Protraction and arrest disorders: Clinical sciences

Protraction refers to labor progressing at a slower rate than expected, while arrest refers to the complete cessation of labor progress. Given the increased morbidity with prolonged labor and the need for C-section with labor arrests, it’s important to promptly recognize these disorders.

Your first step in evaluating patients for protracted or arrested labor is a focused history and physical. This includes evaluation of the 4 Ps: passage, meaning pelvis; passenger, meaning fetal size and position; power, meaning strength of contractions and maternal pushing efforts; and psyche, referring to the patient’s mental state and social support.

Risk factors for abnormal labor will influence these 4 Ps in a number of ways. Nulliparity can affect ‘passage’, since having a previous birth can open the pelvis for subsequent deliveries. Nulliparity may also affect the patient’s ‘psyche’ if they have insufficient support. Post-term pregnancy or gestational diabetes may result in a larger than average ‘passenger’, while intraamniotic infection and epidural analgesia can affect the ‘power’ of contractions and pushing efforts.

Physical exam findings may reveal risk factors like obesity, which increases the risk of a macrosomic ‘passenger’; or short stature, which is associated with a smaller pelvis. You may also note that the ‘passage’ space feels narrow, possibly from a prior pelvic fracture or simply because of genetic variation.

Additionally, the ‘passenger’ can impact labor if the fetus is macrosomic or in a non-occiput anterior position. A non-reassuring fetal heart rate pattern also raises the risk of protracted or arrested labor, because it limits your ability to target ‘power’ with labor augmentation using a uterotonic agent like oxytocin.

Once your history and physical are complete, assess the phase and stage of labor. Patients in the first stage, from the onset of labor until 10 centimeters dilation, can be further separated by labor phase. Patients are in the latent phase when cervical dilation is less than 6 centimeters. Now’s a good time to check how much time has passed since the onset of labor. If more than 20 hours passed in a nulliparous patient, or 14 hours in a multiparous patient, then we are talking about prolonged latent phase of labor.

There’s actually minimal risk during this time. If you do nothing, contractions usually either stop on their own or pick up and transition to active labor. Therefore, consider expectant management if there are no signs of maternal or fetal distress. You could send the patient walking for a few hours before rechecking the cervical dilation. Alternatively, you may let the patient go home after a single exam with instructions to return when contractions get stronger or if their water breaks.

Sometimes, the patient prefers or requires intervention. Latent labor can be quite painful, so you can offer therapeutic rest, which involves administering a narcotic or benzodiazepine. Usually, the patient can rest, and when they wake up, the contractions have either resolved, or the labor has progressed. Alternatively, you can augment the labor using oxytocin, or by performing an amniotomy to rupture their membranes. Remember that a prolonged latent phase is not an indication for a C-section!

Here are a couple of clinical pearls! When given correctly, oxytocin is very safe. Contraindications include drug hypersensitivity, a non-reassuring fetal status, and any contraindication to labor. Oxytocin should be titrated to the goal of at least moderate contractions every 2 to 3 minutes, depending on fetal tolerance. Avoid tachysystole, which is a contraction frequency of more than 5 in 10 minutes, or contractions lasting longer than 2 minutes, as there’s a risk of fetal distress, uterine rupture, and abruption.

Another important clinical pearl to know is that the latent phase can last 24 hours, or even longer if maternal and fetal status allow. To allow the best chance of vaginal delivery, be sure to administer oxytocin for at least 12 to 18 hours after membrane rupture before diagnosing a failed labor induction or augmentation.

Okay, let’s talk about patients in the active phase of the first stage, meaning between 6 and 10 centimeters of dilation. First, assess their rate of cervical change. Historically, labor progress was considered normal if the cervix dilated at least 1.2 centimeters per hour in nulliparous patients, and 1.5 centimeters per hour in multiparous patients. However, newer data shows that slower progress can occur without maternal or fetal harm.

So, for patients with very little to no cervical change beyond 6 centimeters of dilation, your diagnosis is a protracted first stage of labor. This doesn’t necessarily mean something is wrong, but you can consider intervening to increase the power and frequency of contractions.

Treatments require a reassuring maternal and fetal status because, if there’s fetal distress, intensifying contractions will worsen it. You might place an intrauterine pressure catheter, or IUPC, which helps you determine the strength of each contraction so you can titrate oxytocin augmentation to maximize contractions.