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what are the causes of abnormal fetal position and abnormal fetal position

what are the causes of abnormal fetal position and abnormal fetal position

The main causes of abnormal fetal position are uterine dysplasia, uterine malformation, narrow pelvis, pelvic tumor, fetal malformation, polyhydramnios and so on

1. Pelvic abnormalities often occur in male pelvis or ape pelvis. The characteristics of these two types of pelvis are that the front half of the entrance plane is narrow, which is not suitable for the occipital connection of the fetal head, while the back half is wide, and the fetal head is easy to connect in the occipital posterior position or occipital transverse position. This kind of pelvis is often accompanied by middle pelvis stenosis, which affects the fetal head to rotate forward in the middle pelvis plane and become a persistent occipital posterior position or a persistent occipital transverse position.

2. If the fetal head is not bent well, the fetal spine is close to the maternal spine, which is not conducive to the fetal head bending. The anterior fontanel of the fetal head becomes the lowest part of the fetal head descending, and the lowest point often turns to the front of the pelvis. When the anterior fontanel turns to the front or side, the occipital part of the fetal head turns to the rear or side, forming a continuous occipital posterior position or occipital transverse position.

3. Other uterine atony affects the flexion and internal rotation of fetal head, which is easy to cause persistent occipital posterior position or occipital transverse position. Some scholars have reported that the incidence of occipital posterior position of anterior placenta is high.

The fetal head is mostly connected in occipital transverse position, even if it is connected in occipital posterior position, during delivery, strong uterine contractions can make the occipital part of the fetal head turn forward by 90 ~ 135, and turn into occipital anterior position for natural delivery. If you can't turn to occipital anterior position, you can have the following two delivery mechanisms:

4. In occipital left (right) posterior position, the occipital part of fetal head reaches the middle pelvis and rotates backward by 45 degrees, so that the sagittal suture is consistent with the anterior and posterior diameter of pelvis. The occipital part of fetus faces the sacrum in an occipital posterior There are two ways of delivery: ① The fetal head is better: when the fetal head continues to descend to the anterior fontanelle and reaches under the pubic arch, the anterior fontanelle is the fulcrum, and the fetal head is bent to make the top and occipital part deliver from the anterior edge of perineum. After that, the fetal head was extended, and the forehead, nose, mouth and chin were delivered under the pubic symphysis one after another. This way of delivery is the most common way of assisted delivery through vagina in occipital posterior position. ② Poor flexion of fetal head: When the nasal root appears at the lower edge of pubic symphysis, the nasal root is taken as the fulcrum, and the fetal head is flexed first, and the anterior fontanelle, top and occipital part are delivered from the anterior edge of perineum, and then the fetal head is extended upwards, so that the nose, mouth and chin are delivered from the pubic symphysis one after another. Because the fetal head rotates with a large occipital frontal circumference, it is more difficult to deliver the fetus, and surgical midwifery is often needed.

5. In the occipitotransverse position, the occipitotransverse part is located in the descent process without internal rotation, or the occipitotransverse part of the fetal head in the occipitoposterior position only rotates forward by 45 to become a persistent occipitotransverse position. Although continuous occipitotransverse position can be delivered through vagina, most of them need to turn the fetal head into occipitoanterior position by hand or fetal head suction.

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