In order to judge in a chart, if and how many children a person will have, Lilly advises to look first at the 5th , then the 11th and finally the 1st and check if the signs on theirs cusps are fertile. He then makes a distinction between barren planets (Sun, Mars, Saturn) and fruitful planets (Moon Venus, Jupiter) and invites to check, which of them is in one of aforesaid houses, in the same order 5,11,1. Only after this he says to check the ruler of the 5th house and its placements.(CA p. 604 ff)
However, when it comes to the matter of numbers, Lilly remains pretty vague.
In his nearly 1500 years earlier Carmen Astrologicum, Dorotheus explains a completely different method in order to see, how many children a native will have.
He does not use the houses nor makes he any distinction between barren or fertile planets, but he uses instead Jupiter’s triplicity rulers and their aspects. For Dorotheus, Jupiter was the greater benefic and children “a heaven’s gift”, so they were associated to him.
His technique consists, briefly, in taking the stronger of the two principal triplicity rulers, see where it is located and then count from that sign in zodiacal order until the AC. He is somewhat unclear about how to count exactly, but my understanding is, that if the triplicity ruler is positioned above the horizon, we count from that sign towards the AC. When the ruler is beneath the horizon, we count from the AC to that sign (which is always in zodiacal order and anticlockwise).
Here are the quotes:
Look at the lords of Jupiter’s triplicities,which of them is stronger and calculate its place which is above the earth , and count from it till it reaches the AC: whatever signs are between these two, according to that is the number of his children
If Jupiter and Venus are in what is between these, they indicate an increase in this number, and whatever planet there are they also will increase the number
If these signs have two bodies, then double it.
If in these signs, there are Mars or Saturn, it indicates death of the child, especially if Mars and Saturn are in a bad place. But if these two are in good places, then they indicate an increase of children (…)3)
If you find the lord of Jupiter’s triplicity cadent from the MC, or the IC, then count from the AC to it, whatever number is between them, that is the number of children
If you find the Moon and Venus in Capricorn and Cancer or their triplicities, then see which of them is better in its position, let the strongest be the indicator of children. If they are both in other than these triplicities, then let you consideration be from the Lords of Jupiter’s triplicity
If you find the indicator of the matter of children in the AC or MC or in the sign of fortune, then he will be blessed with children by his youth. If it is in the second from the AC or in the sign of wedding, or in the 8th sign or the cardine under the earth, then children will be born to the native at his middle age.
All these examples are from persons I personally know.
Jupiter is in a fire sign, thus triplicity rulers are 1) Jupiter 2) Sun.
Jupiter is in his own triplicity and in a succeeding sign. As he is stronger than the Sun in Scorpio, he is the planet from which to count to the AC in zodiacal order.
The signs between Jupiter in Aries and the AC in Virgo are Taurus, Gemini, Cancer and Leo. This makes four children. The native has five. One of the signs between AC and Jupiter is a double-bodied, so we add another child. This matches with the natives true number of kids.
This woman has two kids. Let’s see how this shows up in the chart.
Jupiter is in a water sign, and her triplicity rulers are 1) Venus 2) Mars. Venus is stronger. As Venus is in Cancer, and the AC is in Virgo, there is only one sign between them, which would indicate one child. But the presence of Jupiter increases the number, so we see 2 kids.
This is the chart of the well known UK astrologer Deborah Houlding. Her Jupiter is in Pisces on the MC. Following Dorotheus, this position describes 4 children, which in her case holds true.
This woman has her Jupiter ins Gemini, and his triplicity rulers are 1) Saturn 2) Mercury.
Mercury is the stronger planet and the signs between Mercury and the AC are Cancer, Leo and Virgo, which makes three. But there is Mars in the middle, so we subtract one. I am not sure if this woman had an abortion, but I know for sure, she had only two kids.
This is a nighttime chart and Jupiter is in Gemini.
His rulers are 1) Mercury 2) Saturn. Mercury is stronger. In this case we count from the AC to Mercury and find Pisces, Aries and Taurus, which makes 3 kids. In the middle is Saturn. This woman did have an abortion, so the indication is two, which is true.
These are just four chart examples, which all prove the technique of Dorotheus. There will be more research to do about this argument, but I hope this article will lead other astrologers to consider this theory and check its reliability.
 Mercury is judged as “indifferent”, as it asummes the qualities of the planets close to it.