The baby’s position within the uterus, or fetal lie, determines the safety and method of delivery. By the end of pregnancy, the baby typically settles into a vertical position, ideally head-down toward the birth canal. A transverse lie is an uncommon but significant deviation where the baby is situated sideways, presenting a serious challenge to natural birth.
Defining Transverse Lie
A transverse lie describes a fetal position where the baby is situated horizontally across the mother’s abdomen, making the baby’s spine perpendicular to the mother’s spine. This is in contrast to the desirable longitudinal lie, which includes the common cephalic (head-first) presentation and the less common breech (bottom-first) presentation. In a transverse lie, the shoulder, arm, or back is often positioned over the entrance to the pelvis, sometimes referred to as a shoulder presentation. This sideways orientation is common during early pregnancy when the baby has ample space to move freely. The position only becomes a clinical concern if it persists into the late third trimester, typically after 36 to 37 weeks of gestation, because a persistent transverse lie at term makes vaginal delivery impossible.
Factors Contributing to Transverse Lie
A number of specific maternal and uterine factors can prevent the baby from settling into a vertical, head-down position before labor begins. A history of multiple previous pregnancies, known as high parity, is a frequent contributor because the uterine and abdominal muscles may become lax, allowing the baby more room to move and settle sideways. This uterine laxity reduces the tone that encourages a longitudinal alignment. An abnormal amount of amniotic fluid can also influence the baby’s final position. Polyhydramnios, or excessive amniotic fluid, provides too much space, enabling the baby to remain in an unstable or transverse position late in the pregnancy. Conversely, structural issues within the uterus, such as a bicornuate uterus or large uterine fibroids, can physically restrict the space and force the baby into a horizontal lie. Another physical obstruction is placenta previa, where the placenta partially or completely covers the cervical opening. The placenta prevents the baby’s head from descending and engaging in the pelvis, predisposing the baby to a transverse or breech presentation. Multiple gestations, such as twins, also restrict the available space, increasing the likelihood that one or both babies will be found in a non-longitudinal lie.
Diagnosis and Associated Risks
A transverse lie is often first suspected during a routine prenatal physical examination by using Leopold’s maneuvers, which involve systematically feeling the abdomen to determine the baby’s position. The practitioner may be unable to palpate the firm fetal head or buttocks in the upper or lower poles of the uterus, instead feeling a pole on one side and an empty space above the pelvis. An ultrasound is then used to confirm the transverse orientation and assess other factors, such as the location of the placenta and the volume of amniotic fluid.
The primary danger occurs if the mother goes into spontaneous labor before the position is corrected. Because no firm fetal part is positioned to seal the cervix, the baby cannot enter the birth canal, leading to obstructed labor. If labor is allowed to progress with a persistent transverse lie, there is also an increased risk of uterine rupture, especially in mothers who have had previous Cesarean sections.
The most severe risk is umbilical cord prolapse, which occurs when the amniotic sac ruptures and the umbilical cord slips down ahead of the baby into the vagina. With a transverse lie, the cord is highly susceptible to prolapsing because the space is not sealed by the baby’s presenting part. The prolapsed cord becomes compressed between the baby and the mother’s pelvis, rapidly cutting off the baby’s blood and oxygen supply, which constitutes an immediate obstetric emergency.
Management and Delivery Options
When a transverse lie is identified in the final weeks of pregnancy, medical intervention is necessary to prevent the serious risks associated with spontaneous labor. One procedure that may be attempted is the External Cephalic Version (ECV), a manual technique performed by a clinician to turn the baby from the sideways position to the head-down position by applying firm pressure to the mother’s abdomen. ECV is generally attempted around 36 to 37 weeks, provided there are no contraindications such as placenta previa or a non-reassuring fetal heart rate.
If the ECV is unsuccessful or if the baby flips back, close observation and planning become imperative. Women are frequently advised to be admitted to the hospital near term, often around 37 weeks, to ensure immediate medical attention should labor begin or the membranes rupture spontaneously. This in-hospital monitoring is a precaution against cord prolapse.
If the transverse lie persists and the baby cannot be safely turned, a planned Cesarean section (C-section) is the standard and safest delivery route. A scheduled C-section prevents the mother from entering labor, thus avoiding the dangers of obstructed delivery, uterine rupture, and cord prolapse.