How do clefts happen?

The process of the joining of the gum and lip begins behind the gum at about 6 weeks after conception. If it does not happen, there is a complete cleft of the lip and gum. Sometimes, if the process of joining begins and is not completed, the gum may not be affected. The two halves of the palate join at about 8 weeks and this process, too, may be partial or complete so that clefts may just involve the soft palate or the hard and soft palate.