I think there are still too many unanswered questions about it.  For example HCG is used to increase fertility, on the other hand they were testing HCG vaccines years ago to fight cancer.

Cancer cells are actually very similar to fetal cells sharing many of the same characteristics including using HCG coatings to hide from the immune system.  This is why HCG (pregnancy) tests are used to detect certain cancers, especially in men.  We have to keep in mind that because of the male DNA present in the fetus the fetus itself is actually a foreign protein to the woman's immune system.  So the HCG coating protects the fetus from the mother's immune system.

The reason I am emphasizing this is because when they were testing the HCG vaccines for cancer one of the things that they were not telling the women is that the same antibodies that would tag the cancer cells for destruction would also tag a fetus for destruction if the woman became pregnant leading to a spontaneous abortion (miscarriage).

And we know that the body builds a resistance to HCG in a short time.  If this is because of anti-HCG antibodies being formed then how can the HCG promote fertility while not exposing the fetus to anti-HCG antibodies?

And what will these antibodies do to HCG secreting cells in the body?  For example we known that cow's (bovine) milk given to children under the age of two can lead to type 1 diabetes.  The milk contains traces of bovine insulin, which of course is a foreign protein to the human system.  So antibodies are developed to deal with the foreign protein (insulin).  If the antibodies being produced though are of the low affinity (nonspecific) variety instead of the normal high affinity (specific) antibodies the antibodies can also attack the insulin producing beta cells mistaking them for the foreign protein.  Theoretically this could also occur with the injection of the foreign source of HCG.  Of course this part is only an issue in case of pregnancy, but it still must be kept in mind.

Another issue is that HCG is used during pregnancy to maintain progesterone levels.  But progesterone has its own set of side effects ranging from acne and irritability to cancer from activation of HPV viruses.

HCG can also lead to increased estrogen release, which can "feed" existing cancers and interfere with blood sugar regulation.

In addition a potentially serious side effect of HCG injections is ovarian hyperstimulation syndrome (OHSS).  The cysts formed in OHSS are believed to be formed from increased secretion of vascular endothelial growth factor (VEGF) leading to capillary leakage.  The reason this concerns me is because VEGF is the primary compound cancer cells use to develop a vascular network to feed itself.  In other words the tumor secretes several compounds, including VEGF, that stimulate the formation of blood vessels from both the tumor towards a major blood vessel and from the major blood vessel towards the tumor.  Eventually these two growing blood vessels will connect allowing the tumor to have an unlimited food source to grow.

But the primary tumor also secretes angiogenesis inhibitors that block the formation of new blood vessels.  The levels are much lower though than the levels of VEGF and other growth factors.  So the primary tumor is not affected significantly by the angiogenesis inhibitors that it secretes.  The purpose of this is to actually suppress the growth of metastasized cells by secreting the angiogenesis inhibitors in to the bloodstream.  Basically survival of the fittest. This is one of the reasons that secondary cancers tend to pop up after the primary tumor is removed.  The high levels of angiogenesis inhibitors that were suppressing the growth of the metastasized cells has been removed allowing these cells to take hold and grow.

So in short I feel there are too many unanswered questions as to the safety of HCG injections.  Such as effects of anti-HCG antibodies on the fetus, effects of progesterone and estrogen especially on cancer and the effect of increased VEGF release.