How gin came to be called mother’s ruin isn’t explained satisfactorily but there are a number of suggested reasons:
Gin was used to bring on abortions;
In a more light-hearted vein, motherhood was the result of dalliances with British soldiers, renowned for their fondness for gin;
Perhaps more likely, its cheapness and easy availability made it a popular drink for poverty-stricken women struggling to forget their situation in life.
http://www.greatcocktails.co.uk/TheHistoryOfGin.html