An inversion consists of two breaks in one chromosome. The area between the breaks is inverted (turned around), and then reinserted and the breaks then unite to the rest of the chromosome. If the inverted area includes the centromere it is called a pericentric inversion. If it does not, it is called a paracentric inversion.
Notice that in a pericentric inversion one break is in the short arm and one in the long arm. Therefore an example of a cytogenetic nomenclature might read 46,XY,inv(3)(p23q27). A paracenteric inversion does not include the centromere and an example might be 46,XY,inv(1)(p12p31).
When a parent has an inversion there is an increased risk for offspring with an incorrect amount of genetic material. This can lead to babies with birth defects and/or abnromal development or an increased risk for miscarriage. The possible outcomes for a ring gets rather complicated and depends on how big the inversion is, where it is, and what type of inversion is present, paracentric or pericentric.
There are many inversions that occur in the general population that are called normal varients. Including Inv(9) and Inv(2). These inversions are not related to an increased risk of birth defects and/or developmental difficulties.