"Integrated Screening is a way to estimate the chance that a baby will be born with Down syndrome, trisomy 18, or an open neural tube defect. It uses measurements from two blood tests and from a first trimester ultrasound. All of this information is combined, or integrated, with other details about you to tell you more about your developing baby."
"On average, one in about 30 women will have a positive Integrated Screening result. A positive result does not mean that your baby has one of these problems—other factors may affect the test results—so your provider may suggest further testing such as a detailed ultrasound of the baby’s anatomy and/or an amniocentesis."
http://www.dhmc.org/webpage.cfm?site...&item_id=49556
Basically, the tests only give you odds that your baby has or doesn't have these defects, there are false negatives and false positives possible. If the odds are high that something's wrong, they will want to followup with amnio or CVS tests, which are more invasive and carry a very small risk of miscarriage, but they are very decisive (they will be able to tell you for sure what you are dealing with).
I am leaning toward having the integrated screening tests because they are relatively non-invasive and safe for baby, and if they show a likelihood of neural tube defect there are things that can be done (even in-utero) to help repair the damage. If it showed evidence of trisomy 18 I would like to know because those babies are severely affected and rarely make it alive to birth. Downs syndrome is a little bit more difficult call for me, but I would want to be prepared if I were taking on this challenge.