How much useful the pregnil injection to get pregnant?

Depends. Hcg is the "trigger" shot for ovulation. It is used primarily to time ovulation in fertility treatment cycles. There are a small minority of patients either treated or untreated who have an ovulation defect in their own triggering mechanism (the lh surge) for ovulation. In these patients HCG would be helpful as well. Otherwise most women trigger their own ovulation without difficulty.
Pregnyl. Pregnyl is hcg. It helps to trigger the release of an egg from a mature follicle (the house where the egg comes from). It's used in certain cases where a woman may not release the egg on her own. If a woman does ovulate an egg all by herself in a normal situation, then Pregnyl would not be useful in this case.