The role of levothyroxine in obstetric practice

Early Levothyroxine Treatment for Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy: The St Carlos Gestational and Thyroid Protocol

The optimal maternal levels of thyroid hormones (TH) during the first trimester of gestation have not been established, nor has the ideal moment to initiate levothyroxine treatment (LT) to improve the evolution of gestation and fetal development. Cut-off points for Thyroid-stimulating hormone (TSH) <2.5 µIU/mL and free thyroxine (FT4)>7.5 pg/mL have been recommended. There are no data on whether initiation of LT <9th Gestational Week (GW) can have a favourable impact.

OBJECTIVE

To define the TSH/FT4 percentiles corresponding with 2.5 µIU/mL and 7.5 pg/mL levels, respectively, at GW8 (Study 1), and evaluate the effects of protocol-based LT before GW9 on gestation evolution, in women with TSH ≥2.5 µIU/mL and/or FT4≤ 7.5 pg/mL (study 2).

SUBJECTS

2768 consecutive pregnant women attending the first gestational visit from 2013-2014 and 3026 from 2015-2016 were eligible for Study I and 2 respectively. A final 2043 (study 1) and 2069 (study 2) women were assessed in these studies.

RESULTS

Study 1: The FT4 level of 7.5 pg/mL corresponds with the 17.9th percentile, a TSH level of 2.5 µIU/mL with the 75.8^th. Women with TSH ≥2.5 µIU/mL had a history of fetal losses more frequently than those <2.5 (OR 2.33 (95%CI): 1.58-3.12), as did those with FT4 ≤7.5 pg/ml compared to those >7.5 (OR 4.81; 3.25-8.89). Study 2: A total of 1259 women had optimal TSH/FT4 levels (Group 1), 672 (32.4%, Group 2) had suboptimal TSH or T4l, and 138 (6.7%, Group 3) had suboptimal values of both. 393 (58.5%) in Group 2 and 88 (63.8%) in Group 3 started LT before GW9. Mean (SD) GW24 levels were TSH: 1.96 ± 1.22 µIU/mL and FT4: 7.07 ± 1.25 pg/mL. The highest FT4 value was 12.84 pg/mL. The adjusted risk for an adverse event if LT was started early was 0.71 (0.43-0.91) for Group 2 and 0.80 (0.66-0.94) for Group 3.

CONCLUSIONS

Early LT in women with suboptimum levels of TSH/FT4 (≥2.5µIU/mL/≤7.5 pg/ml) at or before GW9 is safe and improves gestation progression. These data support the recommendation to adopt these cut-off points for LT initiation, which should be started as early as possible.

A Meta-Analysis of Pregnancy Outcomes With Levothyroxine Treatment in Euthyroid Women With Thyroid Autoimmunity

CONTEXT

Thyroid autoimmunity (TAI), the most common cause of (sub)clinical hypothyroidism, is associated with adverse pregnancy outcomes. The benefits of levothyroxine (LT4) intervention in women with TAI remain controversial.

OBJECTIVE

The purpose of this analysis is to determine the effect of LT4 on pregnancy outcomes in euthyroid women with TAI.

DATA SOURCES

Databases were searched up to May 2019.

STUDY SELECTION

Randomized controlled trails (RCTs) and retrospective studies that reported effects of LT4 administration on pregnancy outcomes in euthyroid women with TAI were screened.

DATA EXTRACTION

Quality assessment and data extraction were conducted independently by 2 researchers. Conflicts were settled by a third researcher.

DATA SYNTHESIS

Six trials comprising 2249 women were included. Overall, no beneficial effect on pregnancy outcomes was observed with LT4 supplementation. For women with individualized initial LT4 dosages, the risk of miscarriage decreased (relative risk [RR] 0.62, 95% CI: 0.41-0.93, I2 = 28%); there was no difference among women with fixed LT4 dosages (RR 0.96, 95% CI: 0.74-1.24, I2 = 0%). Women who initiated LT4 treatment in early pregnancy had a significantly lower preterm birth rate (RR 0.54, 95% CI: 0.31-0.92, I2 = 0%) than those who received no treatment or placebo. No improvement was observed among women who initiated treatment before conception (RR 1.14, 95% CI: 0.71-1.84, I2 = 0%).

CONCLUSION

No definitive evidence showed improvement of pregnancy outcomes with LT4 supplementation in euthyroid women with TAI. However, therapeutic strategies, especially dosages and initial times of intervention, may be of great importance. Additional large RCTs are needed in the future.

First-trimester placental function in levothyroxine-using pregnant women: a case-control study

We aimed to compare the pregnancy-associated plasma protein-A (PAPP-A) and the uterine artery pulsatility index (UtA PI) levels of euthyroid pregnant women using levothyroxine vs. a control group of uncomplicated pregnancies and to evaluate the effects of different levothyroxine dosages on pregnancy outcomes. We retrospectively evaluated 206 levothyroxine-using pregnant women by looking at their basic placental function markers and obstetric outcomes. A sample of 449 women whose pregnancies concluded with uncomplicated term deliveries composed of our control group. To examine the relationship between the levothyroxine dosages and the frequency of pregnancy complications, levothyroxine users were divided into different groups according to the 75, 100, and 150 mcg cutoffs. The median PAPP-A MoM levels of levothyroxine users were significantly lower at 0.94 vs. 1.11 (p < .001) and the median mean UtA PI was significantly higher than the control group at 2.08 vs. 1.74 (p < .0001). The median birth weight was significantly lower for the levothyroxine users' group at 3292 g vs. 3427 g (p < .0001). Using 75, 100, and 150 mcg dose cutoffs, PAPP-A MoM, mean UtA PI and obstetric complication frequencies were not significantly different among levothyroxine users. Significant changes in placental function markers have been observed in euthyroid levothyroxine-using pregnant women during the first trimester. However, the frequency of obstetric complications does not appear to be dose dependent.