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.
Keywords: Hypothyroidism in pregnancy; levothyroxine; placental function; uterine artery pulsatility index.