Fetal Malpresentation



Fetal Malpresentation


Dana R. Canfield

Robert M. Silver



Introduction

In the past, many cases of fetal malpresentation were managed with safe vaginal deliveries. However, over the past several decades, an increasing percentage of such cases results in cesarean deliveries. This has caused decreased patient satisfaction as well as an increase in cesareans, leading to further complications such as placenta accreta spectrum. Accordingly, an understanding of the causes and management of fetal malpresentation claims a renewed importance. Among the leading indications for cesarean delivery both nationally and internationally, malpresentation is also potentially modifiable. Risk factors for breech, face, brow, and compound presentation, as well as transverse lie are similar and include multiparity, polyhydramnios, and fetal and uterine anomalies. With proper management in the hands of appropriately trained clinicians, the need for cesarean delivery may be safely reduced or prevented in many cases. This chapter discusses opportunities for facilitating safe vaginal birth with both singleton and multiple pregnancies with particular attention paid to external cephalic version (ECV), vaginal breech delivery, and the role of simulation in teaching these procedures.


Terminology and Etiology

In order to discuss malpresentation, a clear understanding of the issue rests in understanding the proper terminology. Lie describes the orientation of the fetal spine with respect to the spine of the mother, whereas presentation refers to the fetal part overlying the pelvic inlet (Figure 46.1A and B). As a fetus grows and matures, the fetal body will generally align itself vertically so that the fetal spine runs parallel to the maternal spine, termed longitudinal lie. As this occurs, the fetal head will generally descend into the pelvis as the presenting part, termed cephalic presentation. Deviations from longitudinal lie, cephalic presentation, or both are grouped and collectively constitute malpresentation or breech.

There are several types of breech. Extension at the hips of one (single) or both (double) legs results in a footling breech (Figure 46.2). If the legs are flexed at both the hips and the knees, it is a complete breech (Figure 46.3). A frank breech occurs when the fetal legs are flexed at the hips and extended at the knees (Figure 46.4).

Malpresentation is common, affecting 3% to 5% of singleton gestations at term.1,2 To better understand risk factors for malpresentation, it is important to note that for a fetus to be longitudinal and cephalic at term, several conditions must be met. First, as the delivery date approaches, the fetal head must have the space and mobility to navigate its way into the pelvis. When this has been achieved, it must engage with the pelvis as the spine remains relatively longitudinal, which involves flexion of the neck and a certain degree of immobility. Risk factors can thus be grouped by the role that they play in preventing this process.

Maternal factors that restrict the initial descent of the fetal head include abnormal placentation, myomata, Müllerian abnormalities, and syncytium. Fetal factors that inhibit flexion of the neck due to decreasing muscle tone, strength, and activity include aneuploidies, myotonic dystrophy, and skeletal abnormalities. In addition, fetal malformations, such as neck masses or hydrocephalus with macrocephaly, are associated with malpresentation. Lastly, prematurity, increasing maternal parity, and polyhydramnios increase fetal mobility by increasing the volume of amniotic fluid relative to the size of the fetus, preventing sustained engagement.








SINGLETON PREGNANCY MALPRESENTATIONS


Breech Presentation

Complicating 3% to 4% of term pregnancies,3 breech presentation is the most common type of malpresentation. The main risks of vaginal breech delivery include occlusion of the umbilical cord, delivery of the body with entrapment of the fetal head (possibly leading to brain injury or death), and trauma to fetal limbs. Although vaginal delivery of term breech pregnancies was once common,
the Term Breech Trial in 2000, which demonstrated that planned cesareans can decrease the risk of perinatal and neonatal mortality or serious morbidity (1.6% for planned cesarean versus 5.0% for planned vaginal delivery), had a dramatic effect on rates of cesarean for breech presentation. Following this trial, there was a substantial increase in cesarean breech deliveries around the world, with the rate increasing from 75% in 1999 to 86% in 2001 in Sweden and from 50% to 80% in the Netherlands in only 2 months after its publication.4 However, 2 years later, a follow-up study of the same neonatal cohort showed no difference in composite outcome of neonatal death and neurodevelopmental delay between children delivered vaginally and those by cesarean (3.1% in the vaginal delivery group compared to 2.8% in the cesarean group).5
















A 2015 Cochrane review comparing planned cesarean with planned vaginal delivery echoed the Term Breech Trial findings by showing a reduced risk of perinatal or neonatal death (relative risk [RR] 0.29%, 95% [confidence interval] CI 0.10-0.86 for three studies including 2396 participants).6 A meta-analysis further supported the findings, showing a twofold to fivefold higher risk of perinatal mortality and morbidity in planned vaginal delivery compared to planned cesarean delivery, with absolute risks of perinatal mortality of 0.3%, fetal neurologic morbidity of 0.7%, birth trauma of 2.4%, 5-minute Apgar scores of <7 of 2.4%, and neonatal asphyxia of 3.3% in planned vaginal delivery groups (27 articles, 258,953 participants).7

It is worth noting that while these findings strongly indicate a reduced relative risk of adverse neonatal outcomes associated with planned cesareans when compared to planned breech delivery, absolute risk remains quite low. Taking this into account, the American College of Obstetricians and Gynecologists (ACOG) released a committee opinion in 2006 recommending a case-by-case evaluation of the safety of vaginal singleton breech delivery.8 There was an interim update to this committee opinion in 2015, which reiterated that planned vaginal delivery of a term singleton breech fetus may be reasonable under hospital-specific guidelines and that the decision about delivery should consider patient wishes and the experience of the healthcare clinician.

However, the ACOG committee opinion does not address breech presentation in preterm deliveries. Most experts advise cesarean delivery for fetuses between 600 and 1500 g (often 24-32 weeks gestation) due to an increased risk for head entrapment owing to increased head to body size ratios. In addition, preterm fetuses are fragile, and their limbs are vulnerable to trauma. A systematic review and metanalysis from 2017 found a decrease in odds of death of 41% for infants undergoing cesarean compared to vaginal breech delivery between 23 0/7 and 27 6/7 weeks’ gestation; the same review noted a 49% decrease in odds of severe ventricular hemorrhage for the cesarean groups.9

These studies are all prone to considerable bias in which clinicians choose cesarean and which clinicians choose vaginal delivery. In addition, there is a much higher baseline rate of overall complications for preterm breech deliveries compared to term deliveries. Nonetheless, infants in this gestational age epoch are typically delivered by cesarean when there is a desire to optimize fetal outcomes. Delivery of a breech fetus weighing less than 600 g at a periviable gestational age (eg, 22 0/7-25 6/7 weeks) poses additional challenges. Vaginal delivery of these fetuses may not be associated with worse outcomes than cesarean delivery, and cesarean often requires a classical incision, which may have adverse effects on the mother in subsequent pregnancies. In addition, the infant is at very high risk for mortality and short-term and long-term morbidity. Accordingly, many patients opt for vaginal delivery with breech presentation between 23 and 25 weeks’ gestation.



External Cephalic Version

In situations where a vaginal delivery is desired, ECV is an evidence-based, low-risk method of converting a fetus in a breech to a cephalic presentation. Given the relatively high success rates and low risks of complications, ECV should be considered a first-line strategy for breech presentation. Per the ACOG Committee Opinion Interim Update in 2015, patients with a term singleton breech fetus without contraindications to the procedure should be offered an ECV, as the small risk of adverse outcomes is significantly lower in women who have successful ECV and outweighs the risks associated with a cesarean delivery.8 A Cochrane review from 2015 demonstrated a reduction in noncephalic presentation at birth (RR of 0.42, 95% CI 0.29-0.61, including 8 trials and 1305 participants), inability to achieve vaginal cephalic birth (RR 0.46, 95% CI 0.33-0.62, including 7 trials and 1253 participants), and cesarean delivery (RR 0.57, 95% CI 0.40-0.82, including 8 trials and 1305 participants) following attempted ECV. This review found no significant differences in Apgar scores, umbilical vein pH levels, neonatal intensive care unit admission, perinatal death, or time from enrollment to delivery.10 Indeed, ECV offers a critical opportunity to lower the rate of primary cesareans, with one case-controlled study discovering that 22,161 cesarean deliveries in the United States could be avoided annually by offering this intervention, assuming a 3.5% breech rate, 50% ECV attempt rate, and 47% success rate.11


Candidate Selection and Preparation for ECV

Although it is low risk and highly effective, ECV does have some relative and absolute contraindications. Among the most widely cited are oligohydramnios, fetal growth restriction, abnormal fetal heart rate tracings, uterine anomaly, ruptured membranes, hypertension of pregnancy, and antepartum bleeding. Some, including anterior placenta and oligohydramnios, are only cited because of their association with a decreased success rate. Others are based on scant or poor-quality evidence, with one systematic review finding data regarding only 6 of 39 mentioned contraindications; five of these six were dismissed based on a low level of supporting evidence.12

While the aforementioned contraindications may be more theoretical than evidence-based and are, therefore, considered relative, there are a small number of absolute contraindications. Although rare, and despite a lack of evidence, extreme caution should be used in offering ECV to women with a history of abruption and preeclampsia with severe features and should be avoided when abruption is clinically suspected. Similarly, severe fetal growth restriction or known fetal compromise should be considered absolute contraindications.12

In predicting the success of an ECV, there are several factors, both modifiable and nonmodifiable, that are considered favorable. Those that are static include multiparity, palpable fetal head, and maternal weight <65 kg,13 as well as posterior placenta, decreased amniotic fluid volume, and a high presenting part. Tocolytics and neuraxial anesthesia are controllable factors that improve rates of success because they have been shown to increase the rate of successful ECV in both multiparous and primiparous women (RR 1.38, 95% CI 1.03-1.85, 25 trials).14 When comparing tocolytic agents, terbutaline resulted in a lower cesarean rate than nifedipine in a randomized trial (56.5% vs 77.3%).15

More recently, neuraxial anesthesia has been proposed as a method for enhancing probability of success for ECV. A 2016 systematic review and meta-analysis of randomized controlled trials found that neuraxial anesthesia use was associated with a significantly higher rate of success (58.4% vs 43.1% with a RR of 1.44, 9 trials, 934 participants).16 Although anesthesia for ECV is associated with increased initial costs, multiple studies have shown overall cost savings with use of neuraxial anesthesia due to a decrease in the cesarean delivery rate.17,18 For example, one study using cost modeling estimated a cost savings in the United States if anesthesia increases success rate by >11% over a presumed baseline of 38%.17 On the other hand, success rates in some centers are higher than 38% and it may be cost-effective to reserve neuraxial anesthesia for failed attempts rather than using it as a first-line approach.

As with any obstetric procedure, counseling patients about risks is critical. In weighing the decision of whether to attempt ECV or proceed with a planned cesarean, patients should be aware of common risks as well as more unusual but serious complications. A systematic review of 44 studies demonstrated that the most common complication is a transient abnormal fetal heart rate pattern, occurring in 5.7% of cases.19 Rare but more serious complications include persistent pathological heart rate pattern (0.37%), placental abruption (0.12%), and vaginal bleeding (0.47%).19 Emergency
cesareans were only performed in 0.43% of cases,16 but patients should be prepared for this possibility.

Rate of operative delivery may be higher after ECV.20,21,22 Reasons are uncertain but may relate to biological differences in breech and cephalic fetuses. Differences in fetal heart rate patterns, lower fetoplacental ratio, and smaller head circumference may contribute to signs of “fetal distress” that prompt clinicians to intervene earlier,20,21,22 while increased risk of nonengagement and asynclitism of fetal head may also prompt operative intervention and are positive predictive factors of success in ECV.20

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Jun 19, 2022 | Posted by in OBSTETRICS | Comments Off on Fetal Malpresentation
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