Isolated Mild Ventriculomegaly

I went in for my fourth ultrasound yesterday at 22 weeks (5 1/2 months). The good news is the "air bubbles" seem to have resolved themselves and are no longer there, which is good news, I thought. But then the doctor came up with something new, and even more ambiguous than the air bubbles: Isolated Mild Ventriculomegaly. To keep things relatively simple, which I need, they measured a space of liquid in the brain and found that my baby is a 1.18 or a 1.2. Scientists consider 1.0 and below to be normal, but 1.5 and above is reason to worry. My baby, of course, had to land somewhere in the middle.
We were told that this will most likely be a normal pregnancy, but there are still risks of chromosomal abnormalities or abnormal brain development. We were given a bunch of options, none of them would be conclusive other than the Amnio, and that would only help me determine if I wanted to terminate the pregnancy. But of course, amnio carries a small chance of miscarriage that Javier and I are not willing to risk.

Our options are:

1. Do nothing and trust that our baby is fine, because he is boy it is more normal to have a larger space of liquid, and there is about an 80% chance that everything will turn out fine.
2. Get some more bloodwork done to see if I had an infection. (Even if I did, there would be nothing I could do about it at this point)
3. Get a fetal MRI to see the baby's brain in more detail (but these are relatively new for fetuses -about 5 years- and results are all over the place. There is no standard set yet so I would be part of a study where I could help other couples with this issue, not necessarily help myself because the data could come back even more confusing. Again, whatever the data results are there would be nothing that could be done to "fix" the issue)
4. Get an amnio to check for chromosomal abnormalities and decide if I want to terminate the pregnancy.

This is all just so mentally stressful, especially the fact that doctors can't clearly tell me if I'm at risk or not. Then I wonder, what does it matter? Javier and I will go through the pregnancy no matter what. The results of these tests will either help me know ahead of time or cause more confusion and stress during the pregnancy. We don't want to over-complicate this pregnancy, so as of right now, we are leaning more towards just doing the blood work and checking for an infection. I'm patient enough to find out the rest later, and have faith that everything is OK due to both our family's health, and my generally healthy lifestyle (minus my love of fast food). Still, I'd give a lot to be able to peer into future of these blog postings and be able to see how things actually turned out...