New Labor Guidance, Part 1
/Back in 2019 we did a two-part series on preventing the primary cesarean (part 1, part 2). That series was based on the joint ACOG/SMFM Obstetric Care Consensus #1. As of the January edition of the Green Journal, ACOG & SMFM have now issued revised guidance in Clinical Practice Guideline #8 that retires the old document and shakes some things up a bit!
In that spirit, we’ll review some definitions following CPG 8 and remark on some of the new changes as we go along.
Part two of CPG 8 also reviews evidence behind some ways to limit intervention in labor and delivery – we’ve podcasted on that before, too – but we’ll save that for a future episode.
Some definitions to get started:
Labor: onset of regular, painful uterine contractions resulting in cervical dilation, effacement, or both.
First stage: the time period from labor onset until full dilation (10 cm) is achieved. This is broken down into:
Latent phase: gradual, slow, early cervical change.
Active phase: time period of more rapid, predictable cervical change.
Second stage: the time period from complete dilation until delivery of the fetus, characterized by maternal pushing efforts.
Third stage: the time period from delivery of the fetus until delivery of the placenta.
How did we come up with these stages?
1950s: Emanuel Friedman publishes graphs of cervical dilation of 1,000 term patients admitted to the hospital in spontaneous labor, and describe the period of rapid cervical change that characterizes “latent” from “active” first stage, in addition to a “deceleration” phase near the end of first stage.
This transition from latent to active in his data was thought to occur at around 4cm cervical dilation.
The 95%ile for active phase dilation was 1.2 cm/h in nulliparas, and 1.5cm/h in multiparas.
2010: Zhang et al publish updated data using the Consortium for Safe Labor
Almost 63,000 term patients at 19 US hospitals with normal perinatal outcomes. Key takeaways:
The transition point from latent to active seemed to occur at around 6cm in both nulliparas and multparas, later than Friedman observed.
The rate of active phase cervical dilation was also slower than Friedman’s observations:
Nulliparas: 0.5 - 0.7 cm/h
Multiparas: 0.5 - 1.3 cm/h
Since 2010, multiple other studies using large data sets have been published – they’re too numerous to review, but in short, there seem to be several clinical factors that might affect labor progress.
Obesity
Hypertension
Gestational age
Multiple gestations
Presence of fetal anomalies
Fetal size
Fetal sex
Latent Phase of First Stage
In the Friedman curve, they demonstrated a 95%ile of latent phase length ranging from 14h in multiparas to 20h in nulliparas.
Subsequently, in the Zhang and other curves, the data was all over the place. A conservative 95th percentile, per ACOG, seems to be around 16 hours.
Likely, this has something to do more with when someone is admitted to the hospital, and characterizing the length of latent phase is difficult to do.
Prolonged latent phase is somewhat associated with adverse obstetrical outcomes, but
The vast majority of people who have prolonged latent phase will either:
1) stop contracting, or
2) achieve active phase, particularly with amniotomy or oxytocin augmentation.
Therefore, there is no recommendation for defining “arrest of latent phase” or “failed latent phase.”
As long as maternal and fetal status are appropriate, latent phase may continue.
Not changed from prior guidance.
What about induced labor and latent phase?
Induced labor is different - there is a definition of “failed induction of labor.”
Induced labor has a much longer potential latent phase, so the guidance is very conservative in order to maximize opportunities to get the patient into the active phase.
Recommendation: Oxytocin should be administered for a minimum of 12-18 hours after membrane rupture before deeming induction unsuccessful.
This recommendation is provided otherwise reassuring maternal/fetal status.
Going beyond 18 hours can be discussed with patients on an individual basis.
This recommendation is based on studies demonstrating only about 5% of patients remain in latent phase after amniotomy with oxytocin administration after 18h.
This is largely an unchanged recommendation, but the previous Obstetric Care Consensus mentioned waiting until 24 hours.
Acknowledged this was based on expert opinion.
So in the context of the CPG, shared-decision making is recommended rather than overtly recommending a 24 hour period after amniotomy to diagnose failed induction.
Active Phase of First Stage
ACOG definitively puts forth a recommendation: the active phase of labor is denoted at 6cm dilation.
This is based on the more conservative Zhang data
They acknowledge there may be a range of individualized starting points between 4-6cm based on individual patients.
The 6cm standard for active phase management allows as many as possible to be ruled in for active phase before the more stringent arrest definitions are applied.
Not changed from prior guidance (Obstetric Care Consensus).
ACOG defines active phase arrest in one of two ways:
No progression in cervical dilation after 6cm with rupture of membranes despite adequate contractions for 4 hours, or
No progression in cervical dilation after 6cm with rupture of membranes despite inadequate contractions and oxytocin augmentation for 6 hours.
Versus the old document, this is largely unchanged.
A protracted active phase can be conservatively defined as less than 1cm of cervical change in 2 hours.
They note slow, but progressive, labor in the first stage should not be an indication for cesarean:
A prospective study of over 300 patients with dysfunctional labor, when provided 4 additional hours of oxytocin, 50.7% of nulliparas and 41.7% of multiparas ultimately delivered vaginally.
This would have equated to a cesarean rate of over 35% without the additional time, versus just 18% with the additional time.
Since providing these recommendations in 2014 with the original Obstetric Care Consensus, real-life benefit to cesarean rates have been mixed / modest at best.
There is not much data at all regarding maternal/neonatal morbidity.
However, the CPG authors describe that this approach likely balances risks of prolonged labor with benefits of avoiding cesarean in a safe way, based on the best data available.
Managing an Abnormal First Stage of Labor
New to this document is an endorsement of an active management approach to the first stage of labor, which includes:
Standard criteria for diagnosis of arrest of labor
Early amniotomy
Administration of oxytocin for protracted labor
One-to-one nursing care
Studies of active management have not shown reduction in cesarean rates, but do point towards lower rates of maternal fever and shorter duration of labor.
Thus, knowing risks of protracted labor, ACOG endorses active management - new to this CPG and stands out as an addition versus the prior Obstetric Care Consensus.
Let’s review the components - we just talked about arrest definitions, so next we’ll talk:
Amniotomy
ACOG recommends amniotomy for patients undergoing augmentation or induction of labor to reduce the duration of labor.
An AHRQ-based systematic review of amniotomy in spontaneous labor determined that it helped reduce length of labor in nullliparas, without increasing risk for cesarean delivery, maternal infection, trauma to the pelvic floor, or postpartum hemorrhage.
There was no difference in rate of cord prolapse, either, in any of the randomized trials analyzed.
When should I perform amniotomy?
This in the literature is broken down into early vs late, where “early” is often defined as amniotomy as soon as feasible.
In one RCT, this was within 1 hour of Foley removal when used for cervical ripening, versus late being beyond 1 hour - higher rates of vaginal delivery within 24h and shorter labor duration in early group.
Another RCT - amniotomy concurrent with oxytocin starting, vs 4 hours after starting oxytocin – demonstrated shorter labor length in nulliparas and no effect on cesarean delivery rates.
Systematic review of four other RCTs of induced labor - average labor reduction of 5 hours, with similar rates of cesarean and no increasing risks of complications.
ACOG concludes that “there is high-quality evidence to recommend early amniotomy as adjunctive to the labor process” – a really significant new recommendation!
Oxytocin use
ACOG recommends either high-dose or low-dose oxytocin regimens as reasonable to use with active labor management to reduce operative deliveries.
Similar to amniotomy, ACOG first discusses early vs late oxytocin augmentation, where early is defined as starting oxytocin once prolonged active phase is identified:
A few meta-analyses demonstrate modest increases in likelihood of vaginal delivery and modest reduction in cesarean birth.
Probably of more controversy is the use of high-dose vs low-dose protocols.
Low dose protocols generally use a starting dose of 0.5 - 2.0 mU/min, and increase by 1-2 mU/min every 15-40 minutes.
High dose protocols use a starting dose of 4 mU/min or higher, and increase by 3-6 mU/min every 15-40 minutes.
The data does not demonstrate any improved or worsened outcomes with one approach versus another, so ACOG states either approach is reasonable.
The previously-mentioned AHRQ systematic review did demonstrate lower cesarean rates and no difference in hemorrhage for nulliparous patients undergoing high-dose protocols – worth a consideration.
ACOG also notes a maximum dose of oxytocin has not been established – that was news to me!
ACOG does add a recommendation to use IUPCs in patients with protracted active labor, or in those whose contractions cannot be monitored externally.
They note IUPCs are a useful tool to help titrate oxytocin while also not causing or increasing adverse events.
Recall, 200 Montevideo units (MVUs) define adequacy, when looking at contraction strength in a ten-minute period.
There is some limited evidence that cesarean delivery is more likely with lower MVUs; but these cut offs, patterns of contractions, and definition of adequacy all need more study!
