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Why do Twins Become Conjoined?

Researchers still do not know why some twins become conjoined. There may be specific genetic reasons responsible for delaying the fertilized egg from splitting into two embryos.

There may also be environmental reasons that prevent the egg from splitting completely. More research is required in order to determine the cause of conjoined twins.

Types of Conjoined Twins

Conjoined twins are classified according to where on their bodies they are attached. Types of conjoined twins include:

• Craniopagus: These twins are attached at the rear of the head.
• Rachipagus: A rare type of conjoining, this occurs when twins are attached at the spine.
• Parapagus: This occurs when twins are attached at the side of the pelvis or stomach.
• Pyopagus: Another rare type of attachment, this occurs when the twins are united at the pelvis.
• Cepalopagus: These twins are joined at both the head and chest, and unfortunately, rarely survive.
• Ischiopagus: This occurs when twins are attached at the front of the pelvis. They share genitals, kidneys, a bladder, and their intestines.
• Omphalopagus: Accounting for 33% of all conjoinings, this occurs when twins are attached at the abdomen.
• Thoracopagus: The most common type of conjoining, this occurs when the twins are attached at the chest. They often share a heart.
• Parasitic: Parasitic twins have extra limbs or heads. This occurs when one twin dies in utero, and is absorbed by the other twin.

Testing for Conjoined Twins

Your health care provider should be able to detect any physical attachment between twins using an ultrasound. Ultrasound exams after the 20th week of pregnancy will allow for the detection of conjoined twins and this information can then be used in order to plan for labor and delivery.

If your twins appear to be conjoined in utero, it is possible that you will go into preterm labor. Your health care provider will monitor you and your twins to ensure that pregnancy progresses as it should.