This is an extremely rare occurrence in humans and is known as heteropaternal superfecundation. We don't know exactly how often this occurs and cases only arise when suspicious family members request DNA testing. But one study estimated that it might occur in as many as one in 400 (0.25%) twin births in the US.
Can twins have different fathers? In rare cases, fraternal twins can be born from two different fathers in a phenomenon called heteropaternal superfecundation. Although uncommon, rare cases have been documented where a woman is pregnant by two different men at the same time.
The occurrence of heteropaternal superfecundation is extremely rare, though difficult to estimate because it is only discovered if paternity is contested. To reiterate, it relies on many events. When multiple ovulation occurs, it then requires the fertilization of both ova, from different sources of sperm.
To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.
Well, what are the odds? Kasraie has found two studies of the incidence of heteropaternal superfecundation, both from the early 1990s. One author claims that one in 400 pairs of fraternal twins (those arising from two eggs) fits the description. The second author puts the figure at one in 13,000 cases of paternity.
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.
Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl. To understand this combination: Males have XY chromosomes, females have XX chromosomes. You have a girl twin when the father's X chromosome combines with the mother's X chromosome.
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.
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.
Superfetation is a rare event that involves getting pregnant a second time while you're already pregnant. It's so uncommon that cases of superfetation often make headlines.
A dad who's one of a twin may inherit the gene, but it won't increase his chances of having twins too, because the gene only affects ovulation. The same dad may pass on the gene to his daughter, who then goes on to get pregnant with twins, making it look like twins have skipped a generation .
If the twins are present on your husband's/partner's side, it won't influence your chances of having twins. Remember, the gene for hyperovulation is only a factor for the mother. If your mother (or your grandmother or aunt) was or had fraternal twins, you might have the gene.
How rare is getting pregnant while you're pregnant? It's extremely rare to get pregnant when you're already pregnant. There have been fewer than ten recorded cases of superfetation in humans.
From watching "The League," we're heard the term Eskimo Brothers for dudes who've slept with the same girl. Urban Dictionary, the source for all things slang, likewise defines Eskimo Sisters -- or Pogo Sisters -- as "two women [who] have slept with the same man in their past."
What is it? 'Mirror image' is a type of identical twinning. It can happen in any type of identical twins. When the split occurs late - more than a week after conception - the twins can develop reverse asymmetric features. This term is not really a type of twin, just a way to describe their physical features.
A rainbow baby is a child born after the loss of a previous pregnancy or newborn. Read Caitlin's story, and learn about her two miraculous rainbow babies. You've heard of a rainbow baby, a child born after the loss of a previous pregnancy or newborn. What's less common is having two rainbow babies in the same home.
Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother's X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother's to make a boy (XY).
Age. 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.
Just like having a boy or a girl in a typical pregnancy, the chance of having boy and girl twins is one in two.
Still, she cautions, a lot more work needs to be done to establish a causal link. Fraternal twins, in which each of two eggs is fertilized by a different sperm cell, occur in about four of every 1000 births. About half of those result in male-female twin pairs.