While there is plenty of data showing that women who are overweight have a harder time conceiving through IVF, we have little data on how IVF success rates improve should the patient go on a diet, and manage to lose weight.
Why This Study Is Special
This is a well-designed, prospective, randomized trial where one group was placed on a four month diet and then underwent IVF. The control arm simply advanced to IVF with no diet. Thus, we get to squarely study the impact of diet on two similar groups. What’s more, the diet arm managed to lose significant weight, so we can address the question of when a diet “works” does it really have an impact. The primary endpoint is live birth rate, which is the gold standard, in our minds.
What Was Tracked & What They Found
First, the diet arm lost a significant amount of weight by the time IVF commenced and their BMI dropped to 29 (versus 35 for the non-diet group). That rate of weight loss, sustained over four months, is impressive.
Second, 10% of the women in the diet group conceived naturally, before IVF even started (versus 2% in the non-diet group). While the difference was highly statistically significant, it’s also distorted because the diet group had an extra four months to conceive compared with the non-diet group, who went immediately to IVF. As such, it’s hard to interpret this set of facts.
Finally, of the women who made it to IVF in both arms, there was a small, and not statistically significant difference in live birth rates of 29% for the diet group versus 27% in the non-diet group.
The Study’s Limitations
There were a few. First, ideally the non-diet arm would have also waited four months to undergo IVF so we could see how many women would have conceived naturally. Second, we would liked to have seen a larger trial: if that 29% vs 27% was replicated in a bigger sample set, that could be considered meaningful. Fourth, the data looked at only the first IVF cycle and not success rates in subsequent cycles. It's quite possible one group ultimately had babies in fewer cycles. Finally, only women with a BMI of 30 – 35 were treated and so it may be hard to generalize the findings to a heavier population where the impact of weight loss could be higher.
If you are a patient with a BMI of 30 – 35, losing weight may not hurt your odds of success, but it may not dramatically improve your odds either.