Study of 54 habitual aborters with low or normal pregnanediol excretion, in a double-blind trial, revealed the spontaneous-salvage rate and the possible benefit of therapy with medroxyprogesterone acetate. The salvage rate in the placebo group with the worst prognosis (never a term pregnancy, low pregnanediol in the current pregnancy) was ten of 13, and the salvage rate in the other placebo groups showed no statistically significant difference. In view of this high spontaneous salvage rate, the numbers required to demonstrate a therapeutic effect of progestin administration are prohibitively large. This indicates the need for new criteria to pinpoint cases with a poor prognosis, and it raises the question whether habitual abortion is a disease entity or a statistical coincidence.
Goldzieher JW. Double-Blind Trial of a Progestin in Habitual Abortion. JAMA. 1964;188(7):651-654. doi:10.1001/jama.1964.03060330031008