As a basis for not considering these Class III devices FDA published a special control guidance document for such devices. This is available at the link provided.
This guidance recommends providing a description of the software algorithm. Section 6 provides a table of risks to health and categories of mitigation measures.
Section 11 addresses software by referring to the general software guidance `Guidance for the Content of Premarket Submissions for Software Contained in Medical Devices” and suggesting that most Labor Monitoring Systems are Moderate level of concern because failure to obtain accurate information may result in
more frequent vaginal examinations that can lead to chorioamnionitis or patient
mismanagement.
Section 7 identifies recommended nonclinical testing to include and use of IEC 60601-2-37 or equivalent.