Will delivery be difficult if the baby's head is large? Mothers hoping for a natural birth often worry about this. In reality, whether the baby can be born smoothly depends closely on the baby's head size and the mother's pelvis. Only when these two parts are well-matched can delivery proceed smoothly. Let's explore the relationship between the fetal head and the pelvis during childbirth.
During routine prenatal checkups, the fetal head size data we obtain is based solely on the biparietal diameter measured by ultrasound, supplemented by the head circumference measurement. However, the fetal skull is covered by skin, hair, and other tissues approximately several millimeters thick. Therefore, there is a difference of several millimeters between the actual size and the measured value.
The fetal position during passage through the birth canal: The chin tucks against the chest, and the head emerges from the posterior part of the skull first.
Both the fetal skull and the mother's pelvis must adapt to each other for delivery to proceed smoothly. Moreover, the fetal position during passage through the birth canal must also cooperate.As the fetus enters the mother's pelvis, it curls its body and begins entry from the back of the head. At this point, the fetus's face faces the mother's side, then rotates downward while gradually turning its cheek toward the mother's back. Upon reaching the end of the birth canal, the fetus tilts its head backward. The mother may feel as if a large ball suddenly wedges between her legs.Once this phase is passed, the baby's head emerges, and the rest of the body follows relatively smoothly.
(1) Crown Presentation
When the fetal head is about to emerge
During the mother's pushing efforts, the top of the fetal head becomes visible—this is called crown presentation. During this stage, the mother must use abdominal pressure (similar to straining during bowel movements) to push the baby out, making it an extremely strenuous process.
(2) Crown Presentation
When the baby tilts its head back, and both the head and face emerge
The mother can see the baby's head even without pushing. This stage is called crown presentation. At this point, the baby is almost born.
Sometimes "abnormal rotation" occurs.
Because the entrance to the birth canal is elliptical, with the transverse diameter longer than the anteroposterior diameter, the fetus must first enter sideways with its face toward one side. As it advances forward, it gradually rotates downward through the bony birth canal, following the curved shape of the pelvis.
The fetal face eventually turns backward, a process called "fetal head rotation."
If this rotation doesn't proceed smoothly, the head may struggle to enter the pelvis even when positioned downward. When the fetal face is oriented toward the mother's abdomen, rotation can be difficult. However, in many cases, if contractions progress well, the position often returns to normal.
However, if fetal heart rate begins to drop or the mother becomes exhausted to the point of physical collapse, it may sometimes be necessary to switch to a cesarean delivery midway.
Reminder: Mothers must cooperate with pushing to ensure a smooth delivery.
If contractions are regular and uterine contractions are strong, even a relatively large fetal head can pass smoothly through the bony and soft birth canal to be born.When the cervix is fully dilated, mothers often feel the urge to push, leading to involuntary straining. At this point, the doctor will instruct you on how to coordinate pushing with contractions. Remember: Following the doctor's guidance to push effectively during contractions is crucial for helping the baby deliver quickly. Therefore, the mother's active participation in pushing is essential.
Vacuum extraction may be necessary
Sometimes prolonged labor causes the mother's strength to wane, leading to weakened contractions or a drop in fetal heart rate. In such cases, the baby needs to be delivered quickly, and vacuum extraction may be performed. This involves placing a cup-shaped suction device on the top of the baby's head and applying suction 2-3 times. It is a minor medical intervention, and its use does not indicate any abnormality.