Similarly, Lien et al. developed a three-dimensional computer model to predict muscles stretch at the time of vaginal delivery [6]. The authors used a model constructed from serial magnetic resonance images from a health nulliparous woman. The model was used to quantify pelvic floor muscles (i.e. iliococcygeus, pubococcygeus and puborectalis muscles) stretch induced by delivery [6]. They observed a sigmoidal relationship between fetal head descent and muscle stretch. The largest tissue strain reached a stretch ratio (tissue length under stretch/original tissue length) of 3.26 in medial pubococcygeus muscle, the shortest, most medial and ventral levator ani muscle. Ileococcygeus, pubococcygeus, and puborectalis muscles reached maximal stretch ratios of about 2.7, 2.5 and 2.3, respectively. Therefore, the authors concluded that medial pubococcygeus muscle is at greatest risk for stretch-related injury [6].

In another paper, focusing on three-dimensional computer-based simulation, Lien et al. studied the increase in pudendal nerve stretch during delivery [4]. They observed that the strain in perineal nerve branches innervating the anal sphincter, posterior labia and urethral sphincter reached values of 33 %, 15 % and 13 %, respectively. Interestingly, 25 % in nerves’ strain is the known threshold to cause permanent damages in peripheral nerves [4]. Figure 3.2 shows pudendal nerve stretch occurring during the second stage of labour.

All these studies, based on computer technology, have several important clinical implications. Further computer-based evaluations are necessary to improve knowledge on this still unclear issue.

In conclusion, the embrace of computerized model allows to evaluate pelvic floor muscles physiology during delivery, thus improving knowledge of phenomena potentially affecting impaired intra and post delivery-related outcomes. Although there are inherent limitations of this methodology, consisting of non-in vivo evaluation of physiological pregnancy-related modification, these tools are effective to evaluate the effects of vaginal birth, thus improving intra- and post-partum outcomes. Further studies, involving more sophisticated software, are warranted in order to improve our knowledge on this issue.