BONE PELVIS
• the base consists of the sacrum, os coccyx and os coxae (os ilium, os ischium, os pubis). It is divided into true (small) and false (large) pelvis by the linea terminalis . The important thing in obstetrics is the true pelvis, and it is divided into three planes as pelvis inlet, mid pelvis and pelvis outlet in terms of delivery.
PELVIC TYPES
• Pelvis types according to the Caldwell-Moloy classification:
Gynecoid pelvis: It is the type in which the spinae are faint and the interspinous distance is > 10 cm. Symphysis pubis angle is 90° or more. It is the most suitable pelvis type for delivery.
Android pelvis: It is the type in which the spines are prominent and the pubis arch is narrow.
Andropoid pelvis: It is the type in which the anteroposterior diameter of the pelvic inlet is larger than the transverse diameter.
Platipelloid pelvis: It is the type in which the anteroposterior diameter of the pelvic inlet is smaller than the transverse diameter. It is the most unfavorable type of pelvis for childbirth.
PELVIC DIAMETER
Pelvis Inlet Diameters
► Transverse diameter (13.5 cm): It is the distance between the linea terminalis.
► Conjugata vera diagonalis (12.5 cm): It is the diameter between the promontorium and the lower edge of the symphysis. It can be measured clinically.
► Conjugata vera anatomica (11 cm): It is the diameter between the promontorium and the upper edge of the symphysis. It cannot be measured clinically. It is calculated by subtracting 1.5 cm from Conjugata vera diagonalis.
► Conjugata vera obstetrica (10.5 cm): It is the diameter between the promontorium and the most protruding inner surface of the symphis. It is approximately 10.5 cm. Not clinically measurable; however, it is calculated by subtracting 2 cm from the conjugata vera diagonalis. It is the narrowest diameter of the pelvic inlet.
Middle Pelvis Diameters
Transverse diameter (10 cm): Interspinous distance. It is the narrowest diameter of the middle pelvis.
Anteroposterior diameter (11.5 cm)
The transverse diameter of the middle pelvis (interspinous distance) is the narrowest part of the bony pelvis.
Pelvis Outlet Diameters
► Transverse diameter (11 cm): It is the distance between the tuber ischiadicum.
► Anteroposterior diameter (9.5-11.5 cm): It is the distance between the symphysis pubis and the sacrum.
FETAL HEAD DIAMETER
• Bitemporal diameter (8 cm): It is the longest distance between two temporal sutures. your fetal head
• Biparietal diameter (9.5 cm): It is the longest distance between the two parietal bones. It is the largest transverse diameter of the fetal head.
• Suboccipitobregmatic diameter (9.5 cm): It is the distance between the great fontanelle and the occipital bone. It is the diameter (32 cm) that makes up the smallest circumference of the head.
• Occipitofrontal diameter (11.5 cm): It is between the top of the nasal root and the most protruding part of the occipital bone. It is the diameter (34.5 cm) that forms the greatest circumference of the head.
• Occipitomental-Diameter (12.5 cm): It is the distance between the chin and the most protruding point of the occiput. It is the largest diameter of the fetal head.
STATUS SHAPES OF FETUS
Habitus
► Defines the intrauterine posture of the fetus (flexion or deflection). It is often in the habit of flexion.
situs
► It expresses the relationship of the long axis of the fetus to the long axis of the mother. It can be longitudinal (99%), transverse and oblique (1%).
In longitudinal situs; It may be vertex, sinciput, occiput, forehead, face or breech presentation.
presentation
► It refers to the structure that enters the birth canal in the front. Cephalic (95%), breech (4%) or Shoulder (1%) or rarely cord presentation may be present.
Position
► Indicates the position of the leading part relative to the right or left of the birth path. Occiput in vertex presentations, chin in facial presentations, sacrum in breech presentations and acromion in transverse (shoulder) presentations are the defining points. (N-1 IJ These can have right and left shapes. In most deliveries, the fetal head enters the pelvis in a transverse position, and left occiput transverse (LOT) is most common.
► Leopold maneuvers are used to determine fetal presentation and position.
Leopold 1------Fundus fetal part is determined (cephalic-podalic)
Leopold 2------The position of the fetal back is determined (fetal situs)
Leopold 3-----The premier (presentation) and engagement is determined
Leopold 4-----Level of the leading part is determined
engagement
Biparietal diameter decreases below the linea terminalis line in occiput arrivals.
In this case, the vertex, which is the most anterior part of the fetus, It comes to the interspinous line. It usually occurs within the last 2 weeks in primigravidas, and usually at the beginning of labor in multiparas.
Level
► It is the distance of the presenting part to the spina ischiadics. Its distance from the pelvic inlet is measured in cm (-) values (-5, -4, -3, -2, -1), while its distance from the outlet is measured in cm (+) values (+1, +2, +3, +4 , +5). Reaching the linea terminalis level of the leading part is expressed as -5, reaching the spina ischiadicas as O (engagement) and being seen at the hatch is expressed as +5 level.
synclitism
► It is the situation where the biparietal diameter is parallel to the pelvic inlet anteroposterior diameter or the sagittal suture is parallel to the transverse diameter. Anterior or posterior lateral deflections are called asynclitism. If the sagittal suture is close to the sacrum, the anterior parietal bone of the fetus is felt first, and this is called anterior asynclitism. If the sagittal suture is close to the symphysis, the posterior parietal bone is palpated first, which is called posterior asynclitism. Moderate ones of asynclitism can be born through the normal vaginal route. However, in severe posterior asynclitism cases, cesarean delivery may be required.
CARDINAL MOVEMENTS OF BIRTH
• These are the movements necessary for the adaptation of the presenting fetal part to the bony pelvis. It is necessary for the fetus to pass through the narrowest pelvis segment (mid pelvis) with the smallest circumference (suboccipitobregmatic diameter). For this purpose, birth takes place with the following cardinal movements in order.
► Engagement: The biparietal diameter plane crosses the pelvic inlet. It can happen in the last weeks of pregnancy or with the onset of labor.
► Descent: In nulliparous, the engagement is usually before the start of labor, while in multiparas, the descent usually begins with the engagement. Although the descent is maximum in the second stage of labor, it can also be in the deceleration phase.
► Flexion: The fetal head flexes when it encounters pelvic resistance. Thus, the long occipitofrontal diameter is replaced by the suboccipitobregmatic diameter, which constitutes the smallest circumference.
► Internal Rotation: With this movement, the occiput turns forward slowly and the nuchal symphysis is placed behind the pubis. In this way, it enters the middle pelvis, which is the narrowest part of the pelvis, with the head biparietal diameter in the interspinous space. Internal rotation is completed when the fetal head reaches the pelvic floor in 95% of cases.
► Extension: When the fetal occiput comes into contact with the lower part of the pubis, due to the fact that the pelvic outlet is up and forward, the uterus is contracted and the head is protruded only by extension, when the patient is strained.
► External Rotation: After the head comes out, the shoulders rotate in such a way that they come to the anterior posterior diameter of the pelvic outlet, thus giving birth to the shoulders.
occiput posterior position
• Fetus is born in occiput posterior position in 2% to 10% of deliveries in vertex presentation. This is not a deflection, but a rotational disorder.
• Risk factors include epidural analgesia, nulliparity, increased fetal weight and occiput posterior birth, anthropoid pelvis and narrow subpubic angle.
• All birth-related complications are more common than occiput anterior. In occiput posterior births, the 2nd stage of labor may be significantly prolonged and 3-4th stage of labor may be prolonged. degree perineal lacerations are more common.
• Manual occiput anterior rotation can be attempted or forceps vacuum can be used during delivery. Cesarean section should be performed even if the head does not pass the pelvic inlet.
parturition
• Parturition is examined in 4 phases and these phases are different from the stages of birth. The stages of birth take place in the third phase of parturition.
► Phase 1 (Silent phase}: Non-contractile uterus, rigid and closed cervix
► Phase 2 (Preparation phase}: Preparation for action begins with cervical and myometrial changes.
► Phase 3 (Birth phase}: It is the phase where the birth takes place.
► Phase 4 (Puerperium phase}: It is the phase where involution takes place.
Phase 1 (silence phase)
• Almost with implantation, a period of silence begins in the myometrium. This period of silence continues until the end of pregnancy. Sometimes there may be weak contractions of the uterus in the later weeks of pregnancy. Braxton Hicks refers to these contractions that do not cause action.
contractions or pseudo-actions. They can be seen in the first 30 weeks and are contractions of 5-25 mmHg in intensity.
|
|
real action |
lying
action |
|
rhythm of contractions |
Regular |
Irregular |
|
Intervals of contractions |
It gets shorter |
Constant |
|
severity of contractions |
It increases more and more |
Constant |
|
Location of discomfort |
back and abdomen |
lower abdomen |
|
Response to sedations |
no effect |
Usually lighter |
|
cervical opening |
THERE IS |
NONE |
PHASE 2 (PREPARATION PHASE)
• In the last 6-8 weeks of pregnancy, mobility begins in the uterus. During this phase, the myometrial and cervical changes necessary for action occur.
• Myometrial changes: Oxytocin receptors increase, gap-junction proteins such as connexin-43 increase, Pg F receptors increase. All of these increase the response to uteotonins. Again in this phase, the lower segment of the uterus begins to form and the leading part of the fetus descends.
• Cervical maturation: Hyaluronic acid increases, dermatan sulfate, which binds collagen fibers, decreases, and as a result, collagen fibers are destroyed and the cervix softens. Although the mechanisms triggering cervical ripening are not fully known, progesterone antagonists (mifepristone}, PgE and PgF20 are known to accelerate cervical ripening.
PHASE I (BIRTH PHASE)
• The 3rd phase of parturition includes 3 phases of birth:
First Stage (Cervical Erasing and Opening Stage)
► It covers the time taken to complete the dilatation of the cervix (10 cm) required for the fetus to pass through the passage. It lasts about 12 hours (the latent phase averages 8 hours, the active phase averages 4 hours).
► Depending on the amount of cervical dilatation, this phase is also divided into phases:
0 latent phase
Active phase: The active phase of labor begins when the cervical dilation is 6 cm. Cervical opening and fetal descent are observed. It is divided into three parts:
- Acceleration phase
- Maximum peak phase
- Deceleration phase
► Uterine contractions that start in labor are completely involuntary contractions and although nerve blockage is provided with epidural analgesia, the frequency and amplitude of the contractions do not decrease. Mechanical stretching of the cervix also triggers uterine contractions (Ferguson's reflex). ;.
The best evidence of adequacy of uterine activity is cervical effacement and patency.
► Contractions are not of the same intensity in the whole uterus. The more active part of the uterus is the upper segment, and the passive part is the lower segment. The junction of the thick upper part and the thin lower segment is the physiological retraction ring. If the thinning in the lower segment is severe, this ring becomes prominent and is called the pathological retraction ring (Bandl ring). Uterine rupture is expected immediately after this development.
Second Stage (Fetus Expulsion Stage)
► This stage includes the period from the completion of dilatation of the cervix until the delivery of the fetus. It is expected to take an average of 50 minutes, a maximum of 2 hours (up to a maximum of 3 hours with regional anesthesia) in nulliparous patients, and an average of 20 minutes, a maximum of 1 hour (2 hours with regional anesthesia) in multiparas.
► Delayed cord clamping is recommended after the fetus is born, except in cases where emergency intervention is required. Delaying cord clamping for 30-60 seconds in preterm and term newborns increases hemoglobin levels and iron stores. It also accelerates neurodevelopment. While this practice reduces the need for blood transfusion, intraventricular bleeding and necrotizing enterocolitis, especially in preterm newborns, the only negative side is that it can cause hyperbilirubinemia.
► Cord entanglement is observed in the neck in 25% of births and it does not normally cause any harm. If the cord is loosely coiled, the shoulders are delivered after the fetal head is released. If the cord is too tightly wrapped, the shoulders should be delivered after the cord is clamped and cut with two clamps.
Third stage (Expulsion of the Placenta)
► This stage covers the time between the expulsion of the fetus and the expulsion of the placenta and fetal membranes and usually lasts less than 10 minutes. If there is no excessive bleeding, it is considered normal for up to 1 hour and waited without intervention. If the placenta is not separated, halas is done by hand.
PHASE 4 (PUERPERIUM PHASE)
• Postpartum hemorrhage is prevented by the contraction of the myometrium within 1 hour following the birth. At the same time, with the arrival of the mother's milk, the baby begins to be breastfed and the oxytocin released by the sucking reflex also helps myometrial contractions.
REGULATION OF MYOMETRIAL CONTRACTIONS IN PARTURITION
• Basically, 5 mechanisms control myometrial contractions in parturation:
► Increased actin-myosin interaction
► Increased oxytocin receptors in myometrium
► Increased intracellular Ca level in the myometrium and/or increased extracellular Ca entry into the cell
► Increased gap junction formation in the myometrium
► Increased production of Connexin 43 protein
• While estrogen from steroid hormone activity activates all the regulatory mechanisms required for myometrial contractions, progesterone inhibits these mechanisms. Parturition occurs during pregnancy, as progesterone dominates estrogen.
It waits in the first phase, that is, the silent phase, but towards the end of the pregnancy, with the decrease in progesterone efficiency, estrogen becomes relatively dominant over progesterone and the parturition passes to the second phase, that is, the preparatory phase.
• Progression of parturition occurs with the loss of activity of progesterone by different mechanisms rather than a decrease in the amount of progesterone (N-04, N 11).
• CRH plasma levels rise dramatically in the last 6-8 weeks of pregnancy and play an important role in parturition physiology. The placenta secretes large amounts of CRH. Maternal CRH level peaks in labor and falls rapidly with birth. Unlike hypothalamic CRH release, placenta! CRH secretion is not under the negative feedback effect of glucocorticoids, but on the contrary, cortisol stimulates CRH secretion from the placenta with a positive feedback effect. Increasingly, CRH directly stimulates myometrial contractility. In addition, increased secretion of cortisol also increases myometrial contractility by increasing prostaglandin synthesis from fetal membranes. Another effect is increased steroidogenesis. CRH increases the production of DHEA-S from the fetal adrenal gland and aromatizes into estrogens in them, resulting in the predominance of estrogen, which is necessary for myometrial contractility, over progesterone.
• Uterotonins that initiate labor. The most well-known among these are oxytocin, prostaglandins, endothelin-1, serotonin, histamine, PAF and angiotensin II.