Odds of Having Twins and Odds of Having Twins After Twins FAQ

Currently, 34 out of 1000 births in the US result in twins. This means you have a 3.4% chance of having twins. This factor does include twins that came about from reproductive assistance.
In spontaneous twins (that is when there is no reproductive assistance), there is a 1 in 250 chance of having twins. This means you have a 0.4% chance of spontaneously conceiving twins.
Of course, it is important to keep in mind there are a lot of factors that can influence your odds of having twins, so this number is just a general idea of what could happen in your pregnancy.

There are several factors that can increase your odds of having twins.
They include:
1. Genetics
The number one factor in conceiving twins is genetics. Fraternal twins are a result of two eggs being released in the same cycle and both being fertilized. This is hyperovulation and is a result of genetics. (This is what makes twins ‘run in families.’ The trait of hyperovulation is passed on.)
2. Age
The older you get, the more likely you are to have twins. After about 35 years of age, your hormones shift and you become more likely to hyper ovulate. (Think of it as your body going through an ‘everything must go sale.’ 😉 )
3. Previous Pregnancies
If you have previously conceived fraternal twins, you are more likely to conceive them again. (Scroll down, there is more on this.)
And overall, the more pregnancies you have had the more likely you are to conceive twins. Scientists aren’t really sure why yet, but it is a trend that has been documented. (And there isn’t a firm number on how many pregnancies it takes.)
4. Height
Taller women are more likely to have twins. Now this doesn’t mean that those of us who would definitely not be considered tall won’t have twins, but it does seem to up the odds.
5. Diet
There is some evidence that diet can influence having twins. (This could be simple causation correlation though, so don’t go out and eat only ‘twin foods’ and assume you will automatically get twins!) Yams, leafy greens, and tapioca are just a few of the foods thought to help your odds of having twins.
6. Race
There are trends in twinning that vary by race. If you are Hispanic or Asian you have smaller odds of conceiving twins. African-American women have the highest twin birth rate. (Source)

Remember, identical twins happen when one fertilized egg splits into two. The odds of having identical twins are not the same as the odds of having fraternal twins.
There are 3 to 4 identical twin births for every 1000 births, so you have about a 0.35% chance of having spontaneous identical twins.

What is very interesting is that the odds of having identical twins don’t seem to change with the factors associated with fraternal twins, they stay pretty constant. And scientists still aren’t completely sure why identical twins happen.

There is about a 3.4% chance of you having fraternal twins. This is the general odds, they can change based on the factors addressed above.

While in singleton births males are more common than females, in twins you are slightly more likely to have female twins. This is due to different death rates in utereo.

The most common twin type is male-female fraternal twins. This is because fraternal twins are more common than identical twins. There is a 25% chance of having girl-girl fraternal twins, a 25% chance of having boy-boy fraternal twins, and a 50% chance of having boy-girl fraternal twins.

This answer depends on what type of twins you had, identical or fraternal, but here is the short version. If your first set of twins are fraternal, your odds of having another set of twins increases. If your first set of twins are identical, your odds of having another set of identical twins actually decreases, and your odds of having a second set of fraternal twins stays the same. (The general twin factors apply too.)

If your first set of twins are fraternal, then your odds of having fraternal twins again jump to 1 in 12. That is a big jump!

Having two sets of identical twins, while not unheard of, is rare. While your odds of having identical twins the first time is about 1 in 250, your odds of having a second set are 1 in 70,000. That’s a 0.0014% chance. (But hey, it happens.)

Your chances of having identical twins do not change based on whether or not you have fraternal twins. It would remain at about 1 in 250.

Having fraternal twins is very different from having identical twins in terms of conception and chances of having twins. So having identical twins does not make you more likely to have fraternal twins. However, after you have already had one set of twins you are older and could have increased the other factors that make you more likely to have fraternal twins as well.

Identical twinning is the result of a single fertilized egg splitting, and as far as science currently knows it does not run in families.

Fraternal twins are the result of two eggs being fertilized, which requires hyperovulation. This can run in families, as all genetic traits can. However, it obviously runs along the female line as women do the ovulating. Boy fraternal twins can pass on the likelihood to hyper-ovulate to their daughters, who then might be more likely to have fraternal twins. This is how twinning appears to skip a generation.