I don't know if you actually want to read something into my words. All I said was that the state of research is scarce and that further research is required.Just because a study is new doesn't in and of itself make its data more accurate or relevant than a study that is old.
300mg is three cups of coffee. It's also the lower bound in the Sasaki study (it was >= 300 mg per day, which means the average consumption for that study is above 300 mg, but not specified. There could be women in there drinking 2000 mg of caffeine per day, there's no upper limit.
Mentioning the genotype is relevant because it was a control factor in the study results you are mentioning. Sasaki only found an impact on head circumference if controlling for one specific genotype. If not controlling for that, there was no difference.
Karaismailoglu's "low dose" was 300 mg of caffeine in 1 liter of water, of which rats drink something like 33 ml per day. That means the rats would be consuming about 10 mg of caffeine on the low-dose. Rats weigh somewhere around 0.5 pounds. So in a body weight comparison against a pregnant adult human who's going to weigh something like 170 lbs on average, that means that for body weight, the "low dose" is equivalent to a human consuming about 3400 mg of caffeine per day. How many cups of coffee is that?
These studies are published. You can go look up how they tested, what they tested, etc. If you're going to use those studies to back up a point, everything the studies said/did is relevant even if you didn't include that information in your post.
It's every woman's choice to err on the side of caution as much as she feels fit. If a woman wants to drop to 0 mg of caffiene during pregnancy, more power to her, that's great. The question here is more about how appropriate for other people to tell a woman how much caution she should exercise, particularly when there's no evidence suggesting any harm with drinking in moderation. You're cherry picking the studies you look at because they back up an assumption, but the body of evidence as a whole doesn't suggest a problem.
Pretty much every pregnant woman has a doctor and those doctors are very capable of advising their patients, and right now the advice that they are giving is that drinking it in moderation is fine. Not "Oooh, that's sorta risky, if you're an addict I guess you can drink some but you're probably gonna miscarry". They're saying, based on the evidence, that moderate consumption looks safe.
I'm not saying that pregnant women should or shouldn't drink caffeine, that's up to them. I'm saying there's no evidence out there that would warrant making this my business (or anyone else's, with exception of their ob/gyn).
But it's a false and very dangerous assumption you just could compare the body weight of a rat and a human being in order to get an equivalent dose. Take Xylitol for instance. Toxic to rats, harmless to humans. Furthermore rats are way more resilient in general.