An implantation dip is a one-day dip in the body's temperature that typically occurs approximately one week after ovulation, according to About.com. This dip is sometimes due to implantation of a fertilized egg in the wall of the uterus.
Fertility Friend points out that an implantation dip is statistically more likely to occur when implantation has occurred. However, it is also possible to see a one-day dip in basal body temperature during the week after ovulation when there is no pregnancy; 11 percent of women show this phenomenon. Conversely, 75 percent of women do not show an implantation dip during the month in which they conceive.