Isolated maternal hypothyroxinemia and adverse pregnancy outcomes: A systematic review

Isolated Maternal Hypothyroxinemia May be Associated with Insulin Requirement in Gestational Diabetes Mellitus

An insulin regimen may be necessary for about 30% of the patients with gestational diabetes mellitus (GDM). We aimed to investigate the association of free T4(fT4) levels with insulin requirement in pregnant women with GDM. We included pregnant women whose TSH levels were within the normal range and who were diagnosed with GDM, and excluded patients with thyroid dysfunction, chronic illnesses, or any previous history of antithyroid medication, levothyroxine, or antidiabetic medication use. The diagnosis and treatment of GDM were based on American Diabetes Association guidelines. Demographic features, previous history of GDM and gestational hypertension were recorded. Baseline (at diagnosis of GDM) fasting blood glucose, HbA1c, TSH, fT4, and fT3 levels were analyzed. We grouped the patients according to their baseline fT4 levels: isolated maternal hypothyroxinemia (IMH) (group A) vs. in the normal range (group B). We grouped those also based on insulin requirement in 3rd trimester. Of the patients (n=223), insulin requirement was present in 56, and IMH in 11. Insulin requirement was more frequent in group A than in group B (p=0,003). HbA1c (≥47,5 mmol/mol) and fT4 level (lower than normal range) were positive predictors for insulin requirement (OR:35,35, p=0,001; and OR:6,05, p=0,008; respectively). We showed that IMH was closely associated with insulin requirement in GDM. Pregnant women with IMH and GDM should be closely observed as regards to glycemic control. If supported by future large studies, levothyroxine treatment might be questioned as an indication for patients with GDM and IMH.

Association of Isolated Hypothyroxinemia and Subclinical Hypothyroidism With Birthweight: A Cohort Study in Japan

Context

Isolated hypothyroxinemia (low maternal free thyroxine [FT4] in the absence of thyroid-stimulating hormone [TSH] elevation) and subclinical hypothyroidism (high TSH in the absence of FT4 elevation) during early pregnancy are common. However, there are limited data regarding pregnancy outcomes, particularly their association with birthweight.

Objective

We assessed the association between isolated hypothyroxinemia and subclinical hypothyroidism during the first trimester and birthweight.

Methods

Analyses were conducted using a database of pregnant women (n = 1105; median age, 35 years) who delivered at the National Center for Child Health and Development, a tertiary hospital in Tokyo. The primary outcomes included the rates of small for gestational age (SGA), large for gestational age (LGA), and low birth weight.

Results

Of the 1105 pregnant women, 981 were classified into the euthyroidism group, 25 into the isolated hypothyroxinemia group, and 26 into the subclinical hypothyroidism group during the first trimester. The prevalence of SGA was significantly higher in isolated hypothyroxinemia and subclinical hypothyroidism groups than the euthyroidism group (28.0% and 19.2%, respectively, vs 5.7%; P < .01). The odds ratio with 95% CI for SGA was 12.51 (4.41-35.53) for isolated hypothyroxinemia and 4.44 (1.57-12.56) for subclinical hypothyroidism in a multivariable adjustment model. Isolated hypothyroxinemia and subclinical hypothyroidism were not significantly associated with LGA and low birth weight.

Conclusion

Pregnant women with isolated hypothyroxinemia and subclinical hypothyroidism in the first trimester have an increased likelihood of SGA. Screening and careful perinatal checkups for isolated hypothyroxinemia and subclinical hypothyroidism may help identify pregnant women at high risk for SGA.

Iodine Intake Based on a Survey from a Cohort of Women at Their Third Trimester of Pregnancy from the Bosque County Chile

Adequate iodine nutrition is fundamental for all humans and is critical during pregnancy and lactation due to iodine forms part of the structure of thyroid hormones (THs) and it is required for THs function. Iodine is a scarce micronutrient that must be obtained from the diet. Sufficient iodine can be found in the nature from seafood and given it is not frequently consumed by Chileans, public health policies state that table salt in Chile must be iodized. Health plans must be monitored to determine if the intake of iodine is being appropriated and the population has not fallen in deficiency or excess. The aim of this work was to evaluate iodine intake in 26 women at the third trimester of pregnancy. Pregnant women are resident from El Bosque a low-income County located in Santiago de Chile. These Chilean pregnant women were recruited by nutritionist at the Centros de Salud familiar (CESFAM). A 24 h dietary recall (24 h-DR) was applied to them to evaluate iodine intake. Samples of urine and blood were taken by health professionals to analyze parameters of thyroid function and to measure urine iodine concentration (UIC). The survey analysis showed that the iodine consumption in these pregnant women derived mainly from salt, bread and milk and not from seafood. The survey analysis indicated that iodine intake was above the requirements for pregnant women. However, the average UIC indicated that iodine intake was adequate, suggesting the need to find a better parameter to determine iodine intake in pregnant women.

Obstetric and offspring outcomes in isolated maternal hypothyroxinaemia: a systematic review and meta-analysis

OBJECTIVE

To examine the association between isolated maternal hypothyroxinaemia (IMH) and adverse obstetric outcomes and offspring outcomes and also investigate the effects of levothyroxine therapy on IMH for the above outcomes.

METHODS

We systematically searched PubMed, EMBASE, and Cochrane Library, and the reference lists of key reviews were hand searched on June 9, 2021. Two authors independently screened titles/abstracts. Full articles were further assessed if the information suggested that the study met the inclusion/exclusion criteria, and two researchers performed data extraction and risk-of-bias assessment using standardized tables. Summary relative risks or the mean difference between maternal effects and offspring outcomes were calculated by a random-effects model.

RESULTS

We identified 38 eligible articles (35 cohort studies and two randomized controlled trials [RCT]). Meta-analysis showed that maternal IMH was associated with increased gestational diabetes mellitus, preterm premature rupture of membranes, preterm birth, fetal distress, and macrosomia outcomes in IMH compared to euthyroid women, and the relative risks were 1.42 (1.03-1.96), 1.50 (1.05-2.14), 1.33 (1.15-1.55), 1.75 (1.16-2.65) and 1.62 (1.35-1.94), respectively. IMH was not associated with placenta previa, gestational hypertension, pre-eclampsia, intrauterine growth restriction, and offspring outcomes like birth weight, low birth weight infants, fetal macrosomia, neonatal intensive care, neonatal death, or fetal head circumference. In addition, we did not find an association between IMH and adverse offspring cognitive defects. Due to insufficient data for meta-analysis, it failed to pool the evidence of levothyroxine's therapeutic effect on IMH and their offspring.

CONCLUSIONS AND RELEVANCE

IMH in pregnancy may relate to a few maternal and offspring outcomes. Moreover, there is currently no sufficient evidence that levothyroxine treatment during pregnancy reduces adverse maternal outcomes and disability in offspring. Further investigation to explore the beneficial effects of levothyroxine therapy is warranted.

Preconception Counseling and Care for Pregnant Women with Thyroid Disease

Thyroid disease is associated with adverse maternal and fetal outcomes. Appropriate reference ranges should be used for the interpretation of test results, although universal screening for thyroid dysfunction is not warranted. Overt thyroid dysfunction requires careful consideration of medication adjustments and close monitoring. Mild thyroid hypofunction has been linked to adverse pregnancy outcomes including preterm delivery, and poor neurocognition in the offspring. This review summarizes the most recent evidence on the counseling and management of women with thyroid disease before and during pregnancy and highlights the areas of controversy in need of further research.

Assessment and treatment of thyroid disorders in pregnancy and the postpartum period

Thyroid disorders are prevalent in pregnant women. Furthermore, thyroid hormone has a critical role in fetal development and thyroid dysfunction can adversely affect obstetric outcomes. Thus, the appropriate management of hyperthyroidism, most commonly caused by Graves disease, and hypothyroidism, which in iodine sufficient regions is most commonly caused by Hashimoto thyroiditis, in pregnancy is important for the health of both pregnant women and their offspring. Gestational transient thyrotoxicosis can also occur during pregnancy and should be differentiated from Graves disease. Effects of thyroid autoimmunity and subclinical hypothyroidism in pregnancy remain controversial. Iodine deficiency is the leading cause of hypothyroidism worldwide. Despite global efforts to eradicate iodine deficiency disorders, pregnant women remain at risk of iodine deficiency due to increased iodine requirements during gestation. The incidence of thyroid cancer is increasing worldwide, including in young adults. As such, the diagnosis of thyroid nodules or thyroid cancer during pregnancy is becoming more frequent. The evaluation and management of thyroid nodules and thyroid cancer in pregnancy pose a particular challenge. Postpartum thyroiditis can occur up to 1 year after delivery and must be differentiated from other forms of thyroid dysfunction, as treatment differs. This Review provides current evidence and recommendations for the evaluation and management of thyroid disorders in pregnancy and in the postpartum period.

The Consumption of Food-Based Iodine in the Immediate Pre-Pregnancy Period in Madrid Is Insufficient. San Carlos and Pregnancy Cohort Study

A pre-gestational thyroid reserve of iodine is crucial to guarantee the increased demand for thyroid hormone production of early pregnancy. An iodine intake ≥150 µg/day is currently recommended. The objective of this study was to assess average pre-gestational food-based iodine consumption in pregnant women at their first prenatal visit (<12 gestational weeks), and its association with adverse materno-fetal events (history of miscarriages, early fetal losses, Gestational Diabetes, prematurity, caesarean sections, and new-borns large/small for gestational age). Between 2015–2017, 2523 normoglycemic women out of 3026 eligible had data in the modified Diabetes Nutrition and Complication Trial (DNCT) questionnaire permitting assessment of pre-gestational food-based iodine consumption, and were included in this study. Daily food-based iodine intake was 123 ± 48 µg, with 1922 (76.1%) not reaching 150 µg/day. Attaining this amount was associated with consuming 8 weekly servings of vegetables (3.84; 3.16–4.65), 1 of shellfish (8.72; 6.96–10.93) and/or 2 daily dairy products (6.43; 5.27–7.86). Women who reached a pre-gestational intake ≥150 µg had lower rates of hypothyroxinemia (104 (17.3%)/384 (21.4%); p = 0.026), a lower miscarriage rate, and a decrease in the composite of materno-fetal adverse events (0.81; 0.67–0.98). Reaching the recommended iodine pre-pregnancy intake with foods could benefit the progression of pregnancy.

Potential Risk Factors for Isolated Hypothyroxinemia in Women of Childbearing Age-Results from Retrospective Analysis

Isolated hypothyroxinemia (IH) unfavorably affects reproduction. This study aimed to evaluate retrospectively if any routinely measured clinical/laboratory parameters are associated with IH among women of childbearing age hospitalized in the endocrine department. A group of 466 female non-pregnant inpatients (age range 13-57 years) was considered. IH (decreased free thyroxine (FT4) with normal TSH) was found in 8/466 patients (1.72%). Vitamin D deficiency (<30 ng/mL) was found in all patients with IH, whereas severe Vitamin D deficiency (<20 ng/mL) was found in 5/6. Vitamin D concentration was lower in IH females. FT4 concentration was lower in patients with severe vitamin D deficiency and correlated positively with vitamin D concentration. Insulin resistance index (IRI) was increased (>1.25) in 5/6 patients with IH. IRI was higher in IH patients and it was the only independent linear factor for IH in the univariate regression. FT4 concentration was lower in patients with increased IRI and correlated negatively with IRI. FT4 concentration correlated negatively with body mass index (BMI) and LDL cholesterol or triglycerides, and positively with HDL cholesterol or HDLC/cholesterol ratio. Vitamin D deficiency, insulin resistance and increased BMI (as potential causative factors), and abnormal lipid profile (as a possible consequence), are associated with IH in women of childbearing age. Eliminating risk factors for hypothyroxinemia may improve reproductive health.

Thyroid Gene Mutations in Pregnant and Breastfeeding Women Diagnosed With Transient Congenital Hypothyroidism: Implications for the Offspring's Health

Fetus and infants require appropriate thyroid hormone levels and iodine during pregnancy and lactation. Nature endorses the mother to supply thyroid hormones to the fetus and iodine to the lactating infant. Genetic variations on thyroid proteins that cause dyshormonogenic congenital hypothyroidism could in pregnant and breastfeeding women impair the delivery of thyroid hormones and iodine to the offspring. The review discusses maternal genetic variations in thyroid proteins that, in the context of pregnancy and/or breastfeeding, could trigger thyroid hormone deficiency or iodide transport defect that will affect the proper development of the offspring.

Effects of isolated maternal hypothyroxinemia on adverse pregnancy outcomes

PURPOSE

There are conflicting results about the effects of maternal hypothyroidism (IMH) on adverse pregnancy outcomes. This study aimed to investigate the relationship between IMH identified in the first trimester of gestation and adverse pregnancy outcomes.

METHODS

In this prospective cohort study, we used data from the Tehran Thyroid and Pregnancy study (TTPs). To diagnose IMH, we considered a threshold of 2.04 for FTI, which was based on the 10th percentile of this marker identified in the 1st trimesters. A generalized linear regression (GLM) model adjusted for the gravidity, urine iodine, and TPOAb status was applied to assess the effects of IMH on adverse pregnancy outcomes, compared to the controls group.

RESULTS

Penalized logistic regression analysis indicated that the adjusted odds ratio (aOR) of Preterm premature rupture of the membranes (PPROM) in women with IMH was 5.43-folder higher than euthyroid group [aOR 5.43, 95% CI (1.40, 21.1), p = 0.01]. Besides, the adjusted odds ratio of low birth weight (LBW) in the IMH group was 2.53-folder higher than the healthy group [aOR 2.53, 95% CI (1.01, 6.33), p = 0.047]. Furthermore, the results of the GLM adjusted model revealed that the mean of neonatal head circumference and weight in the IMH group was around 0.43 cm (95% CI - 0.80, - 0.07, p = 0.02) and 145.4 g (95% CI - 242.6, - 48.1, p = 0.003) lower than euthyroid group, respectively.

CONCLUSIONS

This study demonstrated that women with IMH identified in early pregnancy have a higher odds ratio for developing some adverse pregnancy outcomes, including PPROM and LBW compared to their euthyroid counterparts. Also, the neonatal head circumference and weight in the IMH group were lower than in the euthyroid group.

Associations of Hypothyroxinemia With Risk of Preeclampsia-Eclampsia and Gestational Hypertension

OBJECTIVE

To investigate the association between hypothyroxinemia and the risk of preeclampsia-eclampsia and gestational hypertension.

DESIGN

Historical cohort study.

METHODS

The study included pregnant individuals who delivered live-born singletons and had at least one thyroid function assessment during pregnancy at a tertiary hospital. Hypothyroxinemia was defined as thyroid-stimulating hormone (TSH) levels within the normal reference range and free thyroxine (FT4) levels lower than the tenth percentile. Risk ratios (RRs) with 95% confidence intervals (95% CIs) for preeclampsia-eclampsia and gestational hypertension between women with and without a diagnosis of hypothyroxinemia during pregnancy were estimated using a generalized estimating equation model.

RESULTS

A total of 59,463 women with live-born singletons were included in the analysis. Logistic regression models with restricted cubic spline suggested that there was a U-shaped association between FT4 levels and preeclampsia-eclampsia risk. Compared with euthyroid women, those with hypothyroxinemia had an increased risk of preeclampsia-eclampsia (RR = 1.16, 95% CI: 1.02-1.31), and the risk increased with the increasing severity of hypothyroxinemia (p for trend < 0.001). Moreover, persistent hypothyroxinemia from the first to second trimesters was associated with an increased risk of preeclampsia-eclampsia (RR = 1.37, 95% CI: 1.03-1.83), especially for women with severe hypothyroxinemia (RR = 1.70, 95% CI: 1.12-2.58). In contrast, there was no association between hypothyroxinemia and gestational hypertension.

CONCLUSION

Our study suggested that hypothyroxinemia was only associated with an increased risk of preeclampsia-eclampsia, especially in women with persistent hypothyroxinemia in the first half of pregnancy. Analyses of the associated risk of gestational hypertension with hypothyroxinemia were not significant.