When you are preparing for childbirth, you might hear your doctor mention various fetal positions. Whilst most expectant mothers know about breech or posterior positions, few have heard of asynclitism. Yet this fetal head position affects about 15% of first-time mothers during labour. So what is asynclitism in labour? Knowing about it can help you feel more prepared if your doctor mentions it during delivery. In many hospitals with experienced obstetricians, asynclitism is usually detected and managed safely. Understanding what it means and how it might affect your labour helps you stay informed.
Asynclitism occurs when your baby's head tilts to one side as it moves through your pelvis, rather than remaining straight. Think of it as your baby's head leaning toward one shoulder. Rather than entering the birth canal at the level of the birth canal, it comes through at an angle.
During normal labour, your baby's head should be "synclitic"—meaning the head stays straight and symmetrical. With asynclitism, the head tilts, making one side lower than the other. There are two types:
An asynclitic fetal head position actually starts out normal. In early labour—before 3 cm dilation—babies often enter the pelvis tilted to navigate around the base of your spine. This is nature's way of helping the baby fit. The problem occurs when the head stays tilted after 5 cm dilation. At this point, the baby should straighten out and rotate. When the head remains asynclitic, it has difficulty passing through the narrowest part of your pelvis. Think of it like trying to fit a tilted object through a narrow opening. A straight approach works better. The head of your baby, when tilted, has a larger diameter, making it difficult to pass.
There are several factors that lead to the causes of asynclitic position:
The shape of your pelvis can influence your baby's position during labour. If you have a narrow or unusually shaped pelvis, your baby's head may tilt to one side to find a better fit as it moves through the pelvis.
If your pelvic floor has uneven muscle and ligament tissue, it may cause your baby to tilt.
If your umbilical cord is shorter than average, it may prevent your baby from moving properly, making it difficult for the head to come out in a straight position.
Sometimes babies hold a hand near their face. This extra bulk beside the head can cause it to tilt.
Women carrying twins face a higher risk of asynclitism because space is limited.
The shape of your lower uterus can sometimes create a twist that causes the baby to angle sideways.
If your water breaks suddenly with a strong contraction, the baby's head can drop quickly, whilst still tilted, without time to straighten.
The diagnosis of asynclitism in labour happens through two methods:
During labour, your doctor performs internal examinations to check the cervical dilation and the baby's position. They can feel for asynclitism by noting that the cervix is thicker on one side, that the sagittal suture is off-centre, or that one side of the baby's head sits lower.
Vaginal exams aren't always accurate for diagnosing asynclitism. Individual skill varies among examiners.
Intrapartum ultrasound provides a much more accurate diagnosis. Studies show ultrasound is more reliable than vaginal examination for detecting asynclitism. On ultrasound, asynclitism appears as asymmetry in the baby's skull structures. The doctor looks for specific signs, sometimes called the "squint sign", in which one eye orbit is more visible, or the "sunset sign," in which certain brain structures appear tilted.
Asynclitism can prolong and complicate labour. The tilted head doesn't apply even pressure on the cervix, slowing dilation. You might dilate quickly to 7-8 cm, then progress slows. Pushing can take much longer. Many women report pain concentrated on one side of their hip or pelvis during contractions. If the position doesn't self-correct, you might need vacuum-assisted delivery, forceps delivery, or caesarean section.
Mild asynclitism often corrects itself. As labour progresses, many babies naturally straighten their heads. If asynclitism persists, position changes, walking, squatting, or gentle pelvic rocks might help. In some cases, your doctor might try gentle manipulation or assisted delivery.
Asynclitism might sound scary, but it usually gets better on its own. Most hospitals can check for it with ultrasound or by doing an internal exam. If you don’t have constant ultrasound during labour, just make sure your birth team is experienced and ask questions if things seem slow. Pain relief like an epidural does not cause asynclitism or make it worse. With good care and support, almost all women with asynclitism have a safe delivery.
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Asynclitic position has several causes: pelvic shape variations, uneven pelvic floor muscles, short umbilical cord, baby holding a hand near the face, multiple pregnancies, uterine shape, or sudden water breaking. Sometimes the exact cause isn't known. It's not caused by anything you did wrong. First-time mothers face a higher risk, possibly because pelvic muscles have not been stretched by previous births.
Asynclitism is diagnosed through vaginal examination and ultrasound. During internal exams, doctors feel for a thicker cervix on one side, an off-centre skull suture line, or uneven head descent. Ultrasound provides a more accurate diagnosis, revealing asymmetry in the baby's skull. Ultrasound is more reliable than vaginal examination, especially when there is skull moulding. Many hospitals now use intrapartum ultrasound to improve fetal position assessment.
Yes, an asynclitic position often prolongs labour. When a baby's head is tilted, it doesn't press evenly on the cervix, so labour can slow down. Many women find they get to 7-8 cm quickly, then things start moving slower. Pushing can take longer, too, and the whole process might last a few extra hours. Around 15% of first-time mums go through asynclitism and might need some extra help, but most still have a vaginal birth with good support and patience.
Symptoms include slower-than-expected dilation (often stalling at 7-8 cm), a prolonged pushing stage, one-sided hip or pelvic pain during contractions, irregular contractions, and an asymmetric baby bump appearance. Many women with asynclitism have no noticeable symptoms. The condition is usually detected by healthcare providers through examination or ultrasound rather than by symptoms you would notice yourself.
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