1. If you are member of astrodenist.
2. Go to astrodenist's data bank then Search:
"Family : Parenting : Birthing - Twins, triplets"
The mother whom gave birth to twins/triplets, in many cases even the fathers who have twins/multiple births:
In western tropical charts are usually 5th house cusp in mutual sign (Gemini, Virgo, Sagittarius and Pisces) and/or ruler of the 5th is ruled by
Mercury or in the sign of Virgo or Gemini.
At time, the ruler of the 5th conjuncts/square/opposition/trine
Mercury.
Or
Mercury is in the 5th house cusp.
Simply, is always always about the
Mercury.
For example, 5th house cusp in Aries, but Mars is in Gemini.
Here are some random examples
Example 1)
Family
http://www.astro.com/astro-databank/Research:Twins_Family_1
Mother gave birth to twins (Sons):
5th house Aries, Mars in Virgo 10th, Mars even mutual reception with Mercury in Scorpio in 11th house
http://www.astro.com/astro-databank/Research:Twins_Family_2
Father had twins of the same family (Sons):
5th house cusp starts at the late degrees of Libra, Moon in 5th house Scorpio, Venus ruler of the 5th cusp in Cancer conjuncts Mercury both in 12th. Moon in the 5th trine Venus and Mercury in Cancer.
Example 2)
http://www.astro.com/astro-databank/Hayward,_Susan
Mother had twins (Sons):
5th house Aries, Mars is in Gemini, Mercury in Gemini
Example 3)
http://www.astro.com/astro-databank/Potter,_Herbert_Thomas
Father of twins (Daughters):
5th house cusp starts in the sign of Gemini, Mercury in Taurus, exact conjunction with exalted Moon in Taurus in 3rd. Venus the ruler of Mercury and Moon is herself in Gemini in 4th.
5th house contains Mars and Pluto in Cancer, ruler of 5th house cusp Mercury and Moon both sextile Mars and Pluto.
Review all the charts under the category of
"Family : Parenting : Birthing - Twins, triplets"
And very soon you will see the patterns.
About 119 charts are available under this category.
Personally, even 5th house in mutual signs, when 5th house has relationship with Mercury as I mentioned above will be more likely.