a pair of female ere ibeji twin figures (early 20th-century) in permanent collection of children s museum of indianapolis. yoruba people have highest twinning rate in world.
about 1 in 90 human births (1.1%) results twin pregnancy. rate of dizygotic twinning varies among ethnic groups, ranging high 45 per 1000 births (4.5%) yoruba 10% linha são pedro, tiny brazilian settlement belongs city of cândido godói. in cândido godói, 1 in 5 pregnancies has resulted in twins. argentine historian jorge camarasa has put forward theory experiments of nazi doctor josef mengele responsible high ratio of twins in area. theory rejected brazilian scientists had studied twins living in linha são pedro; suggested genetic factors within community more explanation. high twinning rate has been observed in other places of world, including:
igbo-ora in nigeria
kodinji, located in kerala, india
mohammadpur umri, located in uttar pradesh, india
the widespread use of fertility drugs causing hyperovulation (stimulated release of multiple eggs mother) has caused call epidemic of multiple births . in 2001, first time ever in us, twinning rate exceeded 3% of births. nevertheless, rate of monozygotic twins remains @ 1 in 333 across globe.
in study on maternity records of 5750 hausa women living in savannah zone of nigeria, there 40 twins , 2 triplets per 1000 births. twenty-six percent of twins monozygotic. incidence of multiple births, 5 times higher observed in western population, lower of other ethnic groups, live in hot , humid climate of southern part of country. incidence of multiple births related maternal age did not bear association climate or prevalence of malaria.
predisposing factors
the predisposing factors of monozygotic twinning unknown.
dizygotic twin pregnancies more when following factors present in woman:
she of west african descent (especially yoruba)
she between age of 30 , 40 years
she greater average height , weight
she has had several previous pregnancies.
women undergoing fertility treatments may have greater chance of dizygotic multiple births. in united states has been estimated 2011 36% of twin births resulted conception assisted reproductive technology.
the risk of twin birth can vary depending on types of fertility treatments used. in vitro fertilisation (ivf), due insertion of multiple embryos uterus. ovarian hyperstimulation without ivf has high risk of multiple birth. reversal of anovulation clomifene (trade names including clomid) has relatively less yet significant risk of multiple pregnancy.
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