![]() ![]() ![]() The first letter of the abbreviation denotes the location of the presenting part in the right (R) or left (L) side of the mother’s pelvis. Position is denoted by a three-letter abbreviation. Position is the relationship of the presenting part (occiput, sacrum, mentum, or sinciput ) to the four quadrants of the mother’s pelvis (see Fig. The presentation or presenting part indicates the portion of the fetus that overlies the pelvic inlet. As the head is more extended, the anteroposterior diameter widens, and the head may not be able to enter the true pelvis (see Fig. When the head is in complete flexion, this diameter allows the fetal head to pass through the true pelvis easily ( Fig. Of the several anteroposterior diameters, the smallest and the most critical one is the suboccipitobregmatic diameter (approximately 9.5 cm at term). In a well-flexed cephalic presentation, the biparietal diameter will be the widest part of the head entering the pelvic inlet. The biparietal diameter, which is approximately 9.25 cm at term, is the largest transverse diameter and an important indicator of fetal head size ( Fig. For example, in a cephalic presentation, the fetal head may be extended or flexed in a manner that presents a head diameter that exceeds the limits of the maternal pelvis, leading to prolonged labor, forceps- or vacuum-assisted birth, or cesarean birth.Ĭertain critical diameters of the fetal head are usually measured. The circumference of the fetal hips is usually small enough not to create problems.ĭeviations from the normal attitude may cause difficulties in childbirth. This position creates a shoulder diameter that is smaller than the skull, facilitating passage through the birth canal. Molding can be extensive, but the heads of most newborns assume their normal shape within 3 days after birth.Īlthough the size of the fetal shoulders may affect passage, their position can be altered relatively easily during labor thus one shoulder may occupy a lower level than the other. This capacity of the bones to slide over one another also permits adaptation to the various diameters of the maternal pelvis. Because the bones are not firmly united, however, slight overlapping of the bones, or molding of the shape of the head, occurs during labor. Sutures and fontanels make the skull flexible to accommodate the infant brain, which continues to grow for some time after birth. The posterior fontanel lies at the junction of the sutures of the two parietal bones and the occipital bone, is triangular, and is approximately 1 cm by 2 cm. The larger of these, the anterior fontanel, is diamond shaped, is approximately 3 cm by 2 cm, and lies at the junction of the sagittal, coronal, and frontal sutures. The two most important fontanels are the anterior and posterior ones (see Fig. We have found also that there is typically a much greater need for downward traction initially before then turning outward and upward to take the fetus into flexion for delivery.Fig. For OP presentations, the biparietal diameter is typically much higher than anticipated and Dennen recommends depressing the shanks against the perineum before locking (effectively inching them higher and more anterior on the parietal bone). ![]() Only after the occiput clears the symphysis is this then transitioned to outward then upward to minimize perineal injury. For an OA presentation, this requires direct downward (axis) traction. Last, the correct direction of traction is best achieved by visualizing the presenting part and cardinal movements necessary for delivery. This is easily resolved by moving the left handle so that it falls under the right and the English lock will come together correctly. If, however, the right blade was placed first (as would be the case in a ROA or LOP presentation placing the posterior blade first), then they will appear to come together and be unable to lock. A forceps blade on the correct trajectory should require almost no force, and I remind learners of this by encouraging them to hold the handle with only their fingertips.Īs the forceps lock, if the left blade was placed first, this allows the English lock to come together easily. Doing so starts the blade of the forceps down the sacrum/face (in an OA fetus) rather than along the more hollow space between parietal bone and vagina. Importantly, as the forceps begins its motion, there can be no movement forward or backward of the handle until the maternal thigh is reached. It is important that the cephalic curve (or “palm side” of the blade) is as closely apposed to the fetal scalp as possible, or if the fetal scalp is not visible, then to the maternal introitus. The most frequent struggles are usually encountered in initial placement – particularly of the second blade – and less commonly during traction. ![]()
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