The goal of this observational study is to evaluate the reproducibility of new 3D/4D ultrasound volume analysis techniques in the assessment of anal sphincter integrity and thickness in both pregnancy and immediate postpartum.

The negative impact that OASISs (Obstetric Anal Sphincter Injuries), and possible subsequent anal incontinence, have on women's quality of life has stimulated research in this field in recent decades. However, there are still few studies concerning the topic. The transperineal approach by means of the transvaginal probe in the study of the pelvic floor, anal sphincter and related lesions has helped us to make strides in our knowledge of the anatomy of the pelvic floor and in defining the lesions that may affect it.

The development of ultrasound techniques such as 3D and 4D and new reproducible and increasingly accurate volumetric acquisition modalities shows promise for improving the diagnosis of OASIS and the clinical management of OASIS and consequently the quality of life of women.

With new, simpler techniques of 3D/4D volume analysis of the anal sphincter, the number of operators able to objectively and accurately assess anal sphincter integrity, both in the delivery room and postpartum, could increase. The application and dissemination of an accurate and reproducible technique in the subjective assessment of the anal sphincter could help operators improve and refine the technique of surgical correction of anal sphincter injuries.

The primary objective of the study is to evaluate the reproducibility of novel 3D/4D ultrasound volume analysis techniques, using curvilinear reconstruction of the coronal plane of the anal sphincter combined with contrast enhancement technique (optic OMNIVIEW), in the assessment of anal sphincter integrity and thickness, both in pregnancy and immediate postpartum.

Secondary objectives include:

• Evaluation of the feasibility of new off-line analysis techniques.
• Evaluation of the correlation between thickness and ultrasound integrity of the anal sphincter at the postpartum visit and women's symptomatology in the postpartum.

To reduce bias as much as possible, each operator during each assessment will be "blinded" to the patient's history and all other measurements.

Clinicians who perform more than one measurement per volume will do so at least one month apart between each measurement.

The patient will be treated according to common clinical practice ensuring the standard of care. Patients will not undertake additional visits to those routinely performed. This is an evaluation of new techniques for off-line (in the absence of the patient) analysis of ultrasound volumes that are currently part of routine visits in both pre and postpartum.

Inclusion Criteria:

• Pregnant nulliparous or primiparous women;
• Age between 18 and 44 years
• Acquisition of informed consent form

Exclusion Criteria:

None

Nulliparous and primiparous pregnant women. Participants will be enrolled at the Division of Obstetrics and Prenatal Age Medicine (IRCCS - Azienda Ospedaliero-Universitaria di Bologna Policlinico S. Orsola). Participants will be enrolled during the obstetrical visit or during hospitalization or during visits in the postpartum period.