Anatomically narrow pelvis is a pelvis, the size of which can create an obstacle to the process of childbirth. One or several sizes of such a pelvis are 1.5-2 cm less than the norm. Pathology occurs due to congenital anomalies, rickets, polio, poor living conditions in childhood, stress, intense sports, traumatic injuries and bone tumors. The diagnosis is established before or during pregnancy on the basis of measurements using a pelvic meter, gynecological examination and the results of additional studies. The tactics of delivery are planned individually, a caesarean section may be required.
ICD 10
033.0 033.1 O33.2 O33.3
General information
Anatomically narrow pelvis – reduction of one or more pelvic sizes, creating a mechanical obstacle to the process of childbirth. According to researchers in the field of obstetrics and gynecology, the prevalence of this pathology ranges from 1 to 11% and averages 3-6%. Nowadays, erased variants of an anatomically narrow pelvis are more often revealed. Obstetricians and gynecologists note that problems in childbirth usually arise due to a combination of mild narrowing with other factors. Due to an increase in the average size of the fetus and a decrease in the number of cases of a pronounced anatomically narrow pelvis, a number of specialists point to the need to revise the criteria for this pathology. Pregnancy management and the choice of optimal delivery tactics in women with anatomically narrow pelvis are aimed at preventing perinatal mortality, maternal and newborn injuries.
Causes
A narrow pelvis occurs under the influence of many different factors, including developmental abnormalities, cerebral palsy, malignant and benign neoplasms, osteomalacia, scoliosis, kyphosis, spondylolisthesis, lameness of various genesis (for example, as a result of mismatch of limb length or innervation disorders). In classical works devoted to the problem of an anatomically narrow pelvis, rickets, bone tuberculosis, polio, poor nutrition and hard work in childhood were usually indicated in the list of the main causes, however, these factors are rarely identified nowadays.
Anatomically narrow pelvis can develop under the influence of hormonal changes in the puberty period. Experts note that the increase in the number of patients with a transverse-constricted pelvis is associated with acceleration, since with intensive growth, the pelvis increases in length faster than in width. The connection between the appearance of an anatomically narrow pelvis and professional sports is proved. More than 64% of female athletes suffer from this pathology. In addition, the risk of forming an anatomically narrow pelvis increases with severe stress and constant wearing of tight tight clothing (“denim” pelvis) during puberty.
Pelvic dimensions
To determine the size of the pelvis, the gynecologist makes standard measurements between certain bone protrusions using a pelvis meter or a centimeter tape. The minimum distance between the anterior spine of the iliac bones is 25 cm, between the iliac ridges – 28 cm, between the large trochanter – 30 cm, between the upper angle of the rhombus Michaelis and the upper edge of the pubic articulation (external conjugate) – 20 cm. If one or more of the listed sizes is less than normal, there is reason to suspect an anatomically narrow pelvis.
The fifth dimension (the distance between the most protruding part of the base of the sacrum and the pubic joint, the true conjugate) is determined during a gynecological examination or by calculations. Normally, a specialist cannot reach the protruding part of the sacrum during an examination on a chair, therefore, the calculation of the true conjugate is carried out taking into account the size of the outer conjugate and the circumference of the wrist, or taking into account the size of the diagonal conjugate and the circumference of the wrist. It is also believed that the size of the true conjugate corresponds to the height of the Michaelis rhombus and the Frank index (the distance between the jugular notch and the spinous process of the seventh cervical vertebra). Normally, the value of the true conjugate is 11 cm .
Classification
The most common variants of an anatomically narrow pelvis are:
- Flat – reduced sagittal size
- Transversely narrowed – reduced frontal size
- Generally uniform – all sizes are reduced while maintaining the normal shape.
Rare variants of an anatomically narrow pelvis include:
- Skewed and skewed – with asymmetric halves
- Narrowed due to pathological bone protrusions (exostoses, neoplasms)
- A generally narrowed flat pelvis
- Other forms of a narrowed pelvis.
The degree of narrowing of the pelvis is determined taking into account the magnitude of the true conjugate: 1 degree – 9-11 cm; 2 degree – 7.5-9 cm; 3 degree – 5-7.5 cm; 4 degree – less than 5 cm. Anatomically narrow pelvis of the first degree occurs in more than 90% of cases, the second degree – in 8-9% of cases, the third – in 0.2-0.3% of cases. The fourth degree is extremely rarely diagnosed.
With a transverse narrowed pelvis, the degree of narrowing is estimated using the size of the entrance to the pelvis: 1 degree – 11.5-12.5 cm; 2 degree – 10.5-11.5 cm; 3 degree – less than 10.5 cm.
Diagnostics
The diagnosis is made taking into account the anamnesis of life, the results of general and gynecological examination and ultrasound data. The doctor finds out whether there have been illnesses, operations and injuries that increase the likelihood of developing an anatomically narrow pelvis. During the external examination, the specialist carries out all the necessary measurements, determines the height and weight of the patient, reveals lameness, limitation of joint mobility, curvature of the spinal column. During a gynecological examination, it finds out the size of the true conjugate.
To determine the treatment plan, an obstetrician-gynecologist collects information about previous births and the weight of children born. Then the patient with a suspected anatomically narrow pelvis is sent for ultrasound. In difficult cases, X-ray helviometry is used. The study is prescribed only if there are sufficient indications and is carried out either before the onset of gestation, or for a period of more than 38 weeks. The decision on the need for X-ray examination is made if the risk of birth trauma exceeds the risk of minimal radiation exposure to the fetus.
Indications for X – ray helviometry with an anatomically narrow pelvis are:
- the first pregnancy in a patient older than 30 years;
- complicated labor;
- infertility;
- miscarriage;
- increased risk of intrauterine pathology;
- endocrine disorders;
- somatic diseases;
- developmental abnormalities and skeletal injuries of the mother;
- suspicion of a discrepancy between the size of the fetal head and the size of the patient’s pelvis.
A promising diagnostic method is MRI pelviometry, however, the widespread use of this instrumental technique is difficult due to its high cost.
Childbirth with an anatomically narrow pelvis
With a narrow pelvis, incorrect fetal positions are often detected. Usually, pelvic presentation is diagnosed, less often – transverse and oblique presentation. Due to the insufficient width of the pelvis in late gestation, the fetus is located too high and presses on the diaphragm, causing shortness of breath and cardiac arrhythmias. There is a tendency to overstrain, which, due to the loss of mobility of the skull bones, further increases the risk of complications in childbirth.
Absolute indications for cesarean section are anatomically narrow pelvis of 3 and 4 degrees, deformities and bone neoplasms, pelvic injuries during previous childbirth. In other cases, the issue of the operation is decided individually. In the process of natural childbirth, a number of complications are possible, including premature discharge of water; slowing of the opening of the cervix and lengthening of the first period of labor; weak, too strong or discoordinated labor activity.
There may also be unusually painful contractions, fetal limb prolapse, blood supply disorders and fetal death due to umbilical cord compression, rupture or stretching of the uterus, compression of the patient’s nearby organs by the fetal head, followed by blood supply disruption, tissue necrosis and fistula formation. To prevent these complications, constant monitoring is carried out and special obstetric aids are used.
Prognosis and prevention
The forecast is quite favorable. More than 70% of patients give birth naturally without any complications. Measures to prevent the development of an anatomically narrow pelvis include proper nutrition, moderate physical activity, prevention of physical overload and psychological stress, detection and treatment of pathology of the musculoskeletal system. Preventive measures that allow timely diagnosis of an anatomically narrow pelvis during gestation and choose the right tactics for childbirth are regular visits to a gynecologist, a balanced diet, treatment of diabetes mellitus and overweight, which increase the likelihood of developing a large fetus.
