of the fetal thymus obtained by magnetic resonance and ultrasound imaging

PURPOSE

To compare measurements of the fetal thymus obtained by magnetic resonance imaging (MRI) and ultrasound (US).

MATERIALS AND METHODS

Written informed consent was obtained from the patients that participated in this Institutional Review Board-approved observational study. The study population consisted of 17 pregnant women carrying fetuses between 21 and 34 weeks of gestation with suspected abnormalities. The transverse diameter and perimeter of the thymus were measured in these fetuses at the level of an axial view of the thorax that includes the pulmonary, aorta, and superior vena cava. The degree of agreement between MRI and US measurements was determined using Lin's concordance correlation coefficient and Bland-Altman analysis.

RESULTS

The mean (standard deviation, SD) gestational age at the time of the prenatal evaluation was 28.4 weeks (3.6). The thymus was measured by MRI and US in all cases. Comparison of the measurements from these two imaging modalities demonstrated a relatively good reproducibility with no evidence of systematic error.

CONCLUSION

MRI and US measurements of the fetal thymus during the second half of pregnancy are comparable. This finding suggests that MRI can become a useful adjuvant to US for assessment of the fetal thymus.

Sonographic thymic measurements in Down syndrome fetuses

OBJECTIVE

Children with Down syndrome (DS) can have hypoplastic thymuses with an impaired capacity to liberate newly generated T cells. We sought to determine if the size of the thymus in DS fetuses is different from control fetuses.

METHODS

We performed comprehensive prenatal sonographic evaluation that included measurements of the thymus in 874 control fetuses and in 12 DS fetuses. We used graphic comparisons between thymic measurements obtained from the two groups of fetuses and a nested case-control validation study in which DS fetuses were matched for gestational age with control fetuses using a 2-to-1 ratio to make group comparisons.

RESULTS

The plot analysis showed that more than two-thirds of DS fetuses had sonographic signs of thymic hypoplasia. The nested case-control study confirmed that the thymus of DS fetuses was statistically smaller than the thymus of control fetuses [DS transverse diameter 12.3 mm, interquartile range (IQR) 6.2 vs. control 18.1 mm, IQR 4.4; p < 0.001 and, DS perimeter 30.9 mm, IQR 20.1 vs. control 48.6 mm, IQR 20.4; p < 0.01].

CONCLUSIONS

Our findings suggest that the majority of DS fetuses have smaller thymuses than control. Prenatal measurements of the thymus may be clinically useful in the management of DS pregnancies.

Assessment of the fetal thymus by two- and three-dimensional ultrasound during normal human gestation and in fetuses with congenital heart defects

OBJECTIVES

Our objectives were to compare the size and volume of the developing fetal thymus obtained by two-dimensional ultrasound (2D-US) and three-dimensional ultrasound (3D-US), develop normative data for thymus volume (TV), and investigate TV in fetuses with congenital heart disease (CHD) and normal twin gestations.

METHODS

We studied 321 fetuses (gestational age (GA): 17-39 weeks) including 238 normal singletons, 64 normal twins and 19 singleton fetuses with CHD. We used 2D-US to assess fetal thymus maximum transverse diameter (MTD), maximum transverse area (MTA), anteroposterior diameter (APD) and superoinferior diameter (SID). TV was obtained by 3D-US using virtual organ computer-aided analysis. Measurements were adjusted for estimated fetal weight where appropriate. Linear regression analysis, general linear models and Fisher's Z-transformation were used where appropriate. A nomogram of fetal TV based on singleton gestations was produced according to previously published methods.

RESULTS

Ultrasound assessment of the fetal thymus was possible in 95.3% (306/321) of cases. Both 3D-US and 2D-US measurements were significantly correlated with GA (TV r = 0.989; MTA r = 0.918; MTD r = 0.884; APD r = 0.849; and SID r = 0.816; all P < 0.05). After Fisher's Z-transformation, the correlation between the TV and GA was significantly stronger than that between any individual 2D-US measurement and GA (P < 0.05). Normal twin fetuses had TVs similar to those of singletons adjusted for estimated fetal weight and GA (P = 0.85). TV adjusted for estimated fetal weight and GA was significantly lower in fetuses with CHD than in normal singletons (P < 0.05).

CONCLUSION

2D-US and 3D-US are useful tools for evaluation of the size and volume of the human fetal thymus through gestation. Fetal TV by 3D-US seems to reflect normal development of the thymus in utero better than do 2D-US measurements. Lower TV should be expected in association with CHDs.

Smaller fetal thymuses in pre-eclampsia: a prospective cross-sectional study

OBJECTIVE

To determine whether the thymus is smaller in fetuses of pre-eclamptic mothers than in those of normal controls.

METHODS

This was a cross-sectional, prospective, comparative study of sonographically determined fetal thymus measurements in 39 pregnancies with pre-eclampsia and 70 healthy pregnancies.

RESULTS

Both the diameter and the perimeter of the fetal thymus were smaller in pregnancies with pre-eclampsia than in healthy controls. The means of the thymus diameters were 28.6 ± 5.9 and 32.9 ± 4.5 mm and of thymus perimeters 80.9 ± 16.5 and 93.1 ± 16.6 mm for pre-eclamptic and healthy pregnancies, respectively (P < 0.001). General linear models showed that smaller fetal thymuses in pre-eclampsia were independent of gestational age, estimated fetal weight, small for gestational age status and antenatal steroid use.

CONCLUSIONS

Pre-eclampsia is associated with smaller fetal thymuses.