During labor, healthcare providers monitor a baby’s progress using two distinct measurements that track movement through the birth canal. Cervical dilation tracks how wide the cervix is opening to allow the baby to pass. The second measurement is the baby’s descent into the pelvis, monitored by fetal station. Fetal station provides a standard way to track the baby’s movement downward and predict the likelihood of a vaginal delivery.
What is Fetal Station
Fetal station is a standardized measurement determining how far the baby’s presenting part, typically the head, has moved into the mother’s pelvis. This measurement is relative, relying on specific, consistent anatomical landmarks within the pelvic structure. As the baby moves down with the force of contractions, the fetal station number changes, signaling that delivery is approaching.
The assessment is typically performed by a doctor or midwife during a vaginal examination. By feeling the baby’s head in relation to the internal bony structures, the provider assigns a numerical value to the baby’s position.
The Significance of Zero Station
The concept of “0 Station” is central to understanding the baby’s descent during labor. It defines the moment when the baby’s lowest bony part is aligned with the ischial spines, which are bony prominences located about halfway down the pelvic cavity. These spines represent the narrowest point the baby must pass through for a vaginal birth. When the baby’s presenting part is level with these spines, the fetal station is designated as zero.
Reaching 0 Station signifies a milestone called “engagement,” meaning the largest diameter of the baby’s head has successfully entered the pelvic inlet. For many first-time mothers, this engagement may occur weeks before labor begins, but for others, it happens during active labor.
Mapping Descent The Plus and Minus System
The fetal station is tracked using a numerical scale that maps the baby’s position relative to the zero point. This system uses negative numbers for positions above the ischial spines and positive numbers for positions below them, typically ranging from -5 to +5. Negative numbers, such as -3 or -2, indicate that the baby’s head is still high, or “floating,” in the pelvis. As the baby descends, the numbers progress toward zero, indicating movement deeper into the pelvis. A station of +4 or +5 means the baby’s head is visible at the vaginal opening, often referred to as crowning, and delivery is imminent.
Why Station is Critical to Delivery Planning
Tracking fetal station provides medical teams with information for guiding the labor and delivery process. Station, along with dilation, allows providers to evaluate the rate of labor progression. A lack of change in station over time, even with regular contractions, can signal an “arrest of descent,” which may require intervention. The station measurement also influences decisions regarding when the mother should begin pushing, as waiting until the baby is at a lower station, such as +1 or +2, can shorten the pushing phase. Furthermore, a positive fetal station is a prerequisite for safely performing assisted deliveries, such as using forceps or a vacuum extractor.