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Today’s ultrasound and Doppler studies now indicate that the TTTS is not the major threat anymore. Baby A’s fluid MVP has increased to over 4 Baby B’s has increases slighty nearing 10 (we’re told at >14 the pressure will begin to cause health issues in Baby B. Having said that, right now Baby B is in the 98th percentile: he’s a giant due to all the blood flow he is getting. Baby A is in the 10th percentile for growth. The babies have a 25% size difference which is normal but indicating growth restriction. If Baby A falls below the 10th percentile, the diagnosis will be Selective Intrauterine Growth Restriction (sIUGR) which is similar to TTTS but appears to be even less treatable.

I’ve gathered the below about sIUGR to be prepared for the next ultrasound. There are several sites that explain sIUGR, but I think Children’s Hospital of Philadelphia CHOP does it very well Selective Intrauterine Growth Restriction (sIUGR) | Children’s Hospital of Philadelphia (chop.edu):

What is selective intrauterine growth restriction?

Monochorionic twins are twins that share a single placenta. Selective intrauterine growth restriction (sIUGR) occurs when there is unequal placental sharing which leads to suboptimal growth of one twin. In cases of sIUGR, the estimated fetal weight of the smaller, growth-restricted twin usually falls below the 10th percentile. This will usually result in more than a 25 percent weight difference between the twins.

sIUGR is estimated to occur in approximately 10 percent of monochorionic twin pregnancies. There are three types of sIUGR that are determined by the blood flow pattern in the umbilical artery of the growth-restricted twin.

The Fetal Health Foundation explains that severe cases of monochorionic twins with SIUGR show ultrasound evidence of abnormal blood flow through the umbilical artery of the poorly grown twin. In this circumstance, spontaneous death of this baby within the womb may occur in up to 40% of cases. Because of the blood vessels that link the twin’s circulatory system together, death of one twin may result in severe drop in blood pressure of the other twin and subsequent brain damage (up to 30%) or death (up to 40%). This complication results from the hemorrhage of blood from the appropriately grown twin into the demised SIUGR twin.Because the adverse effects to the appropriately grown twin is mediated through the blood vessels that link the circulations of the twins, it has been suggested that obliteration of these vascular communications may result in improved outcomes for the normally grown twin. Separation of the circulations may be done using the surgical techniques which were originally developed for the treatment of twin-twin transfusion syndrome. (Selective Intrauterine Growth Restriction (SIUGR) – Facts – Fetal Health Foundation)

Causes

The principle cause for the development of sIUGR in monochorionic twins is unequal placental sharing. The growth-restricted twin has a smaller share of the placenta, which over time results in abnormal blood flow and less growth. This could lead to death of the growth-restricted twin. Because the shared placenta also contains shared blood vessels between the twins (vascular communications), sIUGR also impacts the development of the brain and nervous system in the normal twin (neurodevelopment).

Symptoms

There are no physical symptoms of sIUGR that you, as a mother, would feel. sIUGR is a diagnosis made exclusively through ultrasound examination.

Evaluation and diagnosis

Accurate diagnosis is extremely important in distinguishing sIUGR from other diagnoses such as twin-twin transfusion syndrome (TTTS). TTTS and sIUGR both involve a shared placenta, but are differentiated by the type of vascular connections between the twins.

These differences can be very subtle. In TTTS, there is a very characteristic and progressive series of changes that happens to each twin. In sIUGR, the distribution of blood is more balanced, but because the growth-restricted twin has a much smaller portion of the placenta, the resistance in the umbilical artery is much higher than normal, resulting in suboptimal fetal growth.

Types of sIUGR

sIUGR has been classified into three types based on specific blood flow patterns in the umbilical artery of the growth-restricted twin.

Type 1

• Consistent forward flow in the umbilical artery of the growth-restricted twin
• Average age at delivery is 34-35 weeks gestation
• In most cases of type 1 sIUGR, the babies’ condition remains stable throughout the pregnancy, although in up to 15 percent of cases, the sIUGR progresses as the pregnancy continues.
• The overall survival rate for babies with type 1 sIUGR is greater than 90 percent.

Type 2

• Either persistent absent blood flow or persistent reversal of blood flow in the umbilical artery of the growth-restricted twin
• Average age at delivery is 26-32 weeks gestation
• Babies with type 2 sIUGR have a guarded prognosis.
• About 90 percent of cases worsen as the pregnancy continues.
• Extreme preterm delivery is common among babies with type 2 sIUGR, often before the 30th week of pregnancy.

Type 3

• Unpredictable pattern of intermittent blood flow in the umbilical artery of the growth-restricted twin (forward, absent or reversal). In other words, only occasionally is the blood flow in the artery absent or flowing in a reverse direction. This type of blood-flow pattern is unique to monochorionic twins with sIUGR. It occurs when large arterio-arterial connections are present, allowing shared blood to flow back and forth between the twins.
• Average age at delivery is 30 weeks gestation
• In up to 15 percent of cases, the growth-restricted twin may not survive, which can also impact the neurodevelopment of the normally growing twin.
• Whether or not the condition will change or worsen during pregnancy is difficult to predict from the ultrasound images. Babies with type 3 sIUGR are born, on average, during the 30th to 32nd week of pregnancy. Their overall survival rate is 80 percent.

Treatment

Management of sIUGR may include continued observation with ultrasound surveillance or fetal therapy. Your recommended treatment will depend upon the type of sIUGR your twins are diagnosed with.

Treatment options include the following:

Expectant management: This involves continued close ultrasound surveillance throughout the pregnancy. We currently recommend expectant management for most Type 1 sIUGR and dichorionic twins.

Selective cord occlusion: This procedure may be offered if you have monochorionic twins with Type 2 or Type 3 sIUGR. Selective cord occlusion is a minimally invasive procedure that stops blood flow to the growth-restricted twin. The goal is to optimize the outcome for the normally growing twin. The procedure can be performed using bipolar cord coagulation, interstitial laser, or microwave ablation.

Fetoscopic laser photocoagulation: In select cases this minimally invasive surgery can be used to laser ablate (seal) blood vessels that are shared between the babies. Similar to selective cord occlusion, the goal of therapy is to optimize the outcome for the normally growing twin.

Delivery: If sIUGR is discovered later in the pregnancy or the condition progresses after the pregnancy reaches its 24th to 26th week, delivery of the babies may be the best option.
How is selective intrauterine growth restriction (sIUGR) treated after birth?
Most babies with sIUGR are born prematurely, but our goal will be to prolong your pregnancy for as long as possible.

We recommend that your babies are born at a hospital able to care for premature babies.

Treatment for Type 1 sIUGR

You will undergo continued weekly observation with your local maternal-fetal medicine specialist. Weekly or twice weekly ultrasounds closely monitor the growth of both twins and watch for progression to Type 2 or Type 3 sIUGR which may indicate prompt referral for fetal therapy.

Because preterm deliveries are common in pregnancies affected by sIUGR, consultation with neonatology and a specialized delivery center can help you plan for this possibility.

Treatment for Type 2 and Type 3 sIUGR

Along with weekly observation by your maternal-fetal medicine specialist, we may recommend fetal therapy in the form of selective cord occlusion.

Selective cord occlusion is a minimally invasive surgical procedure that seeks to improve the outcome for the normally growing twin by stopping the blood flow to the growth-restricted twin in a way that minimizes impact the neurodevelopment and survival of the normally growing twin. Selective cord occlusion can be performed using bipolar cord coagulation (BCC) or radiofrequency ablation (RFA) procedures.