The quick answer to this question is that, in a twin pregnancy, it is the mother's genes that determine twins. First up, giving birth to identical twins is not genetic, but conceiving fraternal twins is. The mother may have the genetic trait of releasing two eggs in one menstrual cycle.
The gene versions that increase the chance of hyperovulation can be passed down from parent to child. This is why fraternal twins run in families. However, only women ovulate. So, the mother's genes control this and the fathers don't.
Many people believe twins skip a generation, but that's just a myth. The idea that twins skip generations likely comes from the fact that the genetic factors contributing to twins only come from the gestational parent's side.
When both eggs are fertilized, the resulting siblings are fraternal twins. Because this gene can be passed on, the tendency to have fraternal twins can in fact run in families. Identical twins, on the other hand, result from one fertilized egg randomly splitting in two, creating two siblings with identical DNA.
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.
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.
if you're pregnant and over 35 you're more likely to have non-identical twins because you're more likely to release more than 1 egg during ovulation. non-identical twins run on the mother's side of the family, probably because of an inherited tendency to release more than 1 egg.
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.
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.
Identical twins are almost always the same sex, although there are some rare exceptions to this rule. Because identical twins occur when a single fertilized egg splits and forms two embryos, each embryo has the same chromosomes (usually, XX for girls or XY for boys).
Age. 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.
High parity – Having one or more previous pregnancies, especially a multiple pregnancy, increases the chances of having multiples. Race – African-American women are more likely to have twins than any other race. Asian and Native Americans have the lowest twinning rates.
“Having twins is not twice as hard—it's exponentially more difficult,” says Natalie Diaz, author of What To Do When You're Having Two and CEO of Twiniversity, a global support network for parents 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.
Identical (i.e., monozygotic, or MZ) twins share 100 percent of their genes, whereas fraternal (i.e., dizygotic, or DZ) twins generally share only 50 percent of their genes.
Asian Americans and Native Americans have the lowest rates for twins. White people assigned female at birth have the highest rate of higher-order multiple births (triplets or more). This is especially true for those older than 35.
The rate keeps rising for (naturally) two big reasons. More twins are being born now than ever before. Parents are increasingly using in-vitro fertilization and deciding to have children later in life. The twin rate could continue to go up as more nations push these factors higher.
About 1 in 3 of all sets of twin births are vaginal births. You may choose to have an elective caesarean, or your doctor may recommend a caesarean section because of potential complications. Even if you plan a vaginal birth, you may end up having an emergency caesarean section due to complications during labour.
A little more than half of twin pregnancies end in preterm delivery (before 37 weeks). While 40 weeks is the full gestation period of the average pregnancy, most twin pregnancies are delivered at approximately 36 weeks (range 32-38 weeks depending on the type of twin pregnancy).
They come from the same fertilized egg and share the same genetic blueprint. To a standard DNA test, they are indistinguishable. But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints.
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That's not all, Monga says. Women pregnant with twins complain of more back pain, sleeping difficulties, and heartburn than those who are carrying one child. Being pregnant with twins also carries a higher rate of maternal anemia and a higher rate of postpartum hemorrhage (bleeding) after delivery.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA. A boy has XY chromosomes and a girl has XX chromosomes.
Identical twins are also known as monozygotic twins and are the result of a single fertilized egg which splits into two after conception. Identical twins share the same genetic profile including the same sex and blood type.