P–609 The chances of one live birth rates after first ART cycle in minimal stimulation cycle IVF with letrozole only and natural cycle IVF
Authors: Takahashi Y , Hisa N , Kotake R , Suzuki Y , Akimoto S , Igarashi C , Ito H , Harada H , Nakata M , Ono S , Abe T 
Published: August 2021

Abstract

Study question
Are one live birth rates (LBRs) similar in minimal stimulation cycle IVF with letrozole only and natural cycle IVF for the first ART cycle?

Summary answer
LBRs after first ART cycle in minimal stimulation cycle IVF with letrozole only are superior to natural cycle IVF.

What is known already
The addition of letrozole to gonadotropins in ovarian stimulation (OS) may reduce the risk of OHSS, but there is no significant difference were reported in ongoing pregnancy rate or number of oocytes retrieved in the letrozole + FSH group compared to the FSH only. No differences were also reported in clinical pregnancy rates or number of mature oocytes in the additional of letrozole in an GnRH antagonist protocol group compared to the GnRH antagonist group. There are no previous study comparing LBRs after first ART cycle in minimal stimulation cycle IVF with letrozole and natural cycle IVF.

Study design, size, duration
Data for this retrospective cohort study were obtained 643 women, 30–39 years of age started their first ART cycle at one private fertility clinic between January 2016- December 2019.

Participants/materials, setting, methods
A total of 643 women were scheduled their first oocyte retrieval cycle. 118 women started with letrozole (LE) and 525 women started natural cycle (NC). The main strategy for OS in our center is minimal stimulation and natural cycle IVF. Patients consulted with gynecologists to determine their treatment plan based on patients’ preference or their menstrual cycle. All pregnancies generated from oocyte retrieval during the first IVF cycle including fresh and frozen-thaw cycles were registered.

Main results and the role of chance
The number of retrieved oocytes and the normal fertilization rates were significantly higher in the LE than NC (4.4 vs 3.4, 77.6% vs 71.1%), p &lt; 0.05 respectively). There was no significant difference in the clinical pregnancy rates (CPRs) per embryo transfer (ET) (fresh cleavage stage ET: 32.9% vs 28.0%, frozen-thaw blastocyst ET: 39.4% vs 44.9% ns). However, the CPRs and LBRs per oocyte retrieval (OR) were significantly higher in the LE group (39.0% vs 28.6, 33.9% vs 21.9%, p &lt; 0.05 respectively). In a subsequent regression analyses, LBRs per OR of LE was significantly higher than NC as well. (adjusted OR = 1.63 (95% CI: 1.02–2.58, p = 0.041).

Limitations, reasons for caution
The strength of the present study was the use of a large cohort of women who underwent minimal stimulation IVF with letrozole only. Although our results are promising, limited by retrospective cohort study. These interpretations prompted the need for a perspective cohort study to evaluate the efficacy of letrozole.
Wider implications of the findings: When comparing minimal stimulation IVF with letrozole only and natural cycle IVF, we found significantly higher LBRs per OR in minimal stimulation IVF with letrozole only, despite similar CPRs per ET.

Trial registration number
none