This episode appears to be based on the 1992 Dr. Cecil Jacobson case. Jacobson operated a fertility clinic in Virginia, and in March of 1992 was sentenced to five years in prison after it was learned that he inseminated seventy-five of his female patients with his own sperm. Jacobson had led the women to believe they were being inseminated with the sperm of anonymous donors who shared many physical characteristics with their own husbands. He also led many of his patients to believe they had become pregnant and miscarried when in fact they had never actually been pregnant.
HGC stands for Human chorionic gonadotropin which is a hormone produced by the placenta after a fertilized egg implants on the endometrium (the inner layer of the uterine wall). This is the hormone that most home pregnancy tests detect. Its purpose is to signal the ovaries to produce higher levels than normal of the hormone progesterone during the first trimester, which in turn causes a thick lining of blood vessels to develop in the uterus to supply the placenta with the extra blood and nutrients it needs to develop fully in order to accommodate the ever increasing needs of the developing embryo.
George Dzundza, who was in the original line-up of Law and Order, played Dr Cecil Jacobson (upon which this episode is based) in the 1994 movie The Babymaker: The Dr. Cecil Jacobson Story (1994).
Susan Parker clearly lost her mind, which her husband Brandon can attest to. The woman lost any sense of love in their marriage due to the hyper focus on wanting a baby. This was enough to make him give her divorce papers, which lead to her attacking him. He knocked her down in self defense, which lead to her thinking she miscarried from the fall. All in all, Brandon came out ahead of the ordeal; he doesn't have to deal with legal issue of divorce and just has to bury his wife. Sure, there's the immediate grief, but he is finally free.
Despite the Brocks specifically wanting to use the father's sample, Dr Gilbert swapped it out for his own; they weren't asking for an anonymous donor like the others. This completely ruins their plan to use their son as a donor for his sister, whom had leukemia. The Brocks won't testify against him today, but they may just change their tune when their daughter dies due to the son being incompatible as a donor. They can get a DNA test and sue his ass for indirectly causing her death by tampering with the invitro.