Hi,
http://www.Mugu.Com/browse/galton/search/e
ssays/pages/galton-1875-heredity-twins.Htm
says:
you have a bigger chance of having twins then 'normal':
"on comparing the number of twins found among the uncles and aunts of twins with those found in similar classes of society generally, it appears that twin-bearing is hereditary, in so far that there is an excess per cent. Of three individuals of twin birth-in the former group."
http://www.Thebabycorner.Com/pregnancy/exp
erts/pregnancy/pregxa0003.Html says:
"monozygotic (identical) twins are not influenced by race, heredity, age, or number of previous children born of that mother."
http://mypage.Direct.Ca/c/csamson/multiple
s/1formed.Html says:
1. Race - the highest number of twin births are found in nigeria, 1 in 22 births. Other african nations also have high twinning rates. White european and north americans have a rate of about 1 in 34 (low because of fertility treatments....Naturally the rate is about 1 in 80-90). Asians have the lowest twinning rate, about 1 in 125. It is thought that the native diet of nigeria may assist in twinnings. Their diet contains a lot of yams, which contain a hormone (human chorionic gonadotrophin or hcg) that stimulates ovulation.
2. Age - the incidence of twinning is highest from the ages of 35 to 39. After 40 the rate decreases, except among black women, where the rate increases until about age 49. You are more likely to ovulate more than once the older you get.
3. Sexual activity - people will higher sexual activity seem to conceive more twins. This is based on the fact that many twins are conceived in the first three months of marriage, where sexual activity is higher.
4. Height/weight - taller and heavier women seem to have more twins, possible because their bodies can better accomodate more than one baby.
5. Previous children - mothers that already have children are more liekly to have multiples. By the fourth or fifth pregnancy, the chances of having twins is four times higher than for the first pregnancy. This stat may be related to the age of the mother - mom's with more kids are often older when they are in later pregnancies.
6. The pill - I have seen some research that twins seem to occur more right after a women has gone of the pill, possibly because of the fluctuations in hormone levels causing double ovulation.
7. Heredity - if you already have fraternity twins, you are four times more likely to have another set, as many women who have fraternals ovulate more than one egg per cycle on a somewhat regular basis. There is belief that fraternal twinning can be hereditary through the materal line. There is some gaining belief it could also be passed through the paternal line. Contrary to popular belief, they don't always skip a generation, and just because there are fraternal twins in your family doesn't mean you'll have a set. Identical twinning is a stroke of chance, as there is no apparent reason why identical twinning occurs.
8. Fertility treatments - there are two major types - hormone treatments with drugs and reproductive technology which involves surgical procedures. Both have caused the twinning rate to rise dramatically.
Etc.
Gr, mp
(try
www.Google.Com with words 'heredity twins (statistics)')
