What causes Siamese babies?

Question: What causes Siamese babies?
- Keywords:
  baby,
  siamese
Asked by Kalonje to Caroline on 11 Jul 2017.
- Caroline Ogwang answered on 11 Jul 2017:
  
  Hi Kalonje,
  
  Usually a single fertilized egg develops into one baby. Sometimes a single egg divides in half 1 to 2 weeks after it’s fertilized to create a set of identical twins.
  If this egg fails to split completely, it will lead to siamese/conjoined twins. The exact cause of siamese twins is not known.
  
  I hope this answers you.