Among other things, uterine lavage is performed to withdraw at least 50% of in vivo fertilized preimplantation embryos produced after superovulation of a woman and artificial insemination using sperm of her sexual partner. After genetic diagnosis or sex determination or gene therapy, or any combination of any two or more of them, of the recovered embryos and selection of at least one of the embryos to be implanted, the selected embryos are returned to the woman for implantation in her uterus.