Is internal examination necessary for pelvic measurement?

Pelvic measurement is a procedure that needs to be done during the third trimester of pregnancy. Through pelvic examination, we can understand the specific condition of the pelvis in more detail, so as to decide whether the pregnant woman is suitable for natural birth or caesarean section. There are many ways to measure the pelvis, and internal examination is one of them. However, pelvic measurement and internal examination are two different concepts, and pelvic measurement does not necessarily have to be detected through internal examination. Here we will introduce you to the relevant knowledge about pelvic measurement and internal examination.

"Pelvic measurement" is divided into "external pelvic measurement" and "internal pelvic measurement" in professional terminology. As the name suggests, external pelvic measurement is the measurement of some diameters of the pelvis from the "outside", including the iliac crest diameter, iliac spine diameter, sacropubic diameter, and ischial tuberosity diameter. The normal values ​​are 23-26cm, 25-28cm, 18-20cm, and 8.5-9.5cm respectively. If the last one is less than 8cm, the posterior sagittal diameter of the outlet should also be measured to comprehensively judge the size of the pelvis and whether you can give birth on your own.

Whether the fetus can pass through the pelvis and be delivered smoothly is not only related to the size of the fetus but also closely related to the size of the pelvis. The fetus must pass through the pelvis when it is delivered from the mother's body. The speed and smoothness of delivery are closely related to the size and shape of the pelvis. A narrow or deformed pelvis can cause dystocia, and dystocia caused by cephalopelvic asymmetry is also very common. If the pelvis is of normal size but the fetus is too large and out of proportion to the pelvis, dystocia may occur.

2. How to read pelvic measurement data

The size of the pelvis is expressed by the distance between the bones, that is, the size of the pelvic diameter. The size and shape of each person's pelvis vary, affected by individual physical development, nutritional status, genetics and racial differences. Therefore, within the normal range, the lengths of the various diameters of the pelvis also vary to a certain extent. The pelvic diameter values ​​currently described in various materials are the average values ​​of many normal pelvises.

The pelvic shape is normal, but each diameter is more than 2 cm smaller than the lowest value of the normal diameter. It is diagnosed as a small pelvis and dystocia may occur.

If the pelvic shape is slightly abnormal, but all dimensions are greater than the lower normal value, vaginal delivery may be possible.

When the sacropubic external diameter (EC) is less than 18 cm and the diagonal diameter (DC) is less than 11.5 cm, a flat pelvis is diagnosed.

When the pubic arch angle is less than 90°, the ischial tuberosity diameter is less than 8 cm, the sum of the ischial tuberosity diameter and the outlet sagittal diameter is less than 15 cm, and the bone notch width is less than 2 horizontal fingers, it is diagnosed as a funnel pelvis.

Interspinous diameter (IS): The pregnant mother lies on her back with her legs stretched out on the examination bed, and the distance between the lateral edges of the anterior superior iliac spines on both sides is measured and the data is recorded. The normal value is 23 to 26 cm.

Iliac crest diameter (IC): The pregnant mother lies on her back with her legs stretched out on the examination bed, and the widest distance between the outer edges of the iliac crests on both sides is measured and the data is recorded. Measuring the above two items can indirectly understand the transverse diameter length of the pelvic inlet. The normal value is 23 to 26 cm.

Sacropubic external diameter (EC): The pregnant mother lies on her left side with her right leg straight and her left leg bent; the measurement is the distance from the midpoint of the upper edge of the pubic symphysis to the depression below the spinous process of the fifth lumbar vertebra; this diameter can indirectly infer the anteroposterior diameter of the pelvic inlet and is the most important diameter in external pelvic measurement. The sacropubic external diameter is related to the thickness of the bone. The measured sacropubic external diameter minus 1/2 of the radial ulna circumference is equivalent to the anterior-posterior diameter of the pelvic inlet. The normal value is 18 to 20 cm.

Transverse diameter of the outlet (inter-ischial tuberosity diameter): Lie on your back with your legs bent and your hands hugging your knees, so that the hip and knee joints are fully flexed; measure the distance between the inner edges of the two ischial tuberosities. The normal value is 8.5 to 9.5 cm.