The transverse position, or transverse lie, can cause concern for expectant parents as the due date approaches. While this sideways orientation is common during early and middle pregnancy, it is not a safe position for delivery. If the baby remains in this orientation at full term, medical professionals must intervene. The primary goal is to encourage the baby to turn head-down or to plan a delivery method that avoids complications.
Defining Transverse Lie
Transverse lie describes a fetal position where the baby is lying horizontally across the mother’s abdomen, perpendicular to her spine. The baby’s longest axis is positioned at a right angle to the mother’s spine, with the head and feet pointing toward the mother’s sides. The part closest to the birth canal is typically the shoulder, sometimes leading this to be called a shoulder presentation.
This sideways position is normal for much of the pregnancy because the baby has ample space within the uterus to move freely. However, a transverse lie becomes a concern if it persists past 36 or 37 weeks of gestation, when the baby should ideally be settling into a head-down (cephalic) presentation. By term, the incidence is relatively rare, occurring in about one in 300 to one in 500 pregnancies. A persistent transverse lie makes a vaginal birth impossible and requires medical management.
The Primary Risks Associated with Transverse Position
The danger associated with a persistent transverse lie arises only if labor begins while the baby is still in this sideways orientation. Neither the baby’s head nor its buttocks are positioned to enter the pelvis and block the cervix, which is necessary for a safe vaginal delivery. A major acute risk in this situation is umbilical cord prolapse, considered an obstetric emergency.
Cord prolapse occurs when the membranes rupture and the umbilical cord slips down into the birth canal before the baby. Without a firm presenting part to fill the pelvic inlet, the cord can become compressed between the baby’s body and the mother’s pelvis. This compression can severely restrict the baby’s oxygen supply, leading to fetal distress or hypoxia. The risk of cord prolapse is significantly elevated in cases of transverse lie, with some sources estimating the risk as high as 20%.
Another serious complication is obstructed labor, which can lead to uterine rupture. If strong contractions begin with the baby lying sideways, the baby’s shoulder is forced into the pelvic inlet, and the baby cannot pass through the birth canal. This creates an absolute mechanical blockage. If labor is allowed to progress without intervention, the powerful contractions can tear the uterine wall, posing a risk to both mother and baby. A transverse lie must be resolved before the onset of labor.
Medical Approaches to Position Correction
When a transverse lie is confirmed late in the third trimester, the first step is often to attempt an External Cephalic Version (ECV). This non-surgical procedure manually turns the baby into a head-down position by applying firm pressure to the mother’s abdomen. ECV is typically scheduled around 37 weeks of gestation, as this timing balances the chance of the baby turning spontaneously against the risk of the baby reverting to the transverse position after a successful turn.
The procedure is performed in a hospital setting under careful monitoring, often using ultrasound guidance and continuous fetal heart rate monitoring. To help relax the uterine muscles and increase the chances of success, a tocolytic agent, such as terbutaline, may be administered before the attempt. ECV is generally safe, with a low rate of serious complications, and its success rate is around 58% for malpresentations overall.
Delivery Planning and Safety Measures
If the External Cephalic Version is unsuccessful or is medically contraindicated, a planned Caesarean section is the required delivery method for a persistent transverse lie at term. A vaginal delivery is simply not possible for a sideways-lying baby, and attempting one would lead to the severe risks of obstructed labor and uterine rupture. Healthcare providers will schedule the C-section before the onset of labor, typically near the due date, to prevent the mother going into labor spontaneously.
This preventative approach mitigates the risk of cord prolapse. Women with a persistent transverse lie are often recommended to be admitted to the hospital for close observation from about 37 weeks. This ensures immediate action can be taken if the membranes rupture or labor begins. If the water breaks before the scheduled delivery, the mother must go to the hospital immediately, as this event signals a high risk for cord prolapse and necessitates an emergency C-section.