Twins & Multiples

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Can Identical Twins Be Boy and Girl?

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Most of us know about 2 types of twins, namely identical twins and fraternal twins. Most of the boy and girl twins that we know of are often fraternal or dizygotic. But, can identical twins be boy and girl? Let’s find out in this article.

Difference Between Identical and Fraternal Twins

Identical twins are monozygotic, which means that the twins emerged from a single fertilized egg cell which split and later on developed into 2 embryos. However, there are also 2 types of identical twins which are monochorionic-diamniotic twins and monochorionic-monoamniotic twins. On the other hand, fraternal or dizygotic twins emerge from 2 different fertilized egg cells implanted in the womb. Dizygotic twins are separate fertilized egg cells, so they have different amniotic sacs, too.

Fraternal twins are often the type of twins that have different genders. However, dizygotic twins may only share about 50% identical DNA, so generally, some characteristics might turn out alike. But, based on their DNA, fraternal twins might be more different than you think.

When in doubt a twin zygosity test might be what you need. It helps determine the genetics of your twins and whether or not they are predisposed to certain health conditions. However, if you are just curious to know whether your twins are identical or fraternal, this is the test that you might need. The twin zygosity test helps you determine the similarities and differences of your twins.

Do Identical Twins Always Turn Out as The Same Gender?

Identical twins turn out as the same gender about 99.9% of the time. However, scientists and doctors recently discovered a rare type of twins which is called sesquizygotic twins. Sesquizygotic twins were only discovered in 2007. Other twin databases did not show the same pattern in twins, which made the 2007 record the first for this type of twinning. The sesquizygotic twins are also called semi-identical twins which may or may not be the same gender.

twins playing together

Can Identical Twins be Boy and Girl?

Generally, identical twins can only be of the same gender. However, rare cases, such as sesquizygotic (semi-identical) twinning may cause identical twins to be a boy and a girl. The only problem with sesquizygotic twins is that this type of twinning is very prone to genetic defects to one of the twins, such as ambiguous genitalia due to anomalies in the chromosomes of one of the twins.

Moreover, if identical twins end up being of different genders, the male with XY chromosomes may turn out normal, but the female with XO chromosomes might have Turner Syndrome.

Technically speaking, yes there are semi-identical or maternal twins that can be a boy and a girl. However, it is not without risk or genetic anomalies to the fetus. Even though sesquizygotic twins are very rare, the risks of genetic problems in one of the sesquizotic twins are very high.

One of the sesquizygotic twins recorded even had ambiguous genitalia which made it difficult to tell whether the other twin was a boy or a girl. This is due to some problems in the chromosome of the other twin when the egg cell split into two zygotes which eventually became 2 fetuses.

What Are The Chances of Having Boy and Girl semi-Identical Twins?

The chance of having twins is just about 3 in 100, so that is roughly a 3% chance of conceiving twins at any given time. However, with semi-identical twins, it is even rarer. It is estimated that 99.9% of identical twins have the same gender. But, semi-identical twins are so rare that they make up only about 0.1% of the twin populations.

Moreover, the first set of semi-identical twins have only been recorded in 2007 and another set of semi-identical twins was recorded but with ambiguous genitalia. So far, only 2 cases of sesquizotic twins have been recorded as of writing.

Having twins might be a rare occurrence. However, normal semi-identical twins without genetic anomalies are even less likely. Prenatal checkups and adequate nutrition of the pregnant mother may help avoid problems in pregnancy. Semi-identical twins are very rare, but regular checkups are important in any type of pregnancy.

It is very seldom that we see boy and girl twins. Furthermore, it is even less likely that these boy and girl twins are identical. Even though boy and girl twins might look very similar in physical features, genetically speaking they might be more different than you think.

Identical twins are about 90% similar in DNA, contrary to fraternal twins which are only about 50% similar. Physical appearance isn’t always reliable in telling whether twins are truly identical or not. The twin zygosity test is the only sure way to tell whether your twins belong to an identical, semi-identical, or fraternal type.

My Boy and Girl Twins Look Identical, is There Any Chance That They Are Semi-identical?

Twins generally have very similar genetics, so even fraternal twins might look very alike. However, semi identical twins emerged from the same fertilized egg cell which later on separated as different embryos and later on different fetuses.

best playpen for twins

Furthermore, semi-identical twins are very rare, so you might want to run a twin zygosity test on your twins which is the only method to determine whether or not they are semi-identical. If they turn out to be semi-identical twins, it would only be the third case to be recorded since 2007.


Can identical twins be boy and girl? The answer is yes. However, such cases are very rare and prone to genetic problems. Scientists are yet to discover more facts about semi-identical pregnancies and twinning. At the moment, information is very limited and twin databases are yet to record more semi-identical twinning occurrences.


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