Asian and Native Americans have the lowest twinning rates. Caucasian women, especially those over age 35, have the highest rate of higher-order multiple births (triplets or more).
Asian Americans and Native Americans have the lowest twinning rates. White women, especially those older than 35, have the highest rate of higher-order multiple births (triplets or more).
Africa has a high rate of twins born naturally from two separate eggs, and according to the study 80% of twins are now born either in Africa or Asia.
The percent of people who are twins differs by race and ethnicity. In the U.S., twins are most common in African-Americans (36.8 per 1000) and least common in Hispanic/Latino Americans (21.8 per 1000).
Vietnam was the country with the fewest twins (6.2 per 1,000 births) and Benin was the country with the most (27.9 per 1,000). Over time, some of these developing countries saw increases in twins, but some saw decreases and some stayed the same, with any changes tending to be small.
Researchers have long noticed that the Yoruba tribe — whose members live in Nigeria, Benin, Togo, and elsewhere — is a world leader in twins. A 1989 study in the Journal of Reproductive Medicine noted that their twin rate at the time was more than four times higher than that of Caucasians.
Monoamniotic-monochorionic Twins
These types of twins share a chorion, placenta, and an amniotic sac. This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.
About one-third of twins are identical or monozygotic twins (when one fertilised egg divides in half). Two-thirds are non-identical or dizygotic twins (when two eggs are fertilised by different sperm). The chance of any woman having identical twins is one in 300.
However, for a given pregnancy, only the mother's genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father's genes can't make a woman release two eggs.
The Science of Fraternal Twins. Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl.
Race – African-American women are more likely to have twins than any other race. Asian and Native Americans have the lowest twinning rates. Caucasian women, especially those over age 35, have the highest rate of higher-order multiple births (triplets or more).
According to the Office on Women's Health , women who are aged 30 years or older are more likely to conceive twins. The reason for this is that women of this age are more likely than younger women to release more than one egg during their reproductive cycle.
The study found big increases in twinning rates in many European countries in North America and Asia. But 80% of all twin deliveries are now in Africa and Asia, with Africa having the highest twinning rates of all.
The fertility rate in the United States in 2020 was 56.0 per 1,000 women ages 15-44. Of all live births in the United States during 2018-2020 (average), 23.7% were Hispanic, 52.1% were white, 15.2% were black, 0.8% were American Indian/Alaska Native and 6.8% were Asian/Pacific Islander.
Identical twins have 100% of their DNA the same while fraternal twins share only 50%. But what about semi-identical twins? Well, they have 75% of their DNA the same.
For a given pregnancy, the odds of conceiving fraternal twins are only determined by the mother's genetics, not the father's. Fraternal twins happen when two eggs are simultaneously fertilised instead of just one.
While men can carry the gene and pass it on to their daughters, a family history of twins doesn't make them any more likely to have twins themselves. 3 But, if a father passes on the "twin gene" to his daughter, then she may have a higher chance than normal of having fraternal twins.
In fact, one British study tested ESP potential among identical twins and found that they were correct about 25% of the time, the same as any other siblings. There is one particular power though which twins possess, longevity. Fraternal twins live longer than singletons and identical twins longer still.
A big reason for all those twins is an increase in medically assisted reproduction, including in vitro fertilization, ovarian stimulation and artificial insemination. Another reason is that women in many countries are having babies at older ages.
Weight. Women who have overweight or obesity also have a higher chance of conceiving twins naturally. Specifically, the chances are highest if your body mass index (BMI) is above 30, according to a 2005 study that looked at data from more than 51,000 births in the United States.
In the majority of vaginal births, Baby A is born first. But occasionally the twins switch positions at the last minute, and Baby B emerges first, as further noted by the Stanford Medicine News Center. Still, the birth order is relatively straightforward.
The longest interval between the birth of twins is 90 days, in the case of Molly and Benjamin West, dizygotic (fraternal) twins born in Baltimore, Maryland, USA to parents Lesa and David West (all USA) on 1 January and 30 March 1996.
There are more twins in the "millennial generation" than any other generation, thanks partly to a twin boom in the '90s. The main reason was a new technology called in vitro fertilization, which in its early days frequently produced twins, triplets and other multiple births.
The notion that twins always skip a generation is also a myth. The illusion may have arisen because men who inherit the gene from their mothers are unaffected by it ( they do not ovulate), but can still pass it on to their daughters, who, in turn, will have an increased likelihood of conceiving twins.