Influence of mode of delivery on fetal pituitary-thyroid axis

A detailed observational study of maternal and neonatal variables affecting the thyroid-stimulating hormone levels in neonates

Background

Thyroid hormones are essential for fetal growth and the central nervous system development. Thyroid-stimulating hormone (TSH) is the key regulatory hormone. Their levels are quite dynamic in the perinatal period and are influenced by multiple factors. These factors should be taken into consideration during newborn screening. This study aimed to observe the impact of maternal and neonatal factors on neonatal TSH status.

Results

Neonatal TSH (nTSH) depicted a positive correlation with parity (p = 0.066) while negative correlation recorded with maternal blood haemoglobin (p = 0.007) among maternal factors.

New-born length (p = 0.027) and birth weight (p < 0.001) exhibited a negative correlation with nTSH among neonatal factors.

Conclusions

This study concludes that among all the maternal and neonatal factors, birth weight shows the most influence on nTSH. However, the effect may be compounded by other factors. As these risk elements rarely occur singly, it is often difficult to find the exposure which confer the risk on children. These factors should be considered while interpreting the result of the screening program.

Delivery factors and neonatal thyroid hormone levels: a systematic review

Postnatal thyroid hormone changes enable the neonate to be adapted for postnatal life. Several factors can affect this adaption. In this review, we summarized the studies that reported the association among the delivery factors and neonatal thyroid hormones and thyroid stimulating hormone. A comprehensive literature search was performed in PubMed, Web of Science, and Scopus up to March 2020, to identify the studies investigating the relationship between delivery factors, especially the mode of delivery and labor pain, and neonatal thyroid hormones and TSH. Finally, in this review study, of 157 articles obtained in the initial search, 25 eligible studies were reviewed. Various maternal, fetal/neonatal, and obstetric factors affected neonatal TSH and thyroid hormones. Among various influencing factors, mode of delivery, labor pains, and duration of labor have a strong relationship with neonatal thyroid hormones and need to be considered for interpretation of neonatal thyroid status. The majority of the studies revealed that vaginal deliveries (instrumental or natural) lead to higher levels of cord TSH compared to elective cesarean section. This can be explained by the increased secretion of catecholamine during labor. It has been suggested that blood TSH and thyroid hormone levels are affected by perinatal stress events such as maternal anxiety, labor pains, fetal distress, and other stimulants of the catecholamine response. These changes may act as the trigger to increase thyroid hormone levels for adapting of neonates in the first hours after birth. This assumption needs to be re-evaluated by performing comprehensive and well-designed studies.

The role of placental iodine storage in the neonatal thyroid stimulating hormone surge: iodine as a driving force to adapt the terrestrial life

PURPOSE

Iodine plays a pivotal role in adaptation during the transition from intrauterine to extrauterine life. Although it is well known that the placenta plays a role in iodine storage, a relationship between the neonatal thyroid stimulating hormone (TSH) peak and placental iodine concentration has not been established. This study focuses on the role of placental iodine concentration in the TSH surge after delivery.

MATERIALS AND METHODS

This study included 42 mothers and their newborns, none of whom had perinatal risk factors. The following samples were collected to analyze iodine: placental tissue, amniotic fluid (AF), and 24-h maternal urine. Blood was drawn from the umbilical cord (uc), newborns (at the 1st-24th hours), and mothers (at 1st hour) to analyze the following hormones: TSH, freeT4/T3(fT4/fT3), human chorionic gonadotrophin (hCG), prolactin (PRL), follicle stimulating hormone (FSH), luteinizing hormone (LH), and cortisol.

RESULTS

The mean iodine levels of placental tissue, AF, and 24-h maternal urine were as follows: 29.06 ± 45.88 μg/kg, 182.80 ± 446.51 µg/L, and 498.35 ± 708.34 µg/L, respectively. The mean TSH and hCG values were 32.41 ± 13.96mIU/ml and 30.66 ± 18.55mIU/ml, respectively, at the 1st hour. Placental iodine had strong, very strong, and weak negative correlations with TSH, hCG, and PRL, respectively (r_TSH = - 0.763, p < 0.001;r_HCG = - 0.919, p < 0.001; r_PRL = - 0.312, p = 0.044).

CONCLUSION

This study showed that the placental iodine level was inversely correlated with neonatal TSH, hCG, and PRL. It indicates that placental iodine concentration is an efficient driving force shaping the dynamic pattern of the neonatal TSH peak in addition to hCG and PRL surges, which reflects the adaptive effort in the transition from intrauterine to extrauterine life.

Birth Characteristics and Risk of Pediatric Thyroid Cancer: A Population-Based Record-Linkage Study in California

Background: Incidence rates of thyroid cancer in children and young adults (age 0-19 years) have nearly doubled over a recent 15-year period in the United States. Children with thyroid cancer may require long-term therapy and surveillance and are at greater risk for second primary malignancies. High-dose exposure to ionizing radiation is the only known nongenetic risk factor; the vast majority of cases have an unknown etiology. Methods: We conducted a population-based nested case-control study to evaluate the relationship between a range of birth characteristics and the risk of pediatric thyroid cancer. Using linked birth records and cancer registry data from California, we included 1012 cases who were diagnosed with first primary thyroid cancer at the age of 0-19 years from 1988 to 2015 and 50,600 birth-year matched controls (1:50 case to control ratio). We estimated adjusted odds ratios (OR) and 95% confidence intervals (CI) by using multivariable logistic regression models applied to the full population and stratified by thyroid cancer subtypes (papillary and follicular), race/ethnicity (white and Hispanic), and age at diagnosis (0-14 and 15-19 years). Results: Hispanic ethnicity (OR: 1.20 [CI 1.01-1.42]), higher birth weight (OR: 1.11 [CI 1.04-1.18] per 500g), and higher maternal education (13-15 years OR: 1.35 [CI 1.09-1.68], 16+ years OR: 1.35 [CI 1.07-1.71]) were associated with an increased risk of pediatric thyroid cancer, while male sex (OR: 0.21 [CI 0.18-0.25]) and higher birth order (third or higher OR: 0.81 [CI 0.68-0.98]) were associated with a decreased risk. Some heterogeneity was observed across subtype, most notably an elevated OR with higher birth order for follicular thyroid cancer, in contrast to the reduced risk for this category among papillary thyroid cancer cases (p-value for interaction = 0.01). Hispanic ethnicity was a risk factor for papillary, but not follicular thyroid cancer (p-value for interaction = 0.07). Conclusions: In this population-based study of birth characteristics and pediatric thyroid cancer, we identified several important risk factors for pediatric thyroid cancer, including female sex, Hispanic ethnicity, higher birth weight, higher maternal educational attainment, and lower birth order. Our data provide new areas for replication and investigation of biological mechanisms for this poorly understood malignancy.

Advanced Maternal Age, Mode of Delivery, and Thyroid Hormone Levels in Chinese Newborns

Objective: Thyroid hormones are essential for fetal growth and neurodevelopment, however, data on cord blood thyroid hormones are sparse in China where maternal age at childbearing is increasing in recent decades. We aimed to assess cord blood levels of free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH) in full-term Chinese newborns, and examine potential related perinatal factors. Methods: This study included 922 mother-newborn pairs from a prospective birth cohort enrolled in 2012-2013, Shanghai, China. Cord serum concentrations of FT3, FT4, TSH, and TPOAb were measured in newborns. Results: Newborns born via cesarean section had higher cord serum FT3 (mean ± SD: 1.90 ± 1.16 pmol/L) and lower cord serum TSH (5.15 ± 2.60 mIU/L) than those born via vaginal delivery (FT3: 1.62 ± 0.93 pmol/L; TSH: 9.27 ± 6.76 mIU/L). In cesarean section deliveries, the concentration of cord serum FT3 was 0.15 (95%CI: -0.03, 0.33; p = 0.10) pmol/L lower in infants of mothers aged 30-34 years, and 0.57 (95%CI: 0.22, 0.92; p = 0.002) pmol/L lower in infants of mothers ≥35 years compared to infants of mothers <30 years. Large-for-gestational-age (birth weight >90th percentile) was associated with higher TSH (p = 0.02). Similar results were also found in vaginal deliveries. Conclusions: In this Chinese term birth cohort, newborns born via cesarean section had higher cord serum FT3 and lower TSH than those born via vaginal delivery. Advanced maternal age was associated with lower fetal FT3. Further research is needed to understand whether this association may mediate the adverse impact of advanced maternal age on neurodevelopment in early life.

Hyperthyroxinemia at birth: a cause of idiopathic neonatal hyperbilirubinemia?

BACKGROUND

Some neonates develop idiopathic hyperbilirubinemia (INHB) requiring phototherapy, yet with no identifiable causes. We searched for an association between abnormal thyroid levels after birth and INHB.

METHODS

Of 5188 neonates, 1681 (32.4%) were excluded due to one or more risk factors for hyperbilirubinemia. Total thyroxine (TT4) and thyroid stimulating hormone values were sampled routinely at 40-48 hours of age and measured in the National Newborn Screening Program.

RESULTS

Of the 3507 neonates without known causes for hyperbilirubinemia, 61 (1.7%) developed INHB and received phototherapy. Univariate analyses found no significant association between mode of delivery and INHB (vacuum-delivered neonates were a priori excluded). Nonetheless, in cesarean-delivered (CD) neonates, two variables had significant association with INHB: TT4 ≥ 13 µg/dL and birth at 38-38.6 weeks. In vaginally delivered (VD) born neonates, INHB was associated with weight loss > 7.5% up to 48 hours of age. Multivariate logistic regression analysis showed a strong effect of mode of delivery on possible significant association with INHB. In CD neonates, such variables included: TT4 ≥ 13 µg/dL [P = 0.025, odds ratio (OR) 5.49, 95% confidence interval (CI) 1.23-24.4] and birth at 38-38.6 weeks (P = 0.023, OR 3.44, 95% CI 1.19-9.97). In VD neonates, weight loss > 7.5% (P = 0.019, OR 2.1, 95% CI 1.13-3.83) and 1-min Apgar score < 9 (P < 0.001, OR 3.8, 95% CI 1.83-7.9), but not TT4, showed such an association.

CONCLUSIONS

INHB was significantly associated with birth on 38-38.6 week and TT4 (≥ 13 µg/dL) in CD neonates, and with a weight loss > 7.5% in VD neonates. We herein highlight some acknowledged risk factors for neonatal hyperbilirubinemia, and thus minimize the rate of INHB.

Thyroid hormone levels in late preterm, early term and term infants: a study with healthy neonates revealing reference values and factors affecting thyroid hormones

BACKGROUND

Thyroid function tests in neonates have been challenging to interpret because their levels are affected by several neonatal and delivery-related factors. The aim of the study was to evaluate reference values of thyroxine (T4) and thyrotropin (TSH) levels in different gestational age groups and to demonstrate the affect of perinatal factors on thyroid hormones.

METHODS

Medical records of 7616 neonates whose gestational age ranges between 34 and 42 weeks were analyzed retrospectively. Gender, mode of delivery, gestational age, postnatal age and birth weight were noted together with TSH and T4 levels.

RESULTS

Gestational age (r=0.14, p<0.001) and birth weight (r=0.12, p<0.001) had positive correlation with T4 levels, whereas they had no effect on TSH levels. Males had higher TSH and lower T4 levels (p=0.001 for both) compared with females. T4 levels of babies born via vaginal delivery were lower than the ones born via cesarean section (p=0.01). Multivariable analysis yielded gestational age as the only factor affecting T4 levels (p<0.001). T4 and TSH levels based on 2.5-97.5 percentile cutoffs according to gestational age were presented.

CONCLUSIONS

The thyroid hormone ranges given in this study can help pediatricians to interpret the thyroid hormone results with ease.

Perinatal factors associated with neonatal thyroid-stimulating hormone in normal newborns

PURPOSE

This study was to evaluate the effect of neonatal, maternal, and delivery factors on neonatal thyroid-stimulating hormone (TSH) of healthy newborns.

METHODS

Medical records of 705 healthy infants born through normal vaginal delivery were reviewed. Neonatal TSH levels obtained by neonatal screening tests were analyzed in relation to perinatal factors and any associations with free thyroxine (FT4) and 17-α hydroxyprogesterone (17OHP) levels.

RESULTS

An inverse relationship was found between TSH and sampling time after birth. Twin babies and neonates born by vacuum-assisted delivery had higher TSH levels than controls. First babies had higher TSH levels than subsequent babies. Birth weight, gestational age, maternal age and duration from the rupture of the membrane to birth were not related to neonatal TSH. There were no significant differences in TSH level according to sex, Apgar scores, labor induction, the presence of maternal disease and maternal medications. There was a positive association between TSH and 17OHP level but not between TSH and FT4 level. Multiple linear regression analyses showed that sampling time, mode of delivery, birth order, and 17OHP level were significant factors affecting neonatal TSH level.

CONCLUSION

Neonatal TSH levels of healthy normal newborns are related with multiple factors. Acute stress during delivery may influence the neonatal TSH level in early neonatal period.

Effect of maternal and neonatal factors on cord blood thyroid stimulating hormone

BACKGROUND

Congenital hypothyroidism (CH) is most common preventable cause of mental retardation in children. Cord blood Thyroid Stimulating Hormone (CBTSH) level is an accepted screening tool for CH.

OBJECTIVES

To study CBTSH profile in neonates born at tertiary care referral center and to analyze the influence of maternal and neonatal factors on their levels.

DESIGN

Cross retrospective sectional study.

METHODS

Study population included 979 neonates (males = 506 to females = 473). The CBTSH levels were estimated using electrochemiluminescence immunoassay on Cobas analyzer. Kit based cut-offs of TSH level were used for analysis. All neonates with abnormal CBSTH levels, were started on levothyroxine supplementation 10 μg/Kg/day and TSH levels were reassessed as per departmental protocol.

RESULTS

The mean CBTSH was 7.82 μIU/mL (Range 0.112 to 81.4, SD = 5.48). The mean CBTSH level was significantly higher in first order neonates, neonates delivered by assisted vaginal delivery and normal delivery, delivered at term or preterm, neonates with APGAR score <5 and those needing advanced resuscitation after birth. The CBTSH level >16.10 and <1.0 μIU/mL was found in 4.39 % and 1.02 % neonates respectively. The prevalence rate of CBTSH level >16.1 μIU/mL was significantly higher in neonates delivered by assisted vaginal delivery and normal delivery, term and preterm neonates, APAGR score of <5, presence of fetal distress, need for resuscitation beyond initial steps and in those with birth weight of <1.5 Kg. Three neonates were confirmed to have CH after retesting of TSH level.

CONCLUSIONS

The CBTSH estimation is an easy, non-invasive method for screening for CH. The cutoff level of CB TSH (μIU/mL) >16.10 and <1.0 led to a recall of 5.41% of neonates which is practicable given the scenario in our Country. The mode of delivery and perinatal stress factors have a significant impact on CBTSH levels and any rise to be seen in the light of these factors. The prevalence rate of CH after recall was ~3 in 1000 live births.

Using record linkage to investigate perinatal factors and neonatal thyroid-stimulating hormone

AIM

Studies examining the relationship between maternal and infant thyroid parameters have shown conflicting results. Record linkage provides an opportunity to examine the association between maternal and infant thyroid-stimulating hormone (TSH) levels. Our aim was to demonstrate the feasibility of record linkage of newborn screening (NBS), laboratory and birth databases for research by investigating the association between maternal and newborn TSH levels.

METHODS

The records of 2802 women with first trimester serum TSH concentrations were linked with population-based birth data and NBS data containing infant TSH levels. Association between moderately high neonatal TSH levels (>5 mIU/L) and maternal and infant characteristics was evaluated. The correlation and association between maternal and infant TSH levels were assessed using Pearson's correlation coefficient and multivariable linear regression, respectively.

RESULTS

Of maternal and birth records, 99.3% linked with an NBS record. Mother's country of birth, gestational age (>41 weeks) and lower birthweight were associated with neonatal TSH levels >5 mIU/L. Neonatal and maternal first trimester TSH levels were not correlated, although statistically significant (r = 0.05, P = 0.008). The association between neonatal TSH and maternal TSH, after adjusting for maternal age, gestational age and age at NBS testing, was also small (b = 0.039, P = 0.009).

CONCLUSIONS

Record linkage is a feasible and cost-efficient way to investigate the association between maternal factors and neonatal hormone levels. First trimester maternal thyroid levels are not correlated with neonatal TSH levels. This method of outcome assessment can be used for future research examining long-term outcomes for infants with different NBS results.

Thyroid function in late preterm infants in relation to mode of delivery and respiratory support

The relationship between thyroid function, mode of delivery, and illness in infants 34-36 weeks' gestation has not been well studied. We hypothesized that infants born by cesarean delivery and those with increased illness would have a reduction in thyroxine (T4) following birth. Total T4 and thyroid-stimulating hormone were obtained at birth (Time 1) and between days 2 and 5 (Time 2). The study sample included 129 infants 34-36 weeks' gestation. There were no differences in total T4 between infants born by cesarean or vaginal delivery (p=0.18), or between those requiring respiratory support compared to infants not requiring respiratory support (p=0.09). At Time 2, 93% of the study population had a total T4 below one standard error of the reference laboratory mean. In our study sample, despite many infants having a low total T4, there was no association between total T4 levels, respiratory support, or mode of delivery.

Influence of perinatal factors on thyroid stimulating hormone level in cord blood

Background:

The aim of the present study was to determine the effect of various perinatal factors on cord blood TSH among newborns in Isfahan, Iran.

Materials and Methods:

This was a descriptive–analytic cross sectional study which performed in Isfahan Iran. During a period of four months, since February to May 2012 a total number of 440 newborns delivered in Alzahra and Shahid beheshti hospitals were enrolled in the study. For all newborns one mL blood sample from umbilical vein was obtained by one of the project investigators and sent to laboratory for further examinations. Cord blood TSH and birth body weight (BBW), gestational age, history of gestational diabetes mellitus (GDM), apgar at one minute, apgar at five minute, newborn gender and the mother's age were documented. Differences considered statistically significant if P < 0.01.

Results:

440 newborns enrolled in the study, 221 (50.2%) were male and 219 (49.8%) were female. Among study parameters, method of delivery had statistically significant relation with cord blood TSH (P < 0.001), and other factors such as BBW, gestational age, GDM, apgar at one minute, apgar at five minute, newborn gender and the mother's age didn’t have statistically significant relationship with cord TSH level.

Conclusion:

In conclusion we deduce that the only factor that can affect cord blood TSH was method of delivery. Infant with vaginal delivery has higher TSH level in cord blood. Other factors that were evaluated in this study didn’t have any statistically significant relationship.

Serum thyroid hormone levels in healthy children from birth to adulthood and in short children born small for gestational age

CONTEXT

Age-appropriate reference ranges for thyroid hormones are required for detecting pediatric thyroid dysfunction. Data on thyroid hormones and peripheral thyroid metabolism in short children born small for gestational age (SGA) before and during GH treatment are lacking.

OBJECTIVES

Our objectives were to obtain pediatric thyroid hormone reference ranges; to investigate thyroid hormones in short SGA children before puberty, during puberty, and during postponement of puberty by GnRH analog; and to evaluate thyroid hormones during GH treatment.

PATIENTS AND DESIGN

In 512 healthy children (225 females; 0-18 yr), free T(4) (FT(4)), TSH, total T(4), T(3), rT(3), and T(4)-binding globulin were determined. Reference ranges were calculated using the linearity, median, and skewness method. In 125 short SGA children (62 females; mean age 11.3 yr), thyroid hormones were analyzed before and after 2 yr of GH treatment and additional GnRH analog.

RESULTS

Thyroid references showed wide ranges postnatally and age-specific patterns thereafter, similar in boys and girls. Untreated short SGA children had similar FT(4) and T(4) levels as the reference population but significantly higher T(3), rT(3), and T(4)-binding globulin levels. During puberty and during GH treatment, FT(4) and rT(3) significantly decreased, whereas T(3) significantly increased.

CONCLUSION

Age-specific thyroid reference ranges are presented. Puberty and GH treatment both induce changes in peripheral thyroid metabolism, resulting in more biologically active T(3) at the expense of less inactive rT(3), possibly mediated by IGF-I. GH treatment induces altered peripheral thyroid metabolism but does not result in thyroid dysfunction.

Cord blood thyroid tests in boys born with and without cryptorchidism: correlations with birth parameters and in utero xenobiotics exposure

BACKGROUND

In utero exposure to environmental chemicals can result in reproductive toxicity via endocrine disruption mechanisms. Whether some of those contaminants also have an impact on fetal thyroid function or pathways, and, thus, potentially on neuropsychological development, is still debated.

METHODS

We used samples from a cord blood (CB) and milk bank, established for a research on cryptorchidism and xenobiotic exposure to compounds known for their anti-androgenic and/or estrogenic activity, to study CB thyroid tests and their correlation with CB and milk xenobiotics concentrations in boys born in Nice area.

RESULTS

No difference was found in thyroid tests between 60 cryptorchid boys and 76 matched controls (median thyroid stimulating hormone 5.97 vs. 6.55 mUI/L, free thyroxine [fT4] 13.1 vs. 12.9 pmol/L, free triiodothyronine [fT3] 1.9 vs. 2.1 pmol/L), with no influence of season of birth, gestational age, maternal smoking, or mode of delivery (except for higher fT4 in control boys born vaginally). FT4 was correlated with fetal growth only in cryptorchid boys. Since we had previously shown differences between cryptorchid and controls exposure, we studied correlations of thyroid tests with xenobiotics in control boys only. All tested CB or maternal milk was contaminated by one or more selected xenobiotics, mainly polychlorinated biphenyls (PCBs), dichloro diphenyl dichloroethylène (DDE), dibutylphthalate, hexachlorobenzene, and bisphenol A. We found a significant negative correlation between fT4 and concentrations of PCB118, PC180, and DDE in milk (respectively r = -0.342, p < 0.03, r = -0.296, p = 0.031, r = -0.315, p = 0.016), persisting after adjustment for mode of delivery. There was a significant positive correlation of fT3 with milk concentrations of PCB138, PCB153, ΣPCB, and dibutylphthalate (respectively r = 0.31, p = 0.016, r = 0.28, p = 0.029; r = 0.34, p = 0.0079 and r = 0.272, p = 0.0295), with a trend for PCB180 (r = 0.259, p = 0.061). There was no correlation of thyroid stimulating hormone with any of the measured xenobiotics, except for a weak negative trend with CB bisphenol A (r = -0.25, p = 0.077).

CONCLUSIONS

CB thyroid tests are within normal range in cryptorchid boys, similar to controls. Our data in controls suggest a possible weak correlation between in utero exposure to some xenobiotics (PCBs, DDE) and fT3 and fT4 CB concentrations, with usually negative correlations with fT4 and positive with fT3 concentrations, which we speculate could suggest an impact on deiodinases.

The health implications of birth by Caesarean section

Since the first mention of fetal programming of adult health and disease, a plethora of programming events in early life has been suggested. These have included intrauterine and postnatal events, but limited attention has been given to the potential contribution of the birth process to normal physiology and long-term health. Over the last 30 years a growing number of studies have demonstrated that babies born at term by vaginal delivery (VD) have significantly different physiology at birth to those born by Caesarean section (CS), particularly when there has been no exposure to labour, i.e. pre-labour CS (PLCS). This literature is reviewed here and the processes involved in VD that might programme post-natal development are discussed. Some of the effects of CS are short term, but longer term problems are also apparent. We suggest that VD initiates important physiological trajectories and the absence of this stimulus in CS has implications for adult health. There are a number of factors that might plausibly contribute to this programming, one of which is the hormonal surge or "stress response" of VD. Given the increasing incidence of elective PLCS, an understanding of the effects of VD on normal development is crucial.

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.

Birth delivery mode modifies the associations between prenatal polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) and neonatal thyroid hormone levels

BACKGROUND

Developing infants may be especially sensitive to hormone disruption from chemicals including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs).

OBJECTIVE

We investigated relationships between cord serum levels of PCBs and PBDEs and thyroid hormones measured in cord blood serum and neonatal blood spots.

METHODS

We measured PCBs and PBDEs, thyrotropin (TSH), thyroxine (T4) and free T4 (FT4) in cord blood serum from 297 infants who were delivered at the Johns Hopkins Hospital in 2004-2005. We abstracted results of total T4 (TT4) measured in blood spots collected in the hospital and at neonatal visits. We used delivery mode (augmented vaginal deliveries and nonelective cesarean deliveries) as a surrogate for intrapartum stress, which is known to alter cord blood thyroid hormones.

RESULTS

In the full study population, no compounds were associated with a change in average TSH, FT4, or TT4. BDE-100 was associated with increased odds of low cord TT4, BDE-153 with increased odds of low cord TT4 and FT4, and no compounds were associated with increased odds of high TSH. For infants born by spontaneous, vaginal, unassisted deliveries, PCBs were associated with lower cord TT4 and FT4 and lower TT4 measured in neonatal blood spots. PBDEs showed consistent but mainly nonsignificant negative associations with TT4 and FT4 measurements.

CONCLUSIONS

Prenatal PCB and PBDE exposures were associated with reduced TT4 and FT4 levels among infants born by spontaneous, unassisted vaginal delivery. Intrapartum stress associated with delivery mode may mask hormonal effects of PCBs and PBDEs.

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.

The effect of type of delivery and povidone-iodine application at delivery on cord dried-blood-specimen thyrotropin level and the rate of hyperthyrotropinemia in mature and normal-birth-weight neonates residing in an iodine-replete area: report of Tehran Province, 1998-2005

OBJECTIVE

To evaluate the effects of delivery type and of povidone-iodine disinfection at delivery on cord dried-blood-specimen (DBS) thyrotropin (TSH) concentrations.

METHODS

From 1998 to 2005, cord DBSs were collected from live deliveries in Tehran and Damavand, and TSH was assayed by a two-site immunoradiometric assay. Hyperthyrotropinemia was defined as TSH > or =20 mU/L. Vaginal deliveries prepared with povidone-iodine (VGL-PVP-I) or chlorhexidine (VGL-CHL), and cesarean sections prepared with povidone-iodine (CS-PVP-I) disinfection were assessed. Full-term, normal-size newborns were included. Iodine concentrations were measured in urine samples collected from 132 pregnant women immediately prior to delivery.

RESULTS

Median (range) TSH was 5.3 (1.0 to >100) mU/L in VGL-PVP-I (n = 23,432), 5.3 (1.0 to >100) mU/L in VGL-CHL (n = 5658), and 5.0 (1.0 to >100) mU/L in CS-PVP-I (n = 19,016) (p < 0.0001). Median TSH was higher in VGL-PVP-I versus CS-PVP-I (p < 0.0001) and in VGL-CHL versus CS-PVP-I (p < 0.0001). Hyperthyrotropinemia was present in 1.4%, 1.2%, and 0.8% of VGL-PVP-I, VGL-CHL, and CS-PVP-I deliveries, respectively, and was significantly higher in VGL-PVP-I versus CS-PVP-I (p < 0.0001) and in VGL-CHL versus CS-PVP-I (p = 0.005). Median (range) urinary iodine concentration of pregnant women was 176 (20-4600) microg/L.

CONCLUSION

Cord DBS TSH and rates of hyperthyrotropinemia are lower in cesarean section than in vaginal deliveries. Povidone-iodine disinfection at delivery has an effect neither on DBS TSH concentrations nor on the rate of hyperthyrotropinemia in the iodine-replete area of Iran.

The effect of the mode of delivery on neonatal thyroid function

BACKGROUND

We aimed to investigate the effect of the mode of delivery and the type of anesthesia on postnatal thyroxine (T4), free T4 (f-T4) and thyroid-stimulating hormone (TSH) in a large number of healthy full-term neonates.

METHODS

Serum samples for T4, TSH and f-T4 were drawn from neonates at the time of discharge (postnatal days 1-7) in a pilot thyroid-screening program. Six hundred and thirty-eight neonates were grouped as: vaginal delivery (VD; 332), elective cesarean section (elective C/S; 252) and emergency cesarean section (emergency C/S; 54). The elective C/S group was subdivided into local and general anesthesia groups to investigate the influence of the type of anesthesia used on thyroid function.

RESULTS

Mean+/-SD serum T4, TSH and f-T4 levels tended to be higher in the VD group compared to the elective C/S group at almost all time points. However the differences did not reach statistical significance, except for the T4 levels at postnatal day 3 in the VD group, which was higher (195.6+/-37.3 nmol/L) compared to the elective C/S group (160.9+/-34.8 nmol/L) (p < 0.001). The only difference in the anesthesia groups was the slightly higher f-T4 levels from postnatal day 4 in the local anesthesia group compared to the general anesthesia group.

CONCLUSIONS

The mode of delivery or type of anesthesia does not have considerable influence on postnatal thyroid functions in the neonates, although minor differences exist. Therefore similar cut-off values can be used for thyroid screening of term newborns regardless of the mode of delivery or type of anesthesia used.

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.

Influences of perinatal factors on cord blood thyroid-stimulating hormone level

BACKGROUND

Cord blood thyroid-stimulating hormone level is affected by various perinatal factors. The aim of this study is to investigate the relative impact of these factors on the cord blood thyroid-stimulating hormone results in singleton pregnancies.

METHODS

The study group consisted of 20,086 consecutive singleton deliveries over a 3 year period. The effect of mode of delivery, infant sex, gestation at birth, birth weight, and duration of labor on the incidence of false elevation of cord blood thyroid-stimulating hormone was assessed by univariate analysis and logistic regression.

RESULTS

There was an independent positive association between false elevation of cord blood thyroid-stimulating hormone (> or =15.0 mIU/L) and birth weight (p=0.005), male infant sex (p<0.001), and instrumental delivery (p<0.001). Both elective and emergency cesarean section were negatively associated with elevated cord thyroid-stimulating hormone level (p<0.001). When the cutoff level was raised to 40.0 mIU/L, none of the variables examined were significant. The incidence of false positive tests (> or =15.0 mIU/L) was higher in neonates born by cesarean section for failed instrumental delivery and fetal distress than for failure to progress of labor (34.7% vs 4.5% vs 1.3% respectively, p<0.001).

CONCLUSIONS

While the incidence of false positive screening was significantly affected by various perinatal factors when the thyroid-stimulating hormone cutoff level is low, it was unaffected at a high cutoff level. The present study also provides further evidence that cord blood thyroid-stimulating hormone level reflects fetal response to perinatal stress events.

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.

Thyroid hormone levels in cord blood of infants with acidemia at birth

OBJECTIVE

To study the funic thyroid hormone levels in cases were fetal distress during labor resulted in acidemia at birth.

MATERIAL AND METHODS

Arterial and venous levels of TSH, total T4, free T4 and total T3 obtained from cord blood at birth of twelve acidemic fetuses were compared with normal controls.

RESULTS

Acidemic fetuses had a significanly higher TSH levels than controls (16.5+/-2. 1 microI/dl vs. 9.6+/-1.4 microI/dl, P=0.01). Total T3 levels were significantly lower in acidemic fetuses (49.2+/-2.9 ng/dl vs. 63+/-5. 5 ng/dl, P=0.04). Total and free T4 levels were similar and there was no difference between arterial and venous levels of the hormones.

CONCLUSIONS

Birth acidemia from fetal distress during labor is associated with higher TSH levels and lower T3 levels.