P-133 A study of the relationship between in vitro embryo development and maternal hypothyroidism
Authors: Dorjsuren D , Orgilbold C , Budzaya E , Arigbukh E , Nomundari B , Odkhuu E , Munkhzol M , Zesemdorj O U 
Published: June 2023

Abstract

Study question
Are there an association between the maternal thyroid condition and in vitro fertilization (IVF) outcomes?

Summary answer
Maternal hypothyroidism was found to be related to oocyte maturation and blastocyst development.

What is known already
Previous studies have shown that thyroid-stimulating hormone (TSH) levels affect ovarian stimulation in assisted reproductive technology (ART). In addition, changes in serum TSH levels have been linked to a sub-optimal environment for the implantation and development of the embryo. Thyroid-related receptors are present in granulosa cells, ovaries, and the endometrium. In addition, those receptors play a role in ovulation and folliculogenesis. This study aims to determine the association between maternal hypothyroidism and adverse implications for IVF outcomes in IVF/ICSI treated women.

Study design, size, duration
This retrospective study performed 333 cycles of 208 patients with TSH levels ranging from 0.043-16.627 µIU/mL, treated at the RMC National IVF Center between 2019 and 2022. The study population consisted of 1171 oocytes, which were divided into two groups based on their maternal basal TSH levels: normal TSH  ≤ 2.5 µIU/mL (control group, n = 865, euthyroid) and higher TSH  &gt; 2.5 µIU/mL (case group, n = 306, hypothyroid).

Participants/materials, setting, methods
Maternal basal serum TSH levels were measured using Fluorescence Enzyme Immunoassay on the third day of the menstrual cycle. IVF outcome expressed oocyte maturation, fertilization, cleavage, and blastocyst formation rate. Oocytes were divided into mature (metaphase II) and immature (metaphase I and prophase I) groups. Blastocysts are graded by the Kato Ladies Clinic classification system and divided into high potential (A and B grades) and low potential (C, D, and E grades) groups.

Main results and the role of chance
In our study, there was no statistically significant difference in age and partner’s semen criteria between the two groups (p &gt; 0.05). As regards oocyte maturation, MII oocytes retrieved significantly higher in the control group (82.2% vs. 75.8%). Logistic regression analysis found that TSH levels  &gt; 2.5 µIU/mL were related to statistically significantly increased risks of oocyte maturation stages like MI or GV (Age affect adjusted model: B = 0.456, p = 0.005; OR = 1.578, 95% CI = 1.146-2.175). The fertilization, cleavage, and blast formation rates have no differences between the groups. However, 91% (n = 324/356) of higher potential blastocysts in the control group were significantly higher than the case group (79.7%, n = 106/133). While, by the logistic regression analysis found that higher TSH levels ( &gt; 2.5 µIU/mL) were related to statistically significantly increased risks of lower potential for implantation grades (B = 0.947, p = 0.001; OR = 2.579, 95%CI = 1.477-4.502).

Limitations, reasons for caution
The study relied on TSH as the primary indicator of thyroid function and excluded participants with abnormal prolactin levels. Other markers, such as FT4 and TSHR, should also be considered for a thorough evaluation of thyroid function.

Wider implications of the findings
Thyroid dysfunction can negatively impact IVF success, and screening and managing thyroid function in women undergoing IVF are essential. More research is needed to understand the mechanisms and develop strategies to improve oocyte and blastocyst quality.

Trial registration number
not applicable