In Astrological terms, the prenatal epoch starts at the moment of conception. According to the author, "the prenatal epoch is a certain moment of time, occurring approximately at the commencement of the gestative period... when the degree ascending on the eastern horizon, and the longitude of the moon thereat, interchange with the longitude of the moon and the degree ascending at birth, or their respective opposite points." (pg. 19) What this means is that your prenatal moon was your birth ascendant, and your prenatal ascendant is your birth moon, or the opposite points in the zodiac. There are four possibilities: If the natal moon is above or below the horizon at birth, and if it is increasing or decreasing in light. So what good is this? For one thing, it helps explain infant abnormalities, as well as infant mortality, in cases where there are no other astrological factors. It also aids in reading charts for multiple births: Twins, triplets, quads and quints. Closely allied to the Prenatal Epoch is the Law of Polarity, or sex. Properly calculated, the Prenatal Epoch will not only confirm the sex of the individual, it will also serve to rectify the birth-time itself. Unlike other methods of rectification, where absurdly large time changes can result, Prenatal Epoch calculations correct minor errors in clock-time, thus enabling greater precision in forecasting.