Vacuum delivery may be indicated because of reasons related to the mother or reasons related to the baby. The vacuum extractor is used (1) when rapid delivery is necessary to avoid injury to the baby and (2) to avoid cesarean section. The main indications for a vacuum-assisted delivery are listed below.
Normal labor is divided into two stages. The first stage of labor begins with the onset of regular contractions and ends when the cervix is completely dilated. The first stage of labor may last between 12 and 20 hours in a woman who is having her first baby; in a woman who has had a previous vaginal delivery, the first stage of labor may be considerably shorter, lasting seven to 10 hours. The second stage of labor begins when the cervix is fully dilated and ends with the delivery of the baby. During the second stage, the force generated by uterine contractions and the mother's pushing causes the baby to descend through the cervix and birth canal. In a woman having her first baby, the second stage of labor may last as long as one to two hours; women who have previously delivered vaginally may deliver after less than one hour of pushing. The length of the second stage may be affected by several factors including the use of epidural anesthesia, the size and position of the baby, and the size of the birth canal. Maternal exhaustion or inability to push due to strong anesthesia may also prolong the second stage of labor. During this stage, frequent assessment of the progress of labor is made by checking regularly the position of the baby's head in the birth canal. As long as the baby continues to descend and is not experiencing problems, pushing may continue. However, when descent is delayed or when the second stage has been greatly prolonged (usually more than two hours), the doctor may consider performing a vacuum-assisted vaginal delivery.
The effort required for effective pushing can be extremely exhausting. Once pushing has continued for more than an hour, a woman may lose some of the strength necessary to produce the type of pushing necessary to deliver successfully. In these situations, some extra help from the doctor may avoid complications of prolonged pushing. The vacuum extractor allows the doctor to pull while the mother continues to push. The combined forces of maternal pushing and outward traction with use of the vacuum are usually sufficient to deliver the baby.
Epidural anesthesia is commonly used for pain relief during labor. The epidural consists of a thin plastic tube (catheter) that is placed just outside the spinal cord in the lower back; medication that is injected through the epidural catheter bathes the nerves as they leave and enter the spinal cord. The epidural catheter is usually left in place throughout the entire labor and delivery and additional medication may be injected as needed. The epidural is useful during labor because it blocks the nerve fibers that relay the pain signals associated with labor and delivery while the nerves that are necessary for movement and pushing are less effected. In an ideal situation, the patient has the benefit of excellent pain relief and retains the ability to move and even push effectively as needed. However, in order to obtain the maximum pain relief during labor, larger doses of medication are usually required. In these cases, the nerves responsible for movement may also be affected and the patient's ability to produce the necessary pushing force is impaired. A physician may use the vacuum extractor to provide additional force and help deliver the baby when maternal efforts are hindered by the epidural.
Some medical conditions may be aggravated by maternal efforts at pushing or can make effective pushing impossible. During the act of pushing, the mother's blood pressure and pressure in the brain are increased. Women with extremely high blood pressure, certain heart conditions (pulmonary hypertension or Eisenmenger's syndrome), or a history of aneurysm or stroke can experience serious complications from pushing during the second stage of labor. Neuromuscular disorders can cause weakness or paralysis and make effective pushing impossible. In these instances, the vacuum extractor may be used to shorten the second stage of labor. However, forceps delivery may be preferable in these cases because maternal effort is not as essential as it is with the vacuum extractor.
Throughout labor, efforts are made to document the well being of the baby. Most doctors use continuous fetal heart rate monitoring, which consists of recording the patterns of the baby's heart rate and contractions of the uterus, to determine the condition of the baby. Subtle changes in the heart rate pattern may signal fetal compromise. The most concerning of these changes is a prolonged deceleration in which the baby's heart rate drops and fails to return to a normal baseline. In these circumstances, a rapid delivery is required to prevent irreversible damage in the baby. Under the appropriate conditions, a vacuum-assisted delivery can be used to quickly deliver the baby.
Delay or prolongation of the second stage of labor may be the result of an abnormal position of the baby's head. During normal delivery, the baby's chin rests against the chest so the very tip of the baby's skull is the first part to come through the birth canal. Under normal circumstances, the baby is facing toward the mother's tailbone in a position called occiput anterior. This position results in the smallest diameter of the baby's head passing through the birth canal. If the head is slightly tilted to one side (called an asynclytic presentation), facing to the side (occiput transverse position), or facing to the front when the mother is lying on her back (occiput posterior position), the second stage of labor may be delayed and vacuum or forceps delivery can be used to correct the position of the baby and achieve delivery. Forceps are preferred when attempting to rotate or turn the baby's head to a more favorable position. Although the vacuum is not typically used to purposely rotate the baby's head, the use of the vacuum can result in auto-rotation (the baby's head turns by itself as gentle traction is applied).
Several criteria must be met to safely perform a vacuum extraction. Prior to considering a vacuum procedure the doctor will confirm the following:
The cervix must be completely dilated.
If vacuum extraction is attempted when the cervix is not fully dilated, there is a significant chance of injuring or tearing the cervix. Cervical injury requires surgical repair and may lead to problems in future pregnancies.
The exact position of the baby's head must be known.
The vacuum should never be placed on the baby's face or brow. The ideal position for vacuum cup placement is directly over the midline or sagittal suture on top of the baby's head. Vacuum delivery is less likely to succeed if the baby is in an occiput posterior position (facing straight up when the mother is lying on her back).
The baby's head must be engaged within the birth canal.
The position of the baby's head in the birth canal is measured in relation to the narrowest point of the birth canal called the ischial spines. These spines are part of the pelvic bone and can be felt during a vaginal exam. When the top of the baby's head is even with the spines, the baby is said to be at zero station and the baby's head has descended well into the pelvis. Before a vacuum extraction is attempted, the top of the baby's head must be at least even with the ischial spines and preferably descended one to two centimeters below this level. The success of a vacuum delivery is directly correlated with how far the baby's head has descended. When the baby is found to be two or more centimeters past the ischial spines or when the baby's head can be seen at the vaginal opening during pushing, the chances for a successful vacuum delivery are increased.
The membranes must be ruptured.
To apply the vacuum cup to the baby's head, the amniotic membranes must be ruptured. This usually occurs well before a vacuum extraction is considered.
The size of the baby and the shape of the birth canal must be estimated, and the doctor must believe that the baby will "fit" through the birth canal.
There are times when the baby is too big or the birth canal is too small for a successful delivery. Attempting a vacuum extraction in this situation will not only be unsuccessful but may result in serious complications.
The pregnancy must be term or near term.
Because the risks of vacuum extraction are increased in premature infants, vacuum extraction should not be performed before a gestational age of 34 weeks. Forceps may be used in assisted delivery of preterm infants.