This junction of suture lines in a Y shape that is very different from the anterior fontanel.
In cases of fetal scalp swelling or significant molding, these landmarks may become obscured, but in most cases, they can identify the fetal head position as it is engaged in the birth canal.
Occiput Anterior (OA)
Occiput anterior is usually the easiest position for the fetal head to traverse the maternal pelvis.
Shown here is the "direct OA" position. While some fetuses deliver in this position, others deliver slightly rotated clockwise (LOA) or counterclockwise (ROA). Either way, the fetus is still considered to be an an "anterior" position.
Left Occiput Anterior (LOA)
The fetal position is often described using three letters.
Women with this condition who fail to deliver spontaneously are treated with cesarean section, forceps, or vacuum extraction, depending on the clinical circumstances, available resources, and experience of the operator.
Occiput Posterior Occiput posterior positions, including direct OP, LOP (Left Occiput Posterior) and ROP (Right Occiput Posterior) are positions favored by certain internal pelvic shapes. This position has some obstetrical significance.
Normally, if the head is at 0 Station, the biparietal diameter is at the pelvic inlet and the head is fully engaged. In posterior positions, at 0 Station, the biparietal diameter is still a couple centimeters above the pelvic inlet, meaning that the head is not fully engaged.
Forceps are often used to deliver babies in this position, but there is controversy whether the fetus should be delivered in the posterior position, or rotated with the forceps to the anterior position. Much depends on the clinical circumstances and the experience of the operator.
Breech Positions The terms used for breech positions are the same as for cephalic positions, except the sacrum of the fetus is used as the identifying landmark, instead of the occiput.
Sacrum Anterior (SA) means the fetal sacrum is closest to the mother's symphysis.
Left Sacrum Anterior (LSA) means the fetal sacrum is closest to the mother's symphysis and rotated slightly to the mother's left (clockwise from direct SA).
Right Sacrum Anterior (RSA) means the fetal sacrum is closest to the mother's symphysis and rotated slightly to the mother's right (counterclockwise from direct SA).