Not always, and in this case, the study is very light on details on how the selection process was done. The burden of the RCT is on the research team and the quality of the randomization varies between studies.

If a study is going to draw debatable conclusion after 10 years on high dose Vitamin D during pregnancy, I'd expect at least some comment in the study on the general socio economic landscape and grouping.

Regardless, this study looks like a sham to me.