615 © Springer Nature Switzerland AG 2021 A. Malvasi (ed.), Intrapartum Ultrasonography for Labor Management, https://doi.org/10.1007/978-3-030-57595-3_49 Ultrasonographic Evaluation of Normal and Pathologic Puerperium Antonio Simone Laganà, Simone Garzon, Massimo Franchi, and Fabio Ghezzi 49.1 Introduction The puerperium is the period lasting 4–6 weeks after delivery during which all the physiological and anatomical pregnancy- induced changes reverse and return to the pre-pregnancy state. The birth canal, cervix, and uterus, modifed by the adaptation to pregnancy and delivery, undergo a reduction of their volume and remodeling to almost resume their pre-preg- nancy state. During puerperium, both the transvaginal and transabdominal ultrasound scans are well tolerated by women and represent the imaging technique of choice to investigate the cause of early or late complications [1]. Noteworthy, almost half of the maternal deaths were reported related to the postpartum period [2]. Many types of complications have one or more causes that can be assessed by the ultrasound evalua- tion. Although uterine atony is the most frequent cause of pri- mary postpartum hemorrhage (blood loss >500 mL or any blood loss causing hemodynamic instability in the frst 24 h after delivery), retained products of conception (placenta or membranes) need to be excluded. Similarly, retained products of conception, endometritis, or arteriovenous malformations need to be ruled out in the case of secondary postpartum hem- orrhage (blood loss >500 mL between 24 h and 12 weeks after delivery) [3]. Additionally, ultrasound allows identifying and monitoring post-surgical complications after cesarean section, postpartum hematomas, or pelvic abscess [1]. Despite the key role of this diagnostic tool, the reported reliability and validity of ultrasounds in the assessment of the different com- plications are heterogeneous, and the limited specifcity and sensitivity of different ultrasound appearances are determi- nant [4]. On that basis, the knowledge of the normal ultraso- nographic appearance of the genital tract during the physiological puerperal involution is the frst step to achieve an accurate distinction between normal and abnormal devel- opment of puerperium. 49.2 Physiologic Puerperium The uterus is the reproductive organ undergoing the most signifcant changes during puerperium and the ones most investigated by ultrasound in this period. After delivery, the uterus weight is approximately 1000 g, and the uterine fun- dus reaches the level of umbilicus with anterior and posterior myometrial walls 4–5 cm thick. The lower segment is clearly distinct from the corpus and cervix, and the cervix is dila- tated with the margins that correspond to the external uterine orifce [5] (Fig. 49.1). During puerperium, the uterine corpus undergoes signifcant volume and weight reduction primar- ily due to the size reduction of myocytes. After 1 week, the weight is approximately 50% (500 g). In the second week, the uterus is limited to the true pelvis and is no longer pal- pable, and fnally, the weight almost achieves the pre- pregnant value of 50–100 g after 4–6 weeks. The lower segment progressively disappears in a few weeks and becomes the less distinct uterine isthmus. The cervix con- tracts gradually, admitting only two fngers after a few days and becoming more thick and narrow, with the reformation of the endocervical canal at the end of the frst week [5]. Regarding the uterine cavity, the decidua undergoes necrosis and faking of the superfcial layer, while the basal layer gives rise to the new endometrium that regenerates completely within the frst 2 weeks [6]. This process takes more time and is more complex at the placental site, which requires 6 weeks to regenerate completely [7]. The physiological involution of the uterus during puerpe- rium is usually evaluated by palpation of the abdomen to assess the level of the uterine fundus. Nevertheless, this tech- nique does not allow a precise defnition of the entire involu- tion process and can be limited by different constitutional factors [8]. In this scenario, the introduction of ultrasounds 49 A. S. Laganà (*) · S. Garzon · F. Ghezzi Department of Obstetrics and Gynecology, “Filippo Del Ponte” Hospital, University of Insubria, Varese, Italy e-mail: antoniosimone.lagana@uninsubria.it M. Franchi Department of Obstetrics and Gynecology, AOUI Verona, University of Verona, Verona, Italy