Thin Endometrium in IVF: What Happens if the Lining Is Thin?

A thin endometrium in IVF means the lining of the womb looks thinner on an ultrasound scan than the clinic considers suitable for an embryo transfer. The endometrium is the layer that an embryo implants into, and clinics check its thickness and appearance before transfer. If it is thin, the team may change the plan, postpone the transfer or freeze embryos for a later cycle.

Hearing that the lining is thin can be upsetting, especially part way through treatment. It is a common reason for adjusting a cycle, and it does not predict what will happen for you. This guide explains what the scan shows and which questions to ask. It cannot interpret your own scan.

During IVF or in early pregnancy, some symptoms need help straight away and should not wait for the next scan. The NHS lists these warning signs, which can be linked to ovarian hyperstimulation syndrome (OHSS) or an ectopic pregnancy.

• Call emergency services or go to the emergency department for difficulty breathing, chest or upper back pain, pain low down on one side of the tummy, pain in the tip of the shoulder, swelling in any part of the body, or being very thirsty and passing much less urine. Do not drive yourself.
• Contact the fertility clinic or a local urgent advice line as soon as possible for tummy pain and bloating, feeling or being sick, feeling faint, coughing up blood, vaginal bleeding or brown watery discharge, or pain when passing urine or stool.

The lining is measured with an ultrasound scan during the cycle. The American Society for Reproductive Medicine's patient resource notes that the endometrium is usually checked to see whether it has an appropriate thickness and quality.

Thickness is reported in millimetres, but there is no single number used by every clinic, and the cited patient sources do not give one. The clinic also looks at the pattern of the lining and the cycle day. Ask your team what thickness they aim for, why, and how your measurement compares with earlier scans.

The lining grows in response to oestrogen. In a fresh IVF cycle, oestrogen from the developing follicles helps prepare it. In a frozen transfer cycle, some people use oestrogen patches, tablets or injections, and some use no medicines at all. A lining may stay thin if it does not respond as expected in that cycle, and the reason is not always found.

Scarring inside the womb is one known cause. Cleveland Clinic describes Asherman's syndrome as scar tissue inside the uterus, most often after a D&C procedure following a pregnancy, miscarriage or retained placenta, and less often after other womb surgery or infection. Symptoms can include very light or missed periods. It is usually diagnosed with hysteroscopy, a thin camera passed through the cervix, and scar tissue can be removed in the same way.

If your lining has stayed thin across cycles, ask whether the cavity has been checked for scarring, polyps or other problems. Tell the team about any past womb procedures, infections or changes in your periods, as this history helps them decide what to check.

It may be. ASRM's patient resource says that if there is an issue with the endometrium, such as a thin lining or a polyp, the transfer may be cancelled until the uterus can be evaluated fully.

In a fresh cycle, the clinic may suggest freezing all suitable embryos and transferring one later. The HFEA explains that a freeze-all approach lets transfer happen when the lining is well developed. The HFEA rates elective freeze-all as amber for improving the chance of a baby in most patients, meaning the evidence conflicts, and green for lowering the risk of OHSS. It notes that not every embryo survives thawing.

ASRM's resource also says that, in general, the chance of pregnancy with a fresh or frozen embryo may be similar. A postponed transfer is a pause, not a failure. Ask how long the clinic expects to wait before the next attempt and what will be done differently.

Add-ons are optional extras offered on top of standard treatment. The HFEA uses a traffic-light system and currently gives no add-on a green rating for improving the chance of having a baby.

• Intrauterine platelet-rich plasma (PRP): rated red for people with thin or refractory endometrium, because of potential safety concerns and no moderate or high-quality evidence that it improves outcomes. Reported side effects include infection, bleeding or allergic reaction.
• Endometrial scratching: rated amber for most IVF and ICSI patients because high-quality studies conflict. The HFEA describes it as intrusive and potentially painful.
• Endometrial receptivity testing: rated red, the HFEA's rating for add-ons with potential safety concerns or evidence that they may reduce treatment effectiveness.

Bring the scan reports and your cycle details. These questions can help you understand the decision being made.

• What was my lining measurement, and what thickness does this clinic aim for before transfer?
• Has my lining been thin in previous cycles, and has the inside of the womb been checked for scarring or polyps?
• Would a different way of preparing the lining in a frozen cycle be an option for me?
• If you recommend freezing all embryos, what are the benefits and risks in my situation?
• What evidence supports any add-on you are suggesting, how does the HFEA rate it, and what does it cost?
• Who should I contact, and how quickly, if I have pain, bleeding or swelling?

On SameCase, patients and verified doctors share de-identified cases. Reading how others described a thin lining, how their clinics adjusted a cycle and what they asked can help you prepare for your own conversation.

Other people's cases cannot tell you what will happen in your cycle or which approach is right for you. Use them to shape your questions, then talk them through with your fertility team.