Live Birth Rate following IVF Decreases According to BMI, while Rates of Miscarriage and C-Section Increase

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Live birth outcomes in infertile patients with class III and class IV obesity following fresh embryo transfer

A retrospective cohort study, of patients undergoing their first oocyte retrieval and fresh embryo transfer at an academic hospital, was carried out to assess the effect of BMI on clinical pregnancy and live birth rates.

A total of 7296 women were included in this study, who were grouped according to BMI; 18.5-24.9 (Group 1: 4913), 25–29.9 (Group 2: 1566), 30–34.9 (Group 3: 559), 35–39.9 (Group 4: 218), and ≥ 40 (Group 5: 114), n meaning number of women.

The mean age of each group varied between 37 to 38 years of age. Live birth was defined as delivery after 24 weeks of gestational age, whilst delivery before 37 weeks of gestation was classed as preterm.

Initial analysis found that patients with BMI ≥ 40 were significantly more likely to have the fresh embryo transferred cancelled due to; failed fertilization or embryo development, ovarian hyperstimulation syndrome, no oocytes or no mature oocytes.

Significantly spontaneous abortion increased linearly as BMI increased, from 12.6% (Group 1) to 22.2% (Group 5). This corresponded with a linear decrease in live births, dropping from 67.7% (Group 1) to 53.3% (Group 5).

As expected the rate of cesarean sections also increased linearly with BMI, from 39.0% (Group 1) to 61.5% (Group 2). Interestingly the proportion of biochemical pregnancies or preterm deliveries was not significantly different between any of the groups.

Further analysis of the data found that oocyte yield and development was significantly altered according to BMI. This included;

  • Lower number of oocytes retrieved as BMI increased
  • Lower number of mature oocytes retrieved as BMI increased
  • Lower number of zygotes (fertilized egg) as BMI increased
  • Lower number of cryopreserved blastocysts as BMI increased

These results support the growing body of evidence that obesity related infertility is a result of oocyte factors not the uterine.


In this large study, obesity negatively affects the success of IVF, causing a linear increase in spontaneous abortions, from 12.6% to 22.2% as BMI increases, and a linear decrease in the live birth rate from 67.7% to 53.3%, explained by poor oocyte yield and development, and not uterine factors.


  1. Embryos did not undergo preimplantation genetic testing to measure proportion of euploid embryos
  2. Patient management decisions regarding stimulation protocol, IVF or ICSI was not standardised
  3. Results were not adjusted for confounding factors, including neonatal weight or gestational diabetes, which are known to increase the likelihood of cesarean deliveries

Similar studies

Ben-Haroush A, et al. (2018). The influence of body mass index on pregnancy outcome following single-embryo transfer.

Russo M, et al. (2017). Morbid obesity and pregnancy outcomes after single blastocyst transfer: a retrospective, North American study.


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