I've now seen a recent study from August 2005 that shows the effect appears to be far greater than I'd first thought.
For many years, researchers and public health specialists have been assessing the human health impact of prenatal exposure to the estrogenic anti-miscarriage drug, diethylstilbestrol (commonly known as DES or "stilbestrol"). The scope of adverse effects in females exposed to DES (often called "DES daughters") has been more substantially documented than the effects in males ("DES sons"). This paper contributes three areas of important research on DES exposure in males: (1) an overview of published literature discussing the confirmed and suspected adverse effects of prenatal exposure in DES sons; (2) preliminary results from a 5-year online study of DES sons involving 500 individuals with confirmed (60% of sample) and suspected prenatal DES exposure; (3) documentation of the presence of gender identity disorders and male-to-female transsexualism reported by more than 100 participants in the study.(Emphasis added) 500 in the group : and 100+ with GID or full-blown TS. 1 in 5. If only 1 in 10 of those are TS, it's still 1 in 50.
I sound like a broken record, but there are still many psychiatrists who say that the biological basis for TS is not proven. Well, I think for women with male chromosomes whose mothers took DES in pregnancy, it's fairly likely, The contrary hypothesis, that by pure coincidence the number is between 50 and 700 times greater than average, is really remote on a sample of this size. Even if there's "self selection" and other flaws in the study, making it not truly random, such flaws typically give over-estimates by factors of 2 or less.
Now maybe the mothers who took DES were more likely to give the kind of environment that the psychological hypothesis says causes GID. It's not inconceivable that the two factors are not independant. But a factor of 50? That's clutching at straws.
Oh yes - despite the fact that DES was commonly used in the UK in 1957 as an anti-abortifacient, and I was born in early 1958, my mother didn't take it. No, whatever caused my condition, DES is not guilty.