A digital cervical examination, performed late in pregnancy or during active labor, is a tactile assessment used to determine labor progress by measuring cervical dilation and effacement. This internal check also provides important information about the baby’s status, specifically the position and descent of the presenting part, which is typically the fetal skull. The sensation felt by the examiner’s fingers is a combination of the head’s bony structure and its relationship to the surrounding maternal pelvis.
The Direct Sensation of the Fetal Skull
When a caregiver’s fingers encounter the fetal skull through the dilated cervix, the initial sensation is that of a large, smooth, and very firm bony structure. Unlike the soft tissues of the body, the head provides a distinct resistance, often feeling like a tightly stretched, round object.
The most informative tactile features are the lines between the skull plates, known as sutures, and the “soft spots” where multiple plates meet, called fontanelles. Sutures feel like small, slightly raised ridges or grooves separating the individual skull bones, and their flexibility allows the bones to overlap for “molding” during descent through the birth canal. Fontanelles are small openings where the sutures intersect, and they are significant because they help identify the baby’s orientation.
Specifically, the posterior fontanelle is a small, triangular space where three suture lines meet, and it may feel like a small indentation that can admit a fingertip. The anterior fontanelle, located toward the front of the head, is a larger, diamond-shaped space formed by four sutures, though it is less frequently the presenting part in an ideal labor scenario. Identifying these unique features allows the examiner to confirm the presenting part is the vertex (the top of the head) and determine the baby’s rotation within the pelvis. The texture of the head can also be affected by a caput succedaneum, a fluid swelling on the scalp caused by pressure, which can make the bony landmarks less distinct and harder to identify.
Understanding Fetal Station and Descent
The feel of the head changes dramatically based on its vertical position within the pelvis, a measurement known as Fetal Station. Fetal station is a numerical scale that measures how far the baby’s presenting part has descended in relation to fixed bony protrusions in the mother’s pelvis called the ischial spines. These spines are the narrowest point of the mid-pelvis and are designated as the zero point (Station 0) on the scale.
When the presenting part is high in the pelvis and has not yet engaged, the station is measured in negative numbers. At these higher stations, the head may feel like it is floating or that it can be easily pushed up and away from the examining fingers.
When the widest part of the baby’s head has passed the pelvic inlet and is level with the ischial spines, the head is considered “engaged,” and the station is 0. As labor progresses and the head moves further down, the station progresses into positive numbers (+1, +2, etc.). At these positive stations, the head is much more prominent and firm to the touch, often filling the entire vaginal canal and no longer feeling mobile.
How Head Positioning Affects the Examination
Beyond its vertical descent, the baby’s orientation, or Fetal Position, significantly alters what the examiner feels. In the most favorable position, the occiput anterior (OA), the back of the baby’s head faces the mother’s abdomen, which means the most palpable part is the occiput, or the back of the skull. In this position, the small, triangular posterior fontanelle is typically the landmark felt first, indicating an optimal path for rotation and delivery.
If the baby is in an occiput posterior (OP) position, often called “sunny-side up,” the back of the head is facing the mother’s spine, and the face is oriented toward the mother’s abdomen. In this case, the larger, diamond-shaped anterior fontanelle or the brow may be encountered by the examiner’s fingers, which feels different from the smaller, more compact posterior fontanelle. An OP position may make the head feel less uniformly rounded and can be more challenging to assess accurately through a digital examination.
Other variations in head positioning, such as a deflexed head, where the baby’s chin is not tucked fully to its chest, present a different part of the skull. A brow presentation, where the forehead leads, or a face presentation, where the face is the presenting part, would feel less smooth and more irregular than a fully flexed vertex. Identifying these specific bony landmarks and their orientation helps the medical team determine the baby’s position and plan for labor.