How identical twins are formed

By Vincent Kejitan | Monday, Apr 22nd 2019 at 09:26
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Following the Kakamega twin puzzle that has drawn the attention of the entire country, we sought to delve deeper and understand how twins come about.

There are two types of twins – identical or monozygotic (one egg), and non-identical or dizygotic (two eggs) twins. 

Identical twins form when one egg has been fertilised by one sperm and the zygote splits into two.

Dividing this early in conception means that each baby has exactly the same genetic information as the other.

Non-identical twins, on the other hand, form from two completely separate eggs which are fertilised by two completely separate sperm.

Giving birth to twins

Childbirth can give rise to complications when just one baby is present, so twins present extra potential for difficulties.

The babies can be delivered vaginally, but caesarean section delivery may be considered a better alternative in some circumstances.

What increases the chance of twins

Family history

A woman has a slightly higher chance of having twins if she has a family history of twins. A family history of twins on the mother's side increases this likelihood more than a family history on the father's side.

Fertility treatment

According to the American Society for Reproductive Medicine (ASRM), the main factor that increases the chance of having twins is the use of fertility treatments. The various types of fertility treatment available increase the likelihood of twins in different ways.

Some fertility drugs work by stimulating a woman's ovaries, which can sometimes cause them to release more than one egg. If sperm fertilizes both of these eggs, this can result in twins.


According to the Office on Women's Health, women who are aged 30 years or older are more likely to conceive twins. The reason for this is that women of this age are more likely than younger women to release more than one egg during their reproductive cycle.

Racial background

In the U.S., Hispanic women are less likely to have twins than non-Hispanic white women or black women, according to the ASRM.

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