Transient neonatal hyperthyrotropinaemia

Perinatal factors affecting thyroid hormone status in extreme preterm infants

Pragmatic criteria are required for defining transient hypothyroxinemia and to permit entry to clinical trials of thyroxine substitution of only those extreme preterm infants who are hypothyroxinemic. The purpose of this article is to suggest that transient hypothyroxinemia is defined by postnatal serum T(4) levels, which are cord levels corrected to an equivalent gestational age had the fetuses remained in utero, and that those levels are adjusted for the significant prenatal and intrapartum factors. Lowered serum FT(4) levels are not a consistent pathognomonic feature of transient hypothyroxinemia as postnatal FT(4) levels in this large series of preterm infants are within or above the cord values of equivalent gestational age, irrespective of severity of illness. Although serum T(3) and thyroid-stimulating hormone levels do not contribute to the diagnosis of transient hypothyroxinemia, measurement of their levels is nevertheless required for trial monitoring involving thyroxine substitution to avoid inadvertent suppression of the developing hypothalamic-pituitary-thyroid axis by excess T(4) substitution.

Maternal, infant, and delivery factors associated with neonatal thyroid hormone status

BACKGROUND

Thyroid function is dynamic during the perinatal period with many factors potentially influencing maternal, fetal and neonatal TSH and thyroid hormone levels. We sought to identify the impact of numerous maternal, fetal and delivery attributes on thyroid parameters in newborns.

METHODS

This was a cross sectional study of 300 newborns. Detailed information was obtained from medical records and multiple characteristics from the record were tested as predictors of cord blood serum total T4, free T4 and TSH and infant T4 levels from the Maryland newborn screening program.

MAIN OUTCOME

Outcomes are levels of thyroid stimulating hormone (TSH), thyroxine (T(4)), and free T(4) in newborn cord serum and total T(4) in postnatal heelstick bloodspot samples.

RESULTS

Multivariate models identified a number of variables that are independently associated with thyroid hormone levels: higher birth order (lower cord TSH); older maternal age (lower cord total T(4)); pregnancy-induced hypertension and/or preeclampsia (lower cord total T(4) and free T(4)); gestational diabetes (higher cord free T(4)); sexually transmitted disease during pregnancy (lower cord TSH); alcohol use during pregnancy (lower cord TSH); thyroid condition/medications (higher bloodspot total T(4), both neonatal and subsequent); Asian ancestry (higher cord TSH); male sex (higher TSH and lower neonatal bloodspot total T(4)); and C-section (lower cord TSH). Gestational age was independently associated with lower cord TSH, higher cord total T(4), and higher neonatal and subsequent bloodspot total T(4).

CONCLUSIONS

Fetal and newborn thyroid hormone levels during the perinatal period are dynamic and influenced by several biological and delivery related factors. Efforts to identify fetal thyroid disruptors in late gestation must carefully consider these factors.

Predictors of AVP and TSH levels and the timing of first voiding in the newborn

To evaluate obstetric predictors of umbilical cord plasma AVP levels, serum TSH levels and the timing of first voiding, 87 singleton term newborns were divided into three groups: group A, vaginal delivery (n = 30); group B, cesarean section (CS) during labor (n = 26); and group C, elective CS (n = 31). The AVP concentration was 120 (0.7-2170) ng/L in group A, 1.8 (0.01-183) ng/L in group B, and 0.8 (0.01-30) ng/L in group C (p < 0.001). In group A, the TSH concentration was 10.20 (3.5-30.80) mU/L; in group B, 5.40 (2.10-43.00) mU/L; and in group C, 5.30 (2.90-11.00) mU/L (p = 0.001). Duration of labor had a positive correlation with AVP (p < 0.001) and TSH (p = 0.001) concentrations. The timing of first voiding had a positive correlation with gestational age (p = 0.003), volume of additional feeding before first voiding (p < 0.001), and umbilical AVP concentration (p = 0.023). The AVP and TSH concentrations are associated with mode of delivery and duration of labor and AVP levels also with the timing of first voiding in the newborn.

Cord blood thyroid-stimulating hormone level and risk of acidosis at birth

OBJECTIVE

Cord blood thyroid-stimulating hormone level is elevated in neonates who had undergone more perinatal stresses. The present study aimed to evaluate the cord blood acid-base status in neonates with elevated thyroid-stimulating hormone level.

STUDY DESIGN

The study population consisted of 2366 singleton, term pregnancies. Subjects were categorized by their cord blood thyroid-stimulating hormone level into four quartiles, and cord blood acid-base parameters were compared among the four groups. The correlations between cord acid-base parameters and thyroid-stimulating hormone level were also studied.

RESULTS

Cord blood pH was significantly lower in the highest (arterial, 7.27+/-0.08; venous, 7.32+/-0.07) and second highest thyroid-stimulating hormone quartile groups (arterial, 7.29+/-0.07; venous, 7.34+/-0.06) compared to the lowest quartile group (arterial, 7.30+/-0.06; venous, 7.35+/-0.05). Incidences of cord arterial pH < or =7.20 were 4.7%, 6.8%, 10.9%, and 17.3% in lowest to the highest thyroid-stimulating hormone quartile groups, respectively. There was a significant negative correlation between cord blood thyroid-stimulating hormone level and cord arterial and venous pH (r=-0.26, P<0.001). When stratified according to the mode of delivery, the negative correlations remained significant in neonates delivered vaginally and by intrapartum emergency cesarean section but not in neonates delivered by elective cesarean section.

CONCLUSION

Incidence of cord blood acidosis is significantly higher in neonates with elevated thyroid-stimulating hormone level. This findings support the postulation that stress-induced elevation of cord blood thyroid-stimulating hormone level may be mediated through intrapartum fetal hypoxia.

Neonatal hyperthyrotropinemia in gestational diabetes mellitus and perinatal complications

The aim of this study is to explore the relationship between high cord blood thyroid-stimulating hormone (TSH) level and in-utero stress to the fetus in gestational diabetes mellitus (GDM). Cord blood TSH results were analyzed in 1,578 euthyroid infants from singleton pregnancies with GDM: 103 with elevated TSH (>16 mIU/l) and 1,475 with normal TSH. Maternal characteristics, pregnancy outcome and perinatal complications were compared between the two groups. Multiple logistic regression was used to study the association between high cord blood TSH level and various perinatal complications which reflect in-utero stress in GDM after adjusting for the confounding effects of parity, instrumental delivery, cesarean section and baby gender. High cord blood TSH level was found to be associated with the 1-min Apgar score <7 (OR 3.31, 95% CI 1.78-6.16), birth trauma (OR 3.44, 95% CI 1.11-10.69), neonatal jaundice requiring treatment (OR 2.08, 95% CI 1.30-3.32), neonatal sepsis (OR 2.34, 95% CI 1.24-4.42), respiratory complications (OR 3.45, 95% CI 1.37-8.70), neurological complications (OR 8.01, 95% CI 1.91-33.60) and overall perinatal morbidity (OR 2.41, 95% CI 1.58-3.67). Cord blood TSH level seems to be a better and independent indicator of the in-utero stress to the fetus in GDM when compared to the commonly used sugar profile result and HbA1c level.

Cord blood thyroid-stimulating hormone level in high-risk pregnancies

OBJECTIVE

To evaluate the effect of various antepartum conditions on cord blood thyroid-stimulating hormone (TSH) level.

STUDY DESIGN

The study group consisted of 24,892 consecutive singleton deliveries over a period of 4 years. The effect of preeclampsia, glucose intolerance, maternal medical diseases, and antepartum hemorrhage of unknown origin (APHUO) on cord blood TSH level were assessed by univariate analysis and linear regression.

RESULTS

After controlling for potential confounders, there was a significant independent association between cord blood TSH level and preeclampsia (P=0.043), glucose intolerance (P=0.015), and maternal medical diseases (P=0.022). Antepartum hemorrhage of unknown origin was not associated with a higher cord blood TSH level.

CONCLUSION

Cord blood TSH level was significantly elevated in various adverse antepartum conditions. This may be related to the placental insufficiency and fetal hypoxia commonly found in these high-risk pregnancies.

Cord blood thyroid-stimulating hormone level in twin pregnancy

BACKGROUND

Cord blood thyroid-stimulating hormone level is elevated among neonates who undergo more perinatal stress. The aim of this study was to investigate the effect of twin pregnancy on the cord blood thyroid-stimulating hormone level.

METHODS

The study group consisted of 24 910 singleton and 543 twin neonates over a 4-year period. The effect of twin pregnancy on the cord blood thyroid-stimulating level was evaluated. Linear regression analysis was used to control for the effect of mode of delivery, birth weight, and infant sex.

RESULTS

The median cord blood thyroid-stimulating hormone levels (interquartile range) in the singletons and in the twins were 5.8mIU/l (4.2-8.6) and 5.6mIU/l (4.3-7.5), respectively. Linear regression analysis revealed no significant difference between singleton and twin cord blood thyroid-stimulating hormone levels (p = 0.23). Cord thyroid-stimulating hormone levels tended to be higher in second-born twins (p = 0.08) and monochorionic twins (p = 0.097) compared with singleton neonates. Twins with more than 20% weight discordance were associated with a significantly higher cord blood thyroid-stimulating hormone level (p = 0.035).

CONCLUSION

Cord blood thyroid-stimulating hormone level is elevated in some subgroups of twins who are at higher risk of adverse perinatal outcomes. However, the overall effect of multiple pregnancy on the cord blood thyroid-stimulating hormone level is small. Cord blood thyroid-stimulating hormone screening for congenital hypothyroidism is also valid in twin pregnancies.

Levels of cord blood thyroid stimulating hormone after external cephalic version

OBJECTIVE

To investigate the relationship between breech presentation, external cephalic version and levels of cord blood thyroid stimulating hormone.

DESIGN

Case-control study.

SETTING

University teaching hospital.

POPULATION

The study group consisted of 289 consecutive singleton deliveries at term over a four-year period, all of whom had an attempt at external cephalic version performed near term for breech presentation. The control group included 23,001 singleton term deliveries during the same four-year period.

METHODS

Between group differences were compared with the Mann-Whitney U test or chi2 test when appropriate.

MAIN OUTCOME MEASURES

Levels of cord blood thyroid stimulating hormone and the incidence of false positive screening results for congenital hypothyroidism.

RESULTS

Babies who were born vaginally after prior successful external cephalic version had significantly higher median levels of cord blood thyroid stimulating hormone (6.4 vs 6.0 mlU/L, P = 0.034) and the incidence of false positive screening for thyroid stimulating hormone (12.9% vs 7.2%, P = 0.016, OR 1.9) compared with babies with spontaneous cephalic presentation. In babies with a breech presentation born by elective caesarean section, previous attempts at external cephalic version had no effect on cord blood thyroid stimulating hormone levels. There was also no difference in the levels of cord blood thyroid stimulating hormone between cephalic and breech-presenting fetuses born by elective caesarean section. However, breech-presenting babies born by emergency caesarean section after onset of labour had higher median levels of cord thyroid stimulating hormone than those with cephalic presentation (5.1 vs 4.5 mIU/L, P= 0.008).

CONCLUSION

Levels of cord blood thyroid stimulating hormone are elevated in babies born vaginally after a successful external cephalic version. This finding may represent a biological difference in fetal response to the stress of labour in breech-presenting fetuses, which is not correctable by a successful external cephalic version.

Increased incidence of congenital malformations in children with transient thyroid-stimulating hormone elevation on neonatal screening

We investigated the incidence of congenital malformation in all infants with raised thyroid-stimulating hormone (TSH) levels on neonatal screening in Scotland between August 1979 and December 1993. Of 344 infants with elevated TSH, 31 (9%) had one or more malformations: 12 cardiac 15 noncardiac, and 16 dysmorphic syndromes (including 5 with Down syndrome). Criteria were devised to distinguish between definite or probable congenital hypothyroidism and transient TSH elevation. Congenital hypothyroidism was considered definite in 224 (65.1%) infants and probable in 11 (3.2%). Eighty-eight (25.6%) infants had transient TSH elevation, whereas thyroid status was uncertain in 21 (6.1%). In the definite group 12 (5.4%) infants had one or more malformations compared with 13 (14.8%) in the transient group. Cardiac malformation, noncardiac malformation, dysmorphic syndromes, and "sickness" were much more frequent in the transient compared with the definite group: 5.7% versus 1.8%, 8.0% versus 1.8%, 6.8% versus 2.7%, and 37.5% versus 7.1%, respectively. The incidence of congenital malformation in bonafide congenital hypothyroidism is lower than has been previously reported. The high incidence of congenital malformation associated with transient TSH elevation indicates the need to reevaluate the diagnosis of hypothyroidism in all infants with TSH elevation and concurrent illness or malformation.