Relations between the fetal circulation and pituitary-thyroid function

Evaluation of Fetal Thyroid with 3D Gradient Echo T1-weighted MR Imaging

Purpose:

The characteristics of fetal thyroid on magnetic resonance (MR) imaging, including normal thyroid and disorders other than goiter have not been fully evaluated. Our aim was to assess fetal thyroid using three dimensional (3D) gradient echo (GRE) T₁-weighted MR imaging and to examine the usefulness of this modality.

Materials and Methods:

The study included 27 3D GRE T₁-weighted images from 26 fetuses. The largest possible region of interest (ROI) within the thyroid at the slice level depicting the thyroid was manually defined and three circular ROIs on neck muscle were manually defined on the image slices showing the highest signal intensity (SI) of the thyroid. Maximum and mean thyroid-to-muscle SI ratios (SIRs) were then calculated as SIR = maximum or mean thyroid SI/muscle SI.

Results:

The thyroid could not be identified in two cases. Fetal thyroid function was normal in 17 cases, and there were 7 cases of hypothyroidism (6 transient and 1 thyroid dysgenesis). There was no linear relationship between mean and maximum SIR and gestational age. The mean and maximum SIR in the cases of normal fetal thyroid were 1.85 ± 0.20 and 2.61 ± 0.39, and the mean and maximum SIR in fetal hypothyroidism were 1.58 ± 0.20 and 2.13 ± 0.37. Mean (P = 0.0088) and maximum (P = 0.0221) SIR values were significantly different between euthyroid and hypothyroid fetuses.

Conclusion:

Thyroid SIR measurement provided useful information regarding fetal thyroid function.

Gestational nanomaterial exposures: microvascular implications during pregnancy, fetal development and adulthood

Air pollution particulate matter and engineered nanomaterials are encompassed in the broad definition of xenobiotic particles. While the effects of perinatal air pollution exposure have been investigated, elucidation of outcomes associated with nanomaterial exposure, the focus of this review, is still in its infancy. As the potential uses of nanomaterials, and therefore exposures, increase exponentially so does the need for thorough evaluation. Up to this point, the majority of research in the field of cardiovascular nanotoxicology has focused on the coronary and vascular reactions to pulmonary exposures in young adult, healthy, male models; however, as intentional and unintentional contacts persist, the non-pulmonary risks to under-represented populations become a critical concern. Development of the maternal-fetal circulation during successful mammalian gestation is one of the most unusual complex, dynamic, and acutely demanding physiological systems. Fetal development in a hostile gestational environment can lead to systemic alterations, which may encourage adult disease. Therefore, the purpose of this review is to highlight the few knowns associated with gestational engineered nanomaterial exposure segmented by physiological periods of development or systemic targets: preconception and maternal, gestational, fetal and progeny (Abstract figure). Overall, the limited studies currently available provide compelling evidence of maternal, fetal and offspring dysfunctions after engineered nanomaterial exposure. Understanding the mechanisms associated with these multigenerational effects may allow pregnant women to safely reap the benefits of nanotechnology-enabled products and assist in the implementation of exposure controls to protect the mother and fetus allowing for development of safety by design for engineered nanomaterials.

Use of cordocentesis in the management of preterm or growth-restricted fetuses with abnormal monitoring

The dilemma of when to deliver preterm or growth-restricted fetuses with abnormal monitoring is faced by all those treating such patients. Current noninvasive tests for fetal well-being have relatively high false-positive rates. Cordocentesis allows the clinician to directly analyze fetal blood and determine whether the fetus is truly in distress, is suffering from aneuploidy, or is plagued by infection. However, with improved neonatal care, otherwise normal infants of birth weight greater than 1500 gm have very low morbidity and mortality rates and any delay in delivery offered by cordocentesis is probably not justified. It is in the fetus whose estimated weight is below 1500 gm that cordocentesis should be used. If the results are normal, expectant management and the administration of corticosteroids will allow for pulmonary maturation and a more favorable outcome.

Diagnostic value of blood sampling in fetuses with growth retardation

BACKGROUND

Fetuses with intrauterine growth retardation are delivered if they have evidence of distress, as manifested by abnormalities in the fetal heart rate and umbilical-artery blood flow. We studied whether umbilical-blood sampling might provide further information useful for management.

METHODS

We measured hemoglobin and lactate concentrations, oxygen content, pH, blood gas levels, and base deficit in umbilical-vein blood and correlated these measurements with the heart rate and umbilical-artery wave forms recorded by Doppler velocimetry in 56 fetuses with growth retardation. Twenty-one fetuses had normal heart rates and normal results of velocimetry, 24 had normal heart rates and abnormal results of velocimetry (indicative of decreased diastolic flow), and 11 had abnormal heart rates and abnormal results of velocimetry.

RESULTS

None of the 21 fetuses with normal heart rates and velocimetry had hypoxia or acidemia. Of the 24 fetuses with normal heart rates and abnormal velocimetry, 4 (17 percent) had moderate lactic acidosis, 1 (4 percent) had a low pH value, and 3 (12 percent) had hypoxia. Of the 11 fetuses with abnormal heart rates and velocimetry, 7 (64 percent) had lactic acidosis, low blood oxygen content, and low pH values. The absence of end-diastolic flow increased the risk of hypoxia and acidemia. The proportion of fetuses with elevated hemoglobin concentrations was similar among the three groups.

CONCLUSIONS

Assessment of fetal oxygenation and acid-base balance is not indicated in fetuses with growth retardation if their heart rates and the results of velocimetry are normal. If the results of velocimetry are abnormal, fetal-blood sampling can distinguish fetuses that have growth retardation alone from those that also have hypoxia and acidosis, and thus may aid in determining the optimal time of delivery.