Selective Fetal Growth Restriction (sFGR)

sFGR doesn’t usually cause symptoms in a pregnant person. sFGR is diagnosed solely by fetal imaging methods, usually ultrasound.

Monochorionic twins share one placenta, with each having its own section for receiving nutrients and oxygen. But in sFGR, how much placenta each twin gets may not be equal, resulting in one twin receiving more than the other. This can cause the smaller twin not to grow properly, which is known as growth restriction. In these cases, there are connections between the blood vessels of the twins, particularly in cases of growth restriction, which can change the blood flow patterns.

Pregnancies complicated by sFGR have chorionic vascular connections. Specifically, large artery-to-artery connections (anastomosis) may alter blood-flow patterns.

sFGR is usually diagnosed through an ultrasound. Doctors may also use Doppler to measure the blood flow between each fetus.

To determine sFGR, doctors look at the estimated weight of the smaller twin compared to the other twin, and the difference in weight between the twins. To be diagnosed with sFGR, the smaller twin must be below the 10th percentile for gestational age, and there must be a 25% or greater difference in weight between the twins.

Other tests may include:

• fetal echocardiography: a special ultrasound of a fetus’s heart
• magnetic resonance imaging (MRI): to determine if there are any other structural anomalies
   

Surgery isn’t needed for most cases of sFGR. Instead, doctors monitor the twins to ensure they’re doing OK. In cases where one twin grows slower and risks the health of the other twin, doctors will discuss performing one of the following:

• Endoscopic laser surgery: A procedure where a small hole is made in the pregnant person’s abdomen, and a camera called an endoscope is used to look at the uterus. A laser is then used to stop the abnormal connections between twins and prevent any further harm to the healthier twin.
• Selective reduction: A surgery done through a small hole in the pregnant person’s abdomen to prevent harm to the healthier twin when the other is severely compromised and risking the health of both.
• Delivery: Doctors may deliver the twins and provide care in the NICU. The timing of delivery is decided on a case-by-case basis.

Because there are different ways to treat sFGR, the treatment doctors choose depends on the following factors:

• when sFGR started in the pregnancy
• the severity of the growth restriction
• how the pregnant person wants to move forward