Labour Dystocia

Introduction[edit|edit source]

Labor dystocia(LD) is a labor complication where the labor process is abnormally slow or prolonged. It is common in nulliparous women and may disrupt the the process of vaginal delivery making it a major indication for instrumental deliveries or/ and cesarean section (CS) Lowe NK: A Review of factors associated with dystocia and Cesarean section in nulliparous women. J Midwifery womens health. 2007,52(3):216-228 .LD is diagnosed in the first stage of labor (onset of contractions until complete cervical dilation) or the second stage of labor (complete cervical dilation until delivery). Labour dystocia(LD) can not be described without describing the normal labor process. Normal labor is described as uterine contractions that leads to progressive dilation and effacement of the cervix. Caused by fetal malposition, inadequate contractions, poor maternal efforts, or true cephalopelvic disproportion. (Shields SG, Ratcliffe SD, Fontaine P, Leeman L. Dystocia in nulliparous women. Am Fam Physician. 2007 Jun 1;75(11):1671-8. PMID: 17575657.) LD may increase the risk for maternal and neonatal infection, fetal distress, neonatal hypoxia, uterine rupture, and postpartum hemorrhage(Myers ER, Sanders GD, Coeytaux RR, et al. Labor Dystocia [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2020 May. (Comparative Effectiveness Review, No. 226.) Peer Reviewers. Available from:https://www.ncbi.nlm.nih.gov/books/NBK557143/它也可能increase the risk of maternal pelvic floor and genital trauma.(Sheiner E, Levy A, Feinstein U, et al. Risk factors and outcome of failure to progress during the first stage of labor: a population-based study. Acta Obstet Gynecol Scand. 2002 Mar;81(3):222–6. PMID: 11966478. ) Management of LD can significantly affect the outcome of the delivery process.

Pathophysiology[edit|edit source]

LD is a result of problems with: Powers: Poor uterine contraction is a major cause of LD. The force/power of uterine contractions are not strong enough to efface and dilate the cervix in the first stage of labor this significantly affects the progression of labor.

Passenger: The fetus travelling down the birth canal is know as the passenger. LD may occur if the fetal head is too large in proportion to the mother’s pelvis, or when fetal presentation is abnormal.

Passage: The mother's pelvis is referred to as the passage. If the fetal head is large in proportion to mother's pelvis or there is a structural abnormality caused

Diagnosis of Labor dystocia[edit|edit source]

Prolonged latent phase The Latent phase is defined as exceeding 20 hours in patients who are nulliparas or 14 hours in patients who are multiparas. The most common reason for prolonged latent phase is entering labor without substantial cervical effacement. Power For the active phase of labor to be considered adequate, the uterine contractile force produced must exceed 200 MVUs/10 min for An arrest disorder of labor cannot be diagnosed until the patient is in the active phase and the contraction pattern exceeds 200 MVUs for 2 or more hours with no cervical change. Extending the minimum period of oxytocin augmentation for active-phase arrest from 2 up to 4 hours may be considered as long as fetal reassurance is noted with fetal heart rate monitoring.

Pelvis or the size of the passageway inhibiting delivery The shape of the bony pelvis (eg, anthropoid or platypelloid) can result in abnormal labor.

A patient who is extremely short or obese, or who has had prior severe trauma to the bony pelvis, may also be at increased risk of abnormal labor.

Size and/or presentation of the infant Abnormal labor could also be secondary to the passenger, the size of the infant, and/or the presentation of the infant. In addition to problems caused by the differential in size between the fetal head and the maternal bony pelvis, the fetal presentation may include asynclitism or head extension. Asynclitism is malposition of the fetal head within the pelvis, which compromises the narrowest diameter through the pelvis. Fetal macrosomia and other anomalies (including hydrocephalus, encephalocele, fetal goiter, cystic hygroma, hydrops, or any other abnormality that increases the size of the infant) are likely to cause deviation from the normal labor curve.

其他因素,其他因素包括一个低音dose epidural or combined spinal-epidural anesthetics that minimize motor block and may contribute to a prolonged second stage. These have also been associated with an increase in oxytocin use and operative vaginal delivery. However, use of epidural for analgesia during labor does not result in a statistically significant increase in cesarean delivery. [15] Intravenous oversedation has also been implicated as prolonging labor in both the latent and active phases.

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References[edit|edit source]

Lowe NK: A Review of factors associated with dystocia and Cesarean section in nulliparous women. J Midwifery womens health. 2007,52(3):216-228 .