Some women will need help at the end of labour with vacuum extraction or forceps delivery. Baby could become distressed during pushing and need delivery. Or there could be insufficient progress and maternal exhaustion. The requirement to assist delivery is not new and not related to epidural use, as forceps and vacuum extraction were invented prior to the common usage of epidurals.
For many decades the fetal heart has been listened to after each contraction. During a contraction the fetal heart rate will drop due to head compression. If there is a loop of cord somewhere that is being compressed during a contraction (or a problem with blood supply to the placenta) then the fetal heart will stay down after a contraction. This can reduce blood supply and oxygen reaching baby so that baby becomes distressed. Even if the fetal heart recovers to baseline after a contraction, there will be gradual decrease in oxygen reaching baby during the pushing stage due to effects on the placenta.
During the active second stage of labour, maternal effort during each contraction is required for pushing to be successful. There are a lot of mechanical barriers that may delay progress. The tissues of the birth canal are elastic, especially during a first vaginal birth, so baby’s head will descend with pushing but then will go back up again. The head has to be pushed up and around the curve of the pubic bone so that it can come out of the vagina. Progress can be slowed down by the head position in the pelvis.
Head position during labour
During labour the baby’s head can come down through the pelvis facing across from one side to the other (transverse position), so that the side of the head puts pressure on the cervix. Less often the fetal head is facing up (posterior position), so that the back of the head puts pressure on the cervix. Sometimes the baby’s head will start transverse, turn to posterior in the middle of the pelvis and then turn back to transverse.
At the very end of labour, baby’s head turns so that it will come out of the bottom of the pelvis and out of the vagina facing downwards, or in the anterior position. Once the head has exited the vagina, the head returns to either facing across or facing upwards, prior to the shoulders, back and body being born with the back to one side.
In order for the head to turn downwards, baby’s chin has to drop towards the chest as the head flexes. During the pushing stage, if baby's head is still transverse or posterior, the forces of pushing may cause the head to deflex more, making the anterior position less achievable and pushing less successful.
As the head deflexes with pushing, it gives the appearance of the head descending in the vagina, but as soon as the pushing stops the head returns to its previous position and there is no descent. The position of baby’s head can be determined by palpating baby’s scalp and if the head is not turned to anterior, then the position of baby’s head can be corrected with vacuum extraction.
The vacuum extraction cup is designed to suck fluid into one place on the scalp to make an attachment to the scalp. This vacuum attachment is not strong enough to pull babies out and maternal pushing effort is required. The vacuum traction keeps the baby’s head flexed so that baby is encouraged to turn to the anterior position.
When baby’s head is deflexed, the presenting diameter is nearly 2cm larger than when the head is flexed with baby's chin on its chest. The vacuum keeps baby's head presenting with the minimum diameter so that maternal effort is then able to push the baby around, down and out. The vacuum attachment can also stop the fetal head from returning to a higher position between contractions, but its main role is to flex the fetal head into the optimum position for delivery. A Vacuum extraction may convert an hour of pushing into ten minutes of pushing by making it more effective. An episiotomy may be needed to make it easier for baby’s head to emerge from the vagina.
After baby is born, there is a raised area in the scalp where the suction cup pooled the fluid. This rapidly flattens out. There may be discolouration on the scalp for a few days. Occasionally calcification can occur leaving a small lump in the scalp. More rarely bleeding between the layers of scalp can occur. Babies born by vacuum extraction should be closely observed for this possibility so that it can be managed as soon as it is diagnosed. Usually compression of the scalp is sufficient to prevent extension of any bleeding.
There are forceps that can be used to turn the heads of babies but these are rarely used as vacuum extraction is so effective at correcting head position. Forceps can be used to lift baby’s head, which is in an anterior position, over the curve of the pubic bone when maternal effort is not overcoming the mechanical factors delaying delivery. Sometimes a vacuum procedure will turn baby’s head to anterior and then forceps are required to complete the delivery.
Forceps are made of stainless steel and can appear scary. They are simply shaped like very thin cupped hands on long handles so that they can fit where hands will not. Forceps are designed to slide into the vagina on either side of the baby’s head as if a hand was placed on either side of the face over the sides of the head. Once the handles meet they are locked into a position where they cannot move closer in or further out. Forceps maintain a gentle grip on the baby’s head. When there is a contraction and with maternal effort, the forceps are elevated so that the head is lifted out of the vagina. An episiotomy may be required to help the head to deliver.
After a forceps delivery, there may be some marks in the skin on the side of baby’s face. These usually resolve within a few days. Sometimes, there can be compression of the facial nerve in the skin of the face, resulting in a temporary, and very rarely a long-term, decrease in movement of involved facial muscles.
Instrumental Delivery versus Caesarean Section
If baby’s head is in a suitable position in the pelvis for vacuum or forceps, then delivery can be achieved much sooner than If a Caesarean section has to be arranged and performed. Having a vaginal delivery, even if it is assisted, means that it will be more likely to achieve a vaginal delivery in a future pregnancy. Complications of Caesarean section can be avoided.
Occasionally, an attempted vacuum and / or forceps delivery is not successful and an emergency Caesarean section will be required for delivery. If it is uncertain that baby can be delivered by instrumental delivery, then the procedure can be performed in the operating theatre. The team is assembled and everything is prepared for an emergency Caesarean section. Then if an instrumental delivery is unsuccessful, baby can be delivered quickly by Caesarean section without delay.