What is internal rotation of fetal head?
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Background: Improved information about the evolution of fetal head rotation during labor is required. Ultrasound methods have the potential to provide reliable new knowledge about fetal head position. Show
Objective: The aim of the study was to describe fetal head rotation in women in spontaneous labor at term using ultrasound longitudinally throughout the active phase. Study design: This was a single center, prospective cohort study at Landspitali - The National University Hospital of Iceland, Reykjavík, Iceland, from January 2016 to April 2018. Nulliparous women with a single fetus in cephalic presentation and spontaneous labor onset at ≥37 weeks' gestation were eligible. Inclusion occurred when the active phase could be clinically established by labor ward staff. Cervical dilatation was clinically examined. Fetal head position and subsequent rotation were determined using both transabdominal and transperineal ultrasound. Occiput positions were marked on a clockface graph with 24 half-hour divisions and categorized into occiput anterior (≥10- and ≤2-o'clock positions), left occiput transverse (>2- and <4-o'clock positions), occiput posterior (≥4- and ≤8 o'clock positions), and right occiput transverse positions (>8- and <10-o'clock positions). Head descent was measured with ultrasound as head-perineum distance and angle of progression. Clinical vaginal and ultrasound examinations were performed by separate examiners not revealing the results to each other. Results: We followed the fetal head rotation relative to the initial position in the pelvis in 99 women, of whom 75 delivered spontaneously, 16 with instrumental assistance, and 8 needed cesarean delivery. At inclusion, the cervix was dilated 4 cm in 26 women, 5 cm in 30 women, and ≥6 cm in 43 women. Furthermore, 4 women were examined once, 93 women twice, 60 women 3 times, 47 women 4 times, 20 women 5 times, 15 women 6 times, and 3 women 8 times. Occiput posterior was the most frequent position at the first examination (52 of 99), but of those classified as posterior, most were at 4- or 8-o'clock position. Occiput posterior positions persisted in >50% of cases throughout the first stage of labor but were anterior in 53 of 80 women (66%) examined by and after full dilatation. The occiput position was anterior in 75% of cases at a head-perineum distance of ≤30 mm and in 73% of cases at an angle of progression of ≥125° (corresponding to a clinical station of +1). All initial occiput anterior (19), 77% of occiput posterior (40 of 52), and 93% of occiput transverse positions (26 of 28) were thereafter delivered in an occiput anterior position. In 6 cases, the fetal head had rotated over the 6-o'clock position from an occiput posterior or transverse position, resulting in a rotation of >180°. In addition, 6 of the 8 women ending with cesarean delivery had the fetus in occiput posterior position throughout the active phase of labor. Conclusion: We investigated the rotation of the fetal head in the active phase of labor in nulliparous women in spontaneous labor at term, using ultrasound to provide accurate and objective results. The occiput posterior position was the most common fetal position throughout the active phase of the first stage of labor. Occiput anterior only became the most frequent position at full dilatation and after the head had descended below the midpelvic plane. Keywords: active phase; angle of progression; cesarean delivery; fetal head position; head-perineum distance; progress of labor; transabdominal ultrasound; transperineal ultrasound. Usually, labor progresses in this fashion, if the fetus is of average size, with a normally positioned head, in a normal labor pattern in a woman whose pelvis is of average size and gynecoid in shape. There is overlap of these mechanisms. The fetal head, for example, may continue to flex or increase its flexion while it is also internally rotating and descending. You don't need to tell us which article this feedback relates to, as we automatically capture that information for you. This allows us to get in touch for more details if required. Please write a single word answer in lowercase (this is an anti-spam measure) This field is for validation purposes and should be left unchanged.
IntroductionDescribing the mechanism of labour is a common topic for OSCEs and MCQs. Although on the surface it can appear complicated, breaking the process down into individual steps makes it much easier to understand. Normal labour involves the widest diameter of the fetus successfully negotiating the widest diameter of the bony pelvis of the mother via the most efficient route. The mechanism of labour covers the passive movement the fetus undergoes in order to negotiate through the maternal bony pelvis. Labour can be broken down into several key steps. Key stages of labour
For the purposes of this guide, the fetal movements will be described in relation to a cephalic (vertex) presentation with a longitudinal lie. This is a common (low risk) presentation. Pelvic anatomyTo understand the mechanism of labour, you need some basic understanding of pelvic anatomy. Borders of the pelvic inlet
Borders of the pelvic outlet
Pelvic dimensionsTransverse diameterAntero-posterior diameterPelvic inlet13cm11cmMid-pelvis12cm12cmPelvic outlet11cm13cmSince the transverse diameter is greater than the antero-posterior (AP) diameter in the pelvic inlet, the widest circumference of the fetal head descends in a transverse position. However, when it gets closer to the pelvic outlet, the nature of the pelvic floor muscles encourages the fetal head to rotate from a transverse position to an anterior-posterior position, as the AP diameter is greater than the transverse diameter. Fetal head diameter varies depending upon the degree of neck flexionIt is also important to know how the circumference of the fetal head varies with different degrees of neck flexion:
Descent & engagementIt should be noted that descent and engagement occur together, rather than as completely separate/distinct stages, so consider them as 2 parts of the same process/stage. DescentThe fetus descends into the pelvis. In the primigravida this is likely to occur from 38 weeks gestation onwards, in a multigravida woman, this may not occur until labour is established. Descent is encouraged by:
As the head descends, it moves towards the pelvic brim in either the left or right occipito-transverse position (this means the occiput can be facing the left side or right side of the mother’s pelvis). EngagementThis is when the largest diameter of the fetal head descends into the maternal pelvis. The term engagement is referring to the widest part of the fetal head successfully negotiating its way down deep into the maternal pelvis. Engagement is identified by abdominal palpation, where the fetal head is 3/5th palpable or less.
FlexionAs the fetus descends through the pelvis, fundal dominance of uterine contraction exerts pressure down the fetal spine towards the occiput, forcing the occiput to come into contact with the pelvic floor. When this occurs the fetal neck flexes (chin to chest) allowing the circumference of the fetal head to reduce to sub-occipitobregmatic (9.5cm). In this position, the fetal skull has a smaller diameter which assists passage through the pelvis.
Internal rotationThe pelvic floor has a gutter shape with a forward and downward slope, encouraging the fetal head to rotate from the left or right occipito-transverse position a total of 90-degrees, to an occipital-anterior (occiput facing forward) position, to lie under the subpubic arch. With each maternal contraction, the fetal head pushes down on the pelvic floor. Following each contraction, a rebound effect supports a small degree of rotation. Regular contractions eventually lead to the fetal head completing the 90-degree turn. This rotation will occur during established labour and it is commonly completed by the start of the second stage. Further descent leads to the fetus moving into the vaginal canal and eventually, with each contraction, the vertex becomes increasingly visible at the vulva.
CrowningWhen the widest diameter of the fetal head successfully negotiates through the narrowest part of the maternal bony pelvis, the fetal head is considered to be ‘crowning’. This is clinically evident when the head, visible at the vulva, no longer retreats between contractions. Complete delivery of the head is now imminent and often the woman, who has been pushing, is encouraged to pant so that the head is born with control.
Extension of the presenting partThe occiput slips beneath the suprapubic arch allowing the head to extend. The fetal head is now born and will be facing the maternal back with its occiput anterior.
External rotation & restitutionBecause the shoulders at the point of the head being delivered are only just reaching the pelvic floor they are often still negotiating the pelvic outlet and the fetus may naturally align its head with the shoulders. This is called restitution and visually you may see the head externally rotate to face the right or left medial thigh of the mother. During the next contraction, the shoulders, having reached the pelvic floor, will complete their rotation from a transverse position to an anterior-posterior position. Evidence of this manoeuvre happening inside can be visualised by seeing the head externally rotating as the fetus keeps its spine aligned.
Delivery of the shoulders and bodyDownward traction by the healthcare professional will assist the delivery of the anterior shoulder below the suprapubic arch. This is followed by upward traction assisting the delivery of the posterior shoulder. The fetal body will be delivered by the contractions, the health professional’s role is only to assist safe negotiation of this last stage. What is fetal internal rotation?Internal Rotation
As your baby's head descends further, the head will most often rotate so the back of the head is just below your pubic bone. This helps the head fit the shape of your pelvis. Usually, the baby will be face down toward your spine. Sometimes, the baby will rotate so it faces up toward the pubic bone.
What is internal rotation?In anatomy, internal rotation (also known as medial rotation) is an anatomical term referring to rotation towards the center of the body.
Why does internal rotation occur?Hip internal rotation occurs any time you move your thigh bone inward, activating muscles such as the tensor fasciae latae, the upper gluteus muscles, and the inner thigh muscles. You can use hip internal rotation exercises and stretches to improve internal rotator range of motion and help prevent lower body injuries.
What is fetal external rotation?The fourth movement is the external rotation (Table). The fetal body and shoulders are now in the middle of the pelvis and can rotate into the largest anteroposterior plane of the outlet. As this happens, the fetal head rotates to face the mother's right or left thigh.
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