I did a lot of research the moment I found out we might be having twins during my Week 5 Ultrasound. A lot of people think that identical twins are twins that look very much like each other, and fraternal twins are twins that don’t look like each other. That is actually not the case. Identical twins are twins that come from a single embryo (monozygotic twins). That means one egg was fertilized, and it split in the uterus after conception. The twins will share the same DNA, so they tend to look alike. They will also have the same gender, unless there is a genetic defect (which is not what we want). According to what I’ve read, there is no proof that identical twins are hereditary. They are completely random. The reasons why embryos split is unknown. The process of conception has nothing to do with having identical twins. Procedures like In Vitro Fertilization does not result to identical twins. That is why our IVF doctor told us that they had nothing to do with our having twins.

Fraternal twins are twins that come from two eggs that were fertilized by two sperms resulting to two separate embryos (dizygotic). It is a more common type of twin occurring in 67% of all twins. Fraternal twins can result to same sex babies, or male-female babies. They share 50% of their DNA, like any regular siblings. They can look very much like each other or very different from each other – just like some regular siblings look alike, and some don’t. The only difference they have with non-twin siblings is that they were conceived at the same time. There are several factors that contribute to fraternal twins. First is genetics. If there are twins in the family, specifically on the female side, there is a higher likelihood of having twins. That means that the woman is genetically pre-disposed to releasing more than one egg during her ovulation. Second is race. There are more Africans that give birth to twins than any other race in the world. Third is weight. Overweight women tend to give birth to twins more than women with normal/low weight. Fourth is age. Older women have a higher chance of giving birth to fraternal twins. Finally, the biggest factor in this day and age is Assisted Reproductive Technology (ART) like In Vitro Fertilization. This is because couples who undergo IVF usually choose to have several embryos transferred to the woman’s uterus resulting to multiple birth.

So far, from what I observed, doctors don’t seem to care whether the mom is carrying identical or fraternal twins. What they need to know is whether the twins share the same amniotic sac, chorion (the outer membrane surrounding the embryo) and placenta. When my OB gives me a request for an ultrasound, she always specifies that our twins are monozygotic and also writes the specific type of twins. There are three types:

  1. Di-chorionic/Di-amniotic Twins (also called Di-Di Twins) – This type of twins have separate chorion, placenta and amniotic sac. All fraternal twins are Di-Di twins. Only 33% of Di-Di twins are identical. Since di-di twins can be either fraternal or identical, if the twins are the same gender, you can’t know for sure if they are identical or fraternal unless you do a genetic test. In our case, we know they are identical because we had IVF, and we only had one egg fertilized, and one embryo transferred into my uterus. It surprises me that some doctors don’t know that Di-Di twins can be identical.
  2. Di-chorionic/Mono-amniotic Twins (Also called Mono-Di Twins) – This type of Identical twins share a placenta and chorion, but have separate amniotic sacs. When twins share a placenta, they have the same food supply. There is a risk of one twin getting more nutrients than the other, resulting to slower growth of the other twin. On the other hand, the twin getting more nutrients and blood supply may become overloaded with blood. This excess blood puts a strain on this baby’s heart to the point that it may develop heart failure, and also causes this baby to have too much amniotic fluid from a greater than normal production of urine.. This is called twin to twin transfusion syndrome. It can be fatal for one or both twins.
  3. Mono-chorionic/Mono-amniotic Twins (Also called Mono-Mono) – This type of identical twins share placenta, chorionic and amniotic sac. One of the main dangers of this type of twins is entanglement with the umbilical cord. 50% of mono-mono twins die from umbilical cord entanglement.

Our twins are Di-Di twins. They belong to that rare 33%. So, we realize how blessed we are, and how this pregnancy is truly a miracle. It is rare enough that we are having identical twins, and even rarer that they are Di-Di twins. This means that we don’t get to experience the risks of the other types of identical twins.

Having done all this research, does this make me a twin expert? Nah! I am still clueless on how to raise twins. Help!

Written by Alby Laran

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