Do you have diabetes? How far along are you in the pregnancy?
Ketones are a natural by-product of the breaking down of certain foods, and by themselves aren't necessarily a bad thing - although in high enough numbers they can indicate the early presence of Gestational diabetes. If you are overweight, or at risk for gestational diabetes, a high ketone reading may be addressed by doing a glucose tolerance test, where they will make sure your body is processing glucose correctly.
If it turns out that you DO have a risk for gestational diabetes, usually a special diet can bring it under control....and in some rare cases you may require insulin shots and blood glucose monitors.
but without more information, ketones reading +3 could be anywhere from perfectly normal to alarming...so if you can provide some more info maybe we can help.