Evaluation of the therapeutic efficacy of different doses of LT4 in pregnant women with high-normal TSH levels and TPOAb positivity in the first half of pregnancy.

BACKGROUND: The objective was to investigate the efficacy of different doses of levothyroxine therapy among pregnant women exhibiting high-normal thyroid stimulating hormone levels and positive thyroid peroxidase antibodies throughout the first half of pregnancy. METHODS: Pregnant women exhibiting high-normal thyroid stimulating hormone levels and thyroid peroxidase antibodies positivity throughout the initial half of pregnancy were selected from January 2021 to September 2023. Based on the different doses of levothyroxine, the pregnant women were categorized into the nonintervention group (G0, 122 women), 25 µg levothyroxine intervention group (G25, 69 women), and 50 µg levothyroxine intervention group (G50, 58 women). Serum parameters, gastrointestinal symptoms, small intestinal bacterial overgrowth (SIBO), maternal and neonatal outcomes were compared after the intervention among the three groups. RESULTS: After the intervention, in the G25 and G50 groups, the thyroid stimulating hormone, triglyceride and low-density lipoprotein levels were notably less in contrast to those in the G0 group (P < 0.05). The rates of abdominal distension and SIBO in the G25 and G50 groups were notably lower in contrast to the G0 group (P = 0.043 and 0.040, respectively). The G50 group had a lower rate of spontaneous abortion and premature membrane rupture than the G0 group (P = 0.01 and 0.015, respectively). Before 11+ 2 weeks of gestation and at thyroid peroxidase antibodies levels ≥ 117 IU/mL, in contrast to the G0 group, the G50 group experienced a decreased rate of spontaneous abortion (P = 0.008). The G50 group had significantly higher newborn weight than the G0 group (P = 0.014), as well as a notably longer newborn length than the G0 and G25 groups (P = 0.005). CONCLUSIONS: For pregnant women with high-normal thyroid stimulating hormone levels and thyroid peroxidase antibodies positive during the first half of pregnancy, supplementation with 50 µg levothyroxine was more effective in improving their blood lipid status and gastrointestinal symptoms, reducing the incidence of SIBO and premature rupture of membranes, and before 11+2 weeks, TPOAb ≥ 117 IU/mL proved more beneficial in mitigating the risk of spontaneous abortion.

Association of pharmacogenomic, clinical and behavioural factors with oral levothyroxine (LT-4) dose of hypothyroid patients in Sri Lanka: a matched case control study.

BACKGROUND: Hypothyroidism is a common endocrine disorder that exerts a substantial influence on people all over the world. Levothyroxine (LT-4) is the drug of choice for the treatment of hypothyroidism and the starting oral dose is typically ranging from 1.5 to 1.7 µg/kg/day. The target is to achieve an optimum serum TSH level of 0.4-4.0 mIU/L; hence, the dose is titrated accordingly. Once the LT-4 dose is adjusted to obtain the target TSH level, it usually remains stable for a long period of time in most cases. However, some of the patients require frequent dose adjustments and some of them require unusually high doses. Therefore, the aim of this study is to determine the association of pharmacogenomic, clinical and behavioural factors with the oral levothyroxine (LT-4) dose requirement of hypothyroid patients in Sri Lanka. METHOD: This study will be conducted as a matched case-control study and will involve primary hypothyroid patients who visit the diabetes and endocrinology clinic at the National Hospital, Kandy, Sri Lanka. We will recruit a total of 292 cases and select 292 controls from the clinic who are matched in terms of age, sex and Body Mass Index (BMI). An interviewer-administered questionnaire will be used to collect data from the participants (n = 584). Of the 584 patients, blood samples will be collected from a sub-sample (n = 150) for DNA extraction. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) will be performed for single nucleotide polymorphisms (SNP) analysis. DISCUSSION: Frequent dose adjustments of levothyroxine cause a serious economic burden to the healthcare system. By identifying the root causes of the variations in LT-4 dosage, a more comprehensive comprehension of hypothyroidism and its management can be attained in Sri Lanka. Furthermore, upon identification of a positive association/correlation between genetic polymorphisms and the LT-4 dose, SNP profiles can be used as a possible genetic marker for dose adjustment determination in future patients.

Aversion of surgical exploration in patients with complex ovarian cysts secondary to overt hypothyroidism: A series of three cases.

Long-standing, overt hypothyroidism-induced bilateral multiloculated ovarian cysts represent an infrequent occurrence. Our first case, presented with bilateral complex ovarian masses, exhibited overt hypothyroidism symptoms, including lethargy, weight gain and subfertility, prompting consideration for surgical intervention. Similarly, in the second case, a girl aged 11 years with stunting, delayed bone age and academic challenges was referred for surgical exploration due to bilateral complex ovarian masses. Both cases revealed elevated thyroid-stimulating hormone levels during preoperative workup. Commencing levothyroxine replacement therapy resulted in complete regression of ovarian cysts and substantial symptom improvement within an 8-week timeframe. The third case, a previously diagnosed patient with Hashimoto's thyroiditis, benefited from the lessons gleaned in managing the initial cases, responding well to levothyroxine therapy, thereby averting the necessity for surgery in all three instances. These cases underscore the significance of considering thyroid function in the evaluation of ovarian masses and highlight the efficacy of levothyroxine replacement therapy in resolving both hypothyroidism and associated ovarian cysts, thereby obviating the need for surgical intervention.

Analysis of dose-TSH response effect of levothyroxine soft-gel formulation.

Background: Hypothyroidism is treated with daily levothyroxine (LT4). In recent years, soft gel caps of LT4 (LT4-C) have been commercialized, and their performance has been optimized. Since guidelines recommend dose LT4 according to the tablet preparation efficacy, the present study was undertaken to obtain data about the daily requirement, normalized per body weight, of LT4-C. Methods: Patients undergoing LT4-C after total thyroidectomy and radioiodine treatment for differentiated thyroid carcinoma were selected. There was no specific indication of suppression of TSH (i.e., <0.5 or <0.1 mIU/L). Patients were required to maintain a stable LT4 dose during the study period. Patients with interfering factors were excluded from this study. Results: Thirty patients were enrolled (18 females and 12 males; median age, 50 years; median body weight, 71 kg; median LT4-C dose, 1.71 µg/kg/day). The analysis of patient age did not reveal any differences. The LT4-C dose correlated with free-T4 p = 0.03), but not with TSH (p = 0.42) and free-T3 (p = 0.13). TSH was <1.0 mIU/L in 90% of the cases. The LT4-C dose-TSH response effect was analysed by probit regression model: the probability to achieve TSH <1.0 mIU/l was 99% with a dose of 1.84 (95%CI 1.57-2.12) µg/kg/day, 75% with a dose of 1.38 µg/kg/day (95%CI 1.17-1.59), and 50% with a dose of 1.20 (95%CI 0.96-1.43). At ROC curve analysis, the most accurate cut-off of LT4-C dose to achieve TSH <1.0 mIU/l was 1.53 ug/kg/day with 70% sensitivity and 100% specificity. Conclusions: Athyreotic patients can be initially treated with an LT4-C dose lower than previously stated. Therefore, further prospective studies are warranted.

Effect of acupuncture on Hashimoto thyroiditis: A systematic review and meta-analysis.

BACKGROUND: Hashimoto thyroiditis (HT) is a common autoimmune thyroid disease for which there is no specific treatment. Oral levothyroxine sodium tablets significantly improved thyroid function but did not promote a reduction in thyroid-related antibody concentrations. Acupuncture can improve clinical symptoms and thyroid function in HT patients, reduce serum TPOAb and TGAb levels in HT patients, and improve patients' quality of life. METHODS: We conducted a systematic review and meta-analysis to evaluate the effect of acupuncture versus levothyroxine sodium tablets on Hashimoto thyroiditis. We searched Web of Science, Embase, China National Knowledge Infrastructure, WanFang, VIP, SinoMed and the Cochrane Central Registry of Controlled Trials to identify candidate randomized controlled trials (RCTs). RESULTS: A total of 1020 patients participated in 14 randomized controlled trials. The results of meta-analysis showed that acupuncture regulated TPOAb content (mean difference [MD] = -63.18, 95%CI = -91.73 to -34.62, P < .00001), TGAb content (MD = -68.56, 95%CI = -101.55 to -35.57, P < .00001), serum free triiodothyronine (FT3) content (MD = 0.74, 95%CI = 0.20 to 1.27, P < .00001), serum free thyroxine (FT4) content (MD = 1.10, 95%CI = 0.29 to 1.92, P < .00001), TSH content (MD = -2.16, 95%CI = -3.14 to -1.19, P < .00001) had a significant effect. CONCLUSION: Compared with levothyroxine sodium tablets alone, acupuncture can significantly regulate the contents of TPOAb, TGAb, FT3, FT4 and TSH.

Use of thyroid hormones in hypothyroid and euthyroid patients: A survey of members of the Endocrine Society of Australia.

OBJECTIVE: Hypothyroidism is a common endocrine condition usually managed with levothyroxine (LT4). However, controversy remains around the use of liothyronine (LT3). We aimed to investigate the practices of Australian endocrinologists when managing patients with hypothyroidism, their use of LT3 + LT4 combination therapy and use of thyroid hormones in euthyroid patients. DESIGN AND PARTICIPANTS: Members of the Endocrine Society of Australia (ESA) were invited to participate in an online questionnaire. MEASUREMENTS: We analysed questionnaires that had complete demographic data. RESULTS: Eighty-seven questionnaires fulfilled the criteria. LT4 was used as first line treatment for hypothyroidism by all respondents. Only 45% reported that their patients were dispensed the brand of LT4 that they recommend. LT3 (alone or in combination) was prescribed by 44% in their clinical practice. Although 49% of respondents would consider LT3 + LT4 in patients with normal TSH who had ongoing symptoms of hypothyroidism, the inability of LT4 to restore normal physiology was ranked the least likely explanation for persistent symptoms and only 32% would consider it for themselves if they were diagnosed with hypothyroidism. The majority (55%), in accordance with evidence, would not prescribe thyroid hormone to euthyroid individuals but 39% would consider use in euthyroid female infertility with high levels of thyroid antibodies and 11% in euthyroid patients with a simple goitre growing over time. LT4 use in pregnancy was variable among members. CONCLUSIONS: Australian endocrinologists mostly follow international guidelines when prescribing thyroid hormone therapy and many prescribe combination LT3 and LT4 therapy, particularly for patients who remain symptomatic on LT4 monotherapy. Prescribing practices are largely similar to other countries who have completed similar questionnaires.

Thyroid hormone may predict treatment failure in Kawasaki disease.

BACKGROUND: In systemic inflammatory conditions, inflammatory cytokines can cause low thyroid hormone levels. There are no reports discussing the relation between thyroid hormone levels and response to treatment for Kawasaki disease. METHODS: We investigated 67 patients who underwent treatment in the acute phase of Kawasaki disease. We divided patients into two groups based on their response to initial intravenous immunoglobulin (IVIG) treatment: the responder group (n = 40), and the non-responder group (n = 27). The serum levels of the thyroid hormones free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were compared before and after treatment in all patients, and between responder and non-responder groups. RESULTS: The FT3, FT4, and TSH levels were low before the initial treatment and increased significantly after treatment (p < 0.05). The FT3, FT4, and TSH levels before treatment were significantly lower in the non-responder group than in the responder group (p < 0.05). Logistic regression analysis suggested that the addition of pre-treatment FT4 values to Gunma score was useful in predicting treatment failure. CONCLUSIONS: Thyroid hormone and TSH levels were lower in the non-responder group than in the responder group in the initial IVIG treatment for Kawasaki disease. This study suggests that Kawasaki disease in the acute phase is associated with low thyroid hormone levels and TSH. It is possible that these hormone levels predict response to the initial IVIG.

Heart rate in newborns is associated with age, sex and maternal levothyroxine therapy.

AIM: To evaluate the definition and causes of neonatal bradycardias. METHODS: This retrospective study included 135 term-born newborns referred for 24-hour Holter monitoring due to bradycardia. Bradycardia was defined as either a heart rate below 80 beats per minute (standard definition) or a heart rate below our recently published age-specific reference values for neonatal heart rate. RESULTS: The mean (SD) age was 6.1 (1.3) days. With standard definition, 107 newborns (79%) had bradycardia, whereas only 20 (15%) had a minimum heart rate lower than the age-specific reference. Younger newborns had lower heart rates. Each day increased the minimum, mean and maximum heart rate by 1.8 (95% CI: 1.0, 2.6), 4.2 (95% CI: 3.0, 5.3) and 2.1 beats per minute (95% CI: 0.3, 3.8), respectively. Male sex and maternal levothyroxine medication were negatively associated with the mean and maximum heart rate. None of the newborns had a cardiac cause for low heart rate. CONCLUSION: Among term newborns with bradycardias, younger age, male sex and maternal levothyroxine medication were associated with a lower heart rate on Holter monitoring. Given the age-related increase in heart rate, the 80 beats per minute limit as a universal threshold for abnormal heart rate in newborns appears inappropriate.

A Role for Thyroid Testing in Slipped Capital Femoral Epiphysis? 32% Rate of Abnormal Values in Tested Patients.

BACKGROUND: Hypothyroidism is a known risk factor for slipped capital femoral epiphysis (SCFE), and prior studies of hypothyroid-associated SCFE have demonstrated an incidence of up to 6%. However, there is limited evidence and no formal practice guidelines regarding whether patients presenting with SCFE should undergo screening for endocrine disorders. This study aims to investigate the incidence of abnormal thyroid function studies in patients presenting with SCFE. METHODS: This was a retrospective review of all patients aged 0 to 18 years treated for SCFE at a single pediatric hospital from January 2015 to July 2022. On presentation, patients' BMI, thyroid-stimulating hormone (TSH), free T4, vitamin D, creatinine, BUN, and HbA1c levels were documented. Follow-up and treatment for any identified endocrinopathies were noted. In addition, the chronicity, stability, and severity of their slips were recorded. RESULTS: Ninety-eight patients with 106 hips were included in this study. TSH was obtained at the time of initial presentation in 66% (n=65/98) of patients. Median TSH was 2.99 (range: 0.02 to 919, std dev: 132.4). The normal reference range for our institution is 0.5 to 4.5 mcIU/mL. Thirty-two percent (n=21/65) of patients with a documented TSH had an abnormal value. Of those patients who had an elevated TSH, 3 were diagnosed with clinical hypothyroidism and went on to treatment with levothyroxine (n=3/19, 16%), 2 patients had been started on levothyroxine before presentation (n=2/19, 11%), and 2 patients were followed in endocrinology clinic until their TSH levels had normalized without further intervention (n=2/19, 11%). CONCLUSIONS: Screening of our SCFE population revealed a 32% incidence of thyroid abnormalities which affected treatment in 24% of those patients. This is a much higher incidence of hypothyroid-associated SCFE than previously demonstrated in the literature and has prompted us to start including thyroid screening studies as a routine part of our workup for all patients with SCFE. LEVEL OF EVIDENCE: Level III.

Hashimoto's Thyroiditis Negatively Influences Intracytoplasmic Sperm Injection Outcome in Euthyroid Women on T4 Substitution Therapy: A Retrospective Study.

OBJECTIVE: The objective of this study was to analyze the impact of thyroid autoimmunity (TAI) on reproductive outcome parameters of intracytoplasmic sperm injection (ICSI) cycles as compared to TAI-negative ICSI cycles. DESIGN: In this single in vitro fertilization (IVF) center retrospective study, 86 infertile women with elevated thyroid peroxidase or TGAb levels, but euthyroid after thyroxine replacement (study group), were compared to 69 female patients with no thyroid abnormalities (controls). Following ICSI treatment fertilization rate (FR), clinical pregnancy rate (CPR), miscarriage rate (MR), and live birth rate (LBR) were analyzed. MATERIALS, SETTING, METHODS: All subjects with various infertility factors were treated with ICSI in university-based IVF center. Patients in the study group received thyroxine replacement and were euthyroid at IVF treatment. Before the IVF cycles, endocrinological parameters were uniformly assessed: thyroid function and antibodies, reproductive hormones (anti-Müllerian hormone [AMH], follicular stimulating hormone [FSH], luteinizing hormone, E2, PRL, testosterone, DHEAS, 17-OHP, AD) and OGTT (0-60-120 min glucose and insulin). Following descriptive comparison of laboratory parameters, age-adjusted analyses of FR, CPR, MR, and LBR were performed. RESULTS: TAI-positive women were older (mean age 35.31 ± 4.95 vs. 32.15 ± 4.87 years; p = 0.002), had higher FSH (8.4 ± 3.4 vs. 7.4 ± 2.32 U/L; p = 0.024), higher E2 (53.94 ± 47.61 vs. 42.93 ± 18.92 pg/mL; p = 0.025) levels, while AMH (2.88 ± 2.62 vs. 3.61 ± 1.69 ng/mL; p = 0.0002) was lower. There were no differences in TSH levels (1.64 ± 0.96 vs. 1.66 ± 0.65 µIU/mL; p = 0.652) between the two groups. FT3 (2.63 ± 0.58 vs. 2.98 ± 0.55 pg/mL; p = 0.002) was lower and FT4 (1.3 ± 0.29 vs. 1.13 ± 0.21 ng/dL; p = 0.0002) was higher in the TAI-positive group, reflecting clinically irrelevant differences. Egg cell counts (6 ± 3.8 vs. 7.5 ± 3.95; p = 0.015) were lower in TAI and remained so following age adjustment. Although the overall ICSI FR did not differ (62.9% vs. 69.1%, p = 0.12), it was lower for patients under 35 with TAI showing decreasing differences in line with age. The CPR (36.04% vs. 69.56%; p < 0.001) and LBR (23.25% vs. 60.86%; p < 0.001) were lower, the MR (35.48% vs. 12.5%; p = 0.024) was higher in the TAI group, and these differences remained after age adjustment. LIMITATIONS: Since the higher age of the study group may interfere with the effect of TAI, age adjustment calculations were necessary to perform to eliminate this confounding factor. CONCLUSION: Despite optimal thyroid supplementation in clinical or subclinical hypothyroidism, the presence of TAI negatively influences CPR and is connected to a higher MR, thus resulting in a lower LBR after ICSI. Decreased FR with ICSI in TAI patients may also contribute to poorer outcomes, especially in younger women.

Assessment of the likelihood of hypothyroidism in dogs diagnosed with and treated for hypothyroidism at primary care practices: 102 cases (2016-2021).

BACKGROUND: There is a possibility that an incorrect diagnosis of hypothyroidism could be made in euthyroid dogs, and the prevalence of hypothyroidism in the dog population remains unknown. OBJECTIVES: To retrospectively assess the percentage of dogs diagnosed with, and treated for, hypothyroidism at first opinion practice which are likely to be hypothyroid and require levothyroxine supplementation. ANIMALS: One hundred two client-owned dogs were included in this study. MATERIALS AND METHODS: The computerized databases of 7 first opinion practices were searched to identify dogs treated with levothyroxine supplementation. Three European College of Veterinary Internal Medicine-Companian Animals (ECVIM-CA) diplomates independently assigned 1 of 4 clinical assessments to each case as follows: confirmed or likely hypothyroid, hypothyroidism suspected but not confirmed, hypothyroidism considered unlikely, and no reason to suspect hypothyroidism. They commented as to whether or not they thought levothyroxine supplementation was appropriate. RESULTS: The clinical assessments of "confirmed or likely hypothyroid"; "Hypothyroidism suspected but not confirmed"; "Hypothyroidism considered unlikely"; and "No reason to suspect hypothyroidism" was assigned respectively by Clinician 1 to 38.2%, 5.9%, 3.9%, and 52% of cases, by Clinician 2 to 48%, 22.6%, 22.6%, 6.9% of cases, and by Clinician 3 to 55.9%, 11.8%, 13.7% and 18.6%. Clinician 1, Clinician 2, and Clinician 3 considered levothyroxine supplementation not indicated in 58.8%, 52.9%, and 45.1% of cases, respectively. CONCLUSION: These results support the concern that hypothyroidism might be overly and incorrectly diagnosed in first opinion practice, and that thyroid function testing should be performed only in those dogs with a high pretest probability of the disease.

Severe hypothyroidism as a trigger for Brugada-type ECG abnormalities: a case report and literature review.

Brugada syndrome (BrS) is an inherited disorder that can cause ventricular fibrillation and sudden cardiac death in individuals with otherwise structurally normal hearts. Several provoking factors are known to potentially unmask or exacerbate a typical Brugada ECG pattern in predisposed subjects. Hypothyroidism has been suggested as one of these triggers, but the exact mechanisms underlying this relationship remain poorly understood. Moreover, the severity of thyroid dysfunction beyond which a Brugada-type ECG alteration might be triggered is still unclear. We report the case of a 33-year-old male who displayed a Brugada type 1 ECG pattern and was diagnosed with severe hypothyroidism (TSH > 100 mU/L with undetectable levels of fT4 and fT3). Hormonal replacement therapy with levothyroxine was initiated at increasing doses; serial biochemical and ECG controls were performed, initially every 3 weeks up to 15 weeks and afterward every 3 months. The regression of typical Brugada ECG waveforms could be seen at an early stage, when the patient was still taking a low dose of levothyroxine (37.5 µg/day, i.e., one-fourth of his final requirements of 150 µg/day), and laboratory tests still showed a marked alteration of thyroid hormonal parameters. Hypothyroidism may act as a trigger for Brugada-type ECG abnormalities, but a very severe alteration of the hormonal parameters is necessary to prompt these alterations. In our case, the initiation of replacement therapy with levothyroxine rapidly reversed the ECG modifications, even at a low subtherapeutic dose.

Differentiation and Treatment of Hypothyroidism, Functional Hypothyroidism, and Functional Metabolism.

Less than optimal thyroid effects can occur for many reasons, including lack of production, excessive binding, reduced conversion to the active form of thyroid, poor intracellular transport, poor receptor response, or autoimmune and toxicity issues. Differentiation of where the problem or problems causing the symptoms of hypothyroidism to occur is a key to the return to optimal thyroid response and successful treatment outcome. The concept of hypothyroidism, functional hypothyroidism, and functional hypometabolism as an alternative method to describe classical subclinical hypothyroidism symptoms according to the source of the malfunction are discussed in this article. The author also presents a unique method of using standard thyroid measurements to determine the areas of dysfunction and discusses the possible reasons for low production, excessive binding, poor conversion, and suboptimal receptor response. Appropriate treatment options for each area are discussed, including nutritional requirements. Thyroid replacement therapy options are presented and individualization of therapy based on need established with use of the thyroid gradient levels is discussed. Individualization of thyroid therapy will often require the use of compounded T3 or T4/T3 combination therapy. Compounding thyroid replacement allows for avoiding fillers that can interfere with absorption, unwanted diluents, unknown or nonstandardized ingredients from animal sources, providing more sustained action with less side effects, and individualizing the ratio of T4 and T3 initially, and as improvements are made in the patient's ability to convert T4 to T3.

Effects of Levothyroxine Treatment on Fertility and Pregnancy Outcomes in Subclinical Hypothyroidism: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Background: Subclinical hypothyroidism, defined by elevated thyrotropin (TSH) and normal free thyroxine levels, is associated with adverse pregnancy outcomes, including preterm birth, pre-eclampsia, and small for gestational age. Despite the uncertainty regarding the effectiveness of levothyroxine (LT4) treatment on pregnancy outcomes in subclinical hypothyroidism, LT4 is widely administered with a pre-treatment threshold TSH level of 2.5 mU/L. The aim of this study is to investigate the efficacy of periconceptional LT4 treatment for subclinical hypothyroidism, including TSH levels >2.5 mU/L, and identify the characteristics of subclinical hypothyroidism that can benefit from LT4 treatment. Methods: We conducted a systematic review and meta-analysis of randomized controlled trials from inception to February 2023. We analyzed the pooled effects of LT4 on subclinical hypothyroidism before and during pregnancy. The main outcomes before pregnancy were live birth, pregnancy, and miscarriage. The main outcomes during pregnancy were live birth, miscarriage, and preterm birth. We conducted subgroup analyses to compare the effects of LT4 on subclinical hypothyroidism with TSH levels of 2.5-4.0 and >4.0 mU/L. Results: Of the 888 studies identified, 27 full-text articles were screened for eligibility. Five studies on pre-conception treatment with 768 participants and eight studies on treatment during early pregnancy with 2622 participants were analyzed. One of the two studies on pre-conception treatment in subclinical hypothyroidism with TSH >4.0 mU/L had high risk of bias and the other was composed of 64 participants. Pre-conception LT4 treatment had no significant effect in improving rates of live births and pregnancies, or reducing miscarriages (risk ratio [RR], 95% confidence interval): 1.41 (0.84-2.36), 1.73 (0.88-3.39), and 0.46 (0.11-2.00), respectively. LT4 treatment during pregnancy was not significantly associated with higher rates of live births (RR 1.03, 0.98-1.09) nor decreased miscarriage rates (RR 1.01, 0.66-1.53). The effect of LT4 treatment on preterm birth during pregnancy was significantly different depending on the TSH values (p = 0.04); a positive effect was shown in the subclinical hypothyroidism subgroup with TSH >4.0 mU/L (RR 0.47, 0.20-1.10), while no significant effect was observed in the subgroup with TSH 2.5-4.0 mU/L (RR 1.35, 0.79-2.31). Conclusions: Pre-conceptional LT4 treatment for subclinical hypothyroidism does not improve fertility or decrease the incidence of miscarriages. However, further well-designed studies are needed for pre-conceptional treatment, especially in TSH >4.0 mU/L. LT4 treatment during pregnancy had a positive effect on preterm birth; nevertheless, this was only applicable to subclinical hypothyroidism with TSH >4.0 mU/L.