C-Section Scar Defect (Isthmocele/Niche) and Secondary Infertility
If getting pregnant again has been harder after a cesarean, and especially if you've noticed spotting after your period, a scar defect in the uterus is worth asking about. It's common, often harmless, sometimes relevant to fertility, and the evidence on repair is still thin.
An isthmocele, also called a niche or cesarean scar defect, is a pouch-like indentation in the uterine wall where a cesarean incision healed. The European Niche Taskforce defines it on ultrasound as an indentation at the scar at least 2 mm deep.
- It's common after cesarean birth, and most people with one have no symptoms.
- When it matters for fertility, the proposed reasons include blood or fluid collecting in the pouch and in the uterine cavity, local inflammation, and difficulty passing the catheter at embryo transfer.
- Repair is possible hysteroscopically (from inside the uterus) or laparoscopically (from outside). A 2025 meta-analysis reported encouraging pregnancy rates after laparoscopic repair in women with infertility, but 13 of its 17 studies were rated poor quality and most had no comparison group.
In this article
What a niche is
During a cesarean, the uterus is usually opened low down, near the junction of the uterine body and cervix (the isthmus). As the incision heals, the muscle doesn't always knit back to its full thickness. When it doesn't, it can leave a small indentation or pouch facing the inside of the uterus. That's the niche.
Two measurements come up often:
- Niche depth and size: how big the indentation is. The European Niche Taskforce definition requires an indentation of at least 2 mm at the scar on transvaginal ultrasound.
- Residual myometrial thickness (RMT): how much muscle is left between the bottom of the niche and the outer surface of the uterus. A thin RMT affects which repair approach is safer.
How common niches are depends heavily on how they're looked for and defined. A 2025 review in Frontiers in Endocrinology notes reported rates of up to 70% after cesarean, with a minority of people having symptoms. In other words, finding a niche on ultrasound is common, and it doesn't automatically explain infertility.
Signs it might be relevant to you
Niche-related symptoms can include:
- Spotting or brown discharge for several days after your period ends. This is the classic symptom, caused by old blood collecting in the pouch and draining slowly.
- Pelvic pain or painful periods that started after the cesarean
- Fluid in the uterine cavity seen on ultrasound during fertility monitoring
- A difficult or bloody embryo transfer, or a doctor noting the catheter "catches" at the scar
- Secondary infertility after one or more cesarean births
None of these prove a niche is the problem. They're good reasons to ask whether it has been looked for. Our secondary infertility guide covers the wider workup, since a niche is only one possible piece.
How it may affect fertility
The 2025 meta-analysis by Vidal and colleagues summarizes the mechanisms researchers have proposed (drawing on work by Vissers and colleagues):
- Fluid in the cavity. Mucus or blood pooling in the niche and leaking into the uterus may make the environment less receptive to implantation.
- Inflammation. Altered local immune activity around the scar.
- Mechanical effects. Disrupted sperm passage, and fibrous tissue at the scar that can make embryo transfer harder or affect how the uterus contracts.
These mechanisms make sense biologically. What's harder to show is how much a given niche lowers a given person's chance of pregnancy. That's the central uncertainty, and the reason treatment decisions are individual.
How it's diagnosed
| Test | What it adds |
|---|---|
| Transvaginal ultrasound | The usual first test. Shows the niche, its size, and remaining muscle thickness. Often best seen shortly after a period, when blood may be trapped. |
| Saline infusion sonography (saline ultrasound) | Fluid in the cavity outlines the niche more clearly and helps measure it. |
| Hysteroscopy | A camera inside the uterus shows the niche directly and any fluid or abnormal tissue. It can sometimes be combined with treatment. |
| MRI | Sometimes used for surgical planning, especially when the muscle looks thin. |
Ask for the report to include niche measurements and residual myometrial thickness, not just "isthmocele present." Those numbers drive the treatment conversation.
Treatment options
Watchful approach, or working around it during IVF
If the niche is small and causes no fluid or symptoms, many doctors don't treat it. During IVF, some clinics take practical steps, such as checking for fluid before transfer and taking particular care with catheter placement. Ask your clinic what it does when a niche is present.
Hysteroscopic repair (isthmoplasty)
Done through the cervix, this procedure trims the edges of the pouch so blood and fluid can drain instead of collecting. It doesn't add muscle. It is generally considered only when enough muscle remains over the niche, because operating inside the uterus where the wall is thin risks injuring the bladder.
Laparoscopic or robotic repair
Done from the outside, through small abdominal incisions, this approach removes the scarred area and re-sutures the uterine wall, aiming to restore thickness. According to the Vidal review, most studies favor the laparoscopic route when residual muscle is less than 3 mm, because of the bladder-injury risk with hysteroscopy in that range. Some surgeons use a higher threshold.
Any repair means time: recovery, and usually a waiting period before trying to conceive or transferring an embryo. Ask your surgeon specifically how long they want you to wait and why.
What repair studies show (and don't)
The most recent systematic review we found is Vidal and colleagues, Frontiers in Endocrinology, 2025. It looked at reproductive outcomes after laparoscopic isthmocele repair:
| Group | Clinical pregnancy after repair | Live birth (among those who became pregnant) |
|---|---|---|
| Women with infertility | 62% | 72% |
| Women without infertility | 33% | 78% |
| All women | 44% | 72% |
Vidal A, et al. Front Endocrinol 2025;16. Pooled estimates; see limitations below.
Those numbers look encouraging, but read the fine print:
- Weak study designs. 17 studies were included, 14 of them retrospective. On the Newcastle-Ottawa scale, 13 were rated poor quality, 3 fair, and only 1 good.
- Few comparison groups. Most studies didn't compare repair with no repair, so the effect of surgery itself can't be isolated.
- Live birth denominators. Live birth was calculated among women who got pregnant, not all women treated, which flatters the figure.
- Mixed populations and poorly defined infertility in most studies.
- Endometriosis found in 29% of women at surgery, a possible confounder in both directions.
The authors concluded that laparoscopic repair may improve outcomes, particularly when infertility is linked to niche-related problems such as fluid or transfer difficulty, and called for well-designed multicenter trials. That's a fair summary. Repair is a reasonable option in selected cases. It hasn't been proven to help everyone with a niche.
Planning the next pregnancy safely
A cesarean scar is also relevant once you're pregnant. Rarely, a pregnancy implants in or on the scar itself, which is called a cesarean scar pregnancy. The Society for Maternal-Fetal Medicine (Consult Series #49) warns that expectantly managed cesarean scar pregnancy is associated with high rates of severe maternal morbidity, including hemorrhage, placenta accreta spectrum, and uterine rupture. SMFM recommends ending the pregnancy after diagnosis, while noting that the best treatment method is still uncertain.
The practical takeaway: after any cesarean, and especially with a known niche, ask for an early ultrasound in your next pregnancy to confirm where it has implanted. After IVF, your clinic will usually scan early anyway. See our guide to beta hCG after embryo transfer for what happens between a positive test and that first scan. HowToHaveABaby's guide to trying again after a C-section covers spacing and recovery more broadly.
Questions to ask
- Is there a niche, and what are its measurements and my residual myometrial thickness?
- Is there fluid in the niche or the cavity, and at what point in my cycle did you look?
- Do you think the niche is contributing to my infertility, or is it an incidental finding?
- If we repair it, which approach and why? How many of these repairs do you do?
- How long would I need to wait after surgery before trying or transferring?
- If we don't repair it, what will you do differently during IVF or embryo transfer?
- Will I get an early scan in my next pregnancy to check implantation site?
Frequently asked questions
What is an isthmocele?
An isthmocele, also called a niche or cesarean scar defect, is an indentation in the uterine wall where a cesarean incision healed incompletely. The European Niche Taskforce defines it on ultrasound as an indentation at the scar at least 2 millimeters deep.
Can a C-section scar defect cause secondary infertility?
It may contribute in some people. Proposed mechanisms include fluid or blood collecting in the niche and uterine cavity, local inflammation, and difficulty with sperm passage or embryo transfer. Many people with a niche have no symptoms and no fertility problem from it.
Should an isthmocele be repaired before IVF?
Not always. Repair is usually considered when the niche is causing symptoms, fluid in the cavity, transfer difficulty, or unexplained repeated failure. Evidence on repair comes mostly from small retrospective studies without comparison groups, so the decision is individual.
What is the difference between hysteroscopic and laparoscopic repair?
Hysteroscopic repair works from inside the uterus to let trapped fluid drain and does not add muscle. Laparoscopic repair works from outside, removes the scar, and re-sutures the wall. Most studies favor laparoscopy when the remaining muscle is under 3 millimeters because of bladder injury risk with hysteroscopy.
Is pregnancy riskier with a cesarean scar defect?
A prior cesarean scar carries a small risk of a pregnancy implanting in the scar, which SMFM links to serious complications if it continues. Ask for an early ultrasound in your next pregnancy to confirm the location.
Sources
- Vidal A, Geiger J, Vinayahalingam V, et al. High live birth rates after laparoscopic isthmocele repair in infertility: a systematic review and meta-analysis. Front Endocrinol. 2025;16. https://www.frontiersin.org/articles/10.3389/fendo.2025.1507482/full
- Society for Maternal-Fetal Medicine Consult Series #49: Cesarean scar pregnancy (summary, Contemporary OB/GYN). https://www.contemporaryobgyn.net/view/the-society-for-maternal-fetal-medicine-consult-series-49-on-cesarean-scar-pregnancy-summary-of
Medical disclaimer: This article is general education, not medical advice, and it cannot account for your history, test results, or treatment plan. Please make medication and treatment decisions with your own fertility team, and never start, stop, or change a prescribed medication without talking to the prescriber.
If you have severe abdominal pain, heavy bleeding, fainting, or shoulder-tip pain during or after fertility treatment, seek urgent care.