Please go to http://www.whitehouse.gov/ask/ and post a question to USCIS Director Gonzalez to extend the expiration date of the 171H from 18 to 24 months.
Be sure to tell him exactly what sort of burden it would place on your family to have to get a new 171H. It does require a new home study and all the paperwork assosciated with it, a new filing fee and fingerprinting fee. For me this is close to $1800.
Without going into too much detail, tell him a little bit about you. Are you married? Are you single? Is this your first baby?
The idea is to show power in numbers with adoptive families posting a similar question. Don't make it too long so they won't even read it, but be concise with your information.
Thanks! - Kim