Various possible medical reasons, often related to post-surgical conditions.
If pupils are oval from birth and accompanied by other facial abnormalities (such as no eye lashes), and if no clear cause is present, such as a known disease, or DNA altering abuse by one or both parents, then a lesser known cause, and one that is commonly rejected by the medical community, is the genetic results of sexual union between a male Nephilim (a.k.a., 'fallen angel'), and an otherwise normal and usually very attractive human female.
In more pronounced cases, such as multiple grossly variant or non-human features in a new-born baby, the attending doctor in nations will have the baby removed immediately to an isolated ward without life support (not the ICU), informing the mother that the baby was 'still-born'. In most cases, the rejected new-born baby will die on its own. In other cases not. If you doubt this, ask a career mid-wife. I'd like to know where they go when they survive.