Obesity Affects Uterine Receptivity in IVF with Donor Eggs

There have been several blogs expanding on the impact of obesity on success rates with IVF. Miscarriage rates and pregnancy complications are also higher in obese patients. The exact way in which excess weight impacts each component of a woman's reproductive system (egg, embryo, and uterus) is not clear.

But a recent publication by a group from Spain, (Bellver et al., Fertil Steril 2013;100:1050-8) assessed the impact of obesity on uterine receptivity-- that is, the conditions which make the uterus likely to support the development of a pregnancy. This study was interesting because it focused entirely on IVF cycles conducted with donor eggs.

Bellver et al. analyzed data from 9,587 first cycles of egg donation (from normal weight donors) over a period of 12 years. They divided the recipients according to their BMI into 4 groups based on their BMI. Lean with BMI <20 kg/m² (n = 1,458; 15.2%); normal weight with BMI 20 - 24.9 kg/m² (n = 5,706; 59.5%), overweight with BMI 25 - 29.9 kg/m² (n = 1,770; 18.5%), and obese with BMI >30 kg/m² (n = 653; 6.8%). They analyzed the success rates in the four groups. Here are the findings:

In vitro fertilization laboratory parameters did not differ according to BMI. However, implantation, pregnancy, clinical pregnancy, twin pregnancy, and live-birth rates were significantly reduced as BMI increased. In the lean, normal weight, overweight, and obese groups, the implantation rate was 40.4%, 39.9%, 38.5%, and 30.9%, clinical pregnancy rate was 56.9%, 55.9%, 54.3%, and 45.3%, and live-birth rate was 38.6%, 37.9%, 34.9%, and 27.7%, respectively. However, clinical miscarriage rates were similar in all the groups.

They did detailed statistical analysis of their data and quantified the effect of excess weight on reproductive outcome. From a basal clinical pregnancy rate of 40%, one can expect a decrease of 1.08% in the probability of becoming pregnant for every unit of BMI increase. So, for a patient with a BMI of 40 kg/m², the pregnancy rate will decrease by 10 x 1.08 = 10.8%. So instead of a 40% pregnancy rate, the expected pregnancy rate will be only 29.2%! Remember, this is with donor eggs. A recent publication showed that with a BMI of 40 kg/m², the pregnancy rate for regular IVF decreases by a whopping 68%!

The authors concluded that female obesity reduces success rates with egg donation probably as a result of reduced uterine receptivity. They believe that as a general disease, obesity probably affects all the components of the reproductive system: sperm, egg, embryo and uterus. They recommend weight reduction before natural or assisted conception, whether with the patient's own or donor eggs.

At InVia Fertility Specialists, we have been helping our patients lose weight with the Ideal Protein Diet. The results so far have been very encouraging and we will post an update in the immediate future.