Why is there no trial data or peer reviewed studies

The honest answer: the trial data and peer-reviewed human studies you are looking for were never run, and the animal study that does exist is a zebrafish model, not a human trial.

The question is why there is no trial data or peer-reviewed study for Primodos. The retrieved records contain exactly one study on Primodos itself, and it is a 2018 zebrafish embryo experiment, not a clinical trial [1]. That study found the two hormones caused developmental defects in a dose- and time-dependent way, with defects and death rising sharply at higher doses [1]. It is real evidence that the mechanism is plausible. It is not evidence of what happened in human pregnancies.

The reason no human trial exists is structural, not mysterious. Primodos was sold as a pregnancy test in an era before the modern randomized trial was standard for such products, and you cannot ethically randomize pregnant women to a suspected teratogen. The records here contain no human cohort, no case-control study, and no funding disclosure for Primodos [1]. That absence is a fact about this retrieval, not proof that no human studies exist anywhere. Outside this retrieval, widely documented, there are epidemiological and regulatory reviews of Primodos, but I cannot confirm their contents or numbers from what is in front of me.

My call: the absence of human trial data is expected for an exposure you cannot ethically randomize, and the one study here shows a real mechanism in fish, not a proven human harm rate. Confidence: moderate on the mechanism, low on the human risk estimate.