O-252 Cumulative live birth rates (CLBR) in in vitro fertilization per oocyte used, embryo transferred, and embryo transfer impair with increasing female body mass index (BMI)
Authors: Garrido Puchalt N , Pellicer N , Bellver J 
Published: July 2024

Study question

Does the number of oocytes used, embryos transferred, or embryo transfers to achieve specific cumulative live birth rates differ according to female body mass index?

Summary answer

The greater the female BMI, the higher the number of oocytes, embryos and embryo transfers needed to achieve a liveborn, indicating a lower reproductive potential.

What is known already

The negative impact of high female BMI on in vitro fertilization (IVF) cycles has been extensively described in the medical literature, although there is no clear agreement on the potential role of oocytes, embryos, and endometrial receptivity on these results. However, the clinical outcome is commonly assessed per embryo transfer in isolated cycles and less frequently in cumulative cycles from the same cohort of oocytes. The number of oocytes or embryos needed to reach specific clinical goals has been never estimated in comparison to women with other BMIs, which gives a relevant multicycle overview of reproductive outcomes.

Study design, size, duration

This is a multicenter retrospective observational cohort study including a total of 31,289 women undergoing IVF with known BMI and 35,430 embryo transfers performed in 15 IVIRMA centers in Spain, from January 1, 2017, to October 1, 2023 with known outcome. Patients were grouped as Underweight (U, BMI&lt;18.5 kg/m2), Normoweight (N, BMI 18.5-&lt;25 kg/m2), Overweight (Ov, BMI 25-&lt;30 kg/m2), and Obese (Ob, BMI≥30 kg/m2).

Participants/materials, setting, methods

IVF-ICSI cycles with autologous oocytes and partner’s sperm were analyzed according to female BMI. CLBR per oocyte used, embryos replaced, and embryo transfers in consecutive treatments until reaching live birth or abandon were calculated by survival curve analyses with Kaplan-Meier’s methods estimating hazard ratios (HR), and BMI groups compared by with Log-Rank test. Outcomes per embryo transfer/completed cycle and descriptives were compared by chi square tests, and ANOVA where appropriate.

Main results and the role of chance

Mean women’s age was 37.6years, 95%CI(37.5-37.6), 36.9 years95%CI(36.7-37.1), 37.7years95%CI(37.6-37.8), and 37.2years95%CI(37.0-37.4) for N, U, Ov, and OB respectively. Mean stimulation days and serum progesterone concentrations the day of hCG administration were comparable. Estradiol on triggering day was statistically higher(p &lt; 0.05) on U group, 2073pg/ml95%CI(2008-2138), compared to the other groups, N 1942pg/ml95%CI(1926-1957), Ov 1840pg/ml95%CI(1808-1872), and Ob 1789pg/ml 95%CI(1742-1835). Number of aspirated oocytes was higher on Ob 9.47,95%CI(9.23-9.71), compared with N 9.1,95%CI(9.02-9.17),p&lt;0.05.

LBR per embryo transfer was 35.0%95%CI(32.9-37.3) for U, 33.3%95%CI(32.7-33.9) for N, 32.13%95%CI(30.9-33.4) for Ov ad 28.3%95%CI(26.6-30.1) for Ob, p &lt; 0.001. LBR per completed IVF-ICSI cycle (until reaching live birth or using all embryos) was 41.8%95%CI(69.7-43.9) for U, 40.6%95%CI(40.0-41.18) for N, 39.50%95%CI(38.4-40.6) for Ov, and 39.6%95%CI(37.9-41.37) for Ob, being statistically comparable.

Using N as a reference group, HR were 1.07,95%CI(0.98-1.17) for U, 0.98,95%CI(0.93-1.03) for Ov, and 0.90,95%CI(0.84-0.98) for Ob, p-value=0.011, being Ob significantly different compared to N.

Regarding HR per embryo transfer, 0.96,95%CI(0.82-1.13) for U, 0.87,95%CI(0.79-0.96) for Ov and 0.76,95%CI(0.66-0.89) for Ob, being statistically different Ov (p = 0.0055) and OB (p &lt; 0.001) from N. With the total number of embryos transferred, HR were better than N in U group, 1.11,95%CI(1.02-1.20), p = 0.0192 and significantly worse in Ov and Ob, 0.91,95%CI(0.87-0.96) and 0.85,95%CI(0.79-0.92), p &lt; 0.001 on both.

Limitations, reasons for caution

Despite the huge sample of patients included and the statistical approach used, the retrospective design of the study represents its main limitation, thus needing to interpret the findings with caution.

Wider implications of the findings

IVF-ICSI cycles in women high BMI are less efficient than in normoweight women since a greater number of oocytes, embryos and embryo transfers are needed to reach similar CLBRs. This finding highlights again the advice of initiating IVF with an adequate female body weight.

Trial registration number

not applicable