I have hives from an unknown cause. I am taking 1 xyzal (levocetirizine) daily. I am planning for pregnancy. Is it safe?

Probably. Xyzal (levocetirizine) is listed as a class b drug. That means that it does not cause birth anomalies or miscarriage in laboratory animals & there are no reports of such problems in infants of mothers who took xyzal while pregnant. Ethically clinical studies of drugs cannot be performed in pregnant women. Class b is the safest level we have. The decision to use is yours with your ob's guidance.
Still needed? Perhaps you can safely stop taking xyzal (levocetirizine). Hives may be acute (lasting <6 weeks), chronic (>6 weeks) or intermittent (acute but once in a while). Chronic hives last for months to years. Sometimes they resolve for unknown reasons. Only way to know is to withhold xyzal (levocetirizine) for a day or so to see if hives return. If they don't you may be able to avoid this drug. Check with your doctor before you stop.