O-229 Impact of letrozole co-treatment during ovarian stimulation with gonadotropins for in vitro fertilisation (IVF): a multicentre, randomised, double-blinded placebo-controlled trial
Authors: Bülow N. Søderhamn , Skouby S O , Warzecha A K , Udengaard H , Andersen C. Yding , Holt M. Dreyer , Grøndahl M L , Andersen A. Nyboe , Sopa N , Mikkelsen A.L. Englund , Pinborg A , Macklon N S 
Published: August 2021

Study question

Does reducing estradiol levels with letrozole co-treatment during ovarian stimulation with gonadotropins for IVF impact endocrinological and reproductive outcome markers in expected normal responders?

Summary answer

Letrozole co-treatment maintained follicular phase physiological serum estradiol levels, increased gonadotropin and androgen levels, and increased progesterone in the luteal phase.

What is known already

Ovarian stimulation for IVF causes supraphysiologic estradiol levels, which exert pituitary suppression reducing gonadotropin stimulation of the corpus luteum. Furthermore, stimulation may increase progesterone in the late follicular phase, reported to impair clinical outcomes, through a putative effect on endometrial maturation and embryo-endometrial asynchrony. Co-treatment with the highly selective aromatase inhibitor letrozole during ovarian stimulation has been shown to reduce estradiol levels and FSH consumption in poor responders, but conflicting data in relation to oocyte yield and implantation rates. The impact of letrozole co-treatment on hormonal changes and reproductive outcome after co-treatment in normal responders remains to be clarified.

Study design, size, duration

A multicentre double-blinded randomised placebo-controlled trial conducted in 4 fertility clinics at university hospitals in Denmark from August 2016 to November 2018. 159 women were randomised and 129 completed the study; 67 women in the letrozole group and 62 women in the placebo group. The study was conducted in accordance with the Helsinki Declaration and the ICH-Good-Clinical-Practice. Data collection and reporting followed the guidelines of CONSORT to achieve transparent reporting of trials.

Participants/materials, setting, methods

Women with expected normal ovarian reserve received an antagonist IVF protocol with fixed-dose FSH and fresh single embryo transfer. Co-treatment consisted of once-daily 5 mg letrozole or placebo from the start of stimulation until the day of triggering final oocyte maturation with human chorionic gonadotropin. Serum was collected on 7 visits from stimulation start to 8 days after oocyte retrieval. Clinical pregnancy was determined with a viable foetus by vaginal ultrasound at gestational week 7.

Main results and the role of chance

The proportion of patients with progesterone &gt;1.5 ng/ml in the late follicular phase was similar in the letrozole versus placebo group with 6% versus 0%, respectively (OR 0, 95 % CI [0;1.6], P =.12). Mid-luteal progesterone levels &gt;30 ng/ml were observed in 59% versus 31%, respectively, of subjects in the letrozole and placebo group (OR 3.3, 95% CI [1.4;7.1], P =.005). Letrozole treatment decreased estradiol levels by 69% (95 % CI [60%;75%], P &lt;.0001) and increased luteinizing hormone (LH), testosterone, and androstenedione levels significantly in both the follicular and luteal phase. Follicle-stimulating hormone (FSH) concentration was elevated in the letrozole group at stimulation day 5 and at trigger day, and overall FSH consumption was diminished. The ongoing pregnancy rate did not differ between the letrozole and placebo group (31% versus 39% (risk-difference of 8%, 95% CI [-25%;11%], P =.55). Letrozole had no significant additional side effects apart from those frequently seen during ovarian stimulation, though a trend towards less nausea and vomiting was observed in the letrozole co-treated group versus the placebo group (28% versus 44% (risk-difference of 16%, 95% CI [-2%;33%], P =.11).

Limitations, reasons for caution

The diurnal variation of progesterone has been confirmed since this study was completed, hence the timing of the blood samples was not standardized . However, bias is unlikely due to the randomized design. The study was not powered to show an effect on ongoing pregnancy rates.

Wider implications of the findings

Letrozole co-treatment during ovarian stimulation with gonadotropins maintained serum estradiol at physiological levels, increased follicular phase levels of gonadotropins and androgens, and luteal progesterone levels. These data indicate that letrozole co-treatment may ameliorate the detrimental impacts of gonadotropin stimulation during IVF in normal responders.

Trial registration number

NCT02939898 and NCT02946684