Tough one! There is never a right time to have a baby or to decide on what to do with an AN!!
If you are going to wait 6 months for the next MRI, why not see what happens on the pregnancy side/the AN symptom side/your stress level? I personally would not put any contrast into my body while pregnant, so if you do get pregnant, you'd likely want to wait on the follow-up MRI. Yes, ANs grow and 1.5 is not small, but you'll find many successful W&W members on the forum. On the flip side, if you wait to get pregnant, each MRI can potentially damage your body - not good for a baby either. Of course, medical experts will poo-poo the effects of MRIs, but any treatment introduced into the human body has potential side effects, especially long-term. Finally, having an AN is very stressful - dealing with the diagnosis, symptoms, treatment decisions, etc. Stress is not good for pregnancy, so how are you handling the AN?
Just a few things you might want to consider in your decision-making process . . . Best of luck!