The primary principle of the Prenatal Epoch has been stated by Max Heindel in The Message of the Stars, where he says that the body is the product of lunar forces and that the position of the Ascendant, or its opposite, at birth, is the Moon's position at conception. The keyword of the Moon is fecundation or fertility, and it is Jehovah and the lunar Angels that preside at the birth of a child. This is stated in the Cosmo-Conception and other works of the Rosicrucian Philosophy. We thus see that the Moon has primary influence over the formation of the physical body, and that the Ascendant represents merely the transference of the Moon's position from conception to birth.
This law was known to the ancients as the "Truitine of Hermes," from Hermes Trismegistus, who first correctly formulated and stated the law as follows: "The place of the Moon at conception becomes the birth ascendant or its opposite point."
"But this proved to be but one-half of a very important law, for while the Ascendant at birth was the place of the Moon at a certain Epoch, the Ascendant or its opposite point at this Epoch was the place of the Moon at birth -- a very remarkable interchange of factors." --E.H. Bailey.
According to the Ancient Wisdom, "The World-Breath has a definite and periodic pulsation, a systole and diastole action, whereby birth and death are controlled." This idea of periodicity, well established by modern science, furthers the idea that birth can take place only in respect to any single locality at intervals, that these intervals are in accord with lunar motion, and that only every seventh impulse of the World-Breath permits of human births.
The modern version of the Prenatal Epoch we first established by the English astrologer known to the astrological world as Sepharial, in the year 1886. It was published by him in 1890. In this he had the collaboration of a trained and veteran scientist, a doctor, who helped him to establish the primary laws of the Prenatal Epoch by years of painstaking research and actual experiments. This doctor was an expert obstetrician and proved the laws of the Prenatal Epoch by actual firsthand data.
These laws have been further verified, extended, and complemented by the painstaking researches of E.H. Bailey, to whom great credit is due for his many and exact proofs of the Prenatal Epoch. His book upon this subject is considered standard authority, and we are in the main following his very worthy contribution to the subject and are extending him full credit.
One of the primary uses of the Prenatal Epoch is the correction or rectification of the birth time when only the approximate time is given. Another is its utility in determining correctly the sex of the native. Finally, it gives sidelights on the character and inner nature of the individual as fundamental as those of the birth chart.
"As births are brought about in exact harmony with lunar laws, it is shown that intrauterine life is in direct relation with the sidereal world without, that the great fact of maternity is capable of purely astronomical measurement and rule .... The law is nothing less than a mathematical measurement of human life, a stupendous natural fact; nothing more exactly mathematical and matter of fact is to be found in the records of scientists than this record of intra- uterine life, for only through its study will the laws of generation be fully understood." -- Sepharial.
"In the measurement of the intra-uterine period we actually measure the whole future of the individual; alter this one fact -- the moment of conception (or its spiritual counterpart, the Epoch) -- and you change the whole course of the progeny's destiny. If we accept the occult theory that the Prenatal Epoch is the descent of the Ego to the Desire World, then it must show the inherent character of the Ego about to incarnate. It may be stated that the Epoch has a more intimate relationship with the individual than the horoscope at birth, the latter appearing to reject the personality and its heredity and environment. In other words, the Epoch represents the man about to manifest in the flesh, the horoscope denotes actual personal conditions and environments into which he is born. Every birth is directly connected with the Epoch, and every authentic natural birth will, within the limits of an error of observation, yield an Epoch in accordance with the rules to be given."-- Bailey.
For summary, let us restate the fundamental principle of the Prenatal Epoch known as the Truitine of Hermes: "The Ascendant at birth is the place of the Moon at a certain Epoch, ant the Ascendant or its opposite point at Epoch was the place of the Moon at birth."