Fetal Presentation and Position
At term, most babies lie in the uterus upside down and facing the woman’s spine. Several variations are possible, however, and help determine whether any interventions, including a cesarean, will be needed.
The term presentation refers to the way the baby is situated in the uterus. The part of the baby that is closest to the cervix is called the presenting As already discussed, in a normal birth, the head is lowest in the uterus and therefore is the presenting part. (See Figure 8.1) This type of presentation is called a cephalic presentation. More specifically, if the top of the head is felt at the cervix, it is called a vertex presentation. The brow or face can also be the presenting part, but are much less common and can cause difficulty at delivery.
A very small percentage of births involve a transverse lie, or shoulder presentation. The baby lies sideways in the uterus with his shoulder as the presenting part. (See Figure 8.2) With a transverse lie, cesarean delivery is mandatory.
Another presentation is breech, in which the buttocks present first. Breech presentations account for 3 to 4 percent of all deliveries. Labor may be longer than with a vertex presentation because the buttocks are not as efficient a dilating wedge as the top of the head. The most common varieties of breech presentation are the complete breech, in which the fetus sits cross-legged in the bottom of the uterus (see Figure 8.3), and the frank breech, in which the fetus has his legs straight up, with his feet near his face (see Figure 8.4). Less common is the footling breech, which is similar to the complete breech, but in which one or both feet present first. (See Figure 8.5) In the knee breech, the rarest form, the knee, instead of the foot, presents at the cervix.
|Figure 8.1 Cephalic presentation||Figure 8.2 Shoulder presentation, or transverse lie||Figure 8.3 Complete breech presentation.|
|Figure 8.4 Frank breech presentation||Figure 8.5 Footling breech presentation|
The risk to the baby is increased in a breech delivery, thus increasing the possibility of obstetrical intervention. Most doctors routinely perform a cesarean in the case of a breech presentation. While the baby’s buttocks may pass easily through the pelvis, his larger head may cause problems. When determining method of delivery, the doctor takes into account fetal size, type of breech presentation, the woman’s pelvic dimensions and architecture, and progress in labor. He also factors in his own experience in handling vaginal breech deliveries.
The doctor may not realize before labor begins that the fetus is in a breech presentation. If he discovers this during labor, he may order X-ray pelvimetry to determine whether the woman’s pelvic measurements are adequate. If there are no other complications, such as a prolapsed cord, the woman may be able to give birth vaginally. Effective pushing is most helpful in delivering a breech baby. Some doctors use forceps if the second stage is prolonged.
Prior to 30 weeks, a baby has plenty of room to turn around in the uterus and his position is insignificant. If your caregiver discovers that your baby is breech after 30 weeks, you may be able to rotate him into a vertex presentation by doing the following exercise. Lie on your back with your knees bent and your feet flat on the floor. Position several pillows beneath your lower back and buttocks to elevate your pelvis 9 to 12 inches. You can also use an ironing board elevated at a 45-degree angle. Stay in this position for 10 to 15 minutes, three times a day, preferably before meals for the greatest comfort. Continue the routine until the baby rotates. When the baby turns, stop doing the exercise or he may return to breech. Once he has turned, walk a lot to help him settle further down in the pelvis. Be sure to check with your caregiver to confirm the baby’s change in presentation. In one study, an 88.7-percent success rate was reported with this technique. The exercise is also effective in rotating a baby who is lying transverse in the uterus. Check with your caregiver prior to beginning the exercise to make sure there is no medical reason why you should not do it.
In addition to using this position, you may want to visualize the baby turning in the uterus. Relax your body to decrease the abdominal muscle tension. Some women have reported success in turning a breech by placing headphones on the lower abdomen and playing soft music.
This can be done in combination with or separate from the exercise. These women felt that their babies turned to get closer to the music. When your partner talks to his baby, he should position his head low on the abdomen. Other women have used flashlights, pointing the beam at the top of the uterus and slowly moving it down the abdomen. These women believed that the baby may have tried to follow the beam of light. While these methods are anecdotal, they involve minimal risk and may increase the chance of success.
It is also possible to turn a baby from a breech or transverse lie by using external version. This procedure is usually performed in the hospital using the visual guidance of ultrasound. The woman may be given medication to relax the uterine muscle. This makes it easier for the doctor to manipulate the baby into a head-down position, which is done by applying gentle, yet firm, pressure to the woman’s abdomen, pressing on the baby’s head and hip. External version is usually performed at 37 weeks of pregnancy. Prior to this time, the baby’s lungs may not be mature enough if an emergency cesarean needs to be done. After 37 weeks, the doctor is less likely to be able to rotate the baby because of reduced amniotic fluid. In addition, the baby is larger and may have settled into the pelvis. This procedure may even be attempted if the breech is not diagnosed until labor. The risks associated with external version include initiation of labor, soreness to the woman’s abdomen, and, on rare occasions, shearing of the placenta from the uterine wall, which would necessitate an emergency cesarean. The technique should be performed only by a doctor experienced in it.
Position, as used in obstetrics, refers to the relation of the baby’s presenting part to the woman’s pelvis. In a vertex presentation, the baby’s occiput, or back of the head, is the point of reference. The most common position during labor is the anterior position, in which the back of the baby’s head is toward the woman’s abdomen. (See Figure 8.6) A less common position is the posterior position, in which the baby’s occiput is against the woman’s spine. (See Figure 8.7.) A posterior position often results in a prolonged labor accompanied by a groat deal of back discomfort.
|Figure 8.6 Anterior position||Figure 8.7 Posterior position|
Your caregiver may use letters—such as ROA, LOT, ROF, or OP—to identify your baby’s position. The first letter designates your right or left hip. The letter O refers to the baby’s occiput, and the last letter can be either an A for anterior position, a P for posterior position, or a T for transverse position. (In the transverse position, the back of the baby’s head is toward your side.)
For example, if your caregiver says that the position of the baby is ROA, the back of the baby’s head is toward your abdomen, but slightly toward your right side. In an OP position, the back of the baby’s head is directly against your spine, and your baby is “sunny side up.” A normal labor begins with the baby entering the pelvis in a transverse position and then rotating to an anterior position.