Selective Fetal Growth Restriction (sFGR)

In sFGR, the placenta is not divided equally. One twin may have a very small piece of the 'placental pie,' or their umbilical cord may be attached at the very edge of the placenta (marginal or velamentous insertion).

We classify sFGR into three types based on the Umbilical Artery Doppler of the smaller twin (Gratacos Classification):

• Type I: Positive blood flow in the umbilical artery. This has the best prognosis and can often be managed with close monitoring.
• Type II: Persistent absent or reversed blood flow. This is high-risk, as the smaller twin is at constant risk of deteriorating.
• Type III: 'Intermittent' absent or reversed flow. This is the most unpredictable type, caused by very large connecting vessels that allow blood to surge back and forth between twins.

sFGR occurs in about 10-15% of monochorionic (shared placenta) twin pregnancies.

It is typically diagnosed when there is a weight discordance of more than 25% between the twins, or if the smaller twin's estimated weight falls below the 10th (or 3rd) centile for their gestational age.

Early detection during the 12-week and 16-week scans is vital to determine which type of sFGR is present and to plan the monitoring strategy accordingly.

Diagnosis is made through specialized ultrasound assessment:

1. Biometry (Growth): Measuring the head, abdomen, and limb of both twins to calculate the weight difference.
2. Placental Mapping: Looking at where the umbilical cords insert into the placenta.
3. Doppler Profiling: Meticulously checking the blood flow in the umbilical artery, ductus venosus, and fetal brain.

At the MFM Unit, our consultants use the latest high-frequency transducers to capture 'intermittent' flow patterns that general ultrasound might miss, ensuring the classification is accurate.

Management depends on the Type and the gestational age:

• Type I: Usually managed as outpatients with weekly or bi-weekly Doppler scans. Most reach 34-36 weeks safely.
• Type II & III: Require intensive monitoring, often multiple times per week. If the smaller twin shows signs of terminal distress before 26-28 weeks, we may discuss difficult options seperti laser surgery (to separate the vessels) or, in extreme cases, selective reduction to protect the larger twin.
• Corticosteroids: Often given early to mature the babies' lungs in case of an emergency delivery.

The goal of sFGR management is to wait as long as possible to give both twins a chance at survival, while being prepared to deliver if the smaller twin becomes too unstable.

• In Type I, survival is over 90% for both twins.
• In Type II & III, the risk of one twin passing away in the womb is higher. Because they share blood vessels, if the smaller twin dies suddenly, it can cause immediate low blood pressure or brain injury in the larger twin. This 'linked destiny' is why expert monitoring at a specialized MFM center is non-negotiable.

If you have a twin pregnancy and have been told there is a 'size difference' or 'abnormal flow,' you should be seen by a subspecialist who manages complex twins daily.

sFGR is not a 'wait and see' condition; it is a 'watch and act' condition. Our Unit provides the technical expertise and the compassionate counseling required to navigate these high-stakes decisions. We work closely with the Level III NICU teams at Mediclinic to ensure the best possible start for both babies, regardless of their size at birth.