Delivery presentations

medical animation:




Alternative names

Shoulder presentation; Malpresentations; Breech birth; Cephalic presentation; Fetal lie; Fetal attitude
Definition

Delivery presentation describes the way the fetus is positioned to come down the birth canal for delivery. The presentation is defined by fetal attitude, the presenting part, and maternal and fetal landmarks.

Information

THE DELIVERY PROCESS

The delivery process is described in terms of fetal station, lie, attitude, and presentation.

Fetal station:

This is the relationship between the presenting part, whether that be the head, shoulder, buttocks, or feet, and two parts of the maternal pelvis called the ischial spines. Normally the ischial spines are the narrowest part of the pelvis, and are a natural measuring point for the delivery progress. If the presenting part lies above the ischial spines, the station is reported as a negative number from 0 to -3 where each number is a centimeter. If the presenting part lies below the ischial spines, the station is reported as a positive number from 0 to 3 where each number is a centimeter. The baby is said to be "engaged" in the pelvis when it reaches 0 station.

Fetal lie:

This is the relationship between the head to tailbone axis of the fetus and the head to tailbone axis of the mother. If the two are parallel, then the fetus is said to be in a longitudinal lie. If the two are at 90-degree angles to each other, the fetus is said to be in a transverse lie. Nearly all (99.5%) fetuses are in a longitudinal lie.

Fetal attitude:

The fetal attitude describes the relationship of the fetus' body parts to one another. The normal fetal attitude is commonly referred to as the fetal position: the head is tucked down to the chest, with arms and legs drawn in towards the center of the chest. Abnormal fetal attitudes may include a head that is extended back or other body parts extended or positioned behind the back. Abnormal fetal attitudes can increase the diameter of the presenting part as it passes through the pelvis, increasing the difficulty of birth.

Fetal presentation:

Cephalic (head-first) presentation:

Cephalic presentation is considered normal and occurs in about 97% of deliveries. There are different types of cephalic presentation, which depend on the fetal attitude. If the fetus' head is extended back, then the chin, face, or forehead will exit first depending on the degree of extension. This is not considered preferable since this part of the fetal head is not the smallest, thus increasing the difficulty of the birth. Preferably the fetal head is flexed down to the chest resulting in a "vertex" delivery, in which the crown of the head exits first.

A cesarean delivery may be done for any fetal position other than cephalic.

Breech presentation:

Breech presentation is considered abnormal and occurs about 3% of the time. A complete breech birth occurs when the buttocks present first, and both the hips and the knees are flexed. A frank breech occurs when the hips are flexed so the legs are completely drawn up towards the chest. Other breech positions occur when either the feet or knees come first.

Shoulder presentation:

The shoulder, arm, or trunk may exit first if the fetus is in a transverse lie. This type of birth occurs less than 1% of the time. Transverse lie is more common with premature delivery or multiple gestations.

Forceps Delivery and Vacuum Extraction
What is a forceps delivery?
A forceps delivery involves the use of twin steel blades (forceps) to assist in the delivery of a baby. During childbirth, the physician inserts the forceps into the vagina and around the baby’s head. The blades are locked in place and, as the mother bears down, the physician uses them to pull the baby’s head through the vagina. The rest of the baby is delivered normally.

Forceps delivery is not routine and is usually done only in the following circumstances:

The baby’s head is lying on the mother’s pelvis, but fails to descend further
The mother is unable to push because of an epidural
The mother is exhausted
The baby is in a posterior position or is a breech birth
What is a vacuum extraction?
A vacuum extraction is an alternative to forceps delivery, and your physician will decide which is more appropriate for your circumstances. In this procedure, the physician uses an instrument called a vacuum extractor, which has a suction cup that is placed on the baby’s head. A vacuum is created using a pump, and the baby is pulled down the birth canal with the instrument and with the help of the mother’s contractions. The pump can often leave a bruise on the baby’s head.

The Food and Drug Administration notes that two life-threatening complications following the use of vacuum-assisted devices have been reported. These complications are subgaleal hematoma (bleeding in the space between the skull and the scalp) and intracranial hemorrhage (bleeding within the skull).

Be sure to discuss concerns you may have about any of these procedures with your doctor.