When a woman finds out she is expecting twins, she may or may not know to ask what kind. However, there are major differences in fraternal and identical twins. While the average person may not know this, mom will be an expert on twins before the end of her pregnancy.
The differences in the two major types of twins affect the pregnancy, sometimes the birth, and many factors after delivery. Though all twins share a special bond, fraternal and identical twins don't share the exact same amount of genes, and there are factors that affect one kind of twin that don't affect the other.
It's important for mom and dad to learn about these differences, and by the time their children are a year old, they will wish the general public knew more about the differences as well. Since twins earn tons of attention whenever they are out and about, mom and dad are constantly asked the same questions about their children, questions that could be avoided if people understood certain facts about fraternal versus identical twins.
Twins have always fascinated people, and there's good reason for that. The similarities and differences between the different types of twins is amazing, and even just studying one type of twin reveals unique information.
For those who are ready to be informed, the top facts about fraternal and identical twins are provided. This is not only for the novice, but also for the twin mom who is still trying to learn everything she can about this twin thing. The information is vast, so we'll help break it down.
15 Identical Twins' Kids Are Half Siblings, Genetically Speaking
Let's say a set of fraternal twins have children with their partners. The cousins, the children of the twins, will just be cousins like any other children born of siblings. However, when identical twins have kids with their partners, they are actually giving birth to half-siblings, genetically speaking.
Since identical twins carry the same DNA, their children are born with half of that DNA. Things gets even weirder when identical twins marry identical twins. The children of these couples are genetically siblings!
It's true that they don't qualify as half or whole siblings according to other standards, like being born to the same parents or coming from the same womb or from the same sperm. However, from a purely scientific standpoint, they are a bit more than cousins. This is fascinating and weird and is another way identical twins are different from fraternal.
14 Fraternal Twins Can Have Two Different Fathers
Another freaky fact is that fraternal twins can have two different fathers. It's rare, but due to the way fraternals are created, it's entirely possible.
If mom releases more than one egg during her ovulation period, they don’t both have to be fertilized at the same time. Mom may have relations with one man at the beginning of her fertile window, resulting in the fertilization of one egg. She may then be intimate with another man towards the middle of her fertile window, and the other egg is fertilized by him. This equals two partners, two eggs, and twins.
These special sets of twins are considered bipaternal, but unless mom volunteers this information to other people, there's no way to tell. Since fraternal twins can look completely different and come from the same father, it's best not to ever assume.
13 Neither Identical Nor Fraternal Twins Have To Look Alike
Most people have been around twins who look so alike that it's hard to tell them apart. Others have known twins who look nothing alike, the kind nobody knows are twins until they are told. Though it's more likely for fraternal twins to look different, it's possible for identicals to have different appearances as well. There's no guarantee that twins will look alike.
Environmental factors and lifestyle choices have a lot to do with why twins don't always look the same. Even identical twins who take care of their health differently or who make different lifestyle choices can start out looking the same but change completely as they age.
With fraternal twins, they generally start out looking different because they don't share genes. Like any siblings, they share some genes because they come from the same parents, but that's about it. Environmental influences may cause them to look even less alike.
12 Identical Twins Are Not Genetic
One of the most common questions asked to parents of twins is if twins run in their family. This is a valid question for the parents of fraternal twins. For the parents of identical twins, it is not.
The reason? Identical twins are not passed down through the genes or family line. There is a 1 in 250 chance that a woman will become pregnant with identical twins whether anyone in her family has ever had a set of twins or not. In fact, the overall reason that identical twinning occurs is unknown, and it's much harder to trace down factors for this kind of twinning than it is for fraternal twins.
What's difficult is making other people understand this fact. If mom has identical twins, and she had a great aunt who also had an identical twin, everyone assumes there is a genetic connection. This is false, but moms of identical twins tend to find that people believe what they choose despite actual facts.
11 Only Fraternal Twins Can Be Boy And Girl
Nothing beats someone walking up to a parent and asking if the twins are identical when they are different genders. That can't actually happen. Identical twins are going to be the same gender, but fraternal twins may not.
Where fraternal twins are concerned, they can be either a brother/sister, sister/sister, or brother/brother set. The possibilities are vast. However, identical means identical in many of the most important ways, including gender.
Twins who are different genders are less likely to be deemed "the twins" or considered one person walking around in two bodies. That often happens with same sex twins, whether they are fraternal or identical.
There is one extremely rare exception involving boy identical twins. In less than ten reported cases, an anomaly occurred that caused one male twin to lose a Y chromosome after the zygote split. That means this child went on to develop as a female but as one who doesn't develop ovaries. Again, this is so rare that the majority of people will never meet a set of twins that fall into this category.
10 Identical Twin Pregnancies Are Higher Risk
Twin pregnancies are higher risk than singleton pregnancies no matter which type of twins mom is carrying. However, moms carrying identical twins are generally at higher risk of complications than those carrying fraternal.
The reason is all about anatomy in the womb. While fraternal twins have their own placenta and their own amniotic sac, this isn't always true for identical twins. There are a variety of situations when identical twins are in utero, including identicals sharing a placenta, an amniotic sac, and a chorionic sac. Any of these situations elevates the risk to the pregnancy.
Because identical twins generally share a placenta, they are at risk for twin-to-twin transfusion syndrome, a potentially fatal ailment where one twin receives more blood from the placenta than the other. In rare situations where twins share a chorionic and amniotic sac, they can also tie their umbilical cords together, risking both of their lives. Fraternal twins are not subject to these risks, making fraternal twin pregnancies the lowest risk of all twin pregnancies.
9 Only Identical Twins Can Be Mirror Image Twins
When we look in a mirror, our features come back to us, but in a mirrored form. In a quarter of cases, twins actually have a mirror image twin, an identical twin sibling who reflects their features as if they are standing in a mirror facing each other. This happens when reverse assymetrical features occur in the womb, and it can help mom and dad figure out who is who early on when identical twins can look so much alike.
If one twin is left handed, the other may be right. There's also the possibility of freckles or birth marks being on the right side of one twin's body and on the left in the other. This anomaly is interesting to study, but it has no effect on the twin pregnancy or delivery. It just makes it harder for twins who try to trick people by switching places to pull it off!
8 Fraternal Twins Come From Two Eggs
One of the most important distinctions between fraternal and identical twins is that fraternals come from two eggs while identicals come from one. This one detail explains quite a bit about everything else we know about the differences in these types of twins.
When two different eggs are fertilized by two different sperm, the twins resulting from this are fraternal. That means a different genetic code and the possibility that fraternal twins will not look that much alike. When mom has identical twins, it means one fertilized egg splits in two. Because of this, identical twins have many identical or near identical features and genetics.
This is another reason that fraternal twinning can be genetic and identical is not. Fraternal twins occur when mom hyperovulates, meaning she releases more than one egg at a time. This is something that can be inherited, and hyperovulation can be passed down from generation to generation. With identical twins, the egg splitting is simply an anomaly. No one knows why it occurs, and there is no genetic marker.
7 Neither Has Identical Fingerprints
Okay, so we've spent some time talking about how identical means identical, but there is one area where identical twins are more like fraternal twins: neither have identical fingerprints.
How is this possible when identical twins come from the same egg, share a ton of DNA, and live in the same environment? Well, it's true identical twins will probably have similar fingerprints, but the differences come from bone growth and contact with the amniotic fluid. Since the pressure of the amniotic fluid and the differences in the things each baby touches in the womb affect fingerprints, they will not be exactly alike.
Fraternal twins, who have different genes and come from two different eggs, definitely do not have the same fingerprints, but identical twins are often assumed to. Lucky for investigators and police this isn't the case. It's one surefire way to tell identical twins apart.
6 Identical Twins Share DNA
Because they come from one fertilized egg that split, identical twins share identical DNA. However, there are some interesting findings within this one.
Though twins generally carry the same genes, and therefore the same markers for certain diseases, both twins don't always develop the same ailments. One twin can have cancer while another does not, and this is largely attributed to environmental factors. Many genes have to be triggered, and since twins don't live identical lives, one may set off a cancer gene and one may not.
Oddly, though, identical twins separated early in life will tend to be extremely similar. Studies have been done on identical twins who were separated as babies, but came back together later in life. Many of them made similar life choices, and some even gave their children and dogs the same names. Obviously, they are connected.
5 Both Often Have Moms Who Live Longer
Moms of twins are often called supermoms by other people in their lives because of how they handle all the pressures of raising two kids the same age. It turns out that the supermom title may not be far off since a new study shows that moms who conceive twins naturally live longer.
The study on twin moms showed they recovered from birth better, had babies for longer, and outlived moms of singletons. This may be hard for the mom of twins to believe if she is in the throes of feeling exhausted and beaten down from being a parent, but science tells the facts. The thinking is that women who are stronger are chosen to pass their genes on to double the children at the same time. It's an evolutionary explanation.
This only applies for women who conceived naturally because the study was done before fertility treatments were available. No studies have taken place to see if this applies to moms who conceived twins using IVF or other fertility treatments.
4 Fraternal Twins Have Increased Due To Fertility Treatment
Fertility treatment has changed the landscape for multiple births. Due to the medications and procedures involved in conceiving with assistance, twinning has increased, and it's so common for twins to come from fertility treatment that most people assume every twin they know is. That's not the case, but it is fair to say fertility treatments affect the amount of twins conceived.
When it comes to fraternal twins, the chance of conceiving is higher with fertility treatment because more than one embryo is usually transferred. If both, or in some cases three or four, make it, mom will have multiples. Certain medications can increase the risk of hyperovulation, as well.
With identical twinning, no one is sure why there is a slightly increased chance when fertility treatment occurs, and some say the increase is so negligible that it hardly qualifies. Some theorize that a procedure called assisted hatching could be to blame. During assisted hatching, a defect is intentionally introduced to the outside of the egg to help it implant.
However, this may encourage the egg to go ahead and split, creating identical twins.
3 Identical Twins Have Different Categories
In twin speak, fraternal twins are called di-did twins, short for diamniotic/dichorionic. That means they have their own chorionic and amniotic sacs, putting them at less risk for complications with the placenta and making it impossible for them to tie their umbilical cords together. All fraternal twins are di-di.
With identicals, it gets a bit more complicated. What type of twins they are depends on when the egg split. There's monochorionic/diamniotic, also called mono-di. These twins share the outer chorionic sac but have their own amniotic sac. A membrane separates them and keeps them from tying their cords together.
Monochorionic/monoamniotic twins share both an amniotic and chorionic sac, and because of this mono-mono pregnancies are extremely high risk. The twins can tie their umbilical cords together, and if the cords develop a kink, both babies can die.
Still more rare are conjoined twins, a rarity that occurs when the egg splits extremely late. Conjoined twins can be born and separated in certain situations, but the situation is high risk.
2 All Twins Can Have Different Birthdays
Twins usually have to share a birthday, which can be a fun double celebration or a bummer since neither has a special day of their own. However, in some rare cases, twins are born on separate days, and in even rarer cases, in separate years.
Though many twins are born via C-section, almost guaranteeing they will be born within seconds or a couple of minutes from each other, some moms have vaginal deliveries and are subject to the laws of labor. One of those laws is that mom can't control time, and the baby, or babies, will come when they please.
For moms who labor vaginally, the first twin may arrive late one night while the other waits until the clock rolls past midnight to arrive. In this case, separate birthdays! If this happens on the 31st of December, different birthday years!
1 Fraternal Twins Are More Common
Though there are more types of identical twins, fraternal twins are more common. While the number of fraternal twins born rises every year, nothing really affects or changes the number of identical twins born. Having identical twins is a matter of chance, open to any woman who is lucky enough to have an egg split.
The chances of having fraternal twins goes up as women age. It's more likely for the body to drop an extra egg due to changes in the reproductive system as women age, and women are waiting longer to have children. It's also more likely that older women will have to seek fertility treatment to assist them in conceiving, and that increases the chances of conceiving fraternal twins.
Though identical twinning may be slightly affected by fertility treatment, it's not near as much as fraternal twinning. Since fraternal twins run in families, there's also the fact that hyperovulation is passed down, therefore ensuring this type of twinning continues.