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The Science Behind Conceiving Twins

The Science Behind Conceiving Twins

Many people want to have twins, especially identical twins. Having twins is not that rare today; the rate of twins has increased incredibly in the past few years. Read on to learn the science behind conceiving identical and non-identical twins or fraternal twins.

The medical terms for these types of twin babies are Monozygotic (Identical) and Dizygotic (Non-Identical). Other names for non-identical twins are Fraternal Twins and identical twins are called Non-Fraternal Twins.

Let’s take a look at the process of reproduction before you take a look at how identical and non-identical twins form.

The Procedure Of Reproduction: Identical and Non-Identical Twins

During ovulation, a woman’s ovary releases a single oocyte or egg. In this course of time, if those eggs get fertilized by sperm from sexual intercourse. This results in zygote traveling to the woman’s uterus by dividing and duplicating through the procedure of mitosis where it will implant and develop into an embryo which further leads forming into a fetus.


How Do Identical Twins Form?

A woman can conceive identical babies when a sperm fertilizes an ovum which afterwards splits into two. This can happen at a very early stage of development. Splitting up too early is believed to have the same genetic information, helping to be visibly identical.

However, a couple can conceive identical twins, if the woman undergoes fertility assistance. It can help fertilize the egg that returns to her uterus and then the ovum splits into two, resulting in identical twin pregnancy.

Identical Twins

How Do Non-Identical Twins Form?

Non-identical or fraternal twins form when a mother releases completely two separate eggs that are fertilized by two different sperm. These non-identical twins don’t look similar to each other.

According to health experts, identical twins always share the same gender as they share the same genes. So either it’s a boy-boy or girl-girl identical twins. However, in non-identical twins, a woman may deliver the same or opposite gender as the babies share only 50% of the same genes.

So, if you or your spouse is expecting twins, she should deliver either one from the above. However, if you are interested to look at numerous factor that helps conceive twin babies, below is the list.

Un-identical Twins

Factors That Help Conceive Twin Babies

Although, in the past, the rate of twin pregnancy has increased, still, it is uncommon. The American Society for Reproductive Medicine (ASRM) finds one in 25o pregnancies results in twin babies.

Some pediatricians believe the possibilities of a woman to have fraternal twins are more than identical twins.

So, if you desire to have twins, take a look at different factors that increases the likelihood of a woman to deliver twins.


The Office on Women’s Health believes women aged 30 years or more are more likely to have twins. The reason behind it is a woman above 30 is likely to release more than one egg during ovulation than younger women.


Family history plays one of the major factors in conceiving twins. Health experts believe a woman has higher chances of twin pregnancy if she has the family history of twins on her mother’s side.

Fertility Treatments

Couples who opt for fertility treatments are more likely to have twins. The several types of fertility treatments increase the chances of twin babies in different ways. Fertility drugs and In Vitro Fertilization (IVF) can increase the chances of twins.

Identical And Non-Identical Twins

Weight And Height

According to ASRM, heavier or taller women are more likely to conceive non-identical twins than women with lesser weight and normal height. The reasons are still not clear but might be because of better nutrition.

These are some factors that identify the chances of women conceiving twins. However, twin pregnancy may some complications that you should keep in mind.

Risks Of Twin Pregnancy

It is a happy event for a couple and family when a woman is carrying more than 1 baby. However, a mother with twins is at higher risks for complications than a woman carrying a single baby. The complications are as follows:

  • Stillbirth
  • Low Birth Weight
  • Premature Birth
  • Disabilities At Birth And Congenital Health Conditions Such As Cerebral Palsy And Autism
  • Diabetes During Pregnancy
  • Preeclampsia
  • Gestational High Blood Pressure
  • Miscarriage
  • Twin-To-Twin Transfusion Syndrome
  • Cord Entanglement
  • Postpartum Hemorrhage
  • Anaemia
  • Cesarean Delivery

Cesarean Delivery

These are some complications a mother carrying twins might face. This is why it is best for a woman with twins to rest as much as she can.

Key Takeaways.

Although health experts give several factors that increase the chances of having twin babies, these factors do not entirely prove it. Having twins is natural although this article suggests ways to improve conception. If you or your spouse is carrying twins, she will find it in her early ultrasound.

A woman with twins experience symptoms like rapid weight gain and intense morning sickness. So, it is essential that you take care of your health or take care of your partner’s health. Regular consultations with health experts can help you with a healthy pregnancy.

Learn more about fertility and conception, here.

Ovulation Calculator

Ovulation Calculator

Tracking your period cycle, determines your most fertile days and increases your chance of conceiving or applying for birth control.

Ovulation Calculator

Tracking your period cycle, determines your most fertile days and increases your chance of conceiving or applying for birth control.

Ovulation Calculator

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Period Duration



Hello Health Group does not provide medical advice, diagnosis or treatment.


Complications of Multiple Pregnancy/https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=85&ContentID=P08021/Accessed on 17/11/2019

Pregnant with twins/https://www.nhs.uk/conditions/pregnancy-and-baby/what-causes-twins/Accessed on 17/11/2019

Fraternal twins, identical twins and other types of twins/https://raisingchildren.net.au/pregnancy/health-wellbeing/twin-pregnancy/twins/Accessed on 17/11/2019

The Difference Between Identical and Fraternal Twins/https://www.healthychildren.org/English/family-life/family-dynamics/Pages/The-Difference-Between-Identical-and-Fraternal-Twins.aspx/Accessed on 17/11/2019

Twins – Identical and Fraternal

https://www.betterhealth.vic.gov.au/health/ConditionsAndTreatments/twins-identical-and-fraternal Accessed June 29, 2021

Fraternal Twins

https://www.genome.gov/genetics-glossary/Fraternal-Twins Accessed June 29, 2021

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Written by Nikita Bhalla Updated Jun 29, 2021
Fact Checked by Hello Doctor Medical Panel