Identical twins Identical (monozygotic) twins happen when a single egg (zygote) is fertilised. The egg then divides in 2, creating identical twins who share the same genes. Identical twins are always the same sex, so if your twins are identical, you'll have 2 girls or 2 boys.
Identical twins share the same genomes and are always of the same sex. In contrast, fraternal (dizygotic) twins result from the fertilization of two separate eggs with two different sperm during the same pregnancy. They share half of their genomes, just like any other siblings.
And because the death rate in the womb is higher for twins than for singleton births, female twins are more common than male twins.
The chances of having identical twins is relatively rare. For every 1,000 births, identical twins happen every 3rd or 4th. Although, the use of fertility treatments will increase the risk of having identical twins. Identical twins actually make up 0.95% of pregnancies that were conceived with treatment.
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. Like physical appearance and personality, fingerprints are largely shaped by a persons DNA and by a variety of environmental forces.
The study of 381 pairs of identical twins and two sets of identical triplets found that only 38 were genetically identical, Tina Hesman Saey reports for Science News. Most had just a few points of genetic mismatch, but 39 had more than 100 differences in their DNA.
Advances in DNA sequencing make it possible to see unique mutations in their fertilized eggs. It's a breakthrough that could solve unsolved cases, like the rape of a Michigan woman in 1999. Using DNA evidence, detectives located a suspect.
Things like your eye and hair color are controlled by your DNA. This is why identical twins look so much alike -- they share the same DNA. And yet, they aren't exactly alike. They can be hard to tell apart but if you look closely, you see differences.
In 2021, according to the Australian Bureau of Statistics (latest report as of October 2021) there were 4,248 multiple births representing 1.5% of all births (309,996) in Australia. This comprised 4,185 pairs of twins and 63 sets of triplets and higher order multiples.
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
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.
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.
Finding Out Twins' Gender via Ultrasound
You might discover the gender as early as 12 to 13 weeks into the pregnancy. How to find gender in a twin pregnancy is a little tricky as you'll have two very active and squirming babies rolling around inside Mom. One twin may be blocking the view of the other.
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!
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
Twin Zygosity
Fraternal, or dizygotic twins, form from two separate eggs that are fertilized by two separate sperm. The "di" in dizygotic means two, as in deriving from two zygotes (fertilized eggs). The terms identical and fraternal don't describe what the twins look like, but actually how they form.
One placenta and one amniotic sac.
This is the riskiest and rarest type of twin pregnancy. Fetal complications can arise due to tangling of the umbilical cords or an imbalance in nutrients, blood or other vital life supporting systems.
Once the babies are large enough to stay in one position in the womb, the twin lowest in the uterus is known as Baby A and the one furthest from there is Baby B, according to the Stanford Medicine News Center. In the majority of vaginal births, Baby A is born first.
Twins share the same genes but their environments become more different as they age. This unique aspect of twins makes them an excellent model for understanding how genes and the environment contribute to certain traits, especially complex behaviors and diseases.
Having two babies at a time is associated with a longer life, according to a new study. But that's not because doubling up on dirty diapers increases life span; instead, moms of twins are physically stronger in the first place.
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.
At age 7, the mean IQ score of twins was 5.3 points lower than that of singletons in the same family, and at age 9, the score was 6.0 points lower. The lower intelligence of twins in childhood may partly be a consequence of the reduced fetal growth and shorter gestations of twins, say the authors.
Identical twins are completely random. It's not based on family history or genetics. Identical twins form when a single fertilized egg splits and forms two embryos. Now in this case, it's not because of mom or dad.
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.