A caesarean scar niche in plain language
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 or indentation on its inner side, where the muscle is thinner. This is called a niche, an isthmocele or a caesarean scar defect. All three names describe the same thing.
- Lining of the womb (endometrium)
- Pouch in the caesarean scar (niche)
- Thinner muscle over the niche
- Bladder
- Wall of the womb (muscle)
- Cervix (neck of the womb)
- Vagina
Niches are common. Many women who have had a caesarean have a small niche visible on a scan, and most have no symptoms from it. In some women, menstrual blood or fluid collects in the niche and drains slowly, which can cause the symptoms described below. A niche does not usually progress with time, so a delay before treatment does not make it worse or cause harm.
Symptoms
A niche can cause:
- brown spotting or prolonged 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 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 [1].
These symptoms have other possible causes too, and I look for those before attributing them to the scar. Heavy periods are rarely caused by a niche, and treating the niche will not make them lighter.
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. At Parkside Hospital and the CRP Clinic I can perform a transvaginal scan during the consultation. Often I add a saline-contrast scan, 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 I arrange it separately. Sometimes a hysteroscopy (looking inside the womb with a slim telescope) 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. Routine screening for a niche after a caesarean has no specific benefit; what brings a niche to attention is symptoms.
Treatment options
I counsel women about niches in a deliberately balanced way, because the evidence about who benefits from treatment is still developing. I will describe what the niche is doing, set out every reasonable option including no treatment, and advise you whether repair is likely to help you.
- No treatment. If the niche causes few symptoms, or none, leaving it alone is often the right choice, and nothing is lost by waiting.
- Hormonal treatment. For women who are not planning a pregnancy, treatment that makes periods lighter, such as the contraceptive pill or a hormonal coil, can reduce spotting. In my experience it does, 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.
- Hysteroscopic repair (niche resection). For women with 3 millimetres or more of muscle over the niche. Carried out through the cervix, usually as a day case, it seals the small blood vessels at the top of the pouch and trims its lower edge so that blood drains freely instead of collecting. The aim is to improve spotting; it does not rebuild or thicken the wall.
- Keyhole repair (laparoscopic or robotic). For women with less than 3 millimetres of muscle over the niche, or for whom removing the niche and rebuilding the wall would be the better option, which we would talk through together. It removes the thinned scar from outside the womb and rebuilds the wall in layers.
What the evidence shows
In a randomised trial from the Netherlands, women who had hysteroscopic repair typically had four days of spotting a month six months later, compared with seven in women who waited, and the benefit varied from woman to woman [2]. 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.
Studies of keyhole repair report that the wall of the womb is thicker afterwards and that symptoms improve for many women, but these studies are smaller and did not compare repair with no treatment. Whether repair improves the chance of pregnancy is not yet known. I will go through what this means for you, so that you can make the decision that is right for you.
What surgery involves and recovery
Hysteroscopic repair is carried out as a day case, usually under general anaesthetic or sedation, and takes around twenty to thirty minutes. Mild cramping and light bleeding for a few days are normal, and most women return to work within a few days.
Keyhole repair is carried out under general anaesthetic 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 of the womb in layers. Most women stay one night in hospital. I usually advise about four weeks before returning to work; if you work from home and need to, light desk work after about two weeks is often possible.
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 (about these figures). I will explain how these apply to you, and you will receive full written information well before any operation.
Planning a pregnancy
After hysteroscopic repair 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. I recommend an early scan to confirm where the pregnancy has implanted, because a pregnancy can occasionally implant in the caesarean scar, which needs prompt specialist care. 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.
I have written a fuller article on niches, Caesarean scar niche (isthmocele): symptoms, fertility and repair, and you can read more about my work in this area on the fertility and miscarriage surgery page.
