When the long axes of mother and fetus are at right angles to one another, a transverse lie is present. Because the shoulder is placed so frequently in the brim of the inlet, this malposition is often referred to as the shoulder presentation. The baby may lie directly across the maternal abdomen (Fig. 26-1) or may lie obliquely with the head or breech in the iliac fossa (Figs. 26-2A and B). Usually the breech is at a higher level than the head. The denominator is the scapula (Sc); the situation of the head determines whether the position is left or right, and that of the back indicates whether it is anterior or posterior. Thus, LScP means that the lie is transverse, the head is on the mother's left side, and the baby's back is posterior. The part that actually lies over the pelvic brim may be the shoulder, back, abdomen, ribs, or flank. This is a serious malposition whose management must not be left to nature.
The incidence of transverse lie is around 1:500. The incidence is higher before term (as high as 1 in 50 at 32 weeks' gestation).
This abnormality is more common in multiparas than primigravidas because of the laxness of the uterine and abdominal muscles. Similar condition in which there is relatively excess space for the fetus are polyhydramnios and prematurity. Other causes include anything that prevents engagement of the head or the breech, such as placenta previa; an obstructing neoplasm; multiple pregnancies; fetal anomalies; fetopelvic disproportion; contracted pelvis; and uterine abnormalities such as uterus subseptus, uterus arcuatus, and uterus bicornis. In many instances, no etiologic factor can be determined, and we assume that the malposition is accidental. The head happens to be out of the lower uterine segment when labor starts, and the shoulder is pushed into the pelvic brim.
DIAGNOSIS OF POSITION: TRANSVERSE LIE
The appearance of the abdomen is asymmetrical
The long axis of the fetus is across the mother's abdomen
The uterine fundus is lower than expected for the period of gestation. It has been described as a squat uterus. Its upper limit is near the umbilicus, and it is wider than usual
Palpation of the upper and lower poles of the uterus reveals neither the head nor the breech
The head can be felt in one maternal flank. The buttocks are on the other side
The fetal heart is heard best below the umbilicus and has ...