Physiological Changes in Pregnancy

Anatomy

Muscles , Joints and bones

The pelvis is the region found between the trunk and lower limbs. In females, the pelvis is wider and lower than that of their male counterpart, making it more suited to accommodate a fetus during both pregnancy and delivery. It protects and supports the pelvic contents, provides muscle attachment and facilitates the transfer of weight from trunk to legs in standing, and to the ischial tuberosities in sitting.

The cross-sectional anatomy of the female pelvis shows five bones: two hip bones, sacrum, coccyx and two femurs. Each hip bone is formed by the fusion of three bones: the ilium, pubis and ischium. The sacrum and coccyx are also comprised of smaller bones. The first is formed by the fusion of the five sacral vertebrae (S1-S5), and the latter by the fusion of the four coccygeal vertebrae. The femur articulates with the hip, forming the ball-and-socket hip joint.

The joints are supported by some of the strongest ligaments in the body which become more lax during pregnancy leading to increased joint mobility and less efficient load transfer through the pelvis. The pelvic outlet at the base of the pelvis is narrower in transverse diameter when compared with the pelvic inlet; it comprises the pubic arch, ischial spines, sacrotuberous ligaments and coccyx.

Four pairs of abdominal muscles combine to form the anterior and lateral abdominal wall, and may be termed the abdominal corset. Transversus abdominis lies deep to the internal abdominal oblique and external abdominal oblique with the rectus abdominis central, anterior and superficial IO, EO and TrA insert into an aponeurosis joining in the midline at the linea alba. The deep abdominal muscles, together with the pelvic floor muscles, multifidus and diaphragm, can be considered as a complete unit and may be termed the lumbopelvic cylinder. This provides support for the abdominal contents and maintains intra­abdominal pressure. The main function of RA is lumbar spine flexion while the obliques produce side­flexion and rotation of the spine.

The muscles of the back region include the quadratus lumborum, latissimus dorsi, serratus posterior inferior, erector spinae, interspinales and transversospinalis muscles.The muscles present in the thigh region can be split into three sections, anterior, medial and posterior.

The anterior compartment is comprised of the iliopsoas, quadratus femoris, sartorius, and pectineus. The medial compartment is comprised of the adductor magnus, adductor longus, adductor brevis, obturator externus, and gracilis. The posterior compartment is comprised of the biceps femoris, semitendinosus and semimembranosus muscles. In the gluteal region, the muscles seen there are the gluteus maximus, gluteus medius, gluteus minimus and tensor fascia latae, as well as the deeper piriformis, gemellus superior, gemellus inferior and obturator internus muscles.

The pelvic floor includes the levator ani, bulbospongiosus and the deep transverse perineal muscles.