Many of the progesterone support products the clinics use are off licence.
For instance, Crinone is only licensed for 2-4 weeks after fertility treatment, cyclogest is only licensed for premenstrual and post natal depression and they say due to the licensed indications it is unlikely that the drug would be used in pregnancy.
Many clinics from what I can gather use the product you have been prescribed.
The companies cannot say that the drug can be used for an indication unless they have carried out the specific clinical trials necessary. Usage is the responsibility of your doctor in these cases.
Most women who have fertility treament have some form of progesterone support.
The progesterone in all these products is the natural form that your body would naturally produce in pregnancy.