If you go to the multiple birth foundation website it gives you detail of the signs to look for, ie shape of ears, hands etc they also do the test cheaper than elsewhere.
We used their test a couple of years ago, our dts are 9 and we were always told they were non identical due to them having separate placentas, but we were always unsure. Their placentas were fused together at birth, the website says this is indication that the egg split early.
So glad we had it done, kind of felt as a parent it is something I should know for definite!
Congrats by the way xx