My wife is currently pregnant (6 weeks ) and has been constipated for 2 weeks is magnesium citrate safe are is there something better?

Better options: Magnesium citrate is a powerful stimulant laxative that can be rather explosive, so a safer option for simple constipation would be stool softeners (like colace, fiber pills, milk of mag) or miralax, (polyethylene glycol) a kinder, gentler laxative. Always discuss all meds taken during pregnancy with your ob/gyn doctor, as they are used to dealing with this everyday.