Caesarean scar niche (isthmocele): symptoms, fertility and repair

After a caesarean birth, the incision in the lower part of the womb heals with a scar. Sometimes the scar heals with a small pouch on its inner side, where the muscle is thinner than the rest. This is called a niche, an isthmocele or a caesarean scar defect; all three names describe the same thing.

Niches are common, and most cause no symptoms at all. A niche becomes important when it explains symptoms that began after a caesarean and have not gone away. This article describes how I assess whether a niche is the cause, what can be done about it, and how we decide together.

How a niche causes symptoms

Menstrual blood collects in the pouch and drains slowly once the period has finished, and fluid can gather in the niche and in the cavity of the womb. Those two things account for most of what a niche does. A niche can cause:

• brown spotting or light bleeding for several days after a period has finished;
• period pain that is worse than before the caesarean, or pelvic pain at other times;
• difficulty conceiving, which may be linked to fluid collecting in the cavity of the womb;
• during IVF, fluid in the cavity at the time of an embryo transfer, so that the transfer is postponed, or difficulty passing the fine tube (catheter) used for the transfer.

Spotting, pain with bleeding and these fertility problems, when they began after a caesarean and a niche is seen on the scan, are now recognised by an international group of specialists as a condition in their own right ^[2].

A niche may not explain all of your symptoms. Bleeding between periods or after sex may have other causes, including polyps (small overgrowths of the lining), fibroids, hormonal changes, infection and changes in the cervix, and I look for those before attributing the bleeding to the scar. Please keep your cervical screening up to date; screening does not replace investigation of abnormal bleeding, so this kind of bleeding should be checked even if your last result was normal. Heavy periods are rarely caused by a niche, and treating the niche will not make them lighter.

Bleeding after a caesarean, years later

Many women notice that their periods changed after a caesarean and only seek advice years later, often when they are hoping for another baby. Spotting that began after a caesarean and has continued since may well be due to a niche. A niche does not usually progress with time, so a delay before treatment does not make it worse or cause harm.

How I assess a niche

We first take a history, to understand what your problems are, and look at them as a whole, taking into account your wishes, including whether you hope to have another baby, and whether the niche is likely to be having any effect. A woman who wants another pregnancy and a woman who does not may need quite different advice.

The second step is an ultrasound scan. The main test is a transvaginal scan, with the probe placed gently in the vagina. Often I add a saline-contrast scan (sonohysterography), introducing a little sterile saline into the womb through a fine tube, which outlines the pouch clearly. At the CRP Clinic I can do this during the consultation; at Parkside Hospital I scan during the consultation and arrange the saline scan separately. Sometimes a hysteroscopy, a slim telescope passed through the cervix to look inside the womb, adds useful information.

The key information we are looking for is the thickness of the muscle that remains over the niche, the residual myometrium. It decides which operations are safe, and I will tell you the figure. I usually assess a niche at least six months after the caesarean, once the scar has healed, but that is no reason to delay seeing someone about symptoms that worry you.

The choices, from leaving it alone to repair

If the niche is not causing you symptoms, you do not need to treat it, and routine screening for a niche after a caesarean section has no specific benefit. If your symptoms are mild, leaving the niche alone may be the right option for you, and nothing is lost by waiting.

The next step up is to treat the symptoms without an operation. For women who are not planning a pregnancy, hormone treatment that makes periods lighter, such as the contraceptive pill or a hormone-releasing coil, can help. In my experience it reduces spotting, because it reduces the bleeding that collects in the niche, although it has not been tested for this in a trial. I usually suggest three months and then a review; if it has not helped by then, we change the plan rather than persist.

For women who have a thicker layer of muscle over the niche, 3 millimetres or more, hysteroscopic resection may be the right option. It is carried out through the cervix with no incisions on the abdomen, usually as a day case under sedation or a general anaesthetic, in twenty to thirty minutes. I seal the small blood vessels at the top of the pouch and trim its lower edge downwards towards the cervix, so that blood drains freely instead of collecting. The aim is to improve spotting; it does not rebuild or thicken the wall of the womb.

The evidence shows that the treatment is worthwhile, but the effect is modest. In a randomised trial from the Netherlands, women who had the operation had a median of four days of spotting a month six months later, compared with seven in women who waited, and the improvement varied from woman to woman ^[1]. Every woman in that trial had at least 3 millimetres of muscle over the niche; a thinner wall raises the risk of making a hole through the womb or injuring the bladder.

For women who have a very thin layer of muscle over the niche, less than 3 millimetres, or for whom removing the niche and rebuilding the wall would be the better option, which we would talk through together, we recommend keyhole repair, by laparoscopic or robotic surgery. It works from outside the womb, through several small incisions. I free the bladder from the front of the womb, remove the thinned scar, usually with a hysteroscope inside the womb at the same time to locate the niche precisely, and close the wall in layers.

I have been repairing niches by keyhole surgery since 2013. In 2014 my colleagues and I published our technique for laparoscopic niche excision with reconstruction of the wall of the womb ^[3], and in 2019 we published a further kind of caesarean scar defect, a cyst within the scar, with our technique for removing it ^[4].

We have now moved to performing these repairs robotically, because in my experience robotic surgery is more precise, with less blood loss, and allows an even more robust repair, with a thicker layer of muscle afterwards than I achieved by laparoscopy.

Observational studies have shown a thicker wall afterwards and improved symptoms for many women. None compared repair with no treatment, and whether repair improves the chance of pregnancy is not yet proven. Keyhole surgery is not suitable for everyone.

How we decide

We go through the options together, weighing the thickness of the remaining muscle, how much the symptoms trouble you, and whether you want another pregnancy, and then we decide together what the best option is for you. For women who are not planning a pregnancy, hormone treatment is usually the first thing to try, with an operation as the next step if the spotting still bothers you. You do not have to decide at the first appointment.

Recovery and risks

After hysteroscopic resection you go home the same day. Mild cramping and light bleeding for a few days are normal, and most women are back at work within a few days. After keyhole repair, expect one night in hospital and about four weeks before returning to work, or light desk work from home after about two weeks if you need it. I give each patient a personal plan.

The risks of either operation are bleeding, infection, injury to the bladder or nearby organs, and the niche forming again. Keyhole surgery carries a small possibility of converting to an open operation; my open conversion rate is around one in a thousand.

Planning a pregnancy afterwards

After hysteroscopic resection I recommend waiting two months before trying to conceive. After laparoscopic or robotic repair I arrange an ultrasound scan at six weeks to assess the healing; if the wall has healed well with a good thickness of muscle, I recommend waiting until three months after the repair before trying.

When you are pregnant, tell your midwife and obstetric team about the niche and any repair, and give them my letter. I recommend an early scan to confirm where the pregnancy has implanted, because a pregnancy can occasionally implant in the scar (a caesarean scar pregnancy), which needs prompt specialist care. Whether a repair changes the risk of problems later in pregnancy is not known. After a keyhole repair a planned caesarean birth is usually advised, although practice varies and the evidence is limited, and the plan for your birth belongs with your obstetric team.

When to seek advice, and what happens next

See your GP or a gynaecologist if you have had spotting after your periods or new or worse period pain since a caesarean, or if you are having difficulty conceiving after one. If you are having IVF and fluid has been seen in the womb, ask your fertility team whether a niche could be the cause. Seek urgent help if you have heavy bleeding or severe pain in early pregnancy after a caesarean.

If you come to see me, my practice manager, Helen, books the appointment and sends a secure link for any scans or letters you already have. You can ask Helen for the hospital’s fixed price for each operation before you decide. Where I can, I scan you at the consultation, and you leave knowing the thickness of the wall, the choices open to you and my recommendation. A letter follows to you and your GP. You can read more on the caesarean scar niche page, or book an appointment.