Safe dosage of DHEA for IVF ICSI?

Hello,ladies. Does anybody know what is the safe dose of DHEA to improve egg quality prior to IVF. How many weeks ahead of its commencing should I start taking it. My RE only mentioned it, but was not specific on dosage. I have called reception of clinic to ask. I am curious if some of you took it, and had better or worst results. A bit of background information. I will be 40 in January. All my hormonal levels are okay except higher FSH of 13. I have no issues ovulating or any other known medical infertility issues but my tubes have not been tested as we got diagnosed with MIF. I have normal BMI and I am healthy individual. Had 3 biochemical loses with ivf icsi and waiting to do the recurrent loss blood testing panel beginning of December. I ovulated late twice at cd 18 after my third loss. Usually my ovulation is cd 15 or cd 16 rarely cd 14. My lutheal phase ranges from 10 to 12 days mostly 11 last year. My last 2 cycles it was 12 days. Do not know if biochemical lost shifted it.