If you’re trying to have children, there’s a lot to consider. Adding an extra baby to the equation can make for some tricky budgeting, not to mention doubling the effort you’ll need to put into childcare. So, you’re probably asking yourself “What are my chances of having twins?”
The answer varies, depending on whether you’re talking about identical or non-identical twins, as well as a number of factors, ranging from your genetics to your current lifestyle and beyond.
How Do Twin Pregnancies Occur?
Humanity has long held an interest in twins. They feature in most of the world’s various mythologies, such as the divine siblings Artemis and Apollo from Greek mythology (to pick one pair out of many), or the divine Norse twins Freyr and Freyja. But modern medicine has largely demystified the phenomenon of twin births, and let’s go over the basics.
There are (basically) two types of twin – identical and non-identical (or fraternal).
Identical twins happen when an egg that has been fertilized splits into two separate embryos. This means that they have identical genes inherited from their parents, and so they will be the same sex and look very similar. The scientific term for this is monozygotic twins.
Fraternal twins occur when two eggs are fertilized by two different sperm, and then both successfully implant in the womb. These twins – known as dizygotic twins to scientists – share the same amount of genetic material as any other siblings. So, they can be of different sex, and they can potentially look quite different to one another.
How Common Are Twins?
According to the Center for Disease Control (CDC), in 2015 33.5 out of every 1000 live births in the US resulted in twins, which means that there is a 3.35% chance to have twins on average. Their latest data from 2017 puts the rate at 3.33%, a very minor drop that is representative of the now slowly declining rate of twin births over the last decade.
However, the likelihood of having twins is still much higher than it was 30 years ago. The CDC’s National Center for Health Statistics reported that the number of twin births increased by over 75% between 1980 and 2009. There are a few potential reasons for this increase, foremost of which is the increase in the use of fertility treatments, as well as improvements in nutrition, and women having children later in their lives.
Fraternal twins are more likely than identical twins. Fraternal twins account for around two-thirds of all multiple pregnancies. Identical twins account for around 0.5% of pregnancies without fertility treatment.
What Makes Twins More Likely?
As we said, not everything regarding twins has been explained yet. Scientists are yet to uncover exactly why identical twins occur.
But there are a number of factors that have been identified that influence the likelihood of having fraternal twins, including:
The American Society for Reproductive Medicine has reported that the most influential factor in the likelihood of having twins is receiving fertility treatments.
If you are undergoing IVF, they will extract a number of eggs, fertilize them with the donor’s sperm, and then implant multiple fertilized embryos (at least two but rarely more) into your womb in order to increase the chance of a viable pregnancy. This, unsurprisingly, increases the likelihood of having twins, as both embryos can potentially survive for the full term. IVF also doubles the likelihood of identical twins over that of the general population.
Alternatively, some fertility drugs stimulate your ovaries in order to encourage them to release eggs. This can sometimes result in two eggs being released at the same time, which can then both be fertilized by your partner’s sperm and so leave you with two bundles of joy.
A History of Twins
The chances of having fraternal twins are also increased if you have a family history of twins. If you have twins on your mother’s side, this means you have a higher likelihood of conceiving twins yourself, as you are more likely to release multiple eggs when you ovulate.
While a history of twins on the father’s side isn’t strongly linked to a higher likelihood of twins, it does mean that the father is likelier to produce plenty of healthy sperm. So, he may be more likely to release enough to fertilize more than one egg.
Your Weight and Height
Women who are heavier are more likely to have fraternal twins, as are women that are taller than the average. There is no firmly established link, but scientists have theorized that this could be related to better nutrition.
Statistics show that overweight and obese women are more likely to struggle with conceiving. But when they do conceive, the odds of twins are higher than average. This is because having extra body fat causes an increase in the production of estrogen, which can lead to the ovaries being overstimulated and releasing more than one egg.
As for height, women who are around 5’5” are more likely to have twins that those who are closer to 5’4”. Again, this is possibly due to nutrition, but the exact causes are unclear.
As you pass 30, your body produces more follicle stimulating hormone (FSH). This hormone is vital in the development of your eggs before ovulation, and as you get older more is needed in order to stimulate growth. However, this can sometimes lead to overstimulation, and so result in conceiving twins.
Already Having Children
If you already have children, then your chances for twins are higher. If you already have twins, then it’s even more likely that it will happen again.
In the USA, African American women are the most likely to conceive twins, followed by Caucasian women, then Hispanic women, with Asian and Native American women the least likely to have two at a time.
Some early research has indicated that there may be a link between eating dairy products and a higher chance of twins. Researchers theorize that this could be caused by the growth hormones that are given to the cows that are passed on to the milk.
What Are My Chances of Having Twins?
If you are a skinny, short, young woman who has no twins in her family tree, and you aren’t undergoing a fertility treatment, then your chances are pretty slim. However, you might want to keep in mind the possible need for two cribs if you’re over thirty, carrying a few extra pounds, taller than most, have a few kids already, currently undergoing fertility treatment, or if you have relatives on your mother’s side who are twins.