A case report of CFTR modulator administration via carrier mother to treat meconium ileus in a F508del homozygous fetus.

We report elexacaftor-tezacaftor-ivacaftor (ETI) treatment of a F508del carrier who was pregnant with a F508del homozygous fetus. At 23-weeks gestation meconium ileus (MI) was evident on ultrasound including dilated, hyperechoic bowel, which persisted on subsequent imaging. Through shared decision-making, the mother began ETI at 32 weeks with intent to treat fetal MI. The ultrasound findings persisted at treatment day 13, but bowel dilation had resolved by imaging on treatment day 27. A female infant was delivered vaginally at 36 weeks with no complications. The mother continued ETI while breastfeeding. Stool elastase at age 2 weeks was 240 mcg/g. Sweat chloride measurement was 64 and 62 mEq/L. Maternal and infant liver function testing have been normal. Maternal ETI treatment likely led to resolution of the MI and there is evidence supporting continued infant benefit through breastmilk. Logistical and ethical considerations regarding treatment of a carrier mother for infant benefit are discussed.