Twins occur naturally without fertility treatment in about one in 250 pregnancies, triplets in about one in 10,000 pregnancies, and quadruplets in about one in 700,000 pregnancies. There are a lot of wives’ tales about how to tell what your odds are of having twins, but scientific support actually exists for the following.
How to Tell if You Will Have Twins
It’s true that “twins run in families”. A gene has been discovered that makes it more likely that a woman will release more than one egg in a single menstrual cycle, thus increasing her chances of having fraternal (non-identical) twins. This gene can be passed from one generation to the next, thus non-identical fraternal twins run in families.
There is no evidence that identical twins have a genetic influence, so you are not more likely to have twins if there are identical twins in the family.
The mother’s family history is more significant than the father’s, but a family history of fraternal twins in either the mother or the father will increase the couple’s chances of having twins. Women who are part of a non-identical twin set give birth to non-identical twins at the rate of 1 set per 60 births. Non-identical male twins father twins at a rate of 1 set per 125 births.
Do twins skip a generation? Technically this is a myth, however, it may seem this way because men may inherit the gene from their mothers, but because they do not have menstrual cycles they are not affected, but can still pass the gene on to their daughters. Their daughters who inherit the gene will have an increased chance of fraternal twins.
The overall rate of twins for all races in the United States is around 33 per 1,000 live births. Black and non-Hispanic white women have similar rates of twinning, while Hispanic women have a lower chance.
3. Maternal age and prior pregnancy history
The frequency of twins increases with maternal age and number of pregnancies. Women between 35 and 40 years of age with 4 or more children are 3 times more likely to have twins than a woman under 20 without children.
4. Maternal height and weight
Non-identical twins are more common in larger and taller women than in smaller women. This may be related more to nutrition than to body size alone. During World War II, the incidence of non-identical twinning decreased in Europe when food was not readily available.
5. Fertility Drugs and Assisted Reproductive Technology
Infertility treatment increases your risk of having twins, both identical and fraternal. Of women who achieve pregnancy with clomiphene citrate (Clomid), approximately 5% to 12% bear twins; less than 1% have triplets or more. Use of injectable fertility meds, such as gonadotropins, has caused the vast majority of the increase in the multiples we see worldwide.
Approximately 30% of pregnancies resulting from gonadotropins are multiples. While most of these pregnancies are twins, up to 5% are triplets or greater due to the release of more eggs than expected. Twin pregnancies are significantly more risky for the baby and the pregnancy as a whole, and there is a push by infertility medical professionals to reduce the twin rate. Keep in mind that patients and doctors can significantly reduce the rate of twins by limiting the number of embryos transferred with in vitro fertilization (IVF).
Other Creating a Family resources you will enjoy:
- What Twins Can Teach Us About Genetics vs. Environment
- Are Identical Twins More Common After IVF
- Dad Angry that Wife Is Expecting IVF Twins
- Crucial Tips from a Pediatrician on Surviving Your Baby’s 1st Year
What other ways have you heard about how to tell if you will have twins?
Image credit: Peter Kirkeskov Rasmussen