In this study, the investigators aim to evaluate changes in lung function in women with cystic fibrosis (CF) during pregnancy and for 2 years after pregnancy based on exposure to highly effective cystic fibrosis transmembrane conductance regulator (CFTR) modulators.

Advances in medical treatment, including the use of highly effective CFTR modulators have greatly increased life expectancy in women with CF, but the effects of pregnancy on women with CF are yet unknown. It is anticipated that over 90% of the CF population will be on CFTR modulators in the next few years. More knowledge about the effects of CFTR modulators in pregnancy is needed.

This is a prospective, multi-center, observational study to follow pregnant women with CF, conducted at 40 US sites. Women are enrolled in the first trimester of pregnancy and assessed every 3 months during pregnancy and during the first year after delivery, then every 6 months for an additional year. Changes in lung function over the course of pregnancy will be evaluated based on cumulative CFTR modulator use while pregnant while accounting for other factors that may influence changes in pulmonary function: baseline lung function, genotype, history of exacerbations, and pre-existing co-morbid conditions.

Inclusion Criteria:

• Pregnant, intending to continue pregnancy, enrolled in the Cystic Fibrosis Foundation Patient Registry (CFFPR)

Exclusion Criteria:

• None

Study participants will be recruited at Cystic Fibrosis Foundation's Therapeutics Development Network study sites. Pregnant women appearing for regular clinical care at these participating centers will be approached for enrollment.