By Lucy Kean, Consultant Obstetrician, subspecialist in Fetal and Maternal Medicine Nottingham University Hospitals NHS Trust

One of the hardest skills obstetric doctors learn is how to decide whether to try to deliver a baby vaginally or when a caesarean section is the better option in the second stage, and how to balance the risks and benefits to the mother and baby.

The risks are diverse and decision making with informed consent is one of the hardest tasks to achieve in the heat of the moment.

It is unusual that a mother’s birth plan covers all the eventualities of labour and few women make a detailed birth plan in advance.

When help in needed in the second stage to deliver the baby it is usually at the end of a long labour.

The issues surrounding informed consent for this process is a whole article of it’s own and I am not going to rehearse this today, but I am going to cover how the obstetrician makes the critical decisions around how to deliver the baby and what the relative risks and benefits are for each type of delivery.

The Reality of Second Stage Labour

The need for help to deliver a baby in the second stage of labour is surprisingly common. Something that many women remain blissfully unaware of until the need arises. Indeed, the NHS Maternity Statistics for 2022-2023 for England, showed a normal birth (ie birth without any assistance) rate of 49%, meaning that less than half of mothers having a baby in England delivered without any help. The rate for assisted vaginal birth has remained reasonably stable at 12% and the caesarean section rate is now 39% of which approximately 2/3rd are planned elective procedures and 1/3rd are performed as an emergency.

Perineal laceration was experienced by 39% of women which in reality means that if a woman has a vaginal birth there is a 64% chance of needing some stitches, and closer to 85% if it is her first baby.

Indications for help to deliver the baby once the second stage (full dilatation) is reached can broadly be divided into:

1. Concerns regarding the wellbeing of the baby (often termed fetal “distress” or stress) usually reflecting a diverse range of problems such as developing fall in oxygen delivery to the baby or infection in the baby)

2. The need for help because the baby has not delivered after a prerequisite amount of time (3 hours of active pushing for first births and 2 hours for subsequent births)

3. A need to shorten the second stage because the mother is exhausted or pushing is not advised.

Often there is overlap with both maternal and fetal factors playing a part (babies become more at risk of hypoxia and sepsis after prolonged labours). In the NHS 2022-2023 data, fetal “stress” complicated 27% of births.

Ensuring Safe Assisted Birth

Various factors have been shown to reduce the need for intervention in the second stage.

These include:

• 1 to 1 care in labour
• Delaying pushing if a mother has an effective epidural (1-2 hours)
• Upright position if no epidural, or lying on the side if an epidural is present

The Royal College of Obstetricians (RCOG) updated guidance on assisted vaginal birth in 2020 and lays out the pre-requites for attempting an assisted vaginal birth as:

1. Safety criteria for assisted vaginal birth

• Full abdominal and vaginal examination (to establish fetal size and descent of the head)
• The head should be ≤1/5 palpable per abdomen (in most cases not palpable)
• Cervix is fully dilated and the membranes are ruptured
• Station (the leading bony point of the head) at level of ischial spines or below
• Position of the fetal head has been determined (with a new recommendation that ultrasound can be helpful and improves accuracy)
• Caput and moulding is no more than moderate (or +2) (Moderate moulding or +2 moulding is where the parietal bones are overlapped but easily reduced; severe moulding or +3 is where the parietal bones have overlapped and are irreducible indicating cephalopelvic disproportion)
• Pelvis is deemed adequate, ie there appears to be enough room to allow the baby’s head to deliver

2. Preparation of mother must involve:

• Understanding of any maternal preferences that have already been shared
• A clear explanation of what is proposed
• Consent taken and documented in women’s case notes. Written consent is usually taken for women that need delivery in the operating theatre
• Trust must be established and full cooperation sought and agreed with the woman
• Appropriate analgesia: for midpelvic or rotational births, this will usually need a regional block; a pudendal block (local anaesthetic nerve block) may be acceptable depending on urgency and potential ease of delivery; and a perineal block (local anaesthetic to the skin) may be sufficient for low or outlet birth
• The maternal bladder should be emptied
• If an indwelling catheter is in place this should be removed or the balloon deflated
• An aseptic technique should be used

3. Prerequisites for staff are:

• The operator must have the knowledge, experience and skill necessary or be directly supervised by a more senior doctor who has the necessary skills
• Adequate facilities must be available (equipment, bed, lighting) and access to an operating theatre where failure is possible

4. Backup plan:

• For mid-pelvic births, theatre facilities should be available to allow a caesarean birth to be performed without delay;
• A senior obstetrician should be present if an inexperienced obstetrician is conducting the birth
• Anticipate complications that may arise (e.g. shoulder dystocia, perineal trauma, postpartum haemorrhage)
• Personnel should be present who are trained in neonatal resuscitation

Ventouse vs Forceps: Methods and Risks

The two main methods to aid vaginal delivery are ventouse (using a vacuum device) or forceps. Forceps which cradle the head of the baby can be divided into straight (where no rotation of the head is needed), usually Neville Barnes or Simpsons types and rotational forceps (Kielland’s).

Ventouse deliveries are less likely to be successful with failure rates of 1/3rd for the most commonly used Kiwi hand held system, when compared to undertaking a forceps birth which has a failure rate of only 1-5%.

There are some additional potential complications for the mother who needs an assisted vaginal birth. The commonest is significant perineal trauma. The Royal College of Obstetricians and Gynaecologists quote a risk of 3rd or 4th degree tears (which involve the anal sphincter, the muscle responsible for faecal continence and more rarely the rectum) of 1-4% for births performed using a vacuum device (ventouse) and 8-12% when forceps are used. However, 60-80% of women will make a good recovery following recognition and repair.

Bleeding is common after an assisted vaginal birth, usually as a result of trauma and uterine atony (the uterus not contracting well).

The NHS patient leaflets cite the following as complications of assisted vaginal birth for the baby:

• a mark on your baby's head (chignon) being made by the ventouse cup – this usually disappears within 48 hours
• a bruise on your baby's head (cephalohaematoma) – this can happen during a ventouse assisted delivery, but the bruise is usually nothing to worry about and should disappear with time
• marks from forceps on your baby's face – these usually disappear within 48 hours
• small cuts on your baby's face or scalp – these affect 1 in 10 babies born using assisted delivery and heal quickly
• yellowing of your baby's skin and eyes – this is known as jaundice, and should pass in a few days

There are rarer complications not mentioned in the NHS leaflet that include subgaleal haematoma which is bleeding between the periosteum and the aponeurosis of the skull, which can be severe and life threatening to the baby. This is mainly a complication of ventouse deliveries occurring in 3-6/1000. Facial nerve palsy can occur rarely after forceps delivery. Cervical spine injuries have been reported with rotational forceps deliveries and skull fractures and intracranial bleeding have also rarely been reported.

The risks of fetal trauma are slightly higher with ventouse births but significantly increased if sequential instruments are used, leading the RCOG to recommend that if the first instrument fails a senior review must be undertaken and a different approach considered or the procedure abandoned.

Deliveries tend to be more complicated when:

• The mother is overweight (BMI is greater than 30)
• The mother is short (1.55m)
• The estimated fetal weight is greater than 4 kg or the baby is clinically big
• The head circumference measured above the 95th percentile on a recent ultrasound
• The position of the fetal head is occipito–posterior (back to back)
• The level of the fetal head is in the midpelvis or one-fifth of the head is palpable abdominally

The rates of obesity continue to rise with most areas seeing rates of women booking with a BMI of more than 30 of 28%

When considering how to deliver the baby, the operator needs to understand all of the risk factors outlined above.

Ultrasound assessment of the position of the baby (the way the baby is lying in relationship to the maternal pelvis) has been shown to improve the accuracy of this when compared to vaginal examination alone.

The operator should ensure that they have reviewed the latest ultrasound scans and assessed the clinical size of the baby by abdominal palpation and using symphysis fundal height measurement if a recent ultrasound assessment is not available.

Other risk factors such as previous problems such as shoulder dystocia or the presence of diabetes in the current pregnancy will also play a part in decision making.

The Caesarean Section

The alternative to undertaking an assisted vaginal birth is of course, a caesarean section.

Many mothers perceive that a caesarean section is always the safest option for the baby, but this underestimates the short and potential long term problems of this procedure and particularly so when performed late in labour.

In the second stage of labour the cervix is fully dilated and the border between the cervix and the lower segment of the uterus becomes indistinct.

The incision at caesarean section can compromise the integrity of the cervix leading to a significant increase in the risk of very early pre-term birth in subsequent pregnancies. So much so that the NHSE Saving babies lives care bundle version 3 lists second stage CS as a moderate risk factor for subsequent preterm birth. The magnitude of the risk increase may be as high as 6-fold from 2% to 15%.

The procedure itself can be tricky.

Impaction of the fetal head can occur in as many as 15% of second stage CS. Impacted fetal head (IFH) is now a more common cause of fetal injury than shoulder dystocia and is a factor in 10% of the most expensive claims in maternity since 2018.

The risks are higher after a long labour, if there is a malposition of the fetal head (the fetus is not in the occipitoanterior, back to mothers front) or an assisted vaginal birth has already been attempted. It seems to be an increasing problem across the developed world, which may be due to guidelines that have extended the recommended length of second stage.

Disimpaction when IFH occurs is never easy and can result in injury to the fetus (fractures of the skull, limbs, hypoxic brain injury, bleeding below the scalp or into the brain) and significant complications in the mother (uterine extensions, urinary tract damage, haemorrhage, infection).

Various techniques have been tried to deliver the baby when the head is impacted. These include a second person pushing up the head vaginally, using an inflatable device inserted into the vagina to elevate the fetal head (fetal pillow), delivering the bottom of the baby first and then the head (reverse breech) and modifications of this (Padwardhan technique).

Assisted Birth vs Caesarean: Navigating the Grey Zone

The recent scientific impact paper published by the RCOG could not recommend any one method for delivering a disimpacted head over another.

What is clear is that this is an obstetric emergency that requires skills training in advance for all trainees who may face this, to the same level that we train in delivering when shoulder dystocia occurs.

There is no National guideline yet in the UK for managing this condition.

There is good guidance produced by the Society of Obstetricians and Gynaecologists of Canada in 2021 that provides advice not only on the potential manoeuvres, but also on other measures that include:

• Alerting staff
• Positioning the table low to facilitate access
• Giving short acting tocolysis to relax the uterus,
• How to extend the incision if needed.

This provides an excellent template for training in the absence of anything yet in the UK.

In general, the decision between attempting a vaginal birth or undertaking a caesarean section will be needed where there is a higher chance of failure of vaginal birth.

Where the head is very low and optimally positioned an assisted vaginal delivery is considered the safest and quickest method for delivery. When the head is above the mid-pelvis, assisted vaginal delivery should not be attempted and it is an easy decision to undertake a caesarean section.

The middle ground is usually where the fetal head requires rotation to achieve vaginal birth and the head is at or just below the level of the ischial spines (the bony landmark of the mother’s pelvis, used to determine whether the head has descended low enough to have passed through the narrowest part of the pelvis).

In this circumstance experience counts. Recent anecdotal evidence from local Trusts is that when a trial of instrumental delivery is undertaken in theatre, as would be considered good practice for mid-pelvic deliveries, the success rate of vaginal birth is only about 50%, with no attempt being made to deliver the baby vaginally in the other 50% of cases. In historical comparisons successful vaginal birth rates have usually been around 80%. It is likely that a gradual loss of skill in the use of Kielland’s rotational forceps is partly responsible, with fear of creating a more difficult caesarean if an attempt is made and fails also a major anxiety.

Comparative studies of choice of instrument for assisted vaginal birth have consistently demonstrated greater success rates with rotational forceps compared to rotational ventouse or manual rotation (turning the baby’s head using the hand) followed by straight forceps.

In comparison to recourse to caesarean section, a successful assisted vaginal birth causes less maternal bleeding and a lower likelihood of the baby needing admission to the neonatal unit, but causes a greater level of minor trauma to the baby.

There is more maternal perineal trauma when a vaginal delivery is undertaken and this is higher still if sequential instruments are used (usually ventouse followed by forceps), but this must always be balanced against the significantly increased risk of impaction of the fetal head when a caesarean is undertaken after an attempt at an assisted vaginal birth.

Good comparative studies are rare and few assess the impact on future pregnancy outcomes in the risk analysis. 80% of women who have an assisted vaginal birth, will deliver vaginally without assistance in their next pregnancy. Rates of vaginal birth after previous caesarean section rate for most Trusts are now less than 30%, so if a caesarean section is undertaken few women opt to attempt labour next time.

There are risks associated with subsequent pregnancy after caesarean section which include increased risks of abnormally invasive placenta, where the placenta breaches the scar and becomes more difficult to remove, leading to potentially catastrophic bleeding and hysterectomy. This risk increases with each subsequent caesarean section.

The obstetrician will rarely be criticised if a woman has a subsequent preterm birth or abnormally invasive placenta, when the choice was made for caesarean section over assisted vaginal birth in the current pregnancy, whereas a difficult vaginal birth may frequently lead to litigation.

What might constitute negligent practice?

The RCOG guideline provides a clear framework for acceptable practice for assisted vaginal birth. It does not rehearse the potential complications from delivery by Caesarean section and indeed, the guidance provided by the RCOG on consent for Caesarean section only covers planned operations.

The guideline on assisted birth also states “Operators should be aware that no indication is absolute and that clinical judgment is required in all situations”.

If fetal or maternal injury has occurred when the operator has strayed outside the guidelines, establishing negligence will usually be straightforward.

If a practitioner does not have the necessary skills and damage occurs, again, establishing negligence is straightforward.

A failure to take a holistic view and undertake a proper assessment of each individual risk factor might also be considered poor practice.

At organisation rather than individual level:

Lack of appropriate support for middle grade staff when a delivery is anticipated to be difficult might also be viewed as negligent.

Perhaps, given the increasing prevalence of IFH, Trusts may find themselves liable if it can be shown that staff have not been provided training for dealing with this emergency, much in the same way that it became part of mandated skills training to learn how to manage shoulder dystocia, leading to a significant drop in cases of damage to babies from this complication.

From personal experience, provision of good analgesia is key and persisting with delivery vaginally or by Caesarean section when analgesia is inadequate leads to long term psychological sequelae in the mother, with grounds to seek redress.

Whilst I have not covered consent in detail, the absence of evidence of a consent process, or a disregard of maternal wishes have also lead to successful claims.

The grey areas, when damage, either to the mother or baby has occurred, without clear failings will always remain the areas of contention.

Conclusion

Even the most experienced operator can find themselves between a rock and a hard place when faced with delivering a baby safely in the second stage of labour.

I hope I have provided some understanding of the dilemmas faced on a daily basis by obstetricians, some of the available evidence and how decisions are made. That this is a difficult area without, often, easy solutions, is borne out by the huge burden of cost faced by maternity services and the NHS.

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