Speaker A
In this video, we are presenting the maternal-fetal biomechanics, that is, movements that occur for the baby and also for the mother, in the classic gynecological position.
This video explains maternal-fetal biomechanics during childbirth in the classic gynecological position, highlighting challenges for baby and mother.
Key Takeaways
- The classic gynecological position restricts pelvic movement, making childbirth more challenging.
- The baby must perform complex rotations to navigate the fixed pelvic diameters.
- Posterior fetal positioning leads to more painful and prolonged labor with less effective contractions.
- Proper head rotation is essential to prevent shoulder dystocia and facilitate delivery.
- Maternal positioning significantly impacts the biomechanics and ease of childbirth.
Summary
- The video presents maternal-fetal biomechanics in the classic gynecological birthing position.
- In this position, the pelvis is locked with sacroiliac joints immobile and the sacrum unable to nutate.
- Pelvic inlet diameters are mostly fixed due to bone structure, allowing minimal expansion during childbirth.
- The baby enters the pelvis at an oblique angle and must rotate its head to navigate the pelvic midplane.
- The mother's immobility and pelvic rigidity make the baby's passage difficult, requiring significant pushing effort.
- The sacrum's immobility increases pressure on the coccyx, risking dislocation and shoulder dystocia.
- Posterior fetal position causes neck extension, reducing contraction efficiency and causing severe maternal back pain.
- The urge to push may occur prematurely in posterior positions, complicating timing and delivery progress.
- Effective rotation of the baby's head (not shoulders) is critical to avoid shoulder obstruction during delivery.
- The video emphasizes the difficulty and pain of delivery in this position and previews alternative maternal positions.
Chapters
- 00:00Introduction to maternal-fetal biomechanics
- 00:49Pelvic model and constrictions during childbirth
- 01:58Limited pelvic inlet expansion
- 02:18Alignment and engagement axis
- 02:48Challenges of immobile pelvis and pushing axis
- 03:22Baby's entry and rotation in pelvis
- 03:51Sacrum immobility and delivery difficulties
- 04:59Risk of coccygeal dislocation and shoulder dystocia
- 07:31Posterior fetal position and labor pain
- 08:29Timing of urge to push and delivery challenges
Full Transcript — Download SRT & Markdown
Speaker A
In the classic gynecological position, the woman's pelvis is positioned within the opening. Her back is in hyperlordosis, which locks the sacroiliac joints, and the sacrum can no longer nutate.
Speaker A
As well, the ischial tuberosities are unable to move in or out as movements are restricted in the pelvic area.
Speaker A
And the pushing axis is not aligned from the umbilicus to the coccyx. I will now present this pelvic model and its different constrictions, and what will occur during childbirth.
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This opening is referred to as the pelvic inlet. When the cervix is fully dilated, the baby will enter the pelvis at the level of the pelvic inlet.
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One should not have high hopes regarding the range by which the diameters can be altered.
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This part is fixed; it is bone. This part as well, here as well. Therefore, we will only have the possibility of obtaining this movement here.
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Retraction of the promontory, which is somewhat exaggerated here. There you have it, 3 mm according to Mr. Malinas.
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Also, a small movement of the pubic symphysis, which is very limited here below.
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Therefore, one cannot gain much in diameter in the pelvic inlet. We will achieve progress by positioning the uterus in the correct alignment, in the axis of engagement.
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Subsequently, the pelvis behaves like a double-door entrance; when you go through them at the airport or in certain banks, you must open the first door, which is when the baby enters the pelvis.
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Subsequently, it descends, it advances, and the second passage can only open when the first one has closed.
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Then, the second opening will also close, and we will have the final opening, which is this diameter.
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This is the pelvic inlet, the mid pelvis, at the level of the ischial spines, and the pelvic outlet, between the coccyx and the pubis.
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So, in effect, these are like obstacles, and the baby must navigate through them; the baby does all the work.
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If the mother is in a position where she does not move, where the pelvis does not move, and the person assisting does not move, it is the baby who must do everything, and it is a challenge.
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That is what we shall examine. Therefore, in this basic gynecological position, the woman is on her back, with her sacrum blocked.
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We have a baby in the perfect presentation, chin tucked, head down. As this is the perfect baby, we will position it with its back to the left.
Speaker A
It necessarily enters the pelvis at an oblique angle, as the oblique axis is the widest.
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The uterine contractions press here from the sacrum to the apex of the head, provided that the baby's head is flexed.
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If it is like that (extended), it is complicated. So there, you can see, it enters.
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The uterine contractions are very strong. Having reached this point, the baby cannot exit, as the woman is lying on her back.
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It is required to turn. What is turning? He turns his head, not his body.
Speaker A
Therefore, it turns. To manage to position the widest part here, the parietal bones, at the level of the ischial spines of the mid pelvis, thus turning the head, not the shoulders; which already presents an issue with the pushing axis; then, once arrived here,
Speaker A
the sacrum should move, but on the back, it does not move, and we would need it to open at the front, ahead of the baby.
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However, as the mother is on her back, with her legs spread and knees apart, there is no pelvic movement.
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Therefore, it is somewhat difficult, and considerable pushing is required. The more the mother's torso is raised, the more the baby will be positioned in that manner.
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Which does not... It does not facilitate the transmission of forces, and ultimately, upon reaching the pelvic outlet, the baby continues to push forward, since the pelvis is immobile, it's the baby that moves, and the result is significant stretching at the perineum, between the coccyx and the pubis;
Speaker A
however, in this area, there is only skin, no myotatic reflex. Once the baby arrives here, thanks to uterine contractions of 40 kg of force, which is considerable, the head emerges, it completely extends, it is positioned this way, and the baby ascends.
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Once the head is out, as it was forced to turn, it will return to the starting position, repositioning its head in the axis as it engaged.
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At this time, we will attempt to prevent shoulder obstruction, which is a significant complication, wedged shoulders.
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We will attempt to facilitate the passage of the shoulders. It is only at that moment, when the shoulders are delivered, that the mother will be able to grasp the baby and bring it to her chest.
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You can see the trajectory, like that. A minor issue arises if the coccyx is significantly hooked, in an anterior position like so, when the sacrum remains immobile, there is considerable pressure on the coccyx, potentially leading to a dislocation.
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Because considerable force is applied there, and the sacrum does not move. Therefore, there is a risk of coccygeal dislocation, and a risk that this baby could get shoulder dystocia.
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This is for a baby arriving occiput anterior, with the baby's back towards the mother's abdomen.
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If the baby presents in a posterior position, meaning its back is against the mother's back, and most often on the right side, although the reason is unknown, the posterior position, most often on the right. Upon entering the pelvis, the baby will, due
Speaker A
to the sacral promontory, extend his neck, which diminishes the effectiveness of the uterine contractions.
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And when it extends, a fetus, a newborn that brings its head back, activates the Moro reflex.
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Therefore, there is a risk that the baby will extend its arms, which will present a challenge for the shoulders.
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In this position, the baby's weight presses on the sacrum very hard. When the baby presses on the sacrum, it causes a lot of pain in the sacroiliac joints.
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Women say, "I had back labour." It is unbearable to stay on one's back. At that moment, she feels a strong urge to push, a very strong urge to push.
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Because it is as if the baby has arrived at the ischial spines. However, it's not the right time.
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Therefore, when it is stated that the urge to push does not occur in these instances, in this case, it does.
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However, the timing is off. Because it would be necessary for the baby to enter the pelvis.
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He has not yet descended, as the neck is extended. Therefore, it would be important, at that moment, to increase this diameter.
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And it is not possible in this birthing posture. The engagement diameter is reduced. She feels the urge to push; it is not yet time.
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It is lengthy and difficult. And when the baby finally descends, reaching the ischial spines, she no longer feels the urge to push.
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At the time when the power to push is required. And since we do not prefer the baby to be born in the occipito-sacral position to protect the pelvic floor, we will attempt to rotate the baby's head.
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We are turning the head, not the shoulders; if the shoulders turn, it will never come out; it will be wedged at the shoulders. The head will turn,
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a fetus can make a 135-degree rotation to advance the parietal bones at the ischial spines. In these cases, pushing is not highly effective.
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These are deliveries that are lengthy and arduous. And once it has arrived there... The baby may have raised its arms, but if not, it is time to deliver the shoulders.
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And at this moment, the baby will return to its engagement position. He will return here.
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He is looking up at the person who is delivering the baby. And we will attempt, once again, to facilitate the passage of the shoulders.
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Once the head and shoulders have emerged, the baby can be given to the mother, but only once the shoulders have emerged.
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This is a somewhat arduous journey, and it is a very painful, very difficult delivery.
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This is why many mothers who did not want an epidural ultimately request one, as they c
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The epidural further restricts their movement. That was the situation with the woman positioned on her back, legs spread, with a sacrum that can't move.
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What happens to the baby during the pushing phase? The uterus's contractions push on the baby's sacrum, 40 kg of force.
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transmitted to the apex of the head when it is flexed. As soon as the baby is forced to extend the head, the force becomes less effective, which may lead to obstruction at the base of the neck.
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If the head turns, it is worse. The more the mother's torso is raised, the greater the risk of blood flow restriction to the medulla oblongata.
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In regards to the occiput posterior baby, we observed that it rotates 135 degrees to return to an occiput anterior position.
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Therefore, regarding what occurs at the base of the neck, we should avoid head extension and rotations.
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and remain in flexion as much as possible, like a hen's egg. In the oblique axis because it is the widest. All babies are oblique, just as when a piece of furniture is too wide, it will fit at an angle.
Speaker A
In the classic gynecological position, the woman is truly unsupported; there is a great deal of pressure on the perineum. Her knees are very wide apart, which brings the ischial tuberosities closer together, and the sacrum cannot move because the pelvis is hanging. When she pushes,
Speaker A
she pulls on her arms, lifts her head, and pushes downwards; it is impossible to use her abdominal muscles or lift the uterus; everything is pushed downwards, made worse by downward pressure on her head.
Speaker A
In this video, we discussed the maternal-fetal biomechanics as a function of one maternal position.
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In other videos, we shall examine different maternal positions and review the same biomechanics, so that each woman, at the time of delivery, may take a stand.
Topics:maternal-fetal biomechanicsclassic gynecological positionchildbirth mechanicspelvic inletfetal rotationshoulder dystociaposterior fetal positionpelvic outletlabor painuterine contractions
