Is it David Jacobs? Here's an excerpt from his site regarding abductions:
"EGG AND SPERM HARVESTING
It is an unfortunate but constant aspect of the abduction phenomenon that aliens take eggs and sperm from people on a routine basis. For women it involves the introduction of instruments that take either recently matured eggs or invade the ovary for follicles. There is some evidence to suggest that the aliens can accomplish rapid egg maturation and release through Mindscan for harvesting purposes. Harvesting can be accomplished at any age.
For men, sperm is extracted mechanically by a device placed around the genital area. Sometimes these devices are small and portable, other times they are on carts or attached to the wall.
Sometimes abductee women are brought in for sexual relations with men. These are sperm collection procedures and do not reflect any particular interest in sexuality by the aliens."
(source)
He's conducted over 1,200 hypnotic regressions with abductees since '86.