Doping by pregnancy or inducing pregnancy for athletic performance-enhancing benefits has been in public burner for sometimes. Now that the drug testing net is tough in competition and out of competition; pregnancy has becomes easy favourite route of getting an edge on competition.
Although in the cold war era there were spurious allegation of sponsored pregnancy by doping against the eastern block athletes and counter allegation even post the era.
This practice involved getting pregnancy and use the hormonal boost to train and later abort it or few even keep it.
Pregnancy induces surge in progesterone, estrogen and testosterone which increase muscle strength which actually affect physical performance. More enhancing performance can be achieved with increase in hormone like relaxin during pregnancy which is stimulated naturally to loosens the hip joints in preparation of the body for childbirth. But this enhance athletics flexibility.
Postpartum period seem to provide advantage for elites athletes. The cardio-circulatory system change in pregnancy which gives a huge increase in blood volume can be performance helpful by increasing in red blood circulating throughout the body. Both blood volume and red blood cell levels stay high for some time after they have given birth.
The intrigue benefit of pregnant athletes is that their heart is essentially remodeled. While the thickness of their heart wall remains the same, the chamber capacity increases, enabling it to hold a much larger volume of blood. This increases the efficiency with which oxygen is supplied to the muscles, the same mechanism induced by blood doping. With blood being pumped at a far greater rate around body.