Types of Twin Pregnancies – Does it Run in Your Family?

This probably one of the first in a long list of annoying questions/comments that perfect strangers will ask you. It’s usually followed by: “Were they conceived naturally or in vitro?” Like all of the sudden, your sex life becomes a question of national interest.

Be prepared to answer (or ignore) a bunch of questions from people. Going to the grocery store is similar to having the circus in town and you’re the ringmaster. People are fascinated by twins like they would for a two headed cow. They feel compelled to come talk to you and share a slice of life like how their sister-in-law has a cousin who has a neighbor who is a twin…..

In some instances, you might have to become a geneticist and give brief explanations on the different types of twin pregnancies in order to avoid even more questions. Let’s look at the different types, their meaning and possible complications associated with it.

To begin with, we can divide twins into two categories:

  • Dizygotic (fraternal)
    • It’s when two eggs are each fertilized by one sperm
  • Monozygotic (identical)
    • It’s when one egg is fertilized by one sperm

  1. In the dizygotic category, we have only one option:

The Di Di – The non-identical

Di di stands for dichorionic-dizygotic. It means that each embryo has its own amniotic sac and placenta. This is the most common type of twins. It usually occurs when two eggs are fertilized at the same time by two different sperms. Of all the twin pregnancies, this one is simplest in theory because it has fewer complications and the best chances of carrying healthy babies to term. Here are a few potential issues that can occur in any twin pregnancy:

  • Gestational hypertension: Carrying two babies increases the demand for blood flow and is quite demanding on the woman’s organs, so the chances of high blood pressure is almost doubled. Hypertension can lead to pre-eclampsia which in itself can lead to eclampsia and be life threatening, if not treated.
  • Anemia: The increased quantity of blood can lead to iron deficiency. Since your carrying twins, the chances of developing anemia are more than doubled.
  • Gestational diabetes: The placenta produces hormones that will impair the insulin’s action. As the weeks progress, the placenta will produce even more of these hormones and increase your blood sugar. Diabetes can lead to high blood pressure, pre-eclampsia, excessive birth weight, early birth and respiratory distress.

The di di twins are just like any siblings and share about 50% of the DNA except that they are roommates before birth. These twins can be two boys, two girls or a combination of a boy and a girl.

There are some factors that could increase your chances of having di di twins:

  • You are yourself a di di twin (it comes from the mother’s side, sorry boys!)
  • You have a family history of dizygotic twinning
  • You are using fertility drugs
  • You are of average height and weight
  • You are over 35 (chances will double after that age)
  • You had several previous pregnancies.

2. In the Monozygotic category, we have three options depending on when the fertilized egg divided.

Di Di – The other di di but identical this time

If the egg divides between 3 to 4 days after fertilization, you will have di di twins. That means that each embryo will have their own amniotic sac and placenta. They will benefit from the same advantages as the dizygotic twins except they will be genetically identical. Around 33% of all monozygotic pregnancies are di di. They will be subject to the same complication as the dizygotic twins.

Mono Di – The most common identical

My twins are mono-di. If the egg decides between 3 to 8 days after fertilization, you will have mono di twins. Mono di stands for monochorionic-diamniotic. Each embryo will have its own amniotic sac but will share the same placenta. Around 66% of all monozygotic pregnancies are mono di.

Mono di pregnancies a more risky for both the mother and the babies. One of the reasons is that the embryos share a placenta and blood vessels. There are complications that can occur and because of it, you will have more doctor’s appointments and more ultrasounds (prepare a photo album to cherish those moments with your kids later).

Here are some complications that can occur:

  • Twin to twin transfusion syndrome (TTTS): This condition implies abnormal connections between
    Twin to Twin Transfusion Syndrome (TTTS)

    the blood vessels in the placenta. In other words, it allows blood from one twin to flow into the other. When twins share the unique placenta unequally, one may not receive a sufficient quantity of blood, thus nutrients to grow normally. On the other hand, the other twin receives too much blood and that can put strain on the circulatory system. My twins had that complication and it explains why they were born with a 2 pound difference. Even today at five years old, one is still taller and heavier than the other.

  • Gestational hypertension
  • Anemia
  • Gestational diabetes

Mono Mono – The high risk pregnancy

If the egg splits between 8 to13 days after fertilization, you will have mono mono twins. Mono mono stands for monochorionic-monoamniotic. The embryos will share the same amniotic sac and same placenta. Only 1% of all monozygotic pregnancies are mono mono. Of all the twin pregnancies, this one will have to be even more closely monitored since there is a higher risk of complications.

On top of the possible mono di complications, the absence of separate amniotic sacs can lead to the following:

  • Cord entanglement: The closeness makes it particularly easy for the twins to become entangled in each other’s umbilical cords. Also, the entanglement can cause one twin to become stuck in the birth canal during labor. This happens at different degrees in most mono mono pregnancy.
  • Cord compression: As they move around in the womb, one baby can press down the other baby’s umbilical cord thus stopping the flow of blood and nutrients and resulting in fetal death.
With TTTS, even at 5 years old you can still see a difference in height and weight

So, does it run in your family?

So yes, if on the mother’s side there is a history of dizygotic twins, it may increase the chance of her having dizygotic twins. As for monozygotic, science has no explanation as to why it happens. Having identical twins in your family does not increase your chances of carrying monozygotic twins yourself.

As for me, I had mono di twins. I had many follow up visits to the doctor. My babies were in the early stage of twin to twin transfusion syndrome. I suffered from gestational diabetes and hypertension. As a result, I was hospitalized at 33 weeks for pre-eclampsia. I broke my water at 34 weeks exactly and went for c-section. It was August 6, 2013, that I gave birth to Ann-Penelope (4 pounds) and Ann-Pascale (2 pounds). We stayed in the hospital for three weeks.

If you have any questions or comments, please leave them below.






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