Assisted Vaginal Delivery – an Overview

Introduction

Assisted vaginal delivery (AVD) remains, in skilled hands, the most efficient method of expediting birth in the second stage of labour and is associated with fewer adverse maternal and neonatal outcomes than any alternative. This chapter will focus on the history and state of the art as it currently stands, examine important areas of practice and suggest a way forward that will keep AVD at the heart of obstetric practice in the 21st century. The need for such focus is clear – complications of the second stage of labour (fetal compromise, obstructed labour, maternal exhaustion, or maternal medical conditions exacerbated by the act of pushing) remain a major cause of maternal and neonatal mortality and morbidity across the world. Such complications are responsible for 4–13% of maternal deaths in Africa, Asia, Latin America and the Caribbean, and in 2013, obstructed labour alone accounted for 0.4 deaths per 100,000 women worldwide.

Assisted Vaginal Delivery – Historical Context

The invention and evolution of the obstetric forceps were pivotal in the development of the clinical art of obstetrics. They remain one of only a few surgical instruments that remain in use, albeit modified, more than three centuries after their introduction. In contrast, the vacuum extractor, while having its origins some 150 years ago, has only been developed in practical clinical terms over the past half century. Four important events mark the evolution of the obstetric forceps: (1) the invention, (2) the introduction of the pelvic curve, (3) the introduction of axis-traction devices and (4) the return to a modified ‘straight’ forceps for application to the low, transversely placed head.

The Invention of The Forceps

On 3 July 1569 a Huguenot refugee family by the name of Chamberlen disembarked at Southampton. William, the father, may not have been medically qualified but had two sons both named Peter (referred to as ‘Peter the older’ and ‘Peter the younger’) who were both barber surgeons. To add to the confusion there was a third Peter, a son of Peter the younger, known as ‘Dr Peter Chamberlen’, a Doctor of Medicine at Padua (1619), Oxford (1620) and Cambridge (1621) and a Fellow of the College of Physicians (1628). For ease we will refer to them using Peter I, II and III.

For many years invention of the obstetric forceps was attributed to Peter III (Dr Peter Chamberlen), who died in 1683. However, Peter I (1560?–1631) attained greater distinction, attending Anne of Denmark, Queen Consort of James I and other notable women in society in their confinements. For this he was prosecuted and incarcerated in Newgate Prison, but later released after the Queen’s intervention. His brother, Peter II (1572–1626), was also interested in midwifery and he was the first to suggest the creation of an ‘Incorporation of Midwives’. It is likely that Peter I invented the forceps in about 1600, but the secret was kept in the family for more than 100 years. Many attempts were made to trade the instrument in Paris and Amsterdam by Hugh Chamberlen Senior (son of Peter III) but it was not until well into the 18th century that the secret of the forceps became public knowledge. In 1818 a number of the Chamberlens’ instruments were discovered in a concealed chest in Woodham Mortimer Hall, Essex. The Chamberlens’ forceps illustrated in Fig. 15.1 were simple in design, possessing only a cephalic curve. They remained in this form and were regularly used for well over 100 years (1600?–1747). Further brief historical context describing changes to forceps design, the development of vacuum extraction and the invention of rotational forceps will be found in each of the subsequent three chapters.

Current Practice

Since its introduction to routine clinical practice, AVD has been the preferred tool of the accoucheur seeking to reduce maternal and neonatal morbidity in the second stage of labour. In a matched-cohort study, caesarean section (CS) at full cervical dilatation was associated with higher rates of major haemorrhage (>1 L; relative risk [RR] 2.8; 95% confidence interval [CI] 1.1–7.6) and extended hospital stay (≥6 days; RR 3.5; 95% CI 1.6–7.6) for mothers compared with those having vaginal delivery, and higher rates of admission for intensive care (RR 2.6; 95% CI 1.2–6.0) but lower rates of some types of trauma (RR 0.4; 95% CI 0.2–0.7) than for babies delivered by forceps.

Despite this good evidence of the overall benefit of AVD, rates and methods of AVD are highly variable both over time and between countries. AVD is currently performed with varying frequency in both high- and low-income countries. Rates of AVD in selected countries are shown in Fig. 15.2 . In addition to widespread low levels of utilization, some surveys found significant areas where AVD was not used at all – in 2006 this was the case in 17 of 23 Latin American and Caribbean countries, as well as 30% of countries in sub-Saharan Africa and 40% of countries in Asia.

Assisted Vaginal Delivery Within High-Income Countries

Rates of AVD appear to have remained broadly stable within many high-income countries, although the utilization of forceps versus vacuum has changed over time, with forceps declining and the vacuum rates increasing. For example, in the UK in 1980, the overall AVD rate was 12%, with 11.3% of all births being performed with forceps versus 0.7% performed by vacuum. By 2017 the overall rate of AVD was 12.8%, with 7.2% of all births performed by forceps and 5.6% performed by vacuum – this trend is shown in Fig. 15.3 (data adapted from NHS Maternity Statistics, annually from 1980 to 2016).

There has been a similar shift in Australia, where from 1991 to 2013 the overall AVD rate increased, from 12.5% to 18%, with forceps deliveries reducing from 10% of births to 7% while vacuum increased from 2.5% to 11%. However, in the USA rates of AVD (both forceps and vacuum) have consistently declined in the past 30 years, from a level broadly comparable with European countries (9% of all births in 1990) to a current low of 3.12% in 2015, of which forceps were only 0.56% – this trend is shown in Fig. 15.4 (data adapted).

Current Instruments for Assisted Vaginal Delivery and Associated Outcomes

Nonrotational forceps (Simpson, Rhode’s/Neville-Barnes, Anderson, Piper, Wrigley’s, etc.), solid mushroom cup vacuum (Malström, Bird and Kiwi), bell cup vacuum (silastic/silicone) and rotational forceps (Kielland forceps) are the most common obstetric instruments currently in use. The devices are associated with differing adverse outcome profiles and relative benefits for different clinical presentations (i.e. nonrotational versus rotational births), as well as specific differences between devices. The different profiles of benefits and risks of devices, and the variable experience in using them, have an impact on the utilization rates of not only the individual instruments, but also on AVD as a choice relative to CS.

Nonrotational Births

A ‘nonrotational’ birth is an AVD where the fetal head does not require rotation with an instrument by the accoucheur, either actively using rotational forceps/manual rotation or passively using rotational vacuum. In practice this means that the denominator should be no more than 45 degrees from the direct anterior position (e.g. in a vertex presentation, the position should lie between right and left occipitoanterior [ROA and LOA]). ‘Nonrotational’ births can be performed using nonrotational forceps, mushroom cup or bell vacuum. Forceps tend to be more successful and associated with less harm to the baby, but with overall higher morbidity for the mother. The most recent Cochrane review of 10 randomized trials involving 2923 women showed that the use of forceps was associated with a lower risk of failure when used as the primary instrument (RR 0.65) compared with vacuum. While this is an important finding, given the known significantly higher rates of maternal and neonatal adverse outcomes associated with the use of sequential instruments, other significant differences remain. Relative to forceps, vacuum is:

• more likely to be associated with cephalhaematoma (odds ratio [OR] 2.4; 95% CI 1.7–3.4)

• more likely to be associated with retinal haemorrhage (OR 2.0; 95% CI 1.3–3.0)

• more likely to be associated with maternal worries about baby (OR 2.2; 95% CI 1.2–3.9)

• less likely to be associated with significant maternal perineal and vaginal trauma (OR 0.4; 95% CI 0.3–0.5)

• no more likely to be associated with delivery by CS (OR 0.6; 95% CI 0.3–1.0)

• no more likely to be associated with low 5-minute Apgar scores (OR 1.7; 95% CI 1.0–2.8)

• no more likely to be associated with the need for phototherapy (OR 1.1; 95% CI 0.7–1.8) ¹⁶

• and possibly less likely to be associated with higher long-term morbidity as a result of pelvic organ prolapse, although this association has not been shown in recent population-level studies.

Despite the apparent superiority in most maternal and neonatal outcomes for forceps in nonrotational birth, the use of forceps is generally lower worldwide than vacuum.

Rotational Births

A ‘rotational’ birth is an AVD where the fetal head is rotated by the accoucheur, either actively using rotational forceps/manual rotation or passively using rotational vacuum. In practice, this means that the denominator lies more than 45 degrees from the direct anterior position (i.e. in a vertex presentation, the position will usually be occipitotransverse (OT) or occipitoposterior (OP). ‘Rotational’ births can be performed using a mushroom cup vacuum (Bird or Kiwi cup), rotational forceps or manual rotation followed by direct forceps birth (alternatively, vacuum is used). Remember that with successful manual rotation to occipitoanterior (OA) position, ‘deflexion’ is also corrected and this results in smaller presenting diameters. Asking the woman to push can result in a normal birth, especially in multiparous women.

Rotational births have long been perceived by accoucheurs as being proportionally more risky than nonrotational AVDs. The most recent RCOG guideline recommends that they should be conducted in the presence of an experienced operator and in a setting with immediate recourse to CS. Although small studies in the past have shown poorer neonatal outcomes following attempted rotational forceps births compared with CS, more recent, larger studies have shown that attempted rotational birth (using any of the three approaches) is not inherently more risky than second stage CS, with comparable outcomes to nonrotational AVD. This has generated a renewed interest in the technique for the management of malposition of the fetal head at full cervical dilatation.

Debate remains about the most effective instrument for rotation and delivery of the fetal head. While the relative efficacy of all three of these approaches has only been compared in one retrospective cohort study, other studies have examined outcomes for various combinations of two out of the three interventions.

Practical Aspects of Assisted Vaginal Delivery