Inclusion Criteria:

'Mama' sub-study:

• Written informed consent obtained from participant.
• Under the care of Royal Brompton Hospital CF Reproductive and Maternal Health Service
• Age 16 years or above at time of recruitment
• Confirmed diagnosis of CF
• Planning a pregnancy or pregnant at time of recruitment.
• Ability to adhere to the required visits and investigations.

'Mini' sub-study:

• Written informed consent obtained from participant's legal guardian.
• Infants who have one biological parent with a confirmed diagnosis of CF under care of Royal Brompton Hospital Adult CF Service
• Less than 12 months of age at first visit.
• Ability to adhere to the required visits and investigations.

'Midi' sub-study:

• Written informed consent obtained from participant's legal guardian.
• Children who have one biological parent with a confirmed diagnosis of CF who is under the care of Royal Brompton Hospital Adult CF Service.
• Age three to six years at time of visit
• Ability to adhere to the required visits and investigations.

Exclusion Criteria:

'Mama' sub-study:

• Any significant health condition which would cause inability to comply with protocol based on investigator discretion.
• History of lung transplantation

'Mini' sub-study:

• Legal guardians' inability to provide consent to participate in the study.
• Mother of infant has significant comorbidities unrelated to CF which could affect infant outcomes based on investigator discretion.

'Midi' sub-study:

• Legal guardians' inability to provide consent to participate in the study.
• A significant health condition which is known to affect lung function or imaging based on investigator discretion