Ogino-Knaus rule

[ō-gēnō-knous]
n.
  1. The rule of contraception stating that the time in the menstrual period when conception is most likely to occur is approximately midway between two menstrual periods, with conception being least likely just before or just after menstruation. It is the basis of the rhythm method of contraception.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.