If you or your partner comes from a family that has a set of twins, you may be wondering what the odds are of you giving birth to twins.

We may not fully understand why twin pregnancies sometimes occur, but certain factors can increase your chances of having twins. 

This article explains the difference between identical and fraternal twins and reveals some factors contributing to twinning. 

Two Types Of twins:

Identical twins

Identical twins come from a single egg fertilized by a single sperm. It then divides into two separate embryos very early in the pregnancy. 

Embryo splitting seems to happen randomly by chance, so genes do not have anything to do with it. 

As a result, identical twins do not run in the family as genes are not involved in the process [1].  

Both embryos share the same DNA, meaning they have identical genes and look very much alike. 

They will always be the same sex, either both boys or both girls. 

Fraternal Twins (non-identical)

Fraternal twins happen when two different eggs are released and fertilized, each by a single sperm. 

Specific genes predispose some women to hyper to ovulate more than one egg simultaneously, which increases the chance of having twins. 

As a result, fraternal twins run in the family because genes are involved in the process. 

Both embryos do not share the same DNA and may or may not look alike. They will look like regular siblings born years apart. 

Fraternal twins will not necessarily be of the same sex. They can be two boys, two girls, or a boy and a girl.  

Factors Contributing to Twinning

Twins on the father’s side of the family will not influence your chances of having twins. 

After all, mom releases two eggs due to hyperovulation.

Men, of course, do not ovulate. So their DNA will not influence how many eggs the mom releases!

The tendency to have twins is influenced by several factors related to women, as explained below: 

Hyperovulation

Some inherited genes predispose women to hyperovulation.

However, those genes are unknown and require further research to uncover them.

Women with these genes seem to have higher levels of certain hormones related to ovulation.

For example, the hormone FSH (follicle-stimulating hormone) may be higher in mothers of twins.

So if you are a woman who carries the hyperovulation gene, you may be more likely to have twins.

Men do not ovulate, so even if they have inherited that hyperovulation gene from their parents, it does not increase their odds of conceiving twins even if they have multiples in their family.

However, they may pass this gene on to their daughter, who is more likely to release two or more eggs during ovulation and therefore could conceive fraternal twins.

From here comes the theory that twins can skip a generation.

Fertility Treatments

Fertility treatments such as in-vitro fertilization (IVF), intrauterine insemination (IUI), and ovulation induction (OI), can increase your chances of having twins.

Some fertility drugs that are part of the whole treatment work by stimulating your ovaries, causing them to release more than one egg to increase the odds of conception.

During IVF, we extract and fertilize multiple eggs, and we transfer more than one embryo to increase the likelihood of success.

Twins can therefore develop if both embryos implant successfully.

Read this article to check if IUI is right for you.

Age

Older women generally have a higher chance of conceiving twins.

A 35-year-old woman is about four times more likely to have fraternal twins than a woman under 20.

The rising FSH hormone concentrations (as they near menopause) cause more ovarian follicles to mature and release extra eggs during ovulation.

After age 35, however, the chance of having twins naturally decreases.

Height

Taller women are slightly more likely to have twins.

If you are taller than average (at least 5’5” or 165 cm height), you are about two times more likely to have twins than shorter women.

The reasons for this are not clear, but researchers think it may be due to having a higher quantity of a specific protein.

The protein makes the ovaries more sensitive to follicle-stimulating hormone (FSH).

Weight

Women who are overweight also seem to have a higher chance of conceiving twins.

If you have a BMI (body mass index) of 30 or more, you are more likely to have twins.

Probably due to better nutrition, more resources available for a developing fetus, and higher levels of FSH.

Nutrition

Diet can also have an impact on your chance of having twins.

Animal products, particularly dairy, enhance the odds of conceiving twins.

Probably due to more growth hormone, which may stimulate multiple ovulations.

The use of oral contraceptives and increased intake of folic acid may also contribute to twinning.

However, at this point, the results of these studies are inconclusive.

More research is needed to determine the role of these factors in twinning.

Recap:

There is still a lot that is unknown about what causes a couple to have twins.

It is the genes of the mother that control the likelihood of having fraternal twins.

Identical twins do not run in families – they are random.

So if you are a fraternal twin, you are more likely to have twins.

However, if you are an identical twin, your chances to have twins are the same as the general population.