In the last decades, a decrease in operative vaginal delivery (OVD) rates occurred, resulting in increase of caesarean sections (CS) during the second stage of labor. This attitude reflects Clinicians' worries about operative vaginal delivery morbidity, together with a consequent loss of clinical skills in this practice. However, vacuum delivery - when correctly performed - requires less analgesia and gives women higher chances to have a spontaneous vaginal birth in the following pregnancy, whereas emergency C-section is burdened by different maternal and fetal complications. Moreover, should fetal compromise be occurring, time to start the procedure is longer for CS than for vacuum application. Due to the whole of these reasons, operative vaginal delivery is included in the main international guidelines as the best option for the mother and baby, in case of arrest/delay of fetal head descent during second stage of labor, with fetal head at mid/low-pelvic station.
Although women in labor are usually asked to choose the position they prefer and to change position frequently to facilitate the alignment of the fetal head with the birth canal, the vacuum cup is usually applied to a woman lying in the "traditional" gynecological supine position.
Despite several demonstrated advantages, fewer women choose non-recumbent positions, and among them, the so-called "all-fours position" (or "hands-and-knees") which has the higher evidence of benefit. In all-fours, the woman is on her knees, leaning on her hands, with abdomen suspended and hips at right angles to the floor or bed. As demonstrated in different studies, the main advantage given by this posture is the increase of all posterior diameters of the pelvis. This finding implies not only an easier descent of the fetal head, helped by gravity, but also a wider space where fetal head could rotate in case of occiput posterior position, preventing fetal malposition. Additionally, this position lets the sacrum to have more posterior mobility (contra-nutation movement) furtherly widening the outlet no more constricted by the standing surface and reducing sacral pain due to bed-contact. Moreover, as the burden of trunk's weight on the sacrum is decreased in all-fours, women consider the hands-and-knees position a pain-relieving postural choice, especially during the first stage of labor. Regarding maternal outcomes, a recent large randomized controlled trial, involving 1400 women, demonstrated a lower incidence of second-degree perineal lacerations, episiotomy and perineal swelling in hands-and-knees position, and a lower risk of emergency CS, compared to other birth positions.
In the all-fours position, the vaginal space between the fetal head and the vaginal ostium is not influenced by body weight, resulting wider, visible, and easily explorable. Moreover, the risk of vacuum cup sliding is lower because the upward traction is allotted a wider space.
The widening of birth canal obtained with this technique has several, beneficial implications. First, the risk of vaginal tear is lower, since there is no redundant vaginal tissue that could be trapped inside the cup. Second, a wider space allows to constantly maintain the vacuum wire perpendicular to the cup, thus determining a lower risk of detachment, subsequent fetal scalp damage and cephalohematoma (e.g., in presence of caput succedaneum).
Also, this position allows a better propulsive pushing, thanks to a more efficient Valsalva maneuver, thus enabling the Clinician not to exert excessive traction on the fetal head.
Since OVD has a known increased risk of shoulder dystocia, adopting the all-fours position should be beneficial in preventing this fearsome complication, consistent with the point that the hands-and-knees posture is required to perform the Gaskin maneuver, a rescue procedure that easily releases the trapped shoulder by taking advantage of the greater posterior pelvic space in this position.
A potential disadvantage might be the inability of the woman to keep this position for longer than 10-15 minutes. Although OVD duration is routinely much shorter, it is of course mandatory that the timing of OVD performance be carefully monitored.
The investigators recently suggested the implementation of all-fours position in case of operative vaginal delivery and we published a video-simulation of vacuum application on a mannequin. At this time, no other prospective study so far assessed a putative effectiveness of an alternative positioning strategy during OVD for women with arrest of fetal head progression during the second stage of labor.
