Amnio

I'm just at a loss. My sister in law is profoundly mentally handicapped (IQ less than 20- can't eat alone, use bathroom- nothing). Yet my mother in law never found out the reason as to why it happened. Now,  I'm 14 weeks pregnant, my husband and I want to get an amnio to help ease our minds- and our genetic counselor is basically saying we can't because we don't know exactly what my SIL has since there's no diagnosis.- and my MiL won't get one.  In 50% of people with profound mental handicap, there is no diagnosis cause its so hard to find out the cause. I don't know what to do... it's $4,000 out of pocket if my insurance wont cover it- which I don't have.