And because the death rate in the womb is higher for twins than for singleton births, female twins are more common than male twins.
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). Remember that sex and gender are not the same.
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.
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. It sounds like fraternal twins do indeed run in your family!
30% of twins are identical. 50% of non-identical twins have the same gender.
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.
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. This is why we often say the “risk” for having twins comes from the mother.
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.
Girl-boy twins occur when one X egg is fertilized with an X sperm, and a Y sperm fertilizes the other X egg. Sometimes health care professionals identify same-sex twins as fraternal or identical based on ultrasound findings or by examining the membranes at the time of delivery.
Having twins naturally
It's estimated that 1 in 250 pregnancies results in twins naturally, and there are two ways to conceive them.
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.
With twin pregnancies, both the pregnant person and twins face a higher risk of complications. Prenatal checkups occur more frequently with twin pregnancies, making it possible to detect issues in earlier stages. Twin pregnancies are high risk because there are many potential complications.
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.
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.
Fraternal twins — the most common kind of twins — occur when two separate eggs are fertilized by two different sperm. Each twin has his or her own placenta and amniotic sac.
What are the chances 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.
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.
Is there a third type? Traditionally, the science around twins has taught that identical and fraternal are the only two types. But a third type might exist, called polar body or half-identical twins.
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.
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.
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.
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.
Drink Alcohol, Use Drugs, or Smoke. It's never advisable to drink alcohol excessively, smoke, or take drugs, whether you are pregnant or not. When you are pregnant, doing so exposes your unborn babies to toxic substances, raising their risk of birth defects and chronic illnesses.
36 weeks for identical twins sharing a placenta. 35 weeks for an uncomplicated triplet pregnancy. 32-33 weeks for MCMA twins.
Potential health complications in a twin pregnancy
Women with twin pregnancies are more likely to have pregnancy health problems and complications like gestational diabetes, pre-eclampsia, premature labour and bleeding. Twins who share a placenta might have extra complications.