Dear Wendy,
You are correct in being concerned about the impact of your pregnancy and hormones on your neurofibromatosis and gliomas. This is a difficult and complex medical condition. In reviewing the literature, it appears that hormonal stimulation sometimes can affect your tumors, but sometimes does not. You are in a high risk pregnancy situation, and should consult with a high risk pregnancy physician (perinatologist) as soon as possible. Perinatologists are used to dealing with women with serious medical conditions during pregnancy. In addition, you may need consultation with neurologists, imaging specialists and oncologists to ascertain whether or not your gliomas are growing. A perinatologist could guide you through this process.
Hormone levels during pregnancy are high and increase markedly through all three trimesters. The additional progesterone in Prometrium may or may not significantly affect the progesterone level you have just by virtue of being pregnant. You do not state why you are on Prometrium or if any progesterone levels were obtained before putting you on Prometrium. In any medical condition you always try to determine if the benefits of a treatment outweigh the risk. In your case, you would need to take into account the risk of miscarriage or premature labor, your progesterone levels, and whether or not your gliomas are sensitive to progesterone.
Since you state that your doctor is not very familiar with neurofibromatosis, you need the advice of another physician who truly understands your disease in the context of your pregnancy. You may need to go to a university hospital or large medical center to find someone with the expertise to help you. It is possible that a perinatologist could assist you and your current obstetrician, but it is also possible you may be better off under the care of a high risk specialist for the remainder of your pregnancy and delivery.
Best wishes in getting really good care, and a safe pregnancy and delivery.
Mary L. Davenport, M.D.