Selective Intrauterine Growth Restriction (sIUGR)

What is Selective Intrauterine Growth Restriction?

Selective intrauterine growth restriction (sIUGR) is a condition that complicates 10-15% of monochorionic twin pregnancies, where unequal sharing of a single placenta causes inadequate growth in one twin. The placenta provides blood, oxygen and nutrients necessary for development in the womb. When these critical resources are imbalanced, one twin may become malnourished often falling below the 10th percentile in weight. Typically, the other twin grows normally and the difference in weight between the twins exceeds 20%. The growth restriction in the smaller twin may be progressive leading to in utero demise of the smaller twin in some cases. Because the twins share blood circulation in the single placenta, death of the growth-restricted twin may affect the co-twin. In these, the co-twin is at risk for neurological insult resulting in brain and/or organ damage, early delivery or even death. 

How is sIUGR Diagnosed?

Accurate and thorough evaluation is important in distinguishing between sIUGR and other diagnoses that occur in monochorionic pregnancies, such as Twin to Twin Transfusion Syndrome (TTTS).

Your evaluation at The Chicago Institute for Fetal Health will include a high-resolution ultrasound and fetal echocardiogram (performed by a Fetal Cardiologist) followed by a comprehensive team meeting to review the imaging results and put a plan of care in place for the remainder of your pregnancy. 

Ultrasound: All patients receive a Level II anatomy scan, which is a detailed ultrasound looking at your baby from top to bottom. Twins diagnosed with sIUGR have significant differences in growth measurements and also may display abnormalities in amniotic fluid volume and umbilical cord blood flow patterns. 

Fetal Echocardiogram: Echocardiogram is an ultrasound that takes a focused look at the heart function and anatomy of both babies. These imaging studies look at the direction, velocity, and patterns of blood flow while assessing the overall workload of the heart.  

What Criteria are Used to Diagnose sIUGR?

  • Monochorionic twin pregnancy: identical twins that share a placenta.
  • Significant weight discrepancy between the twins (exceeding 20%).
  • Estimated fetal weight of one twin below the 10th percentile.
  • Exclusion of  Twin to Twin Transfusion Syndrome as a cause to the weight discordance.

What are the Different Types of sIUGR?

Once diagnosed, sIUGR is classified according to the blood flow patterns (wave forms) in the umbilical artery of the growth-restricted twin:

  • Type 1 – Continuous forward flow during systole and diastole in the umbilical artery of the growth-restricted twin.
  • Type 2 – Persistently absent or reversed blood flow during diastole in the umbilical artery of the growth-restricted twin.
  • Type 3 – Intermittently absent or reversed blood flow during diastole in the umbilical artery of the growth-restricted twin.

How Do We Treat sIUGR?

Currently, there is no treatment available to correct the underlying cause of sIUGR which results from structural and functional abnormalities in the development of the placenta. However, a number of management options exist and depend on the gestational age, type of sIUGR and other evaluation findings. The majority of the sIUGR pregnancies do not undergo fetal surgery. Rather, they are closely monitored with frequent ultrasounds and are frequently delivered early in the more severe cases. 

Expectant Management

In most cases of sIUGR that develop before 24 weeks, we recommend frequent monitoring with ultrasound and echocardiogram imaging. Typically, the recommendation for Type 1 sIUGR is close ultrasound surveillance throughout pregnancy. Weekly ultrasounds will be performed to observe for signs of the disease progression to Type 2 or Type 3 sIUGR, where intervention may be warranted. In some cases where there is persistent blood flow abnormalities (absent or reversed end diastolic flow) in the umbilical cord, daily monitoring may be recommended to detect any changes in fetal well-being that may necessitate an urgent delivery. This monitoring can be done either as outpatient or by being admitted to the hospital (usually for the remainder of the pregnancy). Expectant management of sIUGR can be complicated because there is a delicate balance in allowing the babies to get as far along in gestation as possible inside the womb to avoid complications of prematurity, without the disease causes irreversible harm to either baby.     

Fetal Surgery

Fetal surgery is only offered when demise of the growth-restricted twin seems imminent at a very early gestational age. The goal of fetal surgery is to separate the circulations within the placenta thereby separating the fates of the twins. Separating the circulations protects the co-twin from damage to its brain or organs as a result of changes in blood pressure that occur when the growth-restricted twin dies.

  • Selective Fetoscopic Laser Photocoagulation (SFLP) – In this procedure, abnormal vascular connections on the surface of the placenta are directly visualized through the use of a small telescope. These connections are coagulated with a laser fiber to separate the placental blood supply between the babies. More detailed information on the SFLP procedure and recovery can be found on the TTTS page under ‘How do we treat TTTS’ by clicking here.
  • Selective Cord Coagulation – In rare cases before 24 weeks, cord coagulation may be offered to stop the blood flow in the growth restricted twin when there are signs of impending demise. The goal of this procedure is to protect the normally growing twin from neurological and organ damage following death of the growth-restricted twin. 


After 24 weeks gestation, early delivery may be recommended if either twin shows signs of fetal distress. Pregnancies complicated by sIUGR often result in preterm delivery. Meeting with a Neonatologist can help patients prepare for this possibility and understand the potential obstacles a preterm baby is at risk for encountering. A delivery plan is individualized for each patient and family after understanding their goals for survival of both twins in balance with the risks associated with prematurity. 

What Are the Outcomes in Patients with sIUGR?

The outcomes of selective intrauterine growth restriction depend on the severity of the growth restriction present and the gestational age at delivery.