Did the major, irreversible divorce (baynunah kubra) occur between the spouses after the first divorce, and the husband's saying "If you do such and such, you are forbidden to me" twice (one of which was under the influence of drugs), then his third explicit divorce "You are divorced" while she was pregnant?

A clear divorce issued by the husband to his pregnant wife is an enforceable divorce. If it was preceded by one divorce, then it counts as two divorces. The husband may take back his wife before the expiration of her waiting period (iddah) by giving birth. As for the prohibition that the husband linked to a specific action with the intention of intimidation and preventing his wife, and he did not intend divorce or dhihar by it, its ruling is the ruling of an oath by Allah. If the wife performs the action sworn against out of forgetfulness, the husband does not break his oath. However, if she performs it intentionally and not out of forgetfulness, the husband has broken his oath and must offer an expiation for an oath (feeding ten poor people, or clothing them, or fasting three days), even if he was drunk when he swore the oath. Furthermore, drug abuse is a major sin and he must repent.