Forceps are designed with a cephalic curve, which fits around the fetal head, and a pelvic curve which fits the pelvis. Short-shanked (eg Wrigley's) forceps are used for lift out deliveries, when the head is on the perineum; long-shanked (eg Neville Barnes) for higher deliveries, when the sagittal suture lies in the AP diameter. Kielland's forceps have a reduced pelvic curve, making them suitable for rotation (only in experienced hands).
Conditions of use
The head must be engaged; the membranes ruptured; the position of the head known and the presentation suitable, ie vertex or face (mentoanterior); there must not be cephalo pelvic disproportion (moulding not excessive); the cervix must be fully dilated and the uterus contracting, and analgesia adequate (perineal infiltration for the episiotomy; pudendal blocks may be sufficient for mid-cavity forceps and ventouse deliveries but not for Kielland's). The bladder must be empty.
Indications for use
Forceps may be used when there is delay in the second stage: this is frequently due to failure of maternal effort (uterine inertia or just tiredness), epidural analgesia, or malpositions of the fetal head. They may be used when there is fetal distress or a prolapsed cord, or eclampsia— all occurring only in the second stage. They are also used to prevent undue maternal effort, eg in cardiac disease, respiratory disease, pre-eclampsia. They are used for the after-coming head in breech deliveries.
Technique
Learn from demonstration. The following is an aide-m moire for non-rotational forceps. Place the mother in lithotomy position with her bottom just over the edge of the delivery bed. Use sterilizing fluid to clean the vulva and perineum; catheterize; check the position of the head. Insert pudendal block and infiltrate the site of the episiotomy (not necessary if she has an epidural). Assemble the blades to check they fit, with the pelvic curve pointing upwards. The handle which lies in the left hand is the left blade and is inserted first (to the mother's left side) and then the right: the handles should lock easily. Traction must not be excessive (the end of bed is not for extra leverage!). Synchronize traction with contractions, guiding the head downwards initially. Do a large episiotomy when the head is at the vulva. Change the direction of traction to up and out as the head passes out of the vulva. If baby needs resuscitation, give to paediatrician. Give vitamin K (p 120). Is thromboprophylaxis needed? See p 16.
Forceps complications
Maternal: Trauma (commoner than with ventouse). Fetal: facial bruising, VII paralysis (usually resolves); brachial plexus injury.
Ventouse
The ventouse, or vacuum extractor, associated with less maternal trauma than forceps is preferred worldwide, but not in the UK. It may be used in preference to rotational forceps because, as traction is applied, with the cup over the posterior fontanelle, rotation during delivery will occur. It can be used through a partially dilated cervix (primips should be almost fully dilated, multips >6cm), but should not be used if the head is above the ischial spines. It is contraindicated for face presentations and for premature babies. A cup is applied with a suction force of 0.8kg/cm2. The baby's scalp is sucked up to form a chignon, which resolves in 2 days. There is increased rate of fetal cephalhaematoma (p 90) and neonatal jaundice so give vitamin K (p 120). Maternal trauma still occurs in ~11%.
If ventouse, low forceps, or mid forceps are needed for 1st delivery, spontaneous rates for 2nd delivery are 91%, 88%, 82% respectively in the absence of induction or augmentation.60 Women having vaginal delivery are more satisfied with the birth, less anxious about the baby, and more likely to breast feed. Only about a third will have vaginal delivery after previous Caesarean Section.
Indications for forceps delivery1
Relative indications (ventouse or Caesarean an alternative)
- Delay or maternal exhaustion in second stage.
- Dense epidural block with diminished urge to push.
- Rotational instrumental delivery for malposition of head.
- Suspected fetal distress.
Specific indications for forceps (forceps delivery is usually superior to ventouse or Caesarean in these circumstances)
- Assisted breech delivery, forceps to deliver head.
- Assisted delivery of preterm infant <34 weeks gestation.
- Controlled delivery of head at Caesarean section.
- Assisted delivery with face presentation.
- Assisted delivery with suspected coagulopathy or thrombocytopenia in fetus.
- Instrumental delivery where maternal condition precludes pushing (eg cardiac disease, respiratory disease).
- Cord prolapse in second stage of labour.
- Instrumental delivery under GA.
1 R Patel 2004 BMJ 328 1303
Obstetric brachial plexus palsy (OBPI)
OBPI complicates <0.5% of live births.
Risk factors
Large birth weight; shoulder dystocia with prolonged 2nd stage of labour; forceps delivery; vacuum extraction; diabetes mellitus; breech presentation. Formerly, the cause of OBPI was excessive lateral traction applied to the fetal head at delivery, in association with anterior shoulder dystocia.
Instrumental-associated OBPI may arise because of nerve stretch injuries after rotations of >90° or from direct compression of the forceps blade in the fetal neck.61 Not all cases of brachial plexus palsy are attributable to traction. Intrauterine factors may play some role.62
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