Dizygotic (DZ) twins, also called fraternal twins, occur when two egg cells are each fertilized by a different sperm cell in the same menstrual cycle. DZ twins are about twice as common as MZ twins, and they are much more likely to run in families.
However, few genes appear to be definitively linked to hyperovulation, so it could just be that genetics in general on the mother's side contribute to the probability of having fraternal twins. Heredity on the father's side, on the other hand, does not increase a couple's odds of having twins.
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. And why your son's family genetics did not play a role in his twins.
So if fraternal twins run in a woman's family, she may be more likely to have fraternal twins herself. If a woman's sister has fraternal twins, she is about 2.5 times more likely to have twins herself. If a woman's mother has fraternal twins, she is about 2 times more likely to have twins.
The genetic predisposition for twins only affects gestational parents. A biological, non-gestational parent can pass down these genetic traits to their children. Still, they won't be more likely to raise twins themselves unless the surrogate, gestational parent also has a family history of twins.
This belief is based on the assumption that twinning is genetic and runs in families. However, if that was truly the case—if there was a twin gene—then twins would occur with predictable frequency in those families that carry the gene. There is no concrete scientific evidence that suggests twins skip a generation.
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.
Factors that increase the chance of twins include: consuming high amounts of dairy foods, being over the age of 30, and conceiving while breastfeeding. Many fertility drugs including Clomid, Gonal-F, and Follistim also increase the odds of a twin pregnancy.
Identical, or monozygotic (MZ), twins have 100 percent of their genes—including those that influence risk for alcoholism—in common, whereas fraternal, or dizygotic (DZ), twins share (on average) only 50 percent of the genes that vary in the population (see figure). Common Environmental Sources.
Most sets of Twins
The first wife (died ante 1770), of Feodor Vassilyev (b. 1707–c. 1782), a peasant from Shuya, Russia, gave birth to 16 sets of twins. Barbara Zulu of Barberton, South Africa bore 3 sets of girls and 3 mixed sets in seven years (1967–73).
A Russian woman named Valentina Vassilyeva and her husband Feodor Vassilyev are alleged to hold the record for the most children a couple has produced. She gave birth to a total of 69 children – sixteen pairs of twins, seven sets of triplets and four sets of quadruplets – between 1725 and 1765, a total of 27 births.
If you are lucky enough to come from a family with a pattern of having twins then genetically you are more likely to as well. So if you, your mother or your maternal grandmother are or were fraternal (non-identical) twins then your chances of having twins may increase to as many as 1 in 7.
Fraternal twins tend to run in families. Researchers think there may be a gene for hyperovulation (the tendency to release more than one egg in a single menstrual cycle). While both males and females could carry the gene, the male would not as a result be at increased risk of having twins.
Just over 3 percent of babies in the United States are now born in sets of two, three or more, with the majority — about 97 percent — of these multiple births being twins. So your chance of having twins is about 3 in 100.
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.
In Australia, twins happen in 1 in every 80 births. This means that 1 in 40 Australians is a twin. The birth rate of identical twins is the same around the world and doesn't vary with the mother's age.
The birth process is similar to giving birth to a single baby. If you're planning a vaginal birth, your health team may recommend that you have an epidural for pain relief.
Twins are more or less equally likely to be female or male. Contrary to popular belief, the incidence of twins doesn't skip generations.
If one identical twin has autism spectrum disorder (ASD), the other twin has a 76 percent chance of also being diagnosed with it. The numbers are lower for fraternal twins.
When people refer to Irish twins, it's important to recognize that although the siblings are close in age, they are not actually twins. In other words, they were not born during the same gestational period. Calling them Irish twins is just an informal way of classifying siblings that are born close together.
Part of the series: Pregnancy Tips. If your husband is a twin, there is no genetic evidence that shows that the chances of you having twins is increased.