Carrier screening is genetic testing for many recessive mutations that cause disease. It is very useful for couples planning to conceive. Our cells have two copies of each of the twenty-three chromosomes, and a mutation in one of the two chromosomes of a pair does not normally cause disease because the normal copy of the chromosome makes the normal protein and compensates for the loss. Such mutations are called recessive mutations. If a disease-causing mutation is present as a recessive mutation, the individual (man or woman) harboring that mutation is called a carrier. These individuals don’t have any symptoms of the disease but carry the risk of transferring the disease to their offspring. Since there are two pairs of each chromosome and only one of the two chromosomes of the pair has the mutation and the other is normal, the “carrier” will be disease free and ignorant of the mutation they have. Cystic fibrosis is one example of recessive mutation and carrier condition. There is no risk of having a baby with the disease if one parent is a carrier and the other is not (both chromosomes are mutation free). However, if both parents are carriers, there is a possibility that the baby may inherit the “abnormal” chromosome of the pair (harboring the mutation) from both parents. So, while the parents had a recessive status and were disease free, the baby born with the abnormal chromosome pair will develop the disease. The prospect of having a baby born with the disease is the reason why it is important for such parents undergo Carrier Screening to get tested before planning to have a baby. Parents should talk to their physician and genetic counselor about undergoing genetic screening to understand the carrier status and the risk of giving birth to a baby with a disease.