Today was the big ultrasound to determine chorionicity of the twins. They are monochorionic, diamniotic. Basically, this means that they are monozygotic (identical) and share a placenta.
For those who are unfamiliar with twinning I'll explain a few things. Twins are either monozygotic or dizygotic. Monozygotic (MZ) twins are often referred to as identical and are the result of one egg splitting after fertilization. Dizygotic (DZ) twins are often referred to as fraternal and are the result of two separate eggs being fertilized.
Dizygotic twins will always have separate placentas, amnions, and chorions although sometimes the two placentas can "fuse" into what appears to be one placenta. The amnion is the inner sac (or membrane) and the chorion is the outer sac. Many people do not realize that the membranes are made up of two separate layers. DZ twins will always have separate amnions and chorions because they result from 2 separate eggs. DZ twinning can run in families and can be increased because of fertility treatments.
Monozygotic twins are trickier. About 1/3 of all twins are MZ and it is unknown what causes MZ twinning. MZ twins can have separate placentas, amnions, and chorions like DZ twins. About 1/2 of MZ twins are dichorionic, diamniotic (DCDA.) About 60% of MZ twins are monochorionic, diamniotic (MCDA) and these twins share a placenta and are at risk for Twin to Twin Transfusion Syndrome (TTTS.) Only 1-2% of MZ twins will be monochorionic, monoamniotic (MCMA) and this is the most dangerous type of twinning because of the risk of cord entanglement.
It's amazing how little some medical professionals know about twinning. The ultrasound technician today did not know what a chorion was and had to call in a doctor. She said she has NEVER seen a monochorionic twin pregnancy before. This is totally wrong because she is the same technician who performed my first u/s with the girls. She told me then that they were fraternal because they were in separate amniotic sacs! She has been giving out bad information to who knows how many people. I think I set her straight today.
Anyway, these twins are again at risk of TTTS. The girls developed acute TTTS at term. We don't know when it happened but fortunately God was watching over us and everything was fine. S was the recipient twin and so she had a very high red blood cell count for about 8 weeks after birth. She would have received a transfusion if we had been in the hospital. L was the donor and was anemic. S has always been chubbier and healthier-looking than her sister. The differences are noticeable even today.
I'm a little worried about TTTS but mostly wondering how difficult this pregnancy will become. I am now "high-risk" and with that comes a probable referral to that doctor I saw last time and wanted to avoid this time. I'm sure he'll be thrilled to see me again! This also means frequent ultrasounds and monitoring because there is a greater chance of growth discordance and of course TTTS. So much for an uneventful pregnancy!
Oh, and one last note. I decided that I will go ahead and find out the gender of these babies. I didn't plan to find out but if something does happen, I want to name them now and not later. I can't explain it but I just feel compelled to know so I'm going with that.
(And yes, I am very excited, thrilled, and can't wait to meet these babies! I'm just also feeling overwhelmed by the possibility of complications. Please don't think that I'm not completely grateful for this blessing because I really am but my head is still spinning from all of the developments in the past few weeks.)
