What is the difference between fetal presentation and position?
In the womb, a fetus has both a presentation and a position. Presentation refers to the baby’s body that leads, or is expected to lead, out of the birth canal. For example, if a baby’s rear is set to come out of the birth canal first, the baby is said to be in “breech presentation.” Position refers to the direction the baby is facing in relation to the mother’s spine. A baby could be lying face-first against a mother’s spine, or face up towards the mother’s belly.
What way should a baby come out during birth?
Vertex presentation is the ‘normal’ way that a baby is positioned for birth and the lowest-risk presentation for vaginal birth. In vertex presentation, the baby is positioned head-first with their occiput (the part of the head close to the base of the skull) entering the birth canal first. In this position, the baby’s chin is tucked into their chest and they are facing the mother’s back (occipito-anterior position). Any position other than vertex position is abnormal and can make vaginal delivery much more difficult or sometimes impossible. If a baby’s chin isn’t tucked into their chest, they may come out face-first (face presentation), which can cause birth injury.
What happens if a baby isn’t in the standard vertex position during birth?
Before delivery, it is critical that the fetus is in the standard vertex presentation and within the normal range for weight and size. This helps ensure the safety of both baby and mother during labor. When the baby’s size or position is abnormal, physician intervention is usually warranted. This may mean simple manual procedures to help reposition the baby or, in many cases, a planned C-section delivery. The failure of healthcare professionals to identify and quickly resolve issues related to fetal size, weight, and presentation is medical malpractice. There are numerous complications related to abnormal weight, size, abnormal position, or abnormal presentation.
In the safest presentation (vertex presentation), the baby is born head first, with the rest of the body following. In a compound presentation, however, there are multiple presenting parts. Most commonly, this means that the baby’s head and an arm come out first at the same time. Sometimes compound presentation can occur with twins where the head of the first twin presents with the extremity of the second twin.
Limb presentation during childbirth means that the part of the baby’s body that emerges first is a limb, an arm or a leg. Babies with limb presentation cannot be delivered safely via vaginal delivery, they must be delivered quickly by emergency C-section. Limb presentation poses a large risk for dystocia (the baby getting stuck on the mother’s pelvis), which is a medical emergency.
Occipitoposterior (OP) position
Approximately 1 out of 19 babies present in a posterior position rather than an anterior position. This is called an occipitoposterior (OP) position or occiput posterior position. In OP position, the baby is head-first with the back part of the head turned towards the mother’s back, rotated to the right (right occipitoposterior position, or ROP), or to the left (left occipitoposterior position, or LOP) of the sacroiliac joint. Occipitoposterior position increases the baby’s risk of experiencing prolonged labor, prolapsed umbilical cord, and use of delivery instruments, such as forceps and vacuum extractors. These conditions can cause brain bleeds, a lack of oxygen to the brain, and birth asphyxia.
When OP position is present, if a manual rotation cannot be quickly and effectively performed in the face of fetal distress, the baby should be delivered via C-section. A C-section can help prevent oxygen deprivation caused by prolonged labor, umbilical cord prolapse, or forceps and vacuum extractor use.
Breech presentation is normal throughout pregnancy. However, by the 37th week, the baby should turn to the cephalic position in time for labor. Breech presentation occurs when a baby’s buttocks or legs are positioned to descend the birth canal first. Breech positions are dangerous because when vaginal delivery is attempted, a baby is at increased risk for prolapsed umbilical cord, traumatic head injury, spinal cord fracture, fatality, and other serious problems with labor.
A face presentation occurs when the face is the presenting part of the baby. In this position, the baby’s neck is deflexed (extended backward) so that the back of the head touches the baby’s back. This prevents head engagement and descent of the baby through the birth canal. In some cases of face presentation, the trauma of a vaginal delivery causes face deformation and fluid build-up (edema) in the face and upper airway, which often means the baby will need a breathing tube placed in the airway to maintain airway patency and assist breathing.
Brow presentation is similar to face presentation, but the baby’s neck is less extended. A fetus in brow presentation has the chin untucked, and the neck is extended slightly backward. As the term “brow presentation” suggests, the brow (forehead) is the part that is situated to go through the pelvis first. Vaginal delivery can be difficult or impossible with brow presentation, because the diameter of the presenting part of the head may be too big to safely fit through the pelvis.
Shoulder presentation (transverse lie)
Shoulder presentation (transverse lie) is when the arm, shoulder or trunk of the baby enter the birth canal first. When a baby is in a transverse lie position during labor, C-section is almost always used as the delivery method. Mothers who have polyhydramnios (too much amniotic fluid), are pregnant with more than one baby, have placenta previa, or have a baby with intrauterine growth restriction (IUGR) are more likely to have a baby in the transverse lie position. Once the membranes rupture, there is an increased risk of umbilical cord prolapse in this position thus, a C-section should ideally be performed before the membranes break. Failure to quickly deliver the baby by C-section when transverse lie presentation is present can cause severe birth asphyxia due to cord compression and trauma to the baby. This can cause hypoxic-ischemic encephalopathy (HIE), seizures, permanent brain damage, and cerebral palsy.