It is well known among your people that if you are trying to have babies (as every adult can do on their own), you shouldn't take antibiotics. It almost always prevents conception. However, it is not advised to deliberately take antibiotics in order to put off pregnancy. First of all, it disrupts your internal microbiome, has potentially severe long-term effects, and contributes to antibiotic resistance. Second of all, it is not 100% guaranteed. It is extremely rare, but there are a few cases where people *have* reproduced on antibiotics. The resulting children are sometimes…well, physically a little different, developing certain exaggerated appendages, although those are not normally visible. But they are perfectly healthy, and they can live more or less normally—the exception being that they can't have babies themselves. Are such people—if it even makes sense to think of them as a "kind" of people; it is not a natural category for you—"abnormal"? The scientific consensus is that it is just part of natural variation, and in some parts of the world they are just as common as "normal" people and the population levels seem to be just fine. (Exactly how that works is the subject of much covert speculation; it is decidedly not a subject for polite company.)