With a partial mole, there may be some normal placenta and the fetus, which is abnormal, begins to develop however, there are usually genetic problems with the baby but the fetus rarely survives past 15 weeks. Rarely, a partial mole will exist with twin pregnancy, however, the other twin rarely survives. In most cases of partial mole, the mother’s 23 chromosomes remain, but there are two sets of chromosomes from the father (so the embryo has 69 chromosomes instead of the normal 46) this most frequently occurs when two sperm fertilize the same egg. HCG levels are often lower than normal with a partial mole. Triploidy is double fertilization of an egg.