Blood Transfusion from Ever-Pregnant Females Associated with Mortality in Males

Using a small sample exposed to the suspected risk and the vast majority not exposed sounds like responsible ethics.

It is not stated, but there should also have been additional safeguards and monitoring. It is normal for studies to be terminated early if they are found to expose participants to either too much danger or if the study group is found to be significantly advantaged (in which case, for example, the whole group is given the beneficial treatment instead of just the small study group).

50% may sound 'fair' or 'equal', but this is about researching ways of saving life, some social notion of fairness or gender equality is not relevant and, if this study is correct, could have caused excessive death. Is it worth people being killed to get the gender balance into the shape you prefer?

Pooling is also done for blood testing they’ll pool samples from a batch together and if the pooled sample comes back positive they’ll discard the entire batch of part of it if subpooling was used.

Red blood cells doses come from a single donor.

I’m not sure about platelets.

Though searching suggests, no, they probably don't have that figure locked down.

>> further research is needed to replicate these findings, determine their significance, and define the underlying mechanism.

To be fair, this is more or less "boiler-plate text" added at the end of every research paper, sometimes I would like to see a research paper that ends with "... and that's all about it".