We are looking to recognize/reference a "born" extension (Boolean) for the Patient resource that could indicate that there is an active record for a not yet born patient. Creation of a distinct record prior to delivery allows for orders (medications, blood products, imaging studies) intended for the newborn just after birth to be placed prior to delivery (while the subject is still a fetus) and allow for relevant conditions and observations for the fetus to be captured so that they are immediately available for a record of a newborn. It is essential that this record be distinct from the maternal record as the medications, blood products, etc... are intended for the newborn and not for the mother.
Use cases are outlined in the Pregnancy, Fetal, and Child Health Record- Domain Analysis Model. See FHIR Resource modeling around page 35.

lminne has modeled a number of options that have been proposed in simplifier.net: https://simplifier.net/internationalbirthandchildmodel

The combination of using the Patient.active indicator along with a "born" extension - http://hl7.org/fhir/StructureDefinition/patient-born - could allow for the following scenarios:
if active=true, born=false --> active fetal record
if active=false, born=false --> indicates fetal demise (or simply that the record is no longer in use and will not transition to a liveborn patient record)
if active: true, born: true --> active (newborn) record [Note: presence of a birthdate could indicate that born=true

Note that some have proposed that "born" could instead be an "unborn" indicator as a Boolean.

Please see the Zulip discussion on this topic as well. Thank you.