Narrow pelvis during pregnancy and its clinical form

The form and size of the pelvis is one of the many physical changes that come with pregnancy that should be taken into account. During childbirth, a narrow pelvis may have consequences for the mother and the infant. Despite being common, this condition can affect the delivery process and necessitate extra care from medical professionals.

Clinical evaluations are frequently used to detect narrow pelvises, which can range in severity. Being aware of the clinical manifestations of a narrow pelvis aids in getting ready for potential labor difficulties. Every case may involve different considerations for overall care and delivery strategies, regardless of how severe the constriction is.

A comprehensive assessment and a customized strategy are needed to manage a narrow pelvis during pregnancy and make sure the mother and unborn child are supported during the birthing process. The risks related to this condition can be successfully managed with the correct medical guidance and preparation, resulting in a more comfortable delivery experience.

Topic	Description
Narrow Pelvis Overview	A narrow pelvis is when the pelvic bones are smaller or shaped differently, which can affect childbirth.
Clinical Form 1	In this form, the pelvic cavity is reduced in size, which may lead to difficulties during labor.
Clinical Form 2	This form involves a more pronounced narrowing of the pelvic outlet, potentially requiring a cesarean section.
Diagnosis	Diagnosis usually involves pelvic measurements and imaging to assess the extent of the narrowing.
Management	Management may include monitoring during pregnancy, planning for possible interventions, and preparing for different delivery options.

What is a “narrow pelvis”?

According to statistical data, pelvic narrowing is diagnosed in varying degrees in approximately 5% of laboring women. Understanding the effects that certain pelvic dimensions may have on the normal course of labor is necessary in order to visualize all the features of this pathology. The baby must pass through the pelvic cavity during the second stage of labor, when the fetus is expelled directly.

An impediment to the child’s normal birth patency is created when the shape, size, or configuration of some bones differs from the norm. This inevitably results in complications during childbirth.

• 2 pelvic bones, which are formed from the ilium, ischium and pubis;
• sacrum;
• coccyx.

Ligaments and cartilaginous tissue connect each of these bone components to the other.

The pelvis differs in size and shape between men and women. It is shallower in women, but it is wider. Female reproductive function explains these gender characteristics.

Traditionally, there are two types of pelvic narrowing:

• anatomical narrowing – the size of one or more bones does not correspond to normal sizes);
• clinical (or functional) narrowing – a relative concept, which means a discrepancy between the pelvic size and the size of the fetal head.

Even in cases where anatomical stenosis is diagnosed, the pelvis may not be clinically narrow. For instance, the pelvis may be clinically normal but the child may still be large despite the fetus’s relatively small weight.

Causes of narrowing

Depending on the type of narrowing, different pathological factors may have contributed to the development of the condition: anatomical defects or differences in the fetus’s size from the birth canal’s size may have been the cause.

The development of anatomical pelvic narrowing is influenced by the following factors:

• various types of reproductive dysfunctions;
• any menstrual cycle disorders or too late onset of menstruation;
• hormonal imbalance;
• infectious diseases;
• disproportionate physical activity in childhood or adolescence, as well as a poor diet.

The development of pelvic dimensions may be adversely affected by the aforementioned factors.

Let us now discuss diseases that cause anatomical narrowing, a pathology that is directly related to these diseases.

Among them are:

• sexual infantilism (underdevelopment of the female reproductive system);
• delayed sexual development, provoked by various factors: neuroendocrine disorders, hereditary diseases, autoimmune processes, inflammatory diseases of an infectious nature, pituitary tumors, etc.;
• rickets (the disease is mainly of the infants associated with the insufficient intake of vitamin D into the body, which is the result of insufficient mineralization of bone tissue);
• osteomulation, as a result of which bone tissue acquires excessive flexibility;
• malignant bones;
• various forms of curvature of the spinal column (kyphosis, lordosis, scoliosis);
• violations of the integrity of the pelvic bones due to injuries;
• Cerebral palsy;

• congenital characteristics of the structure of the body associated with the hereditary factor;
• polio;
• exostosis (benign neoplasm of the bone-cherry nature, which is formed on the surface of the bone);
• generic injuries or damage caused in the intrauterine period of development;
• acceleration (a rapid increase in the body in length, while a significant lag in the formation of pelvic sizes);
• heavy psycho-emotional stress (can provoke the development of "compensatory hyperfunction of the body", as a result of which a transversely narrowed pelvis can form);
• intensive sports activities in childhood and adolescence;
• metabolic disorders;
• insufficient or excessive production of female sex hormones;
• excessive levels of male sex hormones.

The chance of developing different pelvic structural disorders is decreased by the prevention or prompt treatment of these pathologies.

Classification

Anatomical pelvic constriction is classified into multiple categories in clinical medicine. The primary one is predicated on radiological morphological characteristics.

Let’s take a closer look at the various kinds of these constrictions.

• Gynecoid type. Women with this pelvic structure make up more than half of the total number of women in labor. This type is a variant of the norm. Women with this type of constitution have clear gender characteristics: thin waist, wide hips, body weight and height fluctuate within the average indicators.

• Android type. This type of pathological narrowing occurs in every fifth woman in labor. From the name it follows that in this case the formation of the small pelvis occurs according to the male type. Characterized by the presence of a triangular entrance and a slightly smaller exit. The owner of such a pelvic shape is characterized by a body structure similar to a man"s: an undefined waist, massive shoulders, narrow hips, etc. p.

• Anthropoid type. A characteristic feature of this narrowing is the size of the direct size of the entrance and the transverse size are greater than normal indicators. Expectant mothers with such a defect are tall, thin, have narrow hips, massive shoulders.

• Platypeloid type. This type of narrowing is not so common. In this case, the pelvis has a flattened shape from top to bottom. Also, the sacrum here is slightly tilted from behind. Women with this type of narrowing are distinguished by their tall stature and thinness. They have poorly developed muscles and poor skin elasticity.

Types according to Krassovsky

There are other variations of the narrowed pelvis "according to Krassovsky" in addition to this classification. There are differences between the following types:

• Generally uniformly narrowed. The shape of the pelvis corresponds to the norm, but at the same time all the dimensions of the bones are reduced in the same proportions by about 1.5 cm. This form of narrowing is typical for women of average height and normal build.

• Transversely narrowed (Robert"s). This type of narrowing is characterized by a shortening of the transverse dimensions by about 1 cm, as well as a relative decrease or increase in the direct diameter of the entrance. This type of pelvis is found in representatives of the fair sex, built according to the male type, often suffering from hyperandrogenism – increased production of male sex hormones.

• Flat pelvis. There are the following types:

1. simple flat – in this case, there is a decrease in the size of the direct diameters, and the transverse diameter of the entrance, on the contrary, is larger than the clinical norm;
2. flat sacrum – characterized by a narrowing of the direct diameter of the entrance and an increase in all other direct diameters, and the sacrum in this case has a flat shape;

• Obliquely displaced (asymmetrical). The formation of this rather rare form of narrowing occurs due to illnesses suffered in childhood or adolescence or as a result of injuries, such as rickets, hip dislocation, improperly healed fracture of the femur).

• Deformation by tumors. Damage to the pelvis can be due to the occurrence of tumors, exostoses, that is, a benign growth of bone and cartilage tissue.

• Funnel-shaped – such a disorder occurs against the background of some hormonal disorders. The main feature is the narrowing of the outlet from top to bottom in the form of a funnel).

• Kyphotic. Refers to the funnel-shaped type. Due to the deformation of the spinal column, the center of gravity of the body shifts slightly forward.

• Spondylolisthetic. The direct size of the entrance is insufficient due to the displacement of the V lumbar vertebra from the base of the sacrum.

• Osteomalatic. This type of narrowing develops gradually in women of reproductive age. Bone tissue deformation due to osteomalacia leads to pronounced curvature of the pelvis. First, the spinal column is affected, after which the pathological process spreads to the pelvis, chest and limbs.

Degrees of narrowing and measurements

An obstetrician-gynecologist diagnoses "narrow pelvis" based on the findings of measuring the primary obstetric parameters of a pregnant woman’s pelvis.

A specific type of narrowing that is regarded as pathology will be indicated if any of these parameters do not match the indicators that experts accept as the average statistical norm.

In order to measure the pelvis objectively, the physician takes the following measurements.

Lumbosacral rhombus or Michaelis rhombus

This rhombus in the lower back is visible when a woman stands. The obstetrician calculates the separation between the two opposite extremes. Generally, there should be at least 11 centimeters between vertical points and at least 10 centimeters between horizontal ones.

Interosseous size

A woman must lie down on a couch in order to identify this indicator. The obstetrician measures the separation between the two iliac tubercles in this position. This size should normally be at least 25 cm:

• Maximum distance between the iliac bones. Measurement is taken in a supine position. The distance between the most distant points on the iliac bones is determined. This size should be no less than 28 cm.

• Distance between the greater trochanters. In order to take the measurement, a woman needs to lie down on a couch and bend her legs. Here, the distance between the upper ends of the femurs is determined. Normally, this indicator is 30 cm.

External conjugate

The woman must lie on her side with her lower leg bent and her upper leg straight in order to identify this indicator.

The obstetrician measures the distance between the pubic symphysis’s upper nearest point and the apex of the Michaelis rhombus. The external conjugate normally needs to be at least 20 cm.

Lateral conjugate

Measured while the subject is in a lateral position. Here, the pelvimeter’s ends are applied to the left and right anterior and posterior points of the upper zone of the ilium. This value shouldn’t typically be less than 14 cm.

True conjugate

Measuring this indicator is limited to vaginal exams. Finding the true conjugate is currently not required for all expectant mothers. The measurement of this size allows one to determine the extent of pelvic narrowing. The true conjugate should normally measure 11 cm.

An "anatomically narrow pelvis" is the diagnosis made by the obstetrician if any of the listed indicators deviate from the widely recognized standard. According to statistical data, 10% of women who register for pregnancy have some form of narrowing.

As was previously mentioned, altering the true conjugate yields information about the degree of narrowing. Depending on how shortened this size is, experts distinguish between several degrees of pelvic narrowing, which are displayed below:

• 1 degree – IS = 10 cm;
• 2 degree – IS = 8.5 – 9.9 cm;
• 3 degree – IS = 5 – 8.4 cm;
• 4 degree – IS = less than 5 cm.

Narrowing of 1 or 2 degrees is regarded as conditional in clinical practice because there is no assurance that such a pathological deviation will result in complications during pregnancy or during labor.

In obstetric practice, 3 and 4 degrees of narrowing are an uncommon occurrence that are typically observed in women who have experienced severe musculoskeletal injuries or diseases.

Diagnostics

The evaluation of a pregnant woman’s pelvis occurs on the day of her prenatal clinic registration. The gynecologist needs to perform the following diagnostic procedures in order to find any variations in the disruption of the pelvis’ normal structure:

• collection of anamnesis;
• objective examination of the patient, which includes anthropometry, examination, measurement of pelvic dimensions and, if necessary, vaginal examination.

In certain situations, the specialist might turn to further diagnostic techniques like X-ray pelviometry and ultrasonography.

In the process of gathering anamnesis, it is important to take note of the illnesses the woman experienced as well as the circumstances of her early and teenage years. This data might point to the origin of the pelvic structure violation.

The gynecologist can also gather information that will be very helpful in managing the current pregnancy, such as the woman’s menstrual cycle’s beginning, the course of her previous pregnancies, whether any pathologies complicated them, how they ended, etc.

An external examination is the first step in an objective examination of a pregnant woman. The expert considers the composition of the body. The patient’s anthropometric characteristics meet a number of conditional criteria that could point to a likely narrowing. Among them are:

• short stature (less than 160 cm);
• small foot size (less than 36);
• the index finger is shorter than 8 cm, and the length of the hand is less than 16 cm;
• hip circumference is less than 85 cm;
• Soloviev index – the circumference of the wrist is measured at the level of the prominent condyles of the forearm. By assessing this indicator, the specialist can judge the degree of bone thickness. Normally, the Soloviev index should be 14.5-15 cm;
• external signs of hyperandrogenism: excessive body hair, as well as hair growth "in a male pattern", undefined hips and waist, broad shoulders and neck, small breasts, etc.

The gynecologist may also look at the abdomen, the shape of which may also reveal some abnormalities.

A pregnant woman’s musculoskeletal system may be affected by a variety of disorders, so the doctor should be aware of any changes in her gait.

A pelvimeter, a specialized tool, is used to measure the main dimensions of the pelvis, and this measurement is crucial in making a diagnosis. It is only used in obstetrics and has a design that resembles a compass with rounded ends.

According to specific guidelines, roentgenopelviometry should be performed no earlier than 37 weeks into a pregnancy. You can also conduct this diagnostic study while you are in labor.

By using roentgenopelviometry, it is possible to ascertain the curvature of the sacrum, the characteristics of the structure, the shape of the entrance, the degree of inclination of the pelvic walls, and the location of the ischial bones in relation to one another. Furthermore, you can calculate all pelvic diameters using this method of instrumental diagnostics, detect neoplasms, and ascertain the size and location of the baby’s head.

The value of the true conjugate, the location and dimensions of the fetal head, and the manner in which it is inserted into the entrance can all be determined with the aid of an ultrasonography examination.

All of a woman’s pelvic diameters can be measured with a transvaginal sensor.

It is imperative that expectant mothers and their healthcare providers comprehend the implications of a narrow pelvis during pregnancy. Narrow pelvises can be difficult to manage, but with the right care and current medical advancements, they can be effectively managed. Throughout the pregnancy, it is crucial to collaborate closely with a medical team to guarantee the health and wellbeing of the mother and the unborn child.

Potential issues can be addressed early on with the support of routine prenatal checkups and honest communication with healthcare professionals. This proactive approach makes it possible to create a customized birthing plan that takes the unique requirements and circumstances of the mother and child into account. Many women with narrow pelvises can deliver their babies safely and successfully if they receive the right care.

In the end, even though a narrow pelvis may carry some risks, it is controllable with the appropriate care and medical direction. Pregnant women can effectively navigate these challenges and contribute to a positive pregnancy experience by being informed and involved in their care.

Pregnancy-related narrow pelvis can pose unique risks and challenges for both mother and fetus. This condition, which is frequently detected through clinical evaluations, may need to be carefully managed to ensure a safe delivery because it can affect the process of delivery. In order to plan appropriate interventions and be ready for any complications, it is helpful to understand its clinical form. The ultimate goal is to achieve a positive outcome for both mother and child.

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