OUR LETTER TO PARENTS
Diagnosed with SIUGR
We have been where you are and understand. We are all here to help you and it is our honor.
SIUGR, selective intrauterine growth restriction, is a form of TTTS. It is defined as one of the twins being under the 10% for growth and more than a 20% size difference between the babies. It basically means that there is an unequal share of the placenta. Growth charts are usually based on singleton pregnancies. To get a more accurate percentile you can enter the date into this calculator for a twin growth chart developed after analysis of over 2000 twin pregnancies.
The placenta is the babies’ source of nutrition and oxygen. Normally, you are pregnant with one baby and one placenta. With monochorionic twins, there is one placenta that is shared by two babies. This takes place 4-6 days after conception when the embryo miraculously splits to create two identical babies in their own amniotic sac (monochorionic, diamniotic). At this time, their umbilical cords randomly insert into their shared placenta ‘claiming their space’ so to speak. This random cord insertions play a huge role in monochorionic twin pregnancies because if they both implant in the center of the placenta, you have won half the battle in your pregnancy as they will share the placenta fairly equally.
We have been where you are and understand. We are all here to help you and it is our honor.
Types of Cord Insertions
When there is a discordance in size, it is a warning sign that cord insertion is playing a role.
To understand the blood vessels in the placenta, we use the example of a capital “H”. The outer lines of the capital “H” represent the independent blood vessels that only go to Baby A and only go to Baby B. The middle line of the capital “H” represents the shared vessels connecting the babies’ circulations.
The combination of independent blood vessels together with shared blood vessels is unique to every single placenta making each pregnancy with monochorionic twins unique. Adding to the types of blood vessels would be how they flow (artery to artery, vein to vein and artery to vein).
So, you have the percentage of independent blood vessels that each baby has that determines their placental share, the number of shared vessels that connect their circulations, and the direction of the flow of the shared vessels (artery to artery, vein to vein and artery to vein).
After the embryo splits, the umbilical cords for each baby randomly attached to their shared placenta. It is at this time the placental share to each baby is determined. Placental share is the percentage of blood vessels that travel from the placenta independently to just Baby A, and the percentage of blood vessels that travel from the placenta independently to just Baby B. You hope that the placental share is 50-50 to each baby, but it is rare for it to be split perfectly equal. There are varying degrees of unequal placental share, but with SIUGR, the share can be much more unequal. As a result, one baby becomes much smaller and slower in growth than the other. Usually, a size difference between the babies of 20% or less is considered normal. SIUGR can be a reason that the size difference would be higher. You can’t change placental share, but sometimes the shared vessels in the placenta can help direct more blood flow from the larger baby to the smaller baby to help it get to a gestational age that is safer for delivery.
These are the vessels that do not make up the placental share, but are vessels that cross the placenta connecting the vein of one baby to the vein of the other (V-V0, the artery of one baby to the artery of the other (A-A), these are the connections that benefit the smaller baby and give it more blood, and the artery of one baby to the vein of the other.
These are called shared blood vessels, connections or anastomoses all meaning vessels that create a situation where the twins are circulating blood between each other. All monochorionic twins have shared vessels, but not all twins are negatively affected if there is a balance to the back and forth of the blood between the babies.
With TTTS, the shared blood vessels are the connections that are cauterized or sealed shut during laser surgery for TTTS, and the goal is always to cauterize all the connections (you cannot leave the artery to artery that benefit the smaller baby). With SIUGR, this same surgery can be done in more serious situations when there is consistent abnormal blood flow in the umbilical cord.
What is crucial to understand with SIUGR, however, is that after laser surgery, the babies revert back to their placental share only, meaning they only have their independent blood vessels to continue to get oxygen and nourishment to grow. The risk is whether or not the baby will have enough placental share after the surgery to grow to a safe gestational week to deliver.
Whether to decide to do laser surgery involves serious consideration and knowledge of their babies’ situation as every placenta is unique. Some moms decide not to do the surgery for fear of losing the smaller baby and opt for hospital monitoring and early delivery.
Some moms decide to move forward with the surgery if the smaller baby is very affected and it may also be also affecting his or her twin. If so, the specific prayer at this point is for the smaller baby to have enough placenta share afterwards to get to a safer gestational week to deliver.
As stated in the pregnancy section, ultrasounds should take place between 6-8 weeks of pregnancy to determine if there is one placenta or two. By 16 weeks, the ultrasounds must be weekly with a high-risk perinatologist or maternal-fetal medicine specialist (MFM) to look for the signs of SIUGR, TTTS, TAPS and TRAP.
Many doctors may feel every two weeks is sufficient, but it is not. Two weeks is appropriate to get a good weight estimate, but it is a lifetime to wait to monitor for the warning signs of TTTS including TAPS and SIUGR. TRAP should be diagnosed or ruled out by 16 weeks if not much earlier.
The warning signs of SIUGR include a weight difference of the twins of 20% or more together with the smaller baby in the 10th percentile or under for average size for that gestational age. They types of SIUGR are determined by the differences in the blood flow patterns of the smaller baby as seen by doppler ultrasound of the umbilical cord. Depending on the results of the warning signs seen, SIUGR can be diagnosed and is staged in Types 1-3.
You might also see the smaller baby have decreased amniotic fluid. When a baby becomes very malnourished from lack of placental share, his or her body will focus on all nutrients (blood) to go to the heart and brain of the baby and to the kidney last.
Amniotic fluid is basically the urine of the baby, so seeing this warning sign triggers more attention to diagnose SIUGR and make a plan of action to help the baby. When one twin has normal amniotic fluid and the other below 2cm, you can rule out TTTS, but with a size difference, it would appear to be SIUGR.
You have to continue monitoring several times a week to watch for symptoms to change is not every day in some situations.
What is crucial to understand with the staging of SIUGR is that most understand staging to become more serious as the numbers progress. With SIUGR, Type 2 is worse than Type 3! For now, it is Type 2 where surgery is considered as an intervention. The types are classified using the results of the doppler (wave form) in the umbilical artery of the growth restricted twin.
There is tremendous hope for your babies, even if they are diagnosed. It is going to take a lot of support, endless patience, and tortuous days that feel like years, but keep going. You are not alone, and we will help you!
The goal is to deliver at the moment the smaller baby runs out of its share of the placenta and goes into distress and you need to be in the hospital to do that. You never want to try and ‘buy time’ if you see that a baby has stopped growing.
If a baby is not getting enough blood, it is not getting enough oxygen and that is how cerebral palsy can happen or the baby could pass away. The baby in Type 2 SIUGR will have even less shared connections between babies in the placenta that might have helped compensate for the smaller placental share.
Fetoscopic view of the collision front within a placental arterio-arterial anastomosis between monochorionic twins. Here shows a visual depiction of one cause of umbilical artery intermittent absent end diastolic flow in these types of twins. This video is courtesy of Dr. Ramen Chmait, a Medical Advisory Board Member of The TTTS Foundation
We have developed the most important questions to ask your doctor at each ultrasound combining TTTS, including TAPS, SIUGR and TRAP. The answers to these questions should give you information about all forms of TTTS. Ultrasounds should start by 6-8 weeks and become weekly at 16 weeks through delivery.
This is when everything is perfect. If there is any concerns about the weights, fluid levels or dopplers, you must be seen several times a week, if not in some cases be admitted for 24 hour monitoring in the hospital. Take these questions extremely seriously and fight for weekly ultrasounds. You may hear over and over that every 2 weeks is sufficient, but it is not. We have helped too many families who have lost one or both babies in that time period. We are fighting to help save your babies lives.
Change will only happen when parents go back to their doctors and demand the care their babies need. We all want to hear that everything is fine and there is no need to do this or that. But, the truth is that the only way to have that reassurance at that moment is through the answers to these questions and getting the measurements that all the specialist in laser surgery will want to know. We want you to know what a laser doctor wants to know.
The TTTS Foundation highly stresses weekly ultrasounds during a monochorionic pregnancy when everything is perfect. When there is an unequal placental share, ultrasounds may need to be more frequent to monitor the fluid levels and dopplers to see if there is progression of growth discordance and/or movement toward TTTS.
Laser surgery for SIUGR has to be taken very seriously for fear the smaller baby may not have enough placental share to grow after the shared vessels are all sealed. If both babies start to become affected and the smaller baby has continuous reverse flow, the laser surgery may become an option to correct the abnormal dopplers. Laser surgery would always be to try and save both babies.
Twins with unequal placental share often have artery to artery (AV) connections which can help bring more blood flow to the smaller baby and be a protection against TTTS. It is a reason to be very careful in a decision of laser surgery. The symptoms in the baby must be very serious, because all vessels must be cauterized to completely disconnect the babies during this procedure including the AA connections that provide extra blood.
SIUGR is an unequal placental share causing growth restriction in one of the babies. TTTS is an unequal sharing of volume of blood through the babies shared placenta causing an amniotic fluid difference. TTTS can cause a size difference of the babies, but with SIUGR the baby is much smaller under the 10th percentile for growth.
With TTTS, the babies could have a size difference due to one getting more blood volume and the other too little blood volume, yet still have a fairly equal placental share. In that situation, once the TTTS could be treated, the babies would then get normal blood flow and the size difference could improve.
You can absolutely have SIUGR and TTTS at the same time and experience TAPS as well. This is why The TTTS Foundation is education you on ALL forms of TTTS.
It is important to have a plan so that you are prepared to advocate for your family and informed on what to expect in the coming days. We are here to support you in any way you may need.
Carolyn went through TTTS and SIUGR and is now The TTTS Foundation’s SIUGR Coordinator providing hope and compassion to newly diagnosed families out of love for her twin sons.