Conjoined twins are caused by the embryos only partially splitting, rather than forming two separate individuals. Although the twins develop together, they will be physically connected to each other - most often in the chest, abdomen or pelvis - and will share one or more internal organs.

The ultrasound image of a 6-week-old twin fetus is still very small, the indicators will show how the baby is developing and if there are any abnormalities. This is an important milestone in the pregnancy that pregnant mothers need to pay attention to when having a 6-week twin ultrasound.