This is an observational, opportunistic lactation study to be conducted in lactating female participants who are currently receiving therapeutic doses of YORVIPATH as part of their usual care and who have chosen to breastfeed their infant(s). The potential transfer of palopegteriparatide into breast milk will be assessed.

Inclusion Criteria:

• 1. Lactating female participants 18 years of age or older treated with YORVIPATH as part of their usual medical care and who have chosen to breastfeed. Note: The participant must have been taking YORVIPATH for a minimum of 14 days prior to sample collection.
• 2. The major source of infant nutrition must be breast milk (Note: Only one supplemental bottle of no more than up to 8 oz of formula per day will be allowed during the 14 days before start of the study).
• 3. Daily dose of YORVIPATH administered within the last 14 days has been stable.
• 4. Participants recruited from other sources must enroll in the Pregnancy Registry before being allowed to participate in the Lactation Study.
• 5. Written consent or eConsent obtained.

Exclusion Criteria:

• 1. Presence of any medical condition that, in the opinion of the investigator, may impair the ability to breastfeed during this study, including but not limited to mastitis and nipple malformation

Eligible females will be actively recruited from the US participants in the pregnancy registry. Females in the US who want to participate in the lactation study must first enroll in the pregnancy registry and meet the lactation study eligibility criteria study to participate. Females may self enroll into the study or may be enrolled by their healthcare provider (HCP).