While they used to be relatively rare, cesarean section deliveries increased drastically in the United States in the early 2000s and now account for nearly a third of all deliveries, according to the Centers for Disease Control and Prevention. With the rising rates of C-sections, clinicians should be vigilant about screening for associated complications, including defects at the incision site.
A cesarean scar defect (CSD) forms when the incision doesn't heal properly and a defect forms in the location of the scar. The uterine wall thins, leading to the formation of a pouch that fills with fluid, also called an isthmocele or a niche.
Patients who smoke or have diabetes may be at higher risk of developing a CSD, as both conditions can interfere with wound healing. Those who are overweight or had gestational diabetes may also be at an elevated risk of experiencing a CSD, according to a study published in the American Journal of Obstetrics and Gynecology (AJOG).
A cesarean scar defect can cause nonspecific symptoms in patients after a delivery and lead to complications with fertility or future pregnancies. Patients have the best shot at a full recovery and safe deliveries in the future when a CSD is diagnosed and treated early.
Cesarean Scar Defect Complications
A CSD may cause postmenstrual spotting, dyspareunia, pelvic pain and even infertility. While these symptoms can be frustrating and affect a patient's quality of life, one of the most concerning risks is the increased chance of adverse outcomes for future pregnancies if the scar defect isn't treated before a patient conceives. An embryo may implant on the scar or within the niche, called a cesarean scar pregnancy.
Many cesarean scar pregnancies are terminated once detected; if the patient chooses to continue with the pregnancy, they face a higher risk of complications during and after delivery. They may also require a hysterectomy at delivery, or face uterine rupture and other complications that would prevent future pregnancies. Pregnancies that implant on the scar, instead of the niche, tend to have more favorable outcomes, according to a separate study published in AJOG.
How to Diagnose Cesarean Scar Defect Using Ultrasound
Transvaginal ultrasound is useful in detecting a scar defect; however, recent research has found that contrast-enhanced or saline infusion sonohysterography is the preferred tool for diagnosing cesarean scar defect in patients who are not pregnant.
On ultrasound, the niche looks like a hypoechogenic area in the myometrium of the lower uterus. During an ultrasound examination, the physician needs to measure the depth and width of the niche and the residual myometrial thickness (RMT). These measurements can be taken in the midsagittal plane, while the niche length can be measured in the transverse plane. The clinician should also measure uterine anteflexion or retroflexion.
The same American Journal of Obstetrics and Gynecology case report that identified the link between gestational diabetes and CSD defines the threshold for a cesarean scar defect as a niche of at least 2mm deep. It defines a low RMT as 3mm. Myometrial thickness is an important measure because a low RMT is associated with a higher risk of uterine rupture during labor in women with a prior C-section. Women with a cesarean scar defect are more likely to have a lower RMT, according to Obstetrics and Gynecology.
In patients with a suspected cesarean scar pregnancy, a transabdominal or transvaginal ultrasound with color Doppler can provide confirmation. Ultrasound determines the location of the gestational sac, which may be in the anterior wall of the defect. In a cesarean scar pregnancy, the uterus and cervical canal will appear empty, and the myometrium between the bladder and the gestational sac may be missing or diminished. On color Doppler, the peritrophoblastic flow can be seen around the sac.
Physicians can use ultrasound to classify the type of cesarean scar pregnancy and inform interventions if a patient has a live fetus and does not want to terminate it. According to the Journal of Ultrasound in Medicine, Doppler imaging can be used to determine peak systolic velocity (PSV) values, which signal how risky a pregnancy is for the patient. A PSV lower than 39 cm/s is considered safe, while a PSV higher than 83 cm/s is potentially dangerous.
Managing Cesarean Scar Defects
An accurate, early diagnosis of a cesarean scar defect or pregnancy is crucial in providing patients with fertility-preserving options. Research in Obstetrics and Gynaecology suggests that a defect can be seen on gel-infused sonohysterogram as early as six months after a C-section.
Patients who present with symptoms of a scar defect may need to be evaluated early. MD Edge reports that laparoscopic resection can be used to repair the defect and restore the integrity of the myometrium, making it an effective option for those who want to become pregnant in the future. Patients who do not wish to preserve their fertility may undergo hysteroscopic resection.
Early detection of a cesarean scar pregnancy is critical for providing the best outcomes for the patient and predicting the potential for a live birth. Depending on the location of the gestational sac, heartbeat activity and measurements visible on ultrasound, it may be safest for the patient to end the pregnancy with a minimally invasive MTX injection.
Delayed treatment of a cesarean scar pregnancy can lead to gestational sac growth and increased vascularization, which raises the risks of any intervention. Patients who choose to continue these pregnancies need to be monitored carefully for uterine rupture, placenta previa and placenta accreta.
Ultrasound is a critical first-line diagnostic tool for evaluating patients for scar defects or pregnancies, and can inform the best treatment path if either is discovered. An awareness of this complication and its symptoms can help providers guide patients through pregnancy and conception for the safest outcomes possible.