I would not mix any two medications i did not know the compatibility for..some medications when infused together can form a precipitate and clog the needle or IV tubing, as well as render one or both medications inactive or cause great pain at the tissue because the crystalization.(speaking general about medication administration here)..secondly oil and water do not mix....lastly as someone mentioned previously is that if HCG is water based you will not need such a large bore needle...