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Cesarean Section Defects and Subsequent Fertility
Cesarean sections are usually done in over 20% of deliveries globally. In the US, nearly a third of deliveries are by cesarean (31.9% in 2018), with rates above 36.0% in several states.
In the three years following first childbirth, women who delivered their first child by cesarean had lower rates of conception after unprotected intercourse, and fewer of these women had a second child than those who delivered vaginally.
There can be sequelae from cesarean delivery on subsequent ability to conceive. These sequelae are magnified in the presence of a cesarean section scar also called a niche or a cesarean-induced isthmocele.
A niche as defined by their European niche task force as an indentation of the uterine myometrium of at least 2 mm at the site of the cesarean scar assessed by transvaginal ultrasound. The diagnostic criterion of the niche includes a hypoechoic space failed with postmenstrual blood most typically in a triangular shape reflecting a discontinuation of the myometrium at the site of the previous cesarean section. A large niche is defined as an incision of a depth of at least 50-80% of the anterior myometrium, or the remaining myometrial thickness less than 2.2 mm when evaluated by transvaginal ultrasound or less than 2.5 mm when evaluated by sonohysterography.
Niches are observed in 50-60% of women following a cesarean section. Several factors have been shown to be associated with the development of a cesarean section niche. There are some maternal factors that can contribute to poor healing of tissue such as diabetes and smoking. A study by Hayakawa et al., demonstrated that double-layer interrupted sutures reduced the prevalence of a cesarean section myometrial defect after at 30–38 days after surgery.
Cesarean section niches can result in a spectrum of disorders starting with cesarean scar ectopic pregnancy, to increased incidence of placenta previa and uterine rupture associated with major maternal morbidity, and even mortality. Cesarean section niches collect menstrual blood, resulting in abnormal peri-menstrual bleeding or spotting. They also cause pelvic pain, painful menstruation, and dyspareunia. The accumulation of blood in this area may also negatively affect the quality of cervical mucus and semen, as well as interfere with semen transport
Another serious sequela may be the implantation of an embryo within the niche resulting in the development of a cesarean scar ectopic pregnancy. This can be a life-threatening complication if not diagnosed on time and adequately treated. The diagnosis of a niche ectopic pregnancy is invariably challenging, as approximately 30% of patients may not present with any symptoms, and in 70% the symptoms mimic early pregnancy. Transvaginal ultrasound is the most accurate differential test, with a sensitivity of 84.6%. Additionally, saline infusion sonohysterography, MR, 3D US and hysteroscopy may also be helpful.
Several studies have reported spotting in up to 30% of women that develop a niche within 6-12 months compared to 15% of women without a niche. The amount of spotting postmenstrual is correlated to the volume of the niche and inversely correlated to the residual myometrial thickness.
The development of a Cesarean section niche by itself also reduces future fecundity and it is felt that there are three major mechanisms for this to happen. The first is that the defect presents a detrimental environment for sperm penetration and implantation. The niche accumulates intrauterine fluid which has been shown to impair implantation. There is altered immune biology and increased inflammation when the niche is present. The niche itself also distorts the contractility of the uterus.
Several studies have shown that the uterus has a contractile pattern. The fibrosis and interruption of the myometrial layer at the site of the niche can prevent normal contractile patterns. There is accumulation of mucus and blood in the niche which can impair sperm penetration. The second mechanism of decreased fecundity includes a physical barrier for embryo transfer and implantation. A large niche in combination with a strongly retroflexed uterus impairs accessibility for subsequent embryo transfer in a future IVF cycle. This is due to the distorted anatomy at the niche site. The third mechanism of reduced fecundity could be related to gynecologic symptoms which interfere with sexual intercourse and may interfere with opportunities to conceive.
The treatment for cesarean section niches is usually surgical. Patients whose main symptom includes spotting or bleeding abnormally can be readily treated by hysteroscopy.
Repairing the niche itself by laparoscopy can improve future fertility. A prospective study looked at patients who had niches. Patients with no clinical symptoms had a mean residual myometrial layer on transvaginal ultrasonography of 5.39±3.34 mm, which could be used as a good reference to predict the recovery of patients after repair surgery. Zhou et al.