Almost all of us have a piece of tissue running between the underside of our tongue and the floor of the mouth. This is quite normal and prevents the tongue lifting up into the mouth excessively; babies have this too. In healthcare, we call it a frenulum.
In some babies, the frenulum can be thicker than usual, or can extend too far forward (sometimes right to the tip of the tongue); if this is the case, the normal movements of the tongue can be restricted and we describe the baby as being 'tongue-tied'. A tongue-tie can affect breastfeeding by interfering with the baby latching onto the breast or by causing damage to a mother's nipples. Clues are that the baby cannot stick its tongue out beyond the lower gum, that the tongue becomes heart-shaped when the baby tries to stick it our and/or that the upward movement of the tongue is reduced. In these babies it may be necessary to divide the tongue tie. This can be done quickly and easily in the first week of life.
Many women experience difficulty with attachment in the first week of life; this mostly gets better with time but it is often incorrectly attributed to minor degrees of tongue tie. In most cases, it is better to wait until the second week of life before dividing a tongue tie, unless there is very significant nipple damage.
It is very rare for tongue-tie to cause a problem with speech. Occasionally older children with a tongue-tie complain that they find it difficult to lick an ice-cream and, in adolescents, that they experience discomfort with kissing!