This is ridiculous.
https://www.mumsnet.com/articles/electrolytes-during-pregnancy
Encouraging pregnant women to buy wholly unnecessary “supplements” when they can get all the electrolytes they need from normal food and drink feeds into understandable anxieties, and results in women giving their hard earned cash to these charlatans. It’s not a good look, Mumsnet.
If anyone is genuinely dehydrated (e.g. after vomiting or being excessively hot) they would be better off seeking actual qualified medical advice.