Is funnel pelvis hereditary?

Funnel pelvis is actually a type of pelvis. In fact, if a funnel pelvis appears, it will have a certain impact on our future pregnancy and childbirth. So, is funnel pelvis hereditary? As we all know, some physical characteristics of parents will be passed on to the next generation. In fact, there are some genetic characteristics for funnel pelvis, so mothers should pay attention to it when they are pregnant.

The inter-sciatic spine diameter is <10cm, the inter-sciatic tuberosity diameter is <8cm, the sum of the inter-sciatic tuberosity diameter and the posterior sagittal diameter is <15cm, the pubic arch angle is <90°, and the width of the sciatic notch is narrowed. Generally speaking, the female pelvis is wide and short, with smooth, thin pelvic walls and light bones. The upper opening of the pelvis is round or oval, wide front and back, the pelvic cavity is wide and shallow, barrel-shaped, the lower opening of the pelvis is wide, the pubic symphysis is wide, short and low, and elastic, the pubic arch angle is large, at 90 to 100 degrees, the obturator foramen is approximately triangular, and the acetabulum is small.

Differential Diagnosis of Funnel Pelvis

Narrow pelvis

(transversely contracted pelvis): Similar to the ape-type pelvis. The transverse diameters of the pelvic inlet, midpelvis and pelvic outlet are shortened, the anterior-posterior diameter is slightly longer, and the sciatic notch is wide. The measured sacropubic external diameter was normal, but the inter-iliac spine diameter and inter-iliac crest diameter were shortened.

Simple flat pelvis

(simple flat pelvis): The pelvic inlet is flat and round, and the sacral promontory protrudes forward and downward, which shortens the anterior-posterior diameter of the pelvic inlet while keeping the transverse diameter normal.

: Due to rickets in childhood, the bones soften and the pelvis is deformed. The sacral promontory is pressed forward, and the anterior-posterior diameter of the pelvic inlet is significantly shortened, making the pelvic inlet kidney-shaped. The lower part of the sacrum moves backward, losing the normal curvature of the sacrum and becoming straight and tilted backward. The coccyx is hooked and projects toward the pelvic outlet plane. Due to the abduction of the ilium, the diameter between the iliac spines is equal to or greater than the diameter between the iliac crests; due to the eversion of the ischial tuberosity, the angle of the pubic arch increases and the transverse diameter of the pelvic outlet becomes widened.

During childbirth, the pelvis is a constant. A narrow pelvis affects the fetal position and the descent and internal rotation of the fetal presenting part during the delivery mechanism, and also affects uterine contractions. The pelvis is an important factor to consider when estimating the ease of childbirth. During pregnancy, the pelvis should be checked for any abnormalities and cephalopelvic disproportion, and a diagnosis should be made early to decide on the appropriate method of delivery.

Medical history

Ask pregnant women whether they had rickets, polio, spinal and hip tuberculosis, and a history of trauma in their childhood. If the mother is a multiparous woman, we should find out whether she has a history of difficult labor and its cause, whether the newborn has any birth injuries, etc.

General examination

Measure the height. If the pregnant woman's height is below 145cm, she should be alert to the possibility of a small pelvis. Pay attention to the pregnant woman's body shape, whether she has lameness in her gait, whether she has spinal and hip deformities, whether her rhomboid fossa is symmetrical, whether she has a pointed abdomen or a hanging abdomen, etc.

(1) Abdominal shape: Pay attention to the abdominal shape, measure the suprapubic uterine length and abdominal circumference with a ruler, and use B-mode ultrasound to observe the relationship between the fetal presenting part and the pelvis. You can also measure the biparietal diameter of the fetal head, chest diameter, abdominal diameter, and femur length to predict the fetal weight and determine whether the fetus can pass through the bony birth canal smoothly.

(2) Abnormal fetal position: The narrow pelvic inlet is often caused by cephalopelvic disproportion, which makes it difficult for the fetal head to enter the pelvis, resulting in abnormal fetal position, such as breech presentation or shoulder presentation. The narrowness of the mid-pelvis affects the internal rotation of the fetal head that has entered the pelvis, leading to persistent transverse occipital position, posterior occipital position, etc.

(3) Estimation of the cephalopelvic relationship: Under normal circumstances, the fetal head should enter the pelvis 2 weeks before the due date for some primigravidas and after labor for multigravidas. If labor has already begun but the fetal head has not yet entered the pelvis, the cephalopelvic relationship should be fully estimated. Specific method to check whether the head and pelvis are proportional: The pregnant woman empty her bladder, lie on her back with her legs straight. The examiner places his hand above the pubic symphysis and pushes the floating fetal head toward the pelvic cavity. If the fetal head is lower than the plane of the pubic symphysis, it means that the fetal head can enter the pelvis and the head and pelvis are proportional, which is called a negative trans-pubic sign; if the fetal head and the pubic symphysis are on the same plane, it indicates suspected head and pelvic disproportion, which is called a suspected positive trans-pubic sign; if the fetal head is higher than the plane of the pubic symphysis, it indicates obvious head and pelvic disproportion, which is called a positive trans-pubic sign. For pregnant women with a positive trans-pubic sign, they should be asked to take a semi-recumbent position with their legs flexed, and the fetal head trans-pubic sign should be checked again. If it turns negative, it indicates an abnormal pelvic tilt rather than cephalopelvic disproportion.

Pelvic measurement

(1) External pelvic measurement: If the external pelvic diameter is less than the normal value by 2 cm or more, it means that the pelvis is small; if the sacropubic external diameter is less than 18 cm, it means that the pelvis is flat. The diameter between ischial tuberosities is <8cm, the pubic arch angle is <90°, and the pelvis is funnel-shaped. A pelvic oblique diameter (the distance between the anterior superior iliac spine on one side and the posterior superior iliac spine on the other side) and the ipsilateral diameter (the distance between the anterior superior iliac spine and the posterior superior iliac spine on the same side) that differs by more than 1 cm is considered a skewed pelvis.

(2) Internal pelvic measurement: If abnormalities are found in the lateral pelvic measurement, internal pelvic measurement should be performed. The diagonal diameter is <11.5cm, the sacral promontory is prominent, the pelvic inlet plane is narrow, and it is a flat pelvis. Midpelvic plane stenosis and pelvic outlet plane stenosis often exist at the same time. The anterior curvature of the sacrum, the intersciatic diameter, and the width of the sciatic notch (i.e., the width of the sacrospinal ligament) should be measured. If the intersciatic spine diameter is <10cm and the sciatic notch width is <2 horizontal fingers, it is considered a narrow mid-pelvic plane. If the inter-ischial tuberosity diameter is <8 cm, the posterior sagittal diameter of the outlet should be measured and the sacrococcygeal joint mobility should be checked to estimate the degree of narrowing of the pelvic outlet plane. If the sum of the inter-ischial tuberosity diameter and the posterior sagittal diameter of the outlet is less than 15 cm, the pelvic outlet plane is narrow.