Narrow pelvis is an obstetric concept implying a decrease in at least one of the sizes of the female pelvis compared to the norm (anatomical narrowing) or a mismatch in the size of the pelvis and fetus (functional narrowing), making it difficult for the fetus to pass through the bony base of the birth canal. A narrow pelvis in childbirth often contributes to untimely outpouring of water, premature placental abruption, labor anomalies, bleeding, birth injuries of the fetus and mother, postpartum infections. The diagnosis of a narrow pelvis is made by external examination of a pregnant woman, measurement of the size of the pelvis and fetus, vaginal examination, ultrasound, X-ray helviometry. The management of childbirth with a narrow pelvis has its own characteristics and often requires an operational aid.
In obstetrics and gynecology, it is customary to distinguish anatomically and functionally (clinically) a narrow pelvis. An anatomically narrow pelvis is understood as a decrease in all or one of the main dimensions of the pelvis (interosseous, intervertebral, the distance between the distal points of the iliac ridges, the external conjugate) by 1.5-2 or more cm. A functionally narrow pelvis is considered a discrepancy between the anatomical dimensions of the pelvis of the mother to the fetal head, which creates obstacles, sometimes insurmountable, for the birth of a child. t. A., even an anatomically normal pelvis can be functionally narrow (with hydrocephalus, a large fetus) or, on the contrary, an anatomically narrowed pelvis can be functionally complete (with a premature fetus or its hypotrophy). Anatomically narrow pelvis is diagnosed in 1.0—7.7% of women; functionally narrow – in 0.6—1.7% of pregnant women.
The formation of an anatomically narrow pelvis in a woman can be due to numerous reasons. In childhood, congenital anomalies, cerebral palsy, malnutrition, rickets, polio can contribute to this. Male (Android) the type of pelvis occurs in adrenogenital syndrome (congenital adrenal hyperplasia), which is also characterized by other signs of verilization. Pelvic deformities can be caused by osteomalacia, tuberculosis and bone tumors, fractures of the pelvic bones, curvature of the spine (scoliosis, kyphosis, coccyx fractures), spondylolisthesis, dislocation of the hip joint.
During puberty, the secretion of estrogens and androgens has a great influence on the formation of the pelvis. Estrogens contribute to the growth of the pelvis in transverse size and its ossification, androgens – the growth of the pelvis and skeleton in length. Therefore, any hormonal disorder during puberty, leading to a violation of the ratio of estrogens and androgens (hypoestrogenism and hyperandrogenism), can lead to the formation of a narrow pelvis in adolescent girls.
The formation of a narrow pelvis is closely related to adolescent acceleration, which leads to a rapid increase in body length with a slow increase in transverse dimensions. The development of the skeletal skeleton of girls is influenced by psychoemotional overload, stress, increased sports activities, hormone intake.
In obstetric practice, the classification according to the degree of narrowing and shape is of the greatest importance. In accordance with the size of the true conjugate, a narrowing of the pelvis of 4 degrees is distinguished:
- I degree is characterized by the size of the true conjugate from 11 to 9 cm
- II degree – from 8.9 to 7.5 cm
- III degree – from 7.4 to 6.5 cm
- IV degree — from 6 cm or less. Today, in obstetrics, we often have to deal with “erased” forms of a narrow pelvis, i.e. I-II degrees of narrowing.
Among the most common forms of an anatomically narrow pelvis, there are transverse–narrowed (45.2%), flat (simple – 13.6%, flat–bronchitic – 6.5% and a pelvis with a reduced wide part of the cavity – 21.8%), generally uniform-narrowed (8.5%) types. The rare forms of a narrow pelvis (in 4.4% of women) include osteomalacic, funnel-shaped, oblique and obliquely displaced pelvis, as well as pelvic forms narrowed due to exostoses, bone tumors, bone fractures with displacement, etc.
Clinical gynecology also uses a morphological classification based on the results of X-ray helviometry, according to which gynecoid (normal female), androidic, anthropoid, platypelloid forms and various variants of mixed pelvic forms are distinguished. By size, there are small, large and medium female pelvis.
In the diagnosis of a narrow pelvis, attention is paid to the anamnesis of a pregnant woman: peculiarities of development in childhood and puberty, diseases and injuries suffered. To recognize a narrow pelvis, an external examination, measurement of the size of the pelvis and fetus, gynecological examination, ultrasound, X-ray helviometry are performed.
Indirect signs that make you think about the presence of a narrow pelvis in a woman can be height below 160 cm, shortened toes and hands (shoe size hypertrichosis, menstrual cycle disorders, etc. On external examination, the abdomen of primiparous with a narrow pelvis often has a pointed shape, and sagging of the abdomen is observed in repeat births.
Conducting pelviometry allows you to judge the degree of narrowing of the pelvis. At the same time , the following are mandatory for measurement:
1. Transverse parameters:
- distantia spinarum (norm – 25-26 cm)
- distantia cristarum (norm – 28-29 cm)
- distantia trochanterica (norm 30-31 cm)
2. Straight size – conjugata externa (norm – 20-21 cm).
3. Dimensions of the lumbosacral rhombus Michaelis (vertical diagonal – 11 cm horizontal – 10-11 cm).
4. Dimensions of the pubic joint (norm 4 cm).
Additional dimensions can also be determined – lateral conjugates, the volume (circumference) of the pelvis, the angle of inclination of the pelvis. Based on the obtained dimensions, the true conjugate is calculated – the direct size of the entrance to the pelvis, which is the main criterion for judging the presence of a narrow pelvis.
X-ray helviometry allows you to more accurately determine the true dimensions of the pelvis with an error of 2 mm: the plane of entry, the wide part, the narrow part. Ultrasound is used to determine the proportionality of the fetus and the pelvis of the mother, the estimated weight of the fetus, which is extremely important for assessing the prospects of childbirth. By vaginal examination, the capacity of the pelvis is clarified, deformities (exostoses, tumors) are excluded, the value of the diagonal conjugate is determined, etc.
Complications of pregnancy and childbirth with
The course of pregnancy may be uncomplicated or accompanied by the threat of termination at different terms, the development of gestosis and fetoplacental insufficiency. The presence of a narrow pelvis in a woman in labor, provided the average size of the fetal head, its good ability to configuration and active labor activity may not disrupt the course of labor. However, childbirth with a narrow pelvis often has its own characteristic complications.
Most often, the presence is accompanied by an untimely (premature or early) outpouring of amniotic fluid. Untimely opening of the fetal bladder and the outpouring of water often leads to the loss of fetal limbs or umbilical cord loops. The dropped leg or handle of the child creates additional obstacles to the expulsion of the fetus, increasing the risk of birth injuries to the mother and newborn. Pinching the head of the fallen umbilical cord loop can lead to acute hypoxia and fetal death.
The presence of a narrow pelvis contributes to an incorrect position (oblique, transverse) and presentation of the fetus (pelvic, frontal or facial). With a narrow pelvis, there is a greater likelihood of premature placental abruption, the development of weakness or discoordination of labor, and the protracted nature of labor. The long course of labor and the anhydrous interval determine the risks of infection with the development of postpartum endometritis, metrothrombophlebitis.
In the presence of a narrow pelvis, prolonged standing of the fetal head in one plane leads to compression of the pelvic organs, followed by tissue necrosis and the formation of vaginal fistulas. With the development of excessively strong labor activity, the risk of rupture of the perineum, vulva and vagina, uterus increases. Violation of the biomechanism of childbirth often leads to postpartum bleeding and the development of lochiometry, due to poor contractility of the uterus, delayed lochiae.
The presence of a narrow pelvis in a woman in labor almost always poses a threat to the fetus: the child may be born in a state of hypoxia or asphyxia, with impaired cerebral circulation, cranio-spinal injuries, which will require further observation by a neurologist or neurosurgeon, resuscitation, therapeutic measures and long-term rehabilitation.
Tactics of childbirth with a narrow pelvis
The duration of gestation with a narrow pelvis is on average 39 weeks. Usually a woman is hospitalized in the maternity ward 2 weeks before the due date. The absolute grounds for caesarean section are the III – IV st. of the narrow pelvis, bone tumors in the small pelvis, a sharp deformation of the pelvis, the presence of pelvic injuries in previous births. Indications for planned operative delivery are also a narrow pelvis of the first degree in combination with pelvic presentation, a large fetus, a postponed pregnancy, a scar on the uterus, chronic fetal hypoxia, burdened with an obstetric and gynecological history according to the sum of indications.
With an anatomically narrow pelvis in the absence of aggravating factors, childbirth is conducted expectantly with careful monitoring of dynamics, monitoring of cardiotocography and phonocardiography of the fetus, prevention of early rupture of the fetal bladder and fetal hypoxia. Rhodostimulation is used carefully. Surgical aid is indicated in the case of clinically narrow pelvis with the threat of complications for the fetus and the woman in labor.
Prevention of the formation of an anatomically narrow pelvis begins in childhood and includes providing a growing girl with adequate nutrition, a rational rest and exercise regime, moderate physical activity; prevention of injuries and deformations of the bone skeleton. In case of hormonal imbalance affecting the development of the bone pelvis, timely corrective therapy is necessary.
Pregnancy management in women with a narrow pelvis requires consideration of possible risks for the mother and fetus. It is necessary to prevent over-gestation; prenatal hospitalization for the purpose of further examination, clarification of the degree and form of pelvic narrowing, development of optimal delivery tactics.