we tried IVF 3 times b4 getting twins with the 3rd time..

between 1st and 2nd we waited 4 months
between 2nd and 3rd we waited 1 year becoz we had to produce new embryos...

our doctor say we try again after we have rested well and is mentally/physically fit...

Plus ur wife period is back to normal again

with IVF, you can put in the numbers you want.
my colleague put in 2 got twins, and another one more daring, put in 4 and got 4 healthy babies! 

they are fraternal twins .. one boy one girl.. so definitely becoz of IVF

based on my own research and discussion with doctors, for IVF usually put 2~4 embyros, depending on the womb condition...

of coz, depending on ur "luck", all embryos might implant... then it carries a risk of miscarriage or pre-term birth..

sometimes, doctor mite abort some of the fetus in order to save the rest...

like my twins were born pre-term at 27.5 weeks.. they spent a total of 180 days in NICU... cost me around 200k (excluding IVF and delivery cost)

alas.. they are 7 months old now, and except for being underweight.. both are cheerful and healthy..

doctor told me the world record is 12 fetuses... dunno he joking or what 
maybe put in 6 embyros and all split become twims