Why Doesn’T It Stick? Understanding Recurrent Implantation Failure and Pregnancy Loss

If you've experienced repeated pregnancy loss (RPL) or recurrent implantation failure (RIF), you know how deeply painful and isolating this journey can be. Alongside the grief, there can be an overwhelming sense of uncertainty as you search for answers and wonder why this keeps happening.

If you're carrying the weight of these experiences, I want you to know something important: your body did not fail you. Repeated pregnancy loss and implantation failure are far more common than many people realise, yet they're rarely talked about openly. As a result, so many women are left feeling isolated, confused, and searching for answers.

While this is a deeply tender topic, understanding what may be happening can be an important step forward.

Before we go any further, it helps to be clear about what we're actually talking about. While recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL) are related, they're not the same thing. Understanding the difference can bring a sense of clarity to what is often an incredibly confusing and overwhelming experience.

Recurrent Implantation Failure (RIF) is when a good-quality embryo — usually through IVF — has been transferred several times, but a clinical pregnancy never establishes. The embryo simply doesn't "take." This is specific to assisted reproduction, because it requires us to know the embryo itself was good quality going in.

Recurrent Pregnancy Loss (RPL) is different — here, pregnancy does begin. You get a positive test, sometimes even a heartbeat on ultrasound, but the pregnancy is lost, and it's happened two or more times. This can happen whether or not IVF was involved.

So, the simplest way I explain the difference to my patients is this: with RIF, the seed never roots. With RPL, it roots, but something interrupts its growth.

Both are heartbreaking in their own way, and both deserve the same thorough, whole-picture investigation — because as you'll see, so many of the underlying factors overlap between the two.

In over two decades of this work, I've learned it's rarely just one cause. It's usually several factors layered together — egg or sperm quality, the uterine environment, hormones, immune function, sometimes a combination of factors, and sometimes something you'd never expect.

I understand that can feel overwhelming. But more factors also mean more places to investigate — and more chances to change the outcome. That's where the hope lives.

With everyone I see for RIF or RPL, we work through eight key areas:

• Egg quality
• Sperm health
• Uterine structure and lining
• Blood flow and clotting
• Hormonal balance
• Immune tolerance
• The uterine and vaginal microbiome
• Lifestyle and environmental load

Egg quality is one of the biggest pieces of this puzzle, and one of the most misunderstood.

Here's what I want you to sit with: the most common reason a pregnancy doesn't continue in the early weeks is chromosomal. The embryo likely had an abnormality that was simply incompatible with continued development, and the body responded as it was designed to.

This is not a reflection of your fertility. It's often a genuinely random event, and while it does become more common with age, that's simply because egg quality becomes more variable over time.

But age is only one part of a much bigger picture. What I see time and again in my clinic is women being told, "It's your age," when there's often much more to explore.

Oxidative stress, hormonal disruption, nutritional status, and environmental exposures can all influence egg quality at any age.

I tell everyone who sees me that an egg takes roughly 90 days to mature. That means the choices and circumstances during the three months before conception can influence the quality of the egg that's ultimately released. It's one of the reasons I encourage women to think about preconception as a time to optimise their health, rather than simply waiting and hoping for the best.

This is one of the most overlooked parts of the fertility conversation.

Research has shown that couples experiencing recurrent pregnancy loss are more likely to have higher levels of DNA damage in the male partner's sperm. Poor sperm motility, abnormal morphology, and increased DNA fragmentation can all affect embryo quality, which may influence implantation and the likelihood of an ongoing pregnancy.

Fertility is rarely just one person's story. Looking at both partners helps build a more complete picture and can uncover factors that might otherwise be missed.

Think of the uterus less as a passive vessel and more as an active participant. It needs to be structurally and functionally prepared to receive and support an embryo.

From a structural perspective, fibroids, polyps, scar tissue (Asherman's syndrome), a septate uterus, or an endometrial lining that's too thin can all make implantation more difficult. Some of these changes are obvious, while others can be much harder to detect.

But structure is only one part of the picture. The endometrial lining also needs to provide the right environment for an embryo to implant and continue developing during those earliest, most delicate weeks. When the uterine environment isn't functioning as it should, it can become another piece of the fertility puzzle that's worth exploring alongside egg quality, sperm health, and the other factors we've discussed.

Blood flow doesn't always receive much attention in discussions about implantation, but it may play an important role in some cases where implantation repeatedly fails without a clear explanation.

The uterus relies on a healthy blood supply to support implantation and to nourish the developing embryo during those critical early weeks. If uterine circulation is compromised, or if tiny blood clots interfere with blood flow, the embryo may not receive the oxygen and nutrients it needs to continue developing.

One condition that has been associated with recurrent pregnancy loss is antiphospholipd syndrome (APS), an autoimmune disorder that increases the risk of abnormal blood clotting. In some individuals, these clotting abnormalities may interfere with the establishment or maintenance of an early pregnancy. Inherited thrombophilias have also been investigated as a possible contributing factor, although their role in implantation failure remains less certain and is an area of ongoing research.

Because successful implantation depends on a complex interplay of hormonal, immunological and vascular factors, ensuring adequate uterine blood flow is considered an important aspect of creating an environment that can support early embryo development.

Hormonal balance plays a fundamental role in successful implantation and early pregnancy. Even subtle disruptions in hormone levels can affect several aspects of fertility, including ovulation, endometrial receptivity, and the ability to support an early embryo.

Progesterone is particularly important during the luteal phase and the earliest weeks of pregnancy. It helps prepare and maintain the uterine lining after ovulation, creating an environment that supports implantation and early embryonic development. If progesterone levels are inadequate, the uterine lining may not provide the support needed for implantation or ongoing pregnancy.

Thyroid hormones also play a key role in reproductive health. Thyroid dysfunction, including subclinical hypothyroidism, has been associated with reduced fertility and an increased risk of miscarriage. Maintaining normal thyroid function is important for both conception and early pregnancy.

Insulin and metabolic hormones influence ovulation, egg quality, and endometrial receptivity. This is particularly relevant in conditions such as polycystic ovary syndrome (PCOS), where metabolic and hormonal disturbances can affect multiple stages of the reproductive process.

Prolactin is another hormone that can influence fertility. Elevated prolactin levels may interfere with normal ovulation and disrupt the hormonal environment required to establish and maintain an early pregnancy.

In addition to reproductive hormones, homocysteine has been investigated as a factor in recurrent pregnancy loss. Elevated homocysteine levels have been associated with vascular and clotting changes that may affect the environment needed for successful implantation and early placental development, although the strength of this association varies between individuals.

Successful implantation depends on a carefully coordinated balance between reproductive, thyroid and metabolic hormones. When these systems are functioning optimally, they help create the conditions needed for implantation and support healthy early embryo development.

Successful implantation depends not only on a healthy embryo and a receptive uterus, but also on a carefully regulated immune response. During early pregnancy, the maternal immune system must adapt to support the developing embryo while continuing to protect both mother and baby from infection.

Rather than suppressing the immune system, pregnancy involves a finely balanced state of immune regulation. If this balance is disrupted—particularly in the presence of chronic inflammation or certain autoimmune conditions—the environment needed for successful implantation and early placental development may be affected.

One of the best-established immune-related conditions associated with recurrent pregnancy loss is antiphospholipid syndrome (APS), an autoimmune disorder that increases the risk of abnormal blood clotting and pregnancy complications. Other autoimmune conditions, including autoimmune thyroid disease, have also been associated with an increased risk of miscarriage in some individuals. The role of other immune markers, such as antinuclear antibodies (ANA), remains less clear and continues to be an area of active research.

Although immune factors do not explain every case of recurrent implantation failure (RIF) or recurrent pregnancy loss (RPL), they form one important part of the broader picture. Considering immune health alongside genetic, hormonal, anatomical, vascular and metabolic factors can help provide a more comprehensive understanding of the complex processes involved in implantation and early pregnancy.

The role of the microbiome in fertility is one of the most rapidly evolving areas of reproductive research. While many people are familiar with the gut microbiome, fewer realise that the vaginal microbiome also appears to play an important role in reproductive health and successful implantation.

A healthy vaginal microbiome is typically dominated by Lactobacillus species. These beneficial bacteria help maintain an acidic environment, support the body's natural defences, and contribute to an environment that may be more favourable for conception and early pregnancy. When this balance is disrupted—a state known as dysbiosis—the resulting changes in the vaginal environment may promote inflammation and have been associated with reduced fertility and poorer reproductive outcomes.

Researchers are also investigating the role of the endometrial (uterine) microbiome in implantation. Although this field is still developing, early studies suggest that alterations in the microbial environment may influence endometrial receptivity and the complex interactions between the embryo and the uterine lining during implantation.

As with many aspects of implantation, the microbiome is unlikely to act in isolation. Instead, it appears to be one of several interconnected factors—including hormonal balance, immune regulation and inflammation—that together influence the likelihood of a successful pregnancy.

It's important to say from the outset that recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL) are not caused by a lack of effort or by making the "wrong" lifestyle choices. Many people experiencing fertility challenges are already doing everything they can, and these conditions are rarely the result of any single factor.

That said, lifestyle does influence reproductive health. Nutrition, sleep, physical activity, stress, body weight, and exposure to environmental toxins all contribute to the hormonal, metabolic and inflammatory environment that supports conception and early pregnancy. While lifestyle changes cannot guarantee success, they can help create conditions that are more favourable for fertility and complement appropriate medical care.

The months leading up to conception are particularly important. Both egg quality and sperm quality are influenced by health and environmental factors in the weeks and months before fertilisation, making the preconception period a valuable opportunity to support reproductive health.

Perhaps most importantly, focus on changes that are realistic and sustainable rather than striving for perfection. Small, consistent improvements are more achievable—and often more beneficial over time—than trying to overhaul every aspect of your lifestyle at once. Fertility is influenced by many factors, some within your control and others not, so it's important to approach this process with self-compassion as well as commitment.

Recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL) are complex conditions, and there is rarely a single explanation. Instead, successful implantation and early pregnancy depend on the interaction of many factors, including genetics, hormones, immune function, uterine health, blood flow, metabolic health, the microbiome and lifestyle.

An unsuccessful embryo transfer or an early pregnancy loss can be deeply distressing, but it does not define your ability to achieve a successful pregnancy in the future. In many cases, there are evidence-based avenues to explore that may help identify contributing factors and guide appropriate treatment or management.

Every person's fertility journey is different. A thorough, individualised assessment that considers the full clinical picture is often the most effective way to understand the factors that may be influencing implantation and early pregnancy. By taking a comprehensive approach, many people are able to move forward with greater clarity, confidence and hope.

While the science of implantation continues to evolve, our understanding of the factors that influence reproductive success has grown enormously. Continued research is providing new insights into why implantation sometimes fails and, importantly, how outcomes may be improved for many individuals and couples.

If you're experiencing recurrent implantation failure or recurrent pregnancy loss and would like an individualised assessment, I'd be delighted to help you explore the factors that may be affecting your fertility and discuss the evidence-based options available to you.