Clinical & Medical Biochemistry

Abstract

Longitudinal Changes in Thyroid Hormones During Conception Cycles and Early Pregnancy

Kristina Hamilton, Narelle Hadlow, Peter Roberts, Patricia Sykes, Allison McClements, Jacqui Coombes and Phillip Matson

Objective: The aim of this study was to characterize changes in free triiodothyronine (fT3), free thyroxine (fT4) and thyroid-stimulating hormone (TSH) during the follicular and luteal phase and during subsequent early pregnancy in individual women.

Method: TPOAb negative women with a viable pregnancy (n=49) had fT3, fT4 and TSH measured longitudinally in serum samples at baseline/non-pregnant (gestation week 0), ovulation (gestation week 2), mid-luteal phase (gestation week 3) and twice weekly from gestation weeks 4 to 6.5. Patient groups received in their conception cycle either no medication (n=13), low ovarian stimulation, (n=17) or controlled ovarian hyperstimulation (COH) for IVF treatment (n=19).

Results: Women receiving COH had a transient drop in TSH at the time of ovulation followed by a peak at midluteal (p=0.024). Levels of fT3 and fT4 at each gestation week were not significantly different between the treatment groups, whereas TSH levels were significantly higher at all gestation weeks (p=0.036) in the COH group compared to the natural and low stimulation groups. There were significant changes in thyroid function once pregnancy was established (gestation week 4) through to gestation week 6.5, with a gradual decrease in serum fT3 (r=-0.104, p=0.030) and TSH (r=-0.123 p=0.031), whilst fT4 levels remained constant. 3 women (6.1%) had TSH levels >4.0 mU/L during their pregnancy although these were isolated measurements.

Conclusion: Thyroid hormones in individual women did not remain constant but showed discrete changes. TSH was significantly lower at time of ovulation in women who received high doses of ovarian stimulation medication for IVF, and was higher throughout pregnancy than for the other groups. Serum fT3 and TSH decreased significantly during early pregnancy irrespective of medication given in the conception cycle.