EXPLAINER: What are conjoined twins?

Following a complex surgery lasting over six hours, Filipino conjoined twins Olivia Faith and Giana Faith were successfully separated.

The twins, who are from Nueva Ecija, are the fourth set of Filipino conjoined twins to undergo successful separation under a medical program in Riyadh, Saudi Arabia.

What are conjoined twins?

Conjoined twins are identical twins born with parts of their bodies physically connected. This happens when a single fertilized egg does not fully divide into two separate embryos during early development in the womb.

Conjoined twins are extremely rare. Many pregnancies involving conjoined twins end in stillbirth or the babies die shortly after birth, depending on the extent of their connection and whether they share vital organs.

How do conjoined twins form?

One explanation is the Fission Theory. Normally, identical twins form when a single fertilized egg splits into two embryos.

In conjoined twinning, experts believe the split is delayed during the early stages of pregnancy. By the time separation happens, cell development may already be too advanced, preventing the embryos from fully dividing and leaving them partially connected.

What are the different types of conjoined twins?

• Conjoined twins are classified based on the body part where they are joined:
• Thoracopagus – joined at the chest, often sharing organs such as the heart or liver
• Omphalopagus – joined at the abdomen
• Pygopagus – joined at the spine or lower back
• Ischiopagus – joined at the pelvis or hips
• Craniopagus – joined at the head

What makes separation surgery risky?

The surgery becomes more complicated when the twins share vital internal organs such as the heart, liver, or brain. In these cases, the risk of complications is significantly higher.

Studies show that only about 25% of conjoined twins are born alive and may qualify for separation surgery. Among those, the success rate of surgery ranges from 60% to 66.7%.

Long-term survival rates, however, remain low, ranging from 5% to 25%.—MCG, GMA News