Does soy help - or harm - fertility? Whether you should or should not eat soy when trying to conceive is controversial with much conjecturing on both sides of the dileamor. Despite it's problems, soy may have a specific short-term effect in helping to improve pregnancy rates when used after embryo transfer in IVF and hence possibly in natural cycles in the luteal phase also.
In one Italian randomized clinical trial (1) 1500 mg of soy phytoestrogens were given after embryo transfer along with progesterone (50 mg a day) to evaluate the effects of soy on IVF pregnancy rates. Progesterone is always administered at this time during IVF, either by IM shots, suppositories or gels as the ovarian follicles do not produce progesterone as they would in a natural cycle.
The study included 274 IVF cycles and randomized women into two groups, those that received progesterone only, and those who received progesterone and soy phytoestrogens. The soy phytoestrogen supplements were commenced after oocyte retrieval and continued until either the first pregnancy test was negative, or a babies heartbeat was confirmed.
Impressively, the study demonstrated a significantly higher implantation rate, clinical - and ongoing - pregnancy rate and live birth rate in women who received soy phytoestrogen with their progesterone. Take-home-baby rates in the phytoestrogen group were 30% compared to 16% in the progesterone only women leading the researchers to conclude that:
"Although the results of this study encourage the use of phytoestrogens for luteal phase support in patients undergoing IVF-ET program, more studies are necessary to support the hypothesis that phytoestrogens have a beneficial effect in IVF cycles."
Many studies have been done on the merits of giving women estrogen supplementation after embryo transfer, which has been shown to be especially effective in"poor responder" women. This is the first study on the adjunctive use of phytoestrogens showing that plant phytoestrogens may be able to achieve a similar effect.
You should ask your physician about whether or not you should use soy when trying to conceive, if you do decide to add soy to your IVF or luteal phase purchasing an organic product will ensure that you are not using genetically modified soy. Also, soy can be suppressive to thyroid function which is critical to early pregnancy success. You may be able to minimize this effect by taking soy phytoestrogens in the evening, away from the morning dose of thyroid medication, and by using a fermented soy product which reduces it's thyroid suppressive action.
This article is for purely informational purposes and in not intended to diagnose or replace medical or nutritional advice for which you should consult a physician or dietitian.
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(1) Fertility and Sterility, Vol. 82, Issue 6, December 2004, Pages 1509-1513. Phytoestrogens may improve the pregnancy rate in in vitro fertilization–embryo transfer cycles: A prospective, controlled, randomized trial. Unfer, et al.