The below is just my opinion on how I interpret the codes:
Code 646.8 is for complications of pregnancy, and 648.9 is for conditions in the mother that are complicating pregnancy or conditions in the mother that are aggravated by pregnancy.
The way I interpret that is:
646.8 is for symptoms of pregnancy or complications that are caused by the pregnancy.
648.9 is for conditions/diseases the patient can have before pregnancy and may continue to have after pregnancy. They could be diagnosed outside the pregnancy.
To explain my thoughts:
646.8: Seems to be for the symptoms of pregnancy or a complication that you can only have when your pregnant, such as fatigue during pregnancy. That is a bit confusing as a patient could have fatigue without being pregnant but the key term is "during". This means that the fatigue is a symptom of the pregnancy. She could not have fatigue during pregnancy if she wasn't pregnant. Same goes for vaginal discharge during pregnancy, pelvic pain affecting pregnancy and so on.
648.9: Uses the word "condition" which in the medical world usually is used for the word disease, along with that and the other descriptions of codes in the 648.X section, I would only use this code for diagnosed diseases that the patient had that could have been pre-existing prior to pregnancy or diagnosed during the pregnancy. An example of this would be an infectious disease. It is not listed in the 648.X codes but would be considered a current condition in the mother classifiable elsewhere. Other examples I have used with this code are: PPD Positive, Systemic Lupus, Malignant Neoplasm or even Asthma.
I found a few articles here and there related to this but nothing from reliable sources or anything concrete.
I hope that wasn't too confusing, it was hard to get out.
Hope that helps!
Amanda Kane, CPC, COBGC