Read Bill Robert's profile on hCG. Ovitrelle is recombinant hCG instead of hCG extracted from urine, which makes it more stable
hCG Profile
"So, if using HCG for years on end continuously, there might be a slight safety advantage in using recombinant HCG over ordinary HCG. It may be very little advantage, since as mentioned the dimer form also found in ordinary HCG is protective and at least to some extent balances out the beta monomer form. Indeed, ordinary HCG is at the balance which nature provides. Still, if the day comes when recombinant HCG is as easy to obtain as regular HCG, one might prefer it for this reason. It might be an even safer product."
Ovitrelle also has special stabilizers that allow it to stay at 25 C (room temperature) for long periods of time. You can look up the official drug information from the European FDA for proof.