Thin endometrium and implantation problems

After a period, rising oestrogen builds the lining, which thickens and develops a layered pattern on ultrasound. After ovulation, progesterone changes it into a receptive state for a few days. In IVF and frozen embryo transfer, clinicians often replicate this with oestrogen followed by progesterone given as a pessary or gel, as the HFEA describes in its account of womb preparation.

A lining that does not thicken as expected may reflect low oestrogen, reduced blood flow, scarring that stops the tissue regenerating, or damage to the basal layer from earlier surgery or infection.

The causes are varied, and in a good number of people none is found. Doing the work-up systematically makes sure fixable factors are not missed.

• Intrauterine adhesions (Asherman syndrome) after surgery on the womb, such as uterine evacuation, or after infection.

• Previous radiotherapy to the pelvis.

• Chronic endometritis, a long-standing inflammation of the lining.

• Low oestrogen, for example in hypothalamic amenorrhoea or low ovarian reserve.

• Medicines, such as clomifene, which can thin the lining in some women.

• Poor uterine blood flow or fibroids and polyps changing the cavity.

Transvaginal ultrasound is the first step. If the lining is persistently thin, or if there have been repeated unsuccessful transfers, the next test is usually a hysteroscopy, in which a thin camera is passed through the cervix. The NHS lists fertility difficulties and recurrent miscarriage among the reasons for hysteroscopy, and notes cramping afterwards and rare risks of infection and perforation. Scar tissue, polyps and fibroids can be treated at the same visit in many cases.

A biopsy may be taken to look for chronic endometritis. Hormone tests and a review of the cycle help to see whether the lining is receiving enough oestrogen.

Treating an identified cause has the clearest logic: removing adhesions and polyps, treating infection, adjusting oestrogen dosing in a frozen transfer cycle, and reviewing clomifene use. Beyond those, a range of other measures have been tried, including low-dose aspirin, vitamin E, sildenafil, growth factor injections and platelet-rich plasma, with evidence that is limited or inconsistent. The HFEA rates platelet-rich plasma red, meaning evidence suggests it may reduce effectiveness or raise safety concerns.

Freezing all embryos for a later transfer, which lets the lining be prepared in a controlled cycle, is rated amber by the HFEA, meaning the evidence is conflicting. Ask what the clinic evidence is and whether the measure is part of a trial.

Endometrial scratching involves passing a small plastic tube through the cervix to scratch the womb lining before IVF. The HFEA gives it an amber rating, saying it is not clear whether it works, and describes it as intrusive and potentially painful with possible bleeding. For recurrent implantation failure the rating is grey, meaning too little evidence.

Endometrial receptivity testing analyses a biopsy to time the transfer. The HFEA rates it red because evidence suggests it may reduce effectiveness, and it questions whether the test is accurate at finding the window or whether the window is the same each cycle. Microbiome testing is rated grey.

Embryo quality, genetic abnormalities in the embryo, the womb cavity, and sperm factors all contribute, so the womb lining is only one part. Doctors commonly review the full cycle history, consider whether embryo transfer technique can be improved, and look at the womb cavity and any hydrosalpinx. Emotional support is important, because repeated unsuccessful transfers are wearing for couples.