Do Twins Run in Families?

What Causes Twins?

There are two types of twins: fraternal or dizygotic and identical or monozygotic.

A) Fraternal Twins

Fraternal twins develop from two separate eggs and two separate sperm cells. They are the most common type of twin accounting for 70% of all spontaneous twin pregnancies. Fraternal twins can have different gender and appearances and are no more genetically related than any other siblings with the same parents.

So, do fraternal twins run in family? Certain genetic factors make fraternal twins run in families. There’s a higher probability of having twins if you’re the gestational parent and:

• You are a fraternal twin

• You already have fraternal twins

• Your close relative has fraternal twins

Other factors that increase the chances of having fraternal twins include:

• Age : If gestational parents are in their 30s and 40s, they are more likely to give birth to twins as compared to younger parents

• Previous pregnancies : High number of pregnancies increase the odds of twins, especially if you have a prior twin pregnancy

• Ethnicity – People of certain ethnicity have higher chances of fraternal twins such as Nigerians.

B) Identical Twins

Identical twins come from one fertilized egg that splits into two embryos. They have the same DNA. These twins will have the same gender and will also look very similar in their appearances. However, they may not be exactly identical due to environmental factors.

So, do identical twins run in families? Typically, identical twins are not hereditary like fraternal twins. They occur in 3 to 4 births out of every 1000 globally. The cause of identical twins is unknown. Assisted reproductive technology (ART) may increase the odds of having identical twins.