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.
Over the three decades, the twin birth rate rose by 76%, from 1.9% to 3.3 percent of all births. This increase is likely due to the fertility medications and advancing maternal age.
It has been widely assumed that there has been an increase in twins over the years, largely attributed to fertility treatments. But the increase in the multiple birth rate means not just more twins, but also higher order multiples, such as triplets, quadruplets and the like.
It's a common misconception that twins skip a generation in families. There is absolutely no evidence, other than circumstantial, that twins are more likely to occur every other generation.
This is why fraternal twins run in families. However, only women ovulate. So, the mother's genes control this and the fathers don't. This is why having a background of twins in the family matters only if it is on the mother's side.
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).
Most cases of identical twins don't appear to run in families and instead seem to be a spontaneous occurrence, say experts. But there are some families with a larger-than-usual number of identical twins, suggesting there may be a genetic link.
Several factors for causes of embryo splitting were suggested, including maternal age, prolonged embryo culture, ovarian stimulation, and zona pellucida (ZP) manipulation [6].
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.
Fraternal Twins Boy and Girl
Since conception happened for each egg, each egg carries the sex chromosome of the father. A girl has XX chromosomes while a boy has XY chromosomes. A boy-girl combination is the most common form of these kind of twins.
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).
In 2021, according to the Australian Bureau of Statistics (latest report as of October 2021) there were 4,248 multiple births representing 1.5% of all births (309,996) in Australia. This comprised 4,185 pairs of twins and 63 sets of triplets and higher order multiples.
For women born 1870-1899, moms of twins averaged reproductive spans of 14 years 11 months versus 14 years for singleton moms. Both results were statistically significant. Moms of twins also were older at the time of their last birth.
People over 30, and particularly those over age 35, are more likely to conceive twins. 4 This is because the level of follicle-stimulating hormone (FSH) rises as birthing parents get older. FSH is responsible for the development of eggs in the ovaries before they are released.
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
According to The American Society for Reproductive Medicine, women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins. It was previously believed that identical (monozygotic) twins were random — not genetic.
In Nigeria, a growing city called Igbo-Ora is known as the twin capital due to it having the highest rate of twin births in the world. The town is the home of the annual World Twins Festival, which celebrates the many twins that reside in their community.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA.
And because the death rate in the womb is higher for twins than for singleton births, female twins are more common than male twins.
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.
In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.
Twins and other multiple-birth individuals can suffer from much deeper and troubling loneliness than single-born individuals. Separation anxiety, which often begins at birth, is the underlying cause of loneliness for twins.
Vanishing twin syndrome (VTS) is a miscarriage that causes a pregnancy involving twins to become a pregnancy involving one baby. It occurs when one of the embryos detected during an ultrasound stops developing.