There are many myths about how to have twins. Although there are no proven ways to increase the likelihood of conceiving twins, there are certain factors that can make this type of pregnancy more likely.

Twins can occur either when two separate eggs become fertilized in the womb or when a single fertilized egg splits into two embryos.

Having twins is more common now than it was in the past. In fact, twin births have nearly doubled over the last 40 years.

A person has a higher chance of having twins if they conceive with the assistance of fertility treatment or are ages 35 years or older.

In this article, we explore why twin pregnancies occur, how common they are, and factors that can make them more likely. We also explain whether a person can increase their chance of having twins.

Doctors do not fully understand the reasons why twin pregnancies sometimes occur. However, some factors can increase the likelihood of giving birth to twins, including:

  • the person’s age
  • having a family history of twins
  • having fertility treatments

Conception happens when a sperm fertilizes an egg to form an embryo. However, if there are two eggs present in the womb at the time of fertilization or the fertilized egg splits into two separate embryos, a person can become pregnant with twins.

There are two types of twins:

  • Identical twins: This type of pregnancy happens when a fertilized egg splits into two separate embryos. These embryos are monozygotic, which means that they have identical genes. Identical twins are the same sex as each other and look very alike.
  • Nonidentical, or fraternal, twins: This type of pregnancy occurs when there are two eggs present in the womb at the time of fertilization, and sperm fertilize both of them. These embryos are dizygotic, which means that they do not have identical genes and may not be the same sex.

Twins are relatively uncommon, with approximately one in 250 pregnancies resulting in twins.

However, the birth of twins has increased significantly alongside the rise in the use of fertility treatments and with more people choosing to have children at a later age.

A person is more likely to have fraternal twins than identical twins. Identical twins account for only about one-third of multiple pregnancies.

Several factors can increase the likelihood of a person conceiving twins. These include:

Family history

A person has a slightly higher chance of having twins if they have 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. However, this only applies if conception takes place without the use of fertility treatments.

Some people believe that twins can skip a generation, meaning that a person will potentially have twins if one of their grandparents did. However, there is little evidence to support this theory.

Fertility treatment

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 person’s ovaries, which can sometimes cause them to release more than one egg. If sperm fertilize both of these eggs, this can result in twins.

In vitro fertilization (IVF) can also increase the chance of conceiving twins.

Healthcare professionals carry out IVF by extracting a person’s eggs and fertilizing them with a donor’s sperm in a laboratory to produce an embryo. They then transfer the fertilized embryo into the person’s womb.

To increase the likelihood of success, the healthcare professional may place more than one embryo into the womb. Twins can occur if both embryos implant and develop successfully.

Multiple pregnancies carry additional risks, so the healthcare professional will usually limit the number of embryos that they transfer to the person’s womb to reduce the chance of a pregnancy with twins, triplets, or more.

Age

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. If sperm fertilizes two separate eggs, a twin pregnancy can occur.

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 CDC.

There are many unproven claims about how to increase the likelihood of conceiving twins. Some people advise following specific diets or using certain alternative therapies, but there is no scientific evidence to support these methods.

Fertility treatments, particularly IVF and ovary stimulants, do increase the chances of having twins. However, a twin pregnancy is riskier for both the woman and the developing fetuses. For this reason, some fertility clinics advise against implanting multiple embryos during IVF treatment.

The American Society for Reproductive Medicine ASRM recommends that young women who are having their first fertility treatment select just one embryo for transfer to their womb.

As the success of fertility treatment is improving, there is often less need to transfer more than one embryo.

Although certain factors increase the chance of having twins, there is no way to improve the odds of having twins naturally. A person will usually find out that they are pregnant with twins from an ultrasound early on in the pregnancy.

Some symptoms may indicate a twin pregnancy, including more intense morning sickness and very rapid weight gain. Regular medical appointments will improve the chances of a healthy pregnancy.