Objective: To investigate fetal heart rate (FHR) of fetuses whose mothers are under levothyroxin treatment for chronic hypothyroidism.
Study design: Sixty women under chronic therapy with levothyroxin and 180 controls at 37-39 weeks' gestation were studied by Sonycaid Sistem 8002(R) computerized cardiotocography (cCTG) for 30 min. cCTG parameters were expressed as mean and SD and the differences tested for statistics by Student t-test. Furthermore, cCTG parameters were related to levothyroxin dose by regression analysis. Significance was assessed at p < 0.05.
Results: Computerized cardiotocographic tracings of fetuses from mothers under levothyroxin treatment revealed: significant reduction of baseline FHR (130.1 +/- 9.47 vs. 134.9 +/- 4.68 bpm); increased number of FHR decelerations greater than 20 bpm (0.2 +/- 0.41 vs. 0.05 +/- 0.22); reduction of body movements per hour (6.68 +/- 11.72 vs. 10.65 +/- 11.74); and increased uterine contraction peaks (5.15 +/- 4.69 vs. 2.7 +/- 2.57). Those fetuses also showed significantly reduced neonatal weight (2668.2 +/- 766.65 vs. 3215.44 + 523.88 g) and lower 1-min Apgar score (8.6 +/- 0.95 vs. 9.3 +/- 1.11). Regression analysis showed a significant correlation between levothyroxin dose and baseline FHR (r = 0.60; p < 0.0001) and fetal body movements per hour (r = 0.52; p < 0.0001), and an inverse relationship with uterine contraction peaks (r = -0.35; p < 0.006), whilst no correlation was found with the number of FHR decelerations greater than 20 bpm.
Conclusions: Maternal hypothyroidism and levothyroxin treatment influence FHR and cCTG is a sensible tool to reveal that influence.