Zero station means that:

Zero station means that:

• A. The baby's presenting part is at the level of the mother's ischial spines
• B. The baby's presenting part is at the level of the mother's pelvic inlet
• C. The biparietal diameter of the fetal skull is at the level of the mother's iliac crests
• D. The baby's head is high in the pelvis and is still ballottable

Answer: (A)

Fetal descent is tracked relative to fixed pelvic landmarks, with the ischial spines serving as the zero reference point. When the presenting part is at the level of the ischial spines, that is zero station, meaning the head has engaged in the pelvis and is about midway through the birth canal. This position signals progression from high in the pelvis toward further descent and rotation. If the presenting part were at the pelvic inlet or above the spines, that would be a negative station, indicating the head is not yet engaged. A head that is high in the pelvis and ballottable shows it is not engaged, also not corresponding to zero station. The biparietal diameter at the iliac crests isn’t used as a station reference; it doesn’t describe the descent of the presenting part.

Fetal descent is tracked relative to fixed pelvic landmarks, with the ischial spines serving as the zero reference point. When the presenting part is at the level of the ischial spines, that is zero station, meaning the head has engaged in the pelvis and is about midway through the birth canal. This position signals progression from high in the pelvis toward further descent and rotation.

If the presenting part were at the pelvic inlet or above the spines, that would be a negative station, indicating the head is not yet engaged. A head that is high in the pelvis and ballottable shows it is not engaged, also not corresponding to zero station. The biparietal diameter at the iliac crests isn’t used as a station reference; it doesn’t describe the descent of the presenting part.