Mont. Code Ann. § 33-30-1001

A disability insurance plan or group disability insurance plan issued by a health service corporation may not be issued or amended in this state if it contains any disclaimer, waiver, preexisting condition exclusion, or other limitation of coverage relative to the accident and sickness coverage or insurability of newborn infants of the persons insured from and after the moment of birth. Each policy must contain a provision granting immediate accident and sickness coverage, from and after the moment of birth, to each newborn infant of any insured person. The policy or contract may require notification of the birth of a child and payment of a required premium or subscription fee to be furnished to the insurer or nonprofit or indemnity corporation within 31 days of the birth in order to have the coverage extend beyond 31 days.