Disproportion Diagnosis
Assessment of cephalopelvic proportion is performed dynamically. The main methods include:
- Vasten's sign: the physician palpates the relation of the anterior surface of the head to the symphysis. If the head projects above it, this is a sign of disproportion.
- Zangemeister's measurement: an objective method where the distance from the supra-sacral fossa to the fetal head is compared with the external conjugate. Normally, the conjugate should be 2–3 cm greater.
- Monitoring labor progress: disproportion often manifests as a lack of descent of the head despite good uterine activity and pronounced molding of the fetal skull bones.
Dangerous complications
Continuing vaginal delivery in a clinically contracted pelvis leads to severe consequences:
- Threatened uterine rupture: manifested by overdistension of the lower uterine segment and a high-standing retraction ring.
- Soft tissue impingement: prolonged station of the head causes cervical edema, which impedes its dilation.
- Fetal hypoxia: continuous CTG monitoring is mandatory, as the risk of oxygen deprivation increases sharply in the second stage of labor.
Management tactics
Upon confirming the diagnosis of "clinically contracted pelvis", the only correct decision is an emergency cesarean section. Attempts at vaginal delivery in this situation are unacceptable due to the high risk of trauma to the mother and child. If the head is already impacted in the pelvis, the operation requires extreme caution to avoid uterine damage and injuries to the fetal cervical spine.
Briefly: answers to topical questions
What are the objective clinical signs of a threatened uterine rupture in a contracted pelvis?
Objective clinical signs of a threatened uterine rupture include changes in the shape of the uterus, the state of its segments and ligamentous apparatus, as well as specific findings from vaginal examination.
- Uterine shape — somewhat irregular.
- Retraction ring — high and oblique position.
- Round ligaments — asymmetrically positioned, tense, and painful.
- Lower uterine segment — overdistended, thinned, sharply painful, and tense.
- Fetal presenting part — located almost entirely within the overdistended lower segment.
- Tissue edema — edema of the external genitalia, impingement and edema of the cervix.
Vaginal examination reveals the absence of the amniotic sac, full cervical dilation, high station of the fetal head (inconsistent with the degree of dilation), and a large caput succedaneum.
Which degrees of anatomical pelvic contraction are an absolute indication for elective cesarean section?
Absolute indications for elective cesarean section include pronounced degrees of pelvic contraction, as well as the mildest degree in the presence of additional aggravating factors. There are the following strict indications for elective operative delivery during pregnancy:
- Grade II–IV contraction — an anatomically contracted pelvis of these grades is an independent indication.
- Grade I contraction — serves as an indication only in combination with a macrosomic fetus (weight of 3500 g or more).
Spontaneous delivery with Grade I contraction is permitted exclusively with small fetal dimensions (up to 3500 g) and occipital presentation, provided the contraction creates no mechanical obstacles.
Vasten "higher" — cesarean closer: if the head is palpable above the symphysis, vaginal delivery is ruled out.
Class and exam questions
What is the difference between anatomical and clinical pelvic contraction?
An anatomically contracted pelvis is a reduction in the dimensions of the bony pelvis, whereas a clinically contracted pelvis is a functional mismatch between the dimensions of the fetal head and the maternal pelvis that manifests only during labor.
Is it possible to replace the cervix when it is trapped/impaired?
Yes, if dilation is 8 cm or more and the head is at the level of the pelvic inlet by its small segment. If the cervix cannot be manually replaced, a cesarean section is indicated.
Why is oxytocin dangerous in a contracted pelvis?
In multiparous women, oxytocin stimulation against the background of cephalopelvic disproportion can lead to rapid overdistension of the lower uterine segment and its rupture.
What else to study on this topic
- Classification of anatomical pelvic contraction forms.
- Features of the biomechanism of labor in various types of pelvic contraction.
- Soloviev's index and its significance in pelvic assessment.
- Differential diagnosis between clinically contracted pelvis and secondary uterine inertia.
- Prevention of postpartum hemorrhage in complicated deliveries.
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