When you’re pregnant with twins and curious about their gender, you make educated guesses based on what type of twins you’re having.
Most people assume all identical twins have to be the same gender, while fraternal could be the same or different.
That leads to the real question…
Can identical twins be boy and girl?
The vast majority of the time, identical twins are of the same gender. There are differences between fraternal and identical twins, starting with how they are conceived. Fraternal twins may be of different genders, but identicals usually are not. Knowing what makes each type unique allows you to better understand how they end up the same or different genders.
However, new types of twins are still being discovered, and this creates questions that aren’t so easily answered. Advances in science are constantly showing us what is possible when it comes to pregnancy and twins.
Male/Female Identical Twins – Is It Possible?
It’s not likely for truly identical twins to be male/female. Identical twins are of the same gender because they come from the same egg and sperm combination. The fertilized egg splits, and that means each twin ends up with the same genes. They also end up the same gender.
Identical Twins vs. Fraternal Twins
Identical twins and fraternal twins are different in many ways. The way they are formed is where the differences start. From that point on, the journeys diverge.
If you’re pregnant with identical twins, your pregnancy will come with more risks than if you’re having fraternal twins. That’s because fraternal twins usually have their own chorionic and amniotic sacs, and this presents less overall risks to the babies.
Fraternal twins also have the same genetic makeup as any other type of siblings. Identical twins have almost exactly the same genetic makeup. This means that if identical twins have children of their own, their children’s genetic makeup will be closer to half-siblings than cousins.
Fraternal twin rates vary depending on the country. However, the rate of identical twins is the same around the entire world.
Identical twins form when one fertilized egg splits. Since one egg is fertilized before it splits, identical twins have the same genes from both parents. That’s why identical twins are the same gender in the overwhelming majority of cases.
Depending on when the egg splits, identical twins will either be conjoined, mo mo twins, or mo di twins. The difference between mo mom twins and mo di twins is whether or not they have a membrane separating them in the womb.
The majority of identical twins will also share a placenta, and this can make the pregnancy riskier. An uneven distribution of blood supply or nutrients can harm one or both babies. This may require the twins to be taken from the womb early.
Fraternal twins form when two eggs are released instead of one. This is called hyperovulation and may be a trait that is passed down through families. These eggs are then fertilized by separate sperm. This process makes it possible for one twin to be a girl and one twin to be a boy.
Fraternal twins are extremely likely to have their own placenta because they develop from two different eggs. They are called di di twins because they each have their own chorionic and amniotic sacs.
Very Rare Exception to the Rule
There’s another twin type that is extremely rare. These twins are called polar body twins, and the way they form is truly unique.
When an egg splits before it is fertilized, one piece of the split egg will be smaller. The smaller piece is called a polar body, and it isn’t likely that it will survive to be fertilized.
However, if it does survive then both pieces of the egg can be fertilized by different sperm. These twins would have the same chromosomes from mom but different chromosomes from dad. They could also end up being different genders.
What Gender Is Most Common in Identical Twins?
While the data on the gender of identical vs fraternal twins isn’t readily available, we still have some information on the gender of twins overall.
Female twins are more likely to in most cases. This may be due to the fact that girls tend to have a higher survival rate than boys during pregnancy.
What Are Semi-Identical Twins?
Semi-identical twins are extremely rare. They form when one egg is fertilized by two different sperm. When the fertilized egg splits, the resulting twins only share roughly half of their father’s chromosomes. However, they have all of their mom’s chromosomes in common.
Of all the twins ever conceived, only two sets have proven to be semi-identical. This situation is very rare or extremely underreported.
What Percentage of Fraternal Twins Are the Same Gender?
If you’re expecting fraternal twins, you have a 50/50 chance that they will be the same gender.
Boy/Girl Twin Facts
- Boy/girl twins make up half of all fraternal twins.
- Boy/girl twins may not look alike at all.
- All boy/girl twins are fraternal.
- It is possible for boy/girl twins to have different fathers.
Can Twins Have Two Different Fathers?
Fraternal twins can have two different fathers, but identical twins can not. Fraternal twins are conceived when more than one egg is released during ovulation. These eggs are then fertilized by two different sperm.
If one egg is fertilized by one man’s sperm and another is fertilized by a different man’s sperm, then these twins will have two different fathers and be half-siblings. Genetic testing may be the only way to find out if twins have the same paternity.
What Percentage of Twins Are Identical?
Only a third of all twins around the world are identical. One reason fraternal twins are more common is that fertility treatment increases the chances of having fraternal twins. It doesn’t affect the likelihood of having identical twins.
Having twins is an adventure that starts during pregnancy. Know everything you can before your babies arrive.
Mom of three (including identical twin boys), wife, and owner of Parents Wonder. This is my place to share my journey as a mother and the helpful insights I learn along the way.