Twin to Twin Transfusion Syndrome (known as TTTS) is a condition unique to monochorionic twin pregnancies. During a twin pregnancy, there are several factors which contribute to the risk of TTTS. First, the babies must share a single placenta. Fraternal (dizygotic) twins will always have separate placentas (although the two placentas can fuse together) and care not at risk of developing TTTS. Identical (monozygotic) twins can have separate placentas as well (up to 30% of identical twins do have separate placentas) and many doctors will mistakenly diagnosis these pairs as being fraternal twins.
The most common scenario is for identical twins to share a placenta but each baby remains in its own separate amniotic sac. This is called monochorionic/diamniotic (mo/di) because the babies share a chorion (the outer layer of sac) but are separated by an inner dividing membrane-the amnion. The most dangerous scenario is twins who are monochorionic/monoamniotic (or mo/mo) because these twins are inside the same amniotic sac and are at risk of umbilical cord entanglement. Fortunately, mo/mo twins are rare-only around 1% of twins present this way. More commonly, the identical twins are mo/di and these twins are at risk of developing TTTS.
(My belly at 35 weeks pregnant with the first set of twins)
TTTS is a disease of the placenta in which there are abnormal blood vessels which connect the umbilical cords of each baby, enabling them to "share" blood. When the "sharing" becomes unequal, one baby receives too much blood flow and the other does not receive enough. The baby who does not receive enough is known as the "donor" and the baby receiving too much is the "recipient." Obviously, this type of unequal blood flow can harm both babies if left untreated.
There are two different types of TTTS. The most serious type is chronic TTTS, which occurs between 12 and 26 weeks gestation, before the babies are big enough to be born. The second type is acute TTTS which occurs later in pregnancy, or even during labor. Acute TTTS can be resolved with immediate delivery of the babies but chronic TTTS can require treatments such as laser surgery to separate the connecting blood vessels.
TTTS can strike any monochorionic twin pregnancy without warning. Of all monochorionic twin pregnancies, about 15% will go on to develop TTTS. There are about 4,500 cases of TTTS in the US each year.
(Sarah & Leila, just a couple of hours old)
When Leila and Sarah were born in 2006, I had no idea what TTTS was or even whether they were at risk for it. Because I didn't have an ultrasound until 22 weeks (that was when I found out I was carrying twins!) it was impossible to tell whether the girls shared a placenta or whether two single placentas had fused. There is a narrow window of time in which doctors are able to easily tell whether twins are monochorionic by looking for that thin dividing membrane and this is quite early in pregnancy. I was well past that point and the girls were big and crowded inside me, making it impossible for anyone to know whether they were monochorionic.
It wasn't until after their birth that we knew something was wrong. I had wonderful midwives present for the birth and Leila and Sarah were born on the floor of my bedroom. There were no complications other than a loop of cord in front of Leila's head that had to be pushed aside and Sarah's hand trying to come out before her head. The girls were both 7 lbs, 6 oz and healthy. However, acute TTTS had struck sometime in my final days (or hours) of pregnancy.
Because of the unequal blood sharing, the recipient baby in a TTTS case becomes overloaded by the extra blood and suffer from heart failure. The donor suffers from lack of nutrients and poor growth. There are warning signs such as discordant growth and discordant amniotic fluid levels. Doctors also look at the way the umbilical cords are attached to the placenta and how many vessels are in the cords.
One of my girls had a single umbilical artery but there were no other factors to indicate TTTS was developing. After their birth their pediatrician was alarmed at hoe red Sarah's skin looked. Blood tests revealed that Sarah was polycythemic as a result of acute TTTS and that left her skin red for months. Leila (the donor) was anemic and looked pale and thin in comparison to her twin. There were no lasting effects of the TTTS and we were blessed that everything turned out just fine.
(My ginormous belly just days before Nathan & Ryan were born)
With my next pregnancy, I suspected right away that I carrying twins again. Everyone assured me that I was crazy, and I tried to believe them. Finally, I went for an ultrasound at 9 weeks and found out that I was indeed carrying a second set of twins. On top of that news, I learned that they were also monochorionic twins.
I ended up seeing the same OB for backup care that I had seen with the girls. He was very knowledgeable about TTTS and was amazed that I was carrying a second set of identical twins. Because the odds of having two sets of identical twins were already high, he assured me that the odds of having two sets of twins with TTTS would be astronomical. Indeed, when I consulted with a leading expert in TTTS research, he also reassured me that it would be almost unheard of to develop TTTS again. He knew of only 2 cases of that happening.
And then, in an incredible twist of fate, TTTS struck again. After a long pregnancy full of conservative monitoring, acute TTTS reared its ugly head. This time, things were different. And scary.
Just days from my due date, I started to have an incredible pain in my groin/hip/leg. I thought for sure that it was a baby pressing on a nerve and tried everything to fix it. When all failed, I ended up in the hospital. A recent ultrasound (notoriously inaccurate in the third trimester) showed that both babies were the same size and were big and healthy. Despite the ultrasound results, things were not well. There was a significant growth discordance and Baby B was in distress. When they were watching me overnight, Baby B's heart rate tanked. His heart rate had been having slow decels down to the 70s & 80s, but suddenly it dropped to 50 and then disappeared. That was it. They put me out and I had an emergency cesarean. When I woke up I had no idea what had happened.
(Nathan & Ryan at a few days old)
Ryan (Baby B, my donor) was resuscitated at birth and was thin and pale, but healthy. He weighed 6 lbs, 6 oz. Nathan (my recipient) was 7lbs, 9 oz and was red and plump. Examination of the placenta revealed an unequal sharing and Ryan's umbilical cord had been small and thin.
That is the scary part of TTTS. It can strike anyone and can come on without warning. Close monitoring is important, but having an educated care provider is key. I can't even tell you how many mothers of twins have told me that their doctor said their twins can't be identical because they have separate amniotic sacs. The TTTS Foundation distributes a (free) wonderful handbook for parents and their care providers that will tell you everything you need to know about TTTS.
I consider myself extremely blessed to have my six sweet children. I know that many cases of TTTS are severe and end in the loss of one, or both, babies. The TTTS Foundation is working to stop this through raising awareness of TTTS risk factors and treatments. I'm fortunate to have two healthy sets of TTTS survivors, but many families are not so lucky.
You can help the TTTS Foundation by making a donation or by drawing attention to TTTS. Blog about it, tweet about it, talk about it!