Makajeva Julija, Ashraf Mohsina
Vilnius University, Lithuania, Imperial London Healthcare NHS Trust
University of Health Sciences, Rawalpindi Medical College
The term "presentation" refers to the part of the fetus or the fetal anatomical structure closest to the maternal pelvic inlet during labor. Presentations can be categorized into 4 primary classifications: cephalic, breech, shoulder, and compound. Of these, cephalic presentation is the most common and can be further subclassified into vertex, sinciput, brow, face, and chin. The vertex presentation, where the fetal neck is flexed to the chin, minimizing the head's circumference, is the most common presentation in term labor. Face presentation is an abnormal cephalic presentation where the mentum (chin) is the presenting part. This presentation typically occurs due to hyperextension of the fetal neck, with the occiput (back of the head) touching the fetal back. The incidence of a face malpresentation is rare, occurring in approximately 1 in 600 of all presentations. Brow presentation occurs when the neck is less extended than in face presentation, with the presenting fetal part being the area between the anterior fontanelle and the orbital ridges. Brow presentation is considered the rarest form of malpresentation, with a prevalence of 1 in 500 to 1 in 4000 deliveries. Both face and brow presentations result from extension of the fetal neck instead of flexion. Conditions that lead to hyperextension or prevent neck flexion can contribute to these presentations. Maternal risk factors include preterm delivery, a contracted maternal pelvis, a platypelloid pelvis, multiparity, or a history of previous cesarean delivery. Black pregnant patients have a higher incidence of face and brow presentation than other ethnic groups. Fetal risk factors for face or brow presentation include anencephaly, multiple loops of the umbilical cord around the neck, neck masses, macrosomia, and polyhydramnios. These malpresentations are typically diagnosed during the second stage of labor via a digital examination. During the examination, it is possible to palpate the orbital ridges, nose, malar eminences, mentum, mouth, gums, and chin in cases of face presentation. Based on the chin's position, face presentation can be categorized as mentum anterior, posterior, or transverse. In brow presentation, the anterior fontanelle and face can be felt, but not the mouth and chin. Brow presentation can also be described based on the anterior fontanelle's position as frontal anterior, posterior, or transverse. Diagnosing the exact presentation can be challenging, and face presentation may sometimes be misidentified as frank breech. Bedside ultrasonography can be performed to confirm which malpresentation is present. Ultrasonography can reveal a reduced angle between the occiput and the spine or show that the chin is separated from the chest. However, ultrasonography does not provide significant predictive value regarding the outcome of labor.
“先露”一词指分娩时胎儿或胎儿解剖结构中最靠近母体骨盆入口的部分。先露可分为4种主要类型：头先露、臀先露、肩先露和复合先露。其中，头先露最为常见，可进一步细分为顶先露、额先露、眉先露、面先露和颏先露。顶先露时胎儿颈部向颏部屈曲，使头部周长最小化，是足月分娩中最常见的先露类型。面先露是一种异常头先露，以颏部（下巴）为先露部位。这种先露通常是由于胎儿颈部过度伸展，枕部（后脑勺）触及胎儿背部所致。面先露的发生率很低，在所有先露中约为1/600。眉先露发生时颈部伸展程度低于面先露，胎儿先露部位为前囟门与眶嵴之间的区域。眉先露被认为是最罕见的异常先露形式，在分娩中的发生率为1/500至1/4000。面先露和眉先露均由胎儿颈部伸展而非屈曲所致。导致过度伸展或阻止颈部屈曲的情况可导致这些先露。母体危险因素包括早产、母体骨盆狭窄、扁平骨盆、多胎妊娠或既往剖宫产史。黑人孕妇面先露和眉先露的发生率高于其他种族群体。面先露或眉先露的胎儿危险因素包括无脑儿、脐带绕颈多圈、颈部肿物、巨大儿和羊水过多。这些异常先露通常在分娩第二产程通过指诊诊断。检查时，面先露情况下可触及眶嵴、鼻子、颧突、颏部、嘴、牙龈和下巴。根据颏部位置，面先露可分为颏前位、颏后位或颏横位。眉先露时可摸到前囟门和面部，但摸不到嘴和下巴。眉先露也可根据前囟门位置描述为额前位、额后位或额横位。准确诊断先露类型可能具有挑战性，面先露有时可能被误诊为臀先露。可进行床边超声检查以确认存在哪种异常先露。超声检查可显示枕部与脊柱之间的角度减小或显示下巴与胸部分离。然而，超声检查对分娩结局没有显著的预测价值。
