How do identical twins happen?
Identical twins can also occur when one a woman has undergone fertility assistance and has had one fertilized egg returned to her uterus. If this egg then splits into two, an identical twin pregnancy can result.
Identical twins are not dependent on race, country, or ethnicity. The odds of having identical twins are the same for every couple, in every pregnancy, wherever they live in the world.
Around one in every three sets of twins born is identical, and the remaining 2 of 3 are of the non-identical variety.
What increases the odds of having identical twins?
- Luck needs to be on your side. Identical twins don’t run in families and can happen for any couple with any pregnancy. Non-identical twins are influenced by genetics; women whose mothers or grandmothers had non-identical twins do have more chance of having non-identical twins themselves. But identical twins are just random.
- Some families do seem to have a higher-than-average number of identical twins. This can only be contributed to luck, coincidence, and chance rather than any familial genetic tendency.
How do non-identical twins happen?
Because identical twins share the same genes, they are always the same gender. But non-identical twins may be the same gender or the opposite gender because they only share 50% of the same genetic coding.
Some people still believe that the incidence of having twins skips a generation, but this is not true.
What increases the odds of having non-identical twins?
Having assisted reproductive technology, in particular taking medication which increases ovulation. This makes perfect sense because the more eggs which are supported towards maturity each month, which are then released, means the more that are available to be fertilized.
The more pregnancies a woman has already had, the higher her chances of conceiving with non-identical twins.
If a woman is a fraternal, non-identical twin herself, or if she has siblings who are fraternal twins, or her mother or grandmother had fraternal twins, then she is more likely to have twins as well.
Black African women are more likely to have twins than women from any other ethnic descent.
What causes the fertilized egg to separate into two?
The splitting of one fertilized egg is a malformation of the natural processes of conception.
When are identical twins actually formed?
The stage at which the egg splits will also determine if the babies have their own amniotic membranes and placenta or if they will share. Essentially, the earlier the egg splits, the more independent each twin will be by having their own amnion, chorion, and placenta.
Early splitting also means that the twins are perhaps less identical than those who separate at the late blastocyst stage. Around a quarter of all identical twins are said to be mirror images of each other. This means that the left side of one twin exactly matches the right side of the other. How amazing is that!
Although identical twins share the same DNA and genetic coding, they are still unique little individuals. Small differences separate them, and although at birth they can appear like little clones of each other, they are far from it. As identical twins grow, their unique qualities (particularly in relation to their personalities) become more apparent. The environment in which they are raised as well as their own personalities help to shape the adults they will become. This is exactly the same as any other baby born the world over.
How will I know if I’ve conceived with twins?
Is it obvious at birth that twins are identical?
The only way to be 100% sure is to do DNA testing on each twin and see what genetic information they share. This can be done in the early neonatal period by taking a swab of tissue from inside each baby’s cheek. This is painless and non-invasive.
The other way to check is to take a blood test and do blood grouping. Identical twins will share the same genetic information so the same genetic markers can be identified. Non-identical twins can be very different, much the same as any other siblings with the same parents. They share around half the same genetic information and traits with each other.
What are the risks of having identical twins?
- If the identical twins share a placenta they are at a higher risk of having twin-to-twin transfusion syndrome. This often results in one twin gaining more nourishment than the other and having a higher birth weight as a result.
- There is a risk of umbilical cord entanglement and compression if the twins share an amniotic sac because of the crowded conditions which occur in the mother’s uterus.
- With identical and non-identical twins, there is an increased risk of pregnancy and birth complications. There is also an increased likelihood of prematurity and associated problems.
The information of this article has been reviewed by nursing experts of the Association of Women’s Health, Obstetric, & Neonatal Nurses (AWHONN). The content should not substitute medical advice from your personal healthcare provider. Please consult your healthcare provider for recommendations/diagnosis or treatment. For more advice from AWHONN nurses, visit Healthy Mom&Baby at health4mom.org.