Anomaly of the rotation

Japanese: 回旋異常 - かいせんいじょう（英語表記）Anomaly of the rotation

What is the disease?

As labor progresses, the fetus gradually changes position to make it easier to pass through the birth canal and enter the pelvis. This process is called rotation, and can be assessed by a pelvic examination. Anti-flexion position ( Hankutsu ) , Low horizontal position ( I'm sorry ) , Anterior frontal position ( Zenpo Zentoui ) When abnormal rotation such as the above hinders the smooth progress of labor, this is collectively called abnormal rotation. Below, we will explain normal rotation and its abnormalities.

① First rotation (Figure 17): The fetus in cephalic presentation is in a flexed position with its chin pulled in at the pelvic inlet and touching its chest. This position is the thinnest for the fetus to enter the birth canal, making it easier for the fetus to pass through the birth canal. Conversely, if the fetus is in a position with its chin raised, Anti-flexion position ( Hankutsu ) It is called.

② Second rotation (Figure 18): The fetal head enters the birth canal sideways, gradually rotates as it descends, and when it comes out, it is vertical with its face facing the back of the mother. In this case, the back of the baby's head is in front of the mother's body, so Occipital anterior presentation ( All-Japan High School ) It is called.

An abnormality in the second rotation is when the second rotation does not occur and the fetal head descends sideways until it reaches the pelvic outlet. Low horizontal positioning ( I'm sorry ) , rotate in the opposite direction so that the face faces the mother's ventral side Anterior frontal position ( Zenpo Zentoui ) etc.

③Third rotation (Figure 18): When the fetal head descends to the pelvic outlet in an anterior occipital position, the occipital Pubic bone ( Chikotsu ) The head is fixed under the arm, and using this as a fulcrum, the head, which was in a flexed position, extends forward and is delivered.

④Fourth rotation : After the fetal head is delivered, it returns to its original sideways position. This is called the fourth rotation.

What is the cause?

Pelvic morphological abnormalities Cephalopelvic disproportion ( Self-employed person ) The main cause is when the fetal head is too large compared to the width of the mother's pelvis and cannot pass through the birth canal smoothly.

How symptoms manifest

If labor does not progress despite continued contractions, it is necessary to check for abnormal rotation. Contractions may weaken over time and become feeble contractions, or conversely, they may become stronger and become hypertonic contractions.

Testing and diagnosis

The diagnosis is made using a pelvic examination, ultrasound, and, if needed, x-rays of the pelvis.

Treatment methods

Even if the baby has a rotational abnormality, if the pelvis is wide enough and there is sufficient contraction, the baby can still go through labor. However, if the baby does not progress, Transvaginal ( Construction ) The baby is given up on labour and delivered by Caesarean section.

What to do if you notice an illness

If labour is not progressing well, tests will be carried out to check for possible abnormal rotation.

Shinya Umino

Figure 17 First rotation
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Figure 17 First rotation

Figure 18 Second and third rotations
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Figure 18 Second and third rotations

Source: Houken “Sixth Edition Family Medicine Encyclopedia” Information about the Sixth Edition Family Medicine Encyclopedia

Japanese:

どんな病気か

　分娩の経過とともに、胎児は産道をとおりやすいように少しずつ体の向きを変えながら、骨盤内に進入していきます。これを回旋と呼び、内診によって評価されます。反屈位(はんくつい)、低在横低位(ていざいおうていい)、前方前頭位(ぜんぽうぜんとうい)など回旋の異常のために分娩の順調な進行が妨げられる場合を総称して回旋異常と呼びます。以下に正常な回旋とその異常について説明します。

①第一回旋（図17）：頭位の胎児は骨盤入口部であごを引いて胸につけた屈位をとる。この胎勢が産道に入る姿勢としては最も児頭が細くなって産道をとおりやすくなる。胎児が逆にあごをあげた姿勢をとる場合、反屈位(はんくつい)と呼ぶ。

②第二回旋（図18）：児頭は横向きで産道に入り、下降とともに徐々に回転し、出る時には縦向きで顔面が母体の背側を向く。この場合、母体の前方に子の後頭部があるので前方後頭位(ぜんぽうこうとうい)と呼ぶ。

　第二回旋の異常としては、第二回旋が起こらず、児頭が骨盤の出口付近まで横向きのまま下降する低在横定位(ていざいおうていい)、逆方向に回転して顔面が母体の腹側を向く前方前頭位(ぜんぽうぜんとうい)などがある。

③第三回旋（図18）：児頭が前方後頭位で骨盤の出口まで下降すると後頭部は恥骨(ちこつ)の下で固定され、これを支点として、屈位となっていた頭部が前方に伸展するとともに娩出される。

④第四回旋：児頭は娩出されると、もとの横向きにもどる。これを第四回旋と呼ぶ。