Add Aries Alyson Hannigan to the ranks of those who have given birth on their birthday! She celebrated her 35th birthday on March 24th by delivering her first child, daughter Satyana. According to some sources as many as 5% of newborns share their birthdays with their mothers. When you consider that there are 365 days in a year this becomes quite a mind-boggling statistical anomaly! While astrologers (or anybody else) would certainly not be able to tell you HOW this happens, we can definitely explain why this bond is so strong.
People born on the same day (or sometimes within one day) of one another, even in different years, share the same degree of birth. Alyson and her daughter were both born at 3 degrees Aries. So when planets make an aspect to 3 degrees Aries (like Pluto over there at 3 degrees Capricorn) it affects both of them very similarly. So from the moons cycles every month, to the longer outer planet transits, both people experience the ebbs and flows of this energy together. So the bond between mothers and children born on the same day is generally a very strong one.
I have also noticed a lot of mothers giving birth to children whose natal sun is conjunct their progressed sun. For example, when Scorpio Julia Roberts gave birth to her twins on November 28, 2004, they were born at 6 degrees Sagittarius, within several degrees of Roberts progressed sun at 11 degrees Sagittarius. Capricorn Amanda Peet’s progressed sun was at 26 degrees Aquarius when she gave birth to her daughter, Frankie, who was born at 0 degrees Pisces. These conjuncts are not exact but they are still very close and while to the naked eye they are not as significant as sharing the same actual birth date as a parent, astrologically they are very similar in that they strengthen emotional bonds because passing transits affect them both very closely.