Abnormal presentation of the fetus

　　Factors that affect the engagement of the presenting part before labor, causing a large gap between the presenting part and the pelvis entrance, can all lead to cord prolapse, such as breech presentation, transverse lie, narrow pelvis, cephalopelvic disproportion, and small fetus. There are also some predisposing factors, such as premature rupture of membranes with a long umbilical cord and polyhydramnios. The chance of cord prolapse when the umbilical cord length exceeds 1875px is ten times that of the normal value. When there is polyhydramnios, the intraperitoneal pressure in the amniotic cavity is high, and the cord is easily pushed out during membrane rupture.

　　Umbilical cord entanglement is more likely to occur when the umbilical cord is too long, the fetus is too small, there is too much amniotic fluid, or the fetus moves too frequently. When the umbilical cord is entangled around the fetal body, and then the fetus passes through the umbilical cord loop, a true knot is formed. Cord prolapse is more likely to occur when the presenting part of the fetus cannot be engaged. It is often due to abnormal fetal position, floating head, cephalopelvic disproportion, small fetus, polyhydramnios, or long umbilical cord. There are also some predisposing factors, such as breech presentation, transverse lie, narrow pelvis, cephalopelvic disproportion, and small fetus. Some promoting factors include premature rupture of membranes with a long umbilical cord and polyhydramnios. The chance of cord prolapse when the umbilical cord length exceeds 1875px is ten times that of the normal value. When there is polyhydramnios, the intraperitoneal pressure in the amniotic cavity is high, and the cord is easily pushed out during membrane rupture.

　　When the fetus is full-term and there is a risk factor for cord prolapse, such as polyhydramnios, it is necessary to be vigilant about the possibility of cord prolapse and perform fetal heart rate monitoring during labor. The fetal heart rate slows down during uterine contractions and recovers slowly or irregularly during intervals. After changing positions, the fetal heart rate improves significantly, which should be suspected as occult cord prolapse. Ultrasound Doppler examination can be performed, and if a umbilical blood flow echo image is found next to the fetal head or at the presenting part, the diagnosis can be confirmed. After membrane rupture, if the fetal heart rate suddenly slows down, the possibility of cord prolapse is very high, and an immediate digital and/or vaginal examination should be performed. If a pulsating cord like a finger is found in the cervix, it is a sign of cord prolapse. If the cord prolapses outside the cervix, cord prolapse can be diagnosed. The examiner's hand touching the cord pulsation can monitor the condition of the fetus in utero.

　　The most common abnormal fetal presentation is the persistent posterior position of the fetal head in the pelvis, with insufficient flexion of the fetal head, requiring the larger diameter of the fetal head to pass through the pelvis, which will prolong the labor and may even lead to dystocia. The second most common abnormal presentation is breech presentation, where the presenting part is the buttocks instead of the head, with various breech presentations. The main problem with breech presentation is that the presenting part cannot fully dilate the cervix, leading to difficulty in delivering the fetal head, resulting in cephalopelvic disproportion with difficult delivery of the fetal body but not the head. Subsequently, the newborn may be severely injured, even leading to death. The perinatal mortality rate of breech presentation is four times that of vertex presentation, and immature fetal development and congenital abnormalities are the main causes. Neurological injuries caused by excessive traction on the arms and spine, as well as brain injuries caused by hypoxia, are all increased in breech presentation. When the umbilical cord appears at the vaginal orifice, it is compressed by the fetal head at the pelvis entrance, leading to insufficient oxygen exchange and hypoxemia.

　　Preventive measures for abnormal presentation of the fetus are not to sit on low and soft sofas, as this can press on the abdomen and is not conducive to the fetus turning. When sleeping, one should lie on the left side (or the right side according to your habit), and just take a walk every day (now it is rarely recommended to lie on the knees and chest, that is, to lie on the bed and turn the fetus every day).

　　Abnormal presentation of the fetus can be diagnosed by vaginal examination. During the examination, one can feel the anterior sagittal suture, anterior fontanelle, orbital ridge, eyes, and root of the nose. Due to unfamiliarity with this type of presentation and edema, vaginal examination often causes confusion. The incidence of twin pregnancy is generally 1/70 to 1/80, which can be diagnosed by ultrasound, X-ray, or two different heart rates on fetal electrocardiogram.

      Patients with abnormal presentation of the fetus should eat fluid foods rich in high-quality protein and vitamins, and avoid eating foods that produce gas, such as taro, soybeans, sweet potatoes; avoid eating indigestible foods, such as rice cakes, zongzi, rice dumplings; and avoid eating spicy and刺激性 foods, such as chili, Sichuan pepper, ginger, etc.

　　Obstetricians must make a timely diagnosis and decide whether to use forceps or cesarean section. Once found, it is also impossible to deliver vaginally. The progress of labor is accompanied by cervical dilation and the descent of the fetal head through the birth canal. For women with a posterior position of the fetus, the delivery usually extends by one hour, while for primiparas, it usually extends by two hours. The perinatal mortality rate is not much different from that of the anterior position, and there is also no significant difference in the Apgar score of the newborn. However, since the fetal head passes through the posterior part of the pelvis quickly, it passes through the pelvic outlet with a larger diameter, and the pressure exerted by the occipital bone on the perineum is the greatest during delivery, which increases the risk of perineal tearing and the extension of the incision on the perineum. When a persistent posterior position occurs, there are five possibilities for vaginal delivery:

　　1. Natural Childbirth

　　In a study on anticipated treatment, the incidence of natural childbirth was 45%. Because the baby's head can only be delivered upwards when the face has already appeared below the pubis, the fetal head must pass through the posterior part of the pelvis, at which time it exerts pressure on the perineum. These babies seem to 'want' to be delivered through the rectum. However, labor is often easy.

　　2. Manual Rotation

　　For a long time, midwives and obstetric nurses believed that a fetus in a posterior position could be changed by placing the mother in various positions, such as lying on the side, squatting, walking, lying on the stomach, or arching the back (making the fetus uncomfortable and turning itself around!). If these methods do not work, manual rotation in the second stage for a long time has become a convincing alternative, as it can be tried during vaginal examination. If successful, it can greatly accelerate labor. If not, it does not cause any damage.

　　The key to manual rotation is to increase the natural and normal rotation force. Rotation normally occurs when the flexed fetal head touches the muscles at the pelvic floor, i.e., the levator ani sling. The operator must first flex the fetal head. Place one hand at the posterior part of the pelvis over the occiput. The operator's hand actually imitates and strengthens the action of the levator ani sling, like a wedge to flex the fetal head. Then, use the fingers of the examining hand to grip any palpable fontanel or cranial suture, applying the rotation force to the head. Some operators also use their thumb to grip the head. Attempt rotation during uterine contractions, or when the mother pushes downward, forcing the fetal head down to the levator ani sling (and the operator's hand), which is the natural mechanism of flexion and rotation. An experienced assistant will massage the fetal shoulders along the direction of rotation around the pubis or abdominal pressure. Manual rotation can also be performed when the patient is in the lithotomy position, or Sims lateral position, or knee-chest position. Abdominal thrusting is impractical when in the knee-chest position.

　　A common issue encountered is which hand to use for rotation of the fetus. If the fetus is in the occiput posterior position, the operator will naturally use their dominant hand. However, if the fetus has already rotated to some extent, becoming right occiput posterior or left occiput posterior, then the rotation should take the 'shortest distance'. Therefore, the right occiput posterior position should be rotated clockwise, and the left occiput posterior position should be rotated counterclockwise. The hand that can rotate forward during rotation (like closing a book) should be used; the left hand for right occiput posterior position and the right hand for left occiput posterior position 4. (Type C).

　　Manual rotation is part of the obstetric 'soft skill'. This is a skill that is often overlooked, requiring neither technical skills nor equipment. Its risk is low. With more practice, confidence and skill improve. Successful manual rotation can shorten the second stage of labor and avoid the use of instruments, even cesarean section.

　　3. Vacuum-assisted delivery

　　Vacuum-assisted delivery is a viable option in persistent occiput posterior position. Even when the operator is unsure of the fetal position due to deformation of the fetal head, edema, or overlapping cranial sutures, the vacuum extractor can be safely used. It can successfully extract the fetal head from the occiput posterior position. In addition, the vacuum extractor promotes rotation by flexing the fetal head and pulling it downward to the levator ani sling, facilitating delivery in the occiput anterior position. The vacuum extractor allows the fetal head to find the optimal delivery plane. Many operators are surprised to see that the fetal head can rotate 180 degrees during traction, sometimes occurring at the last moment before delivery. To promote the flexion of the fetal head, the vacuum extractor head should be placed as close as possible to the fetal head's occiput posteriorly. (See Chapter 8: Assisted Vaginal Delivery) The rotation force should not be directly applied to the vacuum extractor head, as this can cause cutting injuries to the scalp and also cause the vacuum extractor head to slip. The mechanism of delivery and the use of vacuum extraction, forceps, or natural delivery in the occiput posterior position are the same: the fetal head takes a more posterior position through the pelvis. Like any vacuum-assisted delivery, the handle of the vacuum extractor should form a 90° angle with the plane of the vacuum extractor head, otherwise it will slip.

　　4. Forceps Delivery

　　All general indications are applicable to forceps delivery. Forceps can be used for posterior position as well as for posterior position. It is only because the posterior position itself does not constitute a sufficient indication for the use of forceps.The mechanism of delivery is similar to that of natural delivery in the posterior position. In fact, the head is not delivered by extension, but by flexion. The fetal surface must first pass through the lower part of the symphysis pubis before the fetal head can be flexed upwards, so the traction force on the forceps should be more towards the back and longer than that of the anterior position delivery. The pressure on the perineum will be very strong, even causing III and IV degree lacerations..

　　Occasionally, with posterior position and prolonged second stage of labor, severe fetal head edema and swelling may occur. As a result, the top of the fetus's head may be exposed in the middle of the pelvis or even on the perineum. A careful examination will find that the fetal head is elongated and the biparietal diameter has not even connected. In these cases, it is impossible and dangerous to try to assist delivery with forceps. Cesarean section is required at this point, where the fetus can be easily extracted from the pelvis, thus confirming that it has not connected.

　　5. Forceps Rotation

　　Only experienced operators trained in Scanzoni technique or Kielland technology can perform it. These techniques are now rarely used in most American hospitals. If the posterior position cannot be safely delivered through the vagina, cesarean section is the backup delivery method.