A uterine window is a defect in the wall of the uterus, typically arising at the site of a previous Cesarean section incision. Medically known as uterine scar dehiscence, this condition involves a significant thinning of the muscle layer (myometrium) at the scar, making it almost transparent. This weakened area may not withstand the stress of a subsequent pregnancy, raising the risk of a complete uterine rupture. The severity of the defect, often called a niche, dictates the level of risk and the treatment approach, which may include surgical repair.
Identifying and Assessing Uterine Scar Dehiscence
The presence of a uterine window is often discovered incidentally, such as during a repeat Cesarean delivery or when a woman seeks evaluation for chronic pelvic pain or irregular bleeding. Doctors use imaging techniques to assess the integrity of the scar, focusing on the thickness of the remaining healthy muscle tissue.
Transvaginal ultrasound (TVS) is the primary diagnostic tool used to measure the Residual Myometrial Thickness (RMT). RMT is the muscle tissue remaining between the defect and the outer layer of the uterus. A smaller RMT measurement indicates a thinner, weaker scar, which is associated with a higher risk of complications in a future pregnancy.
It is important to distinguish between uterine dehiscence and a uterine rupture. Dehiscence is an incomplete separation where the muscle layers have thinned but the outer uterine covering remains intact. A rupture is a tear through all three layers of the uterine wall, which is a life-threatening emergency. Magnetic Resonance Imaging (MRI) is also an option for evaluating the defect in complex cases, but TVS remains the most common method.
Surgical Correction of the Uterine Window
A uterine window can often be corrected, which significantly lowers the risk for a subsequent pregnancy. The repair procedure, sometimes called hysterorrhaphy or scar revision surgery, is an elective operation performed when the patient is not pregnant. This allows the uterus time to heal completely before conception.
The goal of the surgery is to remove the old, weak, fibrous scar tissue and then suture the healthy uterine muscle back together. The most common surgical approach is minimally invasive, typically using laparoscopic or robotic techniques. The surgeon excises the niche and closes the muscle layers with strong sutures, aiming to create a thick, stable scar.
This process effectively increases the RMT, restoring the structural integrity of the lower uterine segment. The repair often resolves symptoms like irregular bleeding associated with the defect. Long-term success is measured by the improvement in myometrial thickness and the ability to carry a subsequent pregnancy safely.
Implications for Subsequent Pregnancies
After a successful surgical repair, the management of future pregnancies changes, offering a more positive outlook for those hoping to conceive again. A waiting period of six to twelve months is required for complete healing before attempting conception. This interval ensures the new scar achieves maximum strength.
For women with a large, unrepaired uterine window, the risk of uterine rupture is too high to attempt a Trial of Labor After Cesarean (TOLAC). A mandatory planned repeat Cesarean section is typically recommended. This C-section is usually scheduled earlier, often between 36 and 37 weeks of gestation, to avoid the stress of labor contractions on the thin scar.
After a successful repair, the risk profile improves, but the decision regarding the mode of delivery remains individualized. Although the repair strengthens the uterus, a repeat Cesarean delivery is still often recommended for maximum safety. Close monitoring is standard in all subsequent pregnancies, using serial ultrasounds to track the thickness and stability of the repaired scar.