Miscarriage caused by the immune system.
One of Dr. Lee's notable findings is that there is an immune-suppressing effect in the uterus from higher doses of progesterone. This is important, because when conception takes place, half of the baby's chromosomes are from the male and half of them from the female.
That makes the baby's tissue DNA different from the mother's because of the contribution of the father. If there's not a good tissue match, the difference will create tissue rejection. If you try to do a skin graft or a kidney or heart transplant and the tissue isn't the same, the body will reject it.
But this doesn't happen with pregnancy.
Because of the progesterone response in the uterus. It's a site-selective action that doesn't occur anywhere else in the body; therefore, the baby is not rejected. By giving more progesterone after conception, you thus increase the likelihood that the baby will survive.