No offense to a certain relative, but I was recently told that they hoped my identical twins would be one boy and one girl so they would be easier to tell apart. Hmmm.... I think some people need the skinny on some twin basics, call it twinforming you so you are not twignorant. Too many made up words? Okay, I'll stop.
What is the difference between fraternal and identical twins?
Fraternal twins happen when 2 eggs are fertilized by 2 sperm, creating twins who share the same amount of genetic infomation as normal siblings. Fraternal twins can be boy/boy, girl/girl, or boy/girl and look as much (or as little) alike as two siblings normally do.
Identical twins happen when 1 egg is fertilized by 1 sperm, and the resulting embryo splits and creates 2 babies. Twins share all of the same basic genes, and therefore are always the same gender. Our babies will either be two boys or two girls and look alike.
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| Identical twins come from one egg and sperm, fraternal twins come from two eggs and two sperm. |
How do we know we are having identical twins if we don't even know the gender yet?
The egg can spilt at various stages of development. This creates different combinations of sacs in the womb that are visible on early ultrasound images. Some types of identical twins cannot be diagnosed this early because they look like fraternal twins in the womb.
Egg splits days 1-3: Babies will have separate gestational sacs and separate amniotic sacs. Babies will each have their own placenta. This happens 20-30% of the time and the babies will look just like fraternal twins in the womb. This is the safest type of twin pregnancy because with separate placentas, they babies are not competing with one another for nourishment. Called monozyotic dichorionic/diamniotic (di/di) twins.
Example of two separate gestational sacs, which would be either fraternal twins or di/di twins.
Egg splits days 4-8: Babies will share a gestational sac and placenta, but have separate amniotic sacs. This happens 60-70% of the time and is the case with our babies. Separate amniotic sacs prevent the umbilical cords from wrapping around the babies, but there is a risk of Twin to Twin Tranfusion Syndrome, where one baby takes most of the nourishment resulting in drastic growth difference between the babies in utero. Doctors will monitor our babies closely and this doesn't usually happen until after 22 weeks. Called monozygotic monochorionic/diamniotic (mono/di) twins.
Video of our babies showing one gestational sac and individual amniotic sacs.
Egg splits days 9-13: Babies share gestational sacs, placentas, and amniotic sacs. This happens 1-2% of the time. Increasingly risky pregnancy, but babies can be born healthy. Called monozygotic monochorionic/monoamniotic (mo/mo) twins.
Egg splits days 14 +: This results in conjoined twins and is very rare.
Image showing the effect of time on the development of identical twins. Top line is 1-3 day split, middle line is 4-8 days split, and bottom line is 8-13 day split. Ours are like the middle line, which is the most common type of identical twins.
Do twins run in your family?
They do now! Genetically speaking, fraternal twins will run in a woman's family. A woman whose mother had identical twins is likely to be super fertile like her mom, releasing more than one egg each month resulting in fraternal twins. Geographically, there is a link between fraternal twins and country or origin, possibly due to diet, or just due to heredity.
Identical twins are thought to be a random occurence and not linked to heredity or geography (the rate of identical twinning is roughly the same throughout the world). However, lots of people have multiple sets of identical twins in their families, so even though science says its random, I think science needs to study harder!
Are identical twins caused by fertility drugs?
With many fertility drugs, ovulation (release of an egg) induction is the intended result. Sometimes, it is difficult to induce the production of only one egg per month, and many women produce multiple eggs, resulting in fraternal twins. With IVF, to increase success rates, many doctors transfer 2-3 embryos into the womb. The nice thing about IVF is you have total control over how many embryos you transfer.
We chose to transfer only one embryo due to risks and complications of multiple pregnancies. Well, God had another plan for us and gave us two anyway. Our one embryo split and resulted in two identical twin babies. We are very thankful and blessed. I truly believe that our journey to IVF was meant to lead us to our twins, and when we chose to transfer only one embryo, God laughed and said, " not on my watch, this couple was meant to have twins." Wham, bam, split the egg, and twins it is. So here were are!
That being said, there is a slightly higher incidence of identical twins in IVF patients. I have heard lots of different odds, in vivo conception has a 3 in 1000 (0.3%) chance of identical twins and in vitro conception has a 21 in 1000 (2.1%) chance of identical twins.
I am sticking with act of God!
So really, whose side of the family has the twins?
Yes, you are right, Mike's supersperm caused my egg to split in half. Just like that! Wow! I forgot, that's how we ended up with identical twins.
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