LONDON – Women with hypothyroidism can achieve good results following fertility treatment if they maintain low levels of thyroid-stimulating hormone before assisted conception, according to findings of a 3-year retrospective study.
"An adequate treatment maintaining serum TSH levels below the threshold value of 2.5 mIU/L seems to fully overcome the detrimental effects of hypothyroidism on the rate of success of IVF [in vitro fertilization] and ICSI [intracytoplasmic sperm injection]," Dr. Andrea Busnelli reported at the annual meeting of the European Society of Human Reproduction and Embryology.
"Therefore, women scheduled for IVF-ICSI with adequately treated hypothyroidism can be reassured regarding the success of the procedure[s]," Dr. Busnelli of IRCCS Ospedale Maggiore Policlinico Mangiagalli e Regina Elena, Milan, Italy, added.
Previous research has shown that women with hypothyroidism have less chance of becoming pregnant after assisted conception than those with normal thyroid function. Subsequent findings conflict on whether levothyroxine treatment may (Hum. Reprod. Update 2013;19:251-8) or may not (Thyroid 2012;22:631-6) improve pregnancy rates.
These studies have been performed in a small number of women and TSH levels achieved with levothyroxine therapy were higher than recently recommended (J. Clin. Endocrinol. Metab. 2012;97:2543-65).
The current study therefore looked at whether "adequate" levothyroxine treatment, meaning that which ensured the level of TSH before conception was 2.5 mIU/L or lower, would be able to compensate for the reduced fertility success reported previously.
A total of 137 women with clinical or subclinical treated hypothyroidism participated in the study. At recruitment, their baseline TSH was between 0.4 and 2.5 mIU/L. Each case was age matched to two women with normal thyroid function as a control (n = 274).
Ultrasound was used to confirm any pregnancy, defined as a vital embryo within an intrauterine gestational sac at 4-5 weeks after embryo transfer.
The average age of cases and controls was approximately 35 years, body mass index in both groups was approximately 22 kg/m2, and there were no significant differences in the number of previous deliveries, serum hormone levels, or the cause of infertility leading to fertility treatment. Preconception TSH levels were approximately 1.5 mIU/L.
Looking at the number of assisted reproduction cycles, Dr. Busnelli noted that the duration of controlled ovarian hyperstimulation (COH) was longer for women with hypothyroidism than for their euthyroid counterparts: COH was 10.9 days in cases and 10.1 days in controls (P = .001).
Hyperthyroid women also had a higher chance of cancelled treatment cycles because of a poor response (3.6% vs. 0.7% in euthyroid women, P = .04). Failure to obtain viable embryos also occurred more frequently in hyperthyroid than in euthyroid women, at 17% and 7%, respectively (P = .006). Fertilization rates were also lower (75% vs. 80%; P = .017).
However, there was no difference between cases and controls in terms of the implantation (28% vs. 22%; P = .11), clinical pregnancy (36% vs. 34%; P = .93), or live delivery rates (30% vs. 25%; P = .5).
The presence of antithyroid antibodies did not influence the rates of implantation or termination. There was also no difference in the results comparing women with overt versus subclinical hypothyroidism.
Dr. Busnelli noted, however, that anti-TPO, anti-TG antibodies were not screened for in control women, so this limits the study findings as some in the control population could have had thyroid autoimmunity.
"Our observations suggest that the level of thyroxine may constitute a functional reserve in patients with positive TPO/TG antibodies which is able to compensate for the increased request typical of controlled ovarian hyperstimulation and pregnancy," Dr. Busnelli said.
The study received no commercial financial support. Dr. Busnelli reported having no relevant financial disclosures.