Growth-restricted premature infants are at increased risk for low thyroxine

Endocrine regulation in asymmetric intrauterine fetal growth retardation

OBJECTIVE

The ponderal index (PI) is a widely accepted measure of disproportionate growth or asymmetrical growth retardation by pediatricians worldwide. Identification of disproportionately grown small for gestational age (SGA) neonates by using the ponderal index as a measure of the nutritional status at birth, is important because they constitute a high-risk group among SGA neonates. Poor nutritional status of the mother could have a direct effect on the organs of the developing fetus and/or affect the endocrine milieu in the maternal feto-placental unit resulting in an increased incidence of intrauterine growth-retarded (IUGR)/SGA births. IUGR is a significant risk factor for adult disease. In this study, we have investigated the endocrine adaptation by the fetus to overcome the growth disadvantage caused due to poor nutritional status of the mother.

MATERIALS AND METHODS

We examined the quantitative variations in hormonal and growth factor profiles in paired maternal and cord blood samples obtained from mothers and their neonates who were classified based on their growth status into SGA and appropriate for gestational age (AGA).

RESULTS

(1) A total of 24.7% neonates had a PI < 2, indicating a high incidence of asymmetric IUGR in the population studied. (2) Anthropometric parameters measured in the mothers indicate that the mothers giving birth to neonates with a PI < 2 had poor nutritional status, both prior to and during pregnancy. (3) We observed increased levels of placental lactogen and prolactin and decreased levels of insulin in the cord blood of neonates with PI < 2, while lower levels of insulin-like growth factor 1 (IGF-1) and higher levels of epidermal growth factor (EGF) were observed in their mothers.

CONCLUSION

Poor maternal nutritional status results in fetal adaptation to a growth restricted environment via the modulation of the pituitary-thyroid axis thereby altering the endocrine milieu, thus affecting fetal growth.

Évaluation des taux de TSH, T4L, T3T des nouveau-nés prématurés et à terme hospitalisés

Thyroid hormones are essential for foetus and newborn development. Preterm newborns present low levels for thyroid hormones. These low levels are related with disorder in psychomotor and neurological development. In the literature, several studies concerning newborns treated with thyroid hormone have been realized in different conditions; however, there is no consensus about preterm newborn supplementation benefit.

OBJECTIVE

The aim of the study was to defined hormonal values used for normal and preterm newborns.

MATERIAL AND METHODS

We reported TSH, T3T and T4L levels for 195 normal or preterm newborns, eutrophic or small for gestational age (SGA).

RESULTS

A positive correlation was found between hormonal level and gestational age. This work allowed us to define a threshold for preterm newborn according to their gestational age.

CONCLUSION

Owing to lack of consensus, those values are useful for clinical and biological follow-up of thyroid function for newborns at risk (SGA and preterm before 32 weeks) during the first year of life. Finally, it would be interesting to study systematic supplementation of thyroid hormone for those infants in a prospective study.

Transient Hypothyroxinemia in Severe Hypertensive Disorders of Pregnancy

OBJECTIVE

Assess whether and to what extent thyroid function is affected in pregnant women with early and severe hypertensive disorders and in their newborns.

METHODS

Patients were 80 women with preeclampsia, hemolysis, elevated liver enzymes, and low platelet count syndrome or gestational hypertension combined with fetal growth restriction in the 24th to 34th week of singleton pregnancies. Maternal thyroid hormone levels and thyroid peroxidase antibodies were determined at admission and 3 months postpartum. Neonatal levels were determined from cord blood at delivery. Maternal hypothyroxinemia was defined as free T(4) (fT(4)) value below 9 pM.

RESULTS

At admission 26 (33%) women in the study group had fT(4) levels below 9 pM, with spontaneous normalization during pregnancy. There were no statistically significant differences between thyroid hormone values in women in the study group and 10 normotensive pregnant women in their third trimester. Three months postpartum, 97.5% of patients had normal thyroid hormone levels. Thyroid peroxidase antibodies were elevated in 10% of women postpartum. Their infants, born at a median gestational age of 30 6/7 weeks, had lower cord blood fT(4) and thyroid-stimulating hormone values compared with preterm infants of the comparison group, appropriate for gestational age. Cord blood fT(4) had no correlation with gestational age or maternal fT(4), but there was a significant correlation of cord blood fT(4) with umbilical artery pH.

CONCLUSION

Women with severe hypertensive disorders of pregnancy may have transiently lower fT(4) levels, without evidence of a thyroid disorder. Their neonates have lower fT(4) levels at birth unrelated to maternal fT(4), but related to prenatal acidosis.

LEVEL OF EVIDENCE

II-2.

Antenatal Glucocorticoids Increase Early Total Thyroxine Levels in Premature Infants

BACKGROUND

Hypothyroxinemia is associated with adverse neonatal outcomes including white matter damage, cerebral palsy, poor neurodevelopment and death. It has become increasingly important to understand the natural history and modifiers of thyroid function in the premature infant. It is standard obstetrical practice to offer antenatal glucocorticoids to pregnant women with threatened preterm delivery. Few studies have investigated the effect of antenatal glucocorticoids on neonatal thyroid function.

OBJECTIVE

To examine the association between antenatal exposure to glucocorticoids and early total thyroxine (T4) levels among extremely premature infants.

METHODS

We studied 521 infants born at 4 medical centers. Entry criteria included a gestational age of 23-28 weeks and a serum thyroxine level obtained in the first postnatal week. Receipt of antenatal glucocorticoids was recorded as none, partial, or complete. A complete course consisted of two doses of betamethasone or four doses of dexamethasone within a 48-hour period between 2 and 7 days of delivery. Early total T4 levels were obtained from state-mandated newborn screening programs.

RESULTS

Controlling for potential maternal, perinatal and neonatal confounding variables, infants exposed to a complete course of antenatal glucocorticoids had total T4 levels 0.8 microg/dl higher than their peers who were not exposed to a complete course of antenatal glucocorticoids (p = 0.03).

CONCLUSIONS

Extremely premature infants who received a complete course of antenatal glucocorticoids had significantly higher total thyroxine levels in the first postnatal week. Maternal, perinatal, and early neonatal variables did not completely explain this association. We speculate that antenatal glucocorticoids influence early neonatal thyroid function.

Current concepts in intrauterine growth restriction

Regulation of fetal growth is multifactorial and complex. Diverse factors, including intrinsic fetal conditions as well as maternal and environmental factors, can lead to intrauterine growth restriction (IUGR). The interaction of these factors governs the partitioning of nutrients and rate of fetal cellular proliferation and maturation. Although IUGR is probably a physiologic adaptive response to various stimuli, it is associated with distinct short- and long-term morbidities. Immediate morbidities include those associated with prematurity and inadequate nutrient reserve, while childhood morbidities relate to impaired maturation and disrupted organ development. Potential long-term effects of IUGR are debated and explained by the fetal programming hypothesis. In formulating a comprehensive approach to the management and follow-up of the growth-restricted fetus and infant, physicians should take into consideration the etiology, timing, and severity of IUGR. In addition, they should be cognizant of the immediate perinatal response of the growth-restricted infant as well as the childhood and long-term associated morbidities. A multi disciplinary approach is imperative, including early recognition and obstetrical management of IUGR, assessment of the growth-restricted newborn in the delivery room, possible monitoring in the neonatal intensive care unit, and appropriate pediatric follow-up. Future research is necessary to establish effective preventive, diagnostic, and therapeutic strategies for IUGR, perhaps affecting the health of future generations.

Sequelae of chorioamnionitis

Chorioamnionitis correlates to preterm delivery prior to 30 weeks of gestation. In most studies, proxies of intrauterine infection (clinical chorioamnionitis, histological chorioamnionitis, intra-amniotic increase in cytokines) are associated with acute neonatal morbidity and mortality and, at least to some degree, with neurological impairments (periventricular leukomalacia, intraventricular hemorrhage, cerebral palsy, polymicrogyria), chronic lung disease, and involution of the thymus in the preterm infant. The connection to visual impairment and cognitive deficits is uncertain or unknown. Full-term babies exposed to intrauterine infection often present with depressed Apgar scores and neonatal encephalopathy, and are at markedly increased risk of developing cerebral palsy. The infectious/inflammatory mechanisms involved are incompletely understood, and the types of microbes, as well as the genetic characteristics of the host adaptive and innate immune response, need to be better characterized.