Effect of Levothyroxine Sodium Intake on the Fetal Fraction in Non-Invasive Prenatal Testing: A Cross-Sectional Study

Objective: Non-invasive prenatal testing (NIPT) and fetal fraction (FF) are shown to be affected by various factors like maternal characteristics or medications. Recently medications are now undergoing evaluation as influencing factors. Still no data are presented on the relation between levothyroxine, NIPT and FF results. The study's aim is to assess the effect of levothyroxine sodium on the FF. Material and Methods: This retrospective case control study was conducted with medical records of pregnant women who underwent NIPT between 2016-2020 at our institution. Women with multiple gestation, body-mass index >= 25, abnormal fetal karyotype, pregnancy with assisted reproductive techniques, those without FF report and non-euthyroid patients were excluded. The pregnant euthyroid women included in the study were divided into two groups: using and not using levothyroxine. Maternal characteristics, FF of the NIPT, TSH, FT4 values and levothyroxine dosing were noted and compared between the two groups. Results: Data were collected from 51 pregnant women using levothyroxine and 102 pregnant women who did not. There was no difference in demographic characteristics, also no significant difference was shown in TSH and FT4 between the groups (p=0.180, p=0.920). The mean FF level in pregnant women using levothyroxine is lower, but the situation did not reach statistical significance (p=0.070). Conclusion: The knowledge of relation between FF and medications is largely based on very limited data. This is the first report of assessing levothyroxine effect on FF percentage in NIPT. Levothyroxine sodium was not confirmed to be associated with any significant change in the FF.