No, I did not know it. I used it as the only translation I know of the Russian term погодки (I grew up in Moscow), which literally means kids born a year apart and has no connotation with respect to birth control. But I am not sure that Irish Twins is universally considered derogatory these days: for instance, Irish Twins: Definition, Origin, and What It Means for You says: "Today, the term is typically not intended as an insult, but rather as a way of classifying siblings born close together. For instance, some families might proudly use the term to describe the short timespan between the births of their children."