Multiple pregnancies are very interesting from a scientific point of view. The study of twins helps shed light on what factors are genetic and which are environmental. The question of whether twins are hereditary or not often causes some confusion. If you want to know what your chances are of having twins and if having twins is hereditary, at OneHowTo we'll clear up the confusion.
Types of twins
Before addressing the issue of whether having twins is hereditary, we have to clarify the two types of twins and how they are colloquially known.
The two categories of twins are:
- Identical or monozygotic twins: Refers to the multiple pregnancy which occurs when accidentally and for reasons not yet clearly understood, a single egg that has been fertilized by a single sperm is divided into two, resulting in two children with an identical genetic makeup. This type of twins always produces the same sex and have the same genetic code, meaning that they often look almost exactly the same.
- Fraternal or dizygotic twins: In many countries is simply known as twins, is a pregnancy in which two eggs are fertilized by two sperm, leading to a multiple pregnancy in which each foetus has its own placenta. These twins contain different sets of genes, like regular siblings. In this type of gestation babies can have different sexes. Also, these babies won't be exactly similar, they will look more like regular siblings.
Is having monozygotic (identical) twins hereditary?
There is no evidence or plausible mechanism for a hereditary nature of the conception of identical twins. The chance of having identical twins is 1 in 250, whether you come from a family of twins or not. Interestingly, however, there are some families with a much higher than normal rate of identical twins, indicating that there may be some familial factor that influences this occurence.
It is not yet clear on how exactly the gestation of identical or monozygotic twins occurs. For this reason it is difficult to determine if there is indeed a hereditary possibility that twins be repeated in the next generation.
Is having dizygotic (fraternal) twins hereditary?
The case of dizygotic twins is quite different from identical twins, and there are different factors that can increase the chances of such pregnancies. When asked if having twins is hereditary, the answer is that there is likely a hereditary component to dizygotic twins. Since dizygotic twins happen when the woman releases multiple eggs during ovulation, the process of releasing multiple eggs may be passed down from a mother to her daughter. The hereditary component increases the possibilities up to a 20% in these cases.
While 1 in 80 pregnancies can be twins, women with twins in their families have a higher probability of conceiving twins. Unlike the myth would have you believe, this probability does not skip a generation. If your mother has had twins, you can also have them. When dizygotic twins are present in the father's family, the daughter will have a 20% chance of multiple pregnancy.
Other factors that may increase the likelihood of twins
There are other factors that may increase the propensity to have twins:
- Being over 35 years, due to hormonal activity in this age range you are more likely to have two eggs in one cycle. A woman who gives birth at 37 is 4 times more likely to have fraternal twins than a woman at age 18.
- Having previously had a multiple pregnancy.
- Having Assisted Reproduction Therapy (ART), like ovarian stimulation or In Vitro Fertilization (IVF) significantly increases your chances of having twins.
This article is merely informative, oneHOWTO does not have the authority to prescribe any medical treatments or create a diagnosis. We invite you to visit your doctor if you have any type of condition or pain.
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