The long‐term health risks of ART

Abstract

Since the birth of Louise Brown 39 years ago, scientists have been suspecting that assisted reproductive technologies could create long‐term health risks. While evidence remains inconclusive, ongoing research and improvements help to reduce such risks.

Potential health risks associated with assisted reproduction technology (ART) have been suspected ever since the first IVF baby, Louise Brown, was born in the UK in 1978. These risks have constantly been reassessed in light of epidemiological data as well as animal studies. Yet, even 39 years is not long enough to obtain conclusive proof of significantly increased levels of serious conditions, including cancer, cardiac, or metabolic diseases.

Growing demand for ART

However, evidence has been more than sufficient to stimulate further research across the whole spectrum of treatments for sub‐fertility, given that demand continues to grow around the globe. A number of factors combine to drive up assisted reproduction rates, including rising awareness among infertile couples, technical advances, growing medical tourism, and, above all, the trend among women, especially in developed countries, toward delaying pregnancy into the 30s. As a result, of the 6 million or so babies conceived via ART since 1978, about half were born during the past decade. In the USA, 72,913 babies were born via ART in 2015 representing 1.6% of all births, according to the US Centers for Disease Control and Prevention.

The risk of multiples alone means that ART babies are far more likely to suffer subsequent health problems associated with the greater incidence of being born prematurely.

The situation is similar in Europe, where numbers of ART births increased by 7% between 2012 and 2013, according to the European Society of Human Reproduction and Embryology (ESHRE; https://focusonreproduction.eu/2016/07/05/6-5-million-ivf-babies-since-louise-brown/). The study also noted that ICSI (intra‐cytoplasmic sperm injection) now accounted for two‐thirds of all ART treatments in Europe, mainly owing to male infertility. In ICSI, the embryologist injects a single sperm directly into an ovum, compared with IVF where fertilization takes place in a dish and many sperm swarm around one or a few eggs. The ESHRE emphasized that the trend toward ICSI was driven by its ability to work with just a few sperm from sub‐fertile men, rather than any advantage in success rates or risk factors, which are broadly similar.

Multiple births and low birthweight

The biggest risk by far is associated with multiple births. First, more than one embryo may be transferred into the womb. Second, ART itself seems to increase the chance of a single embryo dividing after fertilization to yield identical twins, for reasons that are not yet fully understood. These two factors combine so that almost a quarter of births resulting from IVF treatment were multiples in 2008, 20 times the average of 1 in 80 among births after natural conception. The risk of multiples alone means that ART babies are far more likely to suffer subsequent health problems associated with the greater incidence of being born prematurely. At least half of twins are born before 37 weeks and have low birthweights, while this is true for 90% of triplets, putting them at much higher risk of long‐lasting serious problems and death, according to the UK Human Fertility and Embryology Association (HFEA).

This has led to a concerted campaign in a number of countries to reduce multiple ART births by encouraging implantation of single embryos only, even if this reduces the chance of conceiving a child for each fertilization cycle. After public consultation, the HFEA set a maximum multiple birth rate target in 2009 for UK clinics, starting at 24% and reducing it stepwise toward an end goal of no more than 10% of all live births. This is still a lot more than the proportion for natural conceptions but reflects a realistic target, which is on course to being met.

Sub‐fertility does not seem to be just an isolated condition, but is often associated with other deficiencies that seem to heighten the risk of various diseases.

Another risk factor clearly associated with ART even in the case of singleton children is birthweight. Low birthweight itself is a predictor of multiple conditions later in life, especially cardiovascular disease, irrespective of how the baby was conceived. ART‐conceived babies have generally lower birthweight, but with one major exception, according to Daniel Brison, Scientific Director at the Department of Reproductive Medicine, Central Manchester University Hospitals, NHS Foundation Trust in the UK. “Babies born from fresh embryo transfer are low birth weight, but those born from embryos that have been frozen have slightly higher birthweight even than those conceived naturally,” he said. The reasons for this disparity are still not clear with Brison citing several contending theories. One is that cryopreservation of embryos causes some molecular changes, while another is that only the fittest embryos survive the freezing and thawing process, although that seems less likely. Brison favors the idea that by the time frozen embryos are implanted, the mother's uterine environment has returned to normal, whereas it is high in estrogen at the time when fresh embryos go in after the hormone treatment that precedes it. The latter theory in particular is being tested, but meanwhile, the risks directly associated with low birthweight in ART can be mitigated by use of frozen embryo transfers, Brison commented.

Health risks for the mother

Although the focus has been mostly on children, there are also concerns over health risks for the mothers of ART‐conceived offspring. The strongest association here is with ovarian cancer: A UK study reported a significantly increased risk among mothers conceiving children as a result of IVF 1. The authors examined records from the HFEA of all women who had used ART in the UK between 1991 and 2010 for cancer outcomes, deaths, and emigrations. With 8.8 years' average follow‐up, 386 ovarian cancers occurred in 255,786 women, which represents an increased risk sufficient to prompt a further study into tumor progression and histopathological sub‐type of the mother.

The children conceived as a result of ART are still in general quite young, which limits our ability to assess the spectrum of risks.

One question this study, still to be published, should help to resolve is whether the increased risk of ovarian cancer is associated with the ART procedure itself or the underlying fertility problems. According to Alastair Sutcliffe, a pediatrician working at University College London Hospitals in the UK, and lead author on the first study, most analyses of the existing dataset suggest that the increased risk resulted from the nature of women needing these treatments in the first place, rather than the hormone treatments to stimulate egg production. Sub‐fertility does not seem to be just an isolated condition, but is often associated with other deficiencies that seem to heighten the risk of various diseases.

Increased risk of cardiovascular diseases?

Research has also focused on health risks that are independent of multiple births and birthweight, including cancer, cardiac, metabolic, and inflammatory conditions, as well as autism and mental retardation. In all these cases, the evidence so far suggests that the risks are relatively slight and no cause for undue alarm among prospective parents. There is strong evidence though that mice conceived by ART have a much higher incidence of various cardiac and metabolic problems than those conceived normally. One of the most comprehensive animal studies found that mice conceived by IVF tend to exhibit significant vascular dysfunction and a shortened life span, reduced by as much as 25% among those challenged by a high‐fat diet compared with those naturally conceived 2.

Furthermore, there is evidence that ART causes epigenetic modifications that are passed down to offspring of ART‐conceived mice. One study found that ART mice had altered methylation at the promoter of the gene encoding endothelial NOS (eNOS), or nitric oxide synthase 3, in the mice aorta 3. eNOS is an enzyme that synthesizes nitric oxide (NO) and is widely believed to play a protective role for the whole cardiovascular system. The ART mouse study found that this altered methylation at the eNOS gene promoter correlated with decreased vascular eNOS expression and NO synthesis, but was restored to normal when a deacetylase inhibitor was administered.

The same team, led by Urs Scherrer from the Swiss Cardiovascular Center at the University Hospital, Bern, proceeded to seek similar evidence for risk of cardiac problems in ART‐conceived humans and reported altered cardiovascular phenotypes in many children conceived by ART 4. This proved more controversial though, because of their conclusion that ART is an important risk factor for cardiovascular disease, which requires a reevaluation and debate over the long‐term safety of ART technology in general.

Too early to draw conclusions

Critics of the study and its conclusions do not contend that these findings are necessarily wrong but that they are premature, given that the oldest ART children are still under 40 with as yet no firm evidence of increased incidence of cardiac disease. They argue that the study conflates various circumstantial factors that do not yet quite add up to conclusive risk. One such factor is a potential link between the fetal environment of a child and subsequent health outcomes in general. This led to the earlier proposal of the fetal reprogramming theory, according to which the environment during embryonic development and through gestation sets the fetal epigenome and therefore determines expression of certain critical genes for the rest of that person's life 5. The extent of these changes on subsequent development and health, as well as whether any of the changes can be passed down to subsequent generations, remains debatable, even if the general idea that epigenome programming occurs in response to events at that stage is broadly accepted.

Another factor affecting both pregnancy rates and possibly health risks for the child that has been fully recognized only recently is the oxygen concentration of the embryo culture conditions…

The Swiss paper, critics argue, conflates the fetal programming theory with the assertion that because ART involves manipulation of the early embryo, which is extremely sensitive to environmental insults, it must alter vascular and cardiac function in children afterward. The study then alludes to the earlier research on mice, which detailed how ART alters the cardiovascular phenotype by epigenetic alterations that were related to sub‐optimal culture conditions at the point of conception. One such critic is Sutcliff. “If there are effects on health resulting from ART we won't see them for a long time,” he said.

Similarly, Louise Brinton, Scientific Advisor for International Activities in the Division of Cancer Epidemiology and Genetics Office of the Director, US National Institutes of Health, suggests that it is premature in light of current evidence to change regulations or recommendations relating to well‐established ART procedures. “I think we are still gathering data to fully address the relationships, so do not see that there has yet been a shift in the assessment of health risks,” she said. “The children conceived as a result of ART are still in general quite young, which limits our ability to assess the spectrum of risks.”

Scherrer though insists that the risks are real and should be taken seriously. “There is no doubt at all that at a very young age the cardiovascular phenotype of ART children is very different from those naturally conceived. We have evidence that kids born from mothers with preeclampsia have roughly three‐fold increased risk of premature stroke,” he said. Preeclampsia is characterized by high blood pressure in the latter stages of pregnancy and is associated with altered cardiovascular phenotype in the offspring, according to Scherrer. “There is little reason to believe that ART children will behave any differently from preeclampsia children.” He agrees though that it will take another 10 to 20 years before this can be confirmed.

Cancer risks

The same is true to a large extent when it comes to cancer risk associated with ART. Among the strongest evidence came from a 2013 evaluation of more than 2 million children born in Denmark between 1964 and 2006, of which 125,844 were offspring of women assessed for infertility 6. The principle finding was that children born to mothers with fertility problems had an 18% higher risk of cancer during childhood and 22% higher risk during young adulthood than those conceived naturally. However, this study looked at women with fertility problems who had not necessarily resorted to ART treatment—indeed many children were born well before the first IVF child. Furthermore, because cancer is rare in young people, it only equates to an additional four cases of childhood cancer and nine cases of cancer in young adults per 100,000 children born to mothers with fertility problems.

Indeed, a more recent study on ART‐conceived children found no evidence at all of elevated risk for solid cancers 7 but observed increased risk both of leukemia and Hodgkin's lymphoma among ART‐conceived children. This was based on analysis of 1,628,658 children born between 1984 and 2011 listed in the Medical Birth Registry of Norway, of which 25,782 were conceived by ART. Of the total 4,554 cancers of all types, 51 occurred in ART‐conceived children, which was not significantly different.

The underlying causes of health risks

There is also much debate about the underlying causes for increased health risks. One of the main candidates is again the sub‐fertility of the women, but also various aspects of the ART procedure itself. This includes the culture medium in which the embryo develops after conception, as well as the oxygen concentration in the incubator where the embryos are grown. “The culture medium has been a big focus of attention since 2010,” Brison commented, referring to a recent study that compared the impact of two embryo culture media in IVF, one known as G5 and the other HTF 8. It found statistically significant differences between the two groups both in pregnancy rates and birthweight, but in opposite directions. Mothers in the G5 media group were more likely to become pregnant but also more likely to have babies with lower birthweight. Brison commented it was possible these differences resulted from some other aspect than the culture medium itself, but thought this unlikely. He has also called on national registers of assisted births to record the culture medium to make data for future comparative studies available. Scherrer argues that more research is needed on culture mediums in animal models. “I see the only chance of making progress being to look at animal models more widely to see whether modifying IVF techniques has any favorable effects on cardio or metabolic or whatever phenotype you are interested in and think about translating the new insight gained into IVF in humans,” he said.

If we have concerns over health risks associated with conventional IVF, those will be really heightened if we're using gametes produced artificially.

Another factor affecting both pregnancy rates and possibly health risks for the child that has been fully recognized only recently is the oxygen concentration of the embryo culture conditions, which in the earlier days of ART was around 20%, the same as in the atmosphere. “But it was found that animals do better at 5% oxygen concentration, closer to that prevailing in the female tract,” Brison explained. One theory is that higher oxygen concentrations enhance generation of reactive oxygen species at this delicate stage of embryonic development. More and more IVF clinics are therefore adhering to lower oxygen concentrations, despite the higher costs involved, which Brison says is a good way of reducing potential risks of IVF.

This is related to another factor, which is the construction of the incubators used to culture the embryos. Until recently, embryos had to be taken out once or twice a day for examination under a microscope, which exposed them to atmospheric conditions, albeit for relatively short periods. Brison suggested this disruption could undermine the benefits of the controlled incubator environment. “Therefore the new generation of culture incubators are very important,” he said. “Now we can examine embryos remotely inside the incubators through time‐lapsed cameras.” While it is difficult to assess whether these and other improvements have decreased health risks over the 39 years that ART have been used, one health‐related factor at least has improved. “We have done a study showing that birth weights have increased quite a lot over the last 25 years,” Brison added.

New technologies, additional risks?

At the same time, new techniques are emerging, raising fresh concerns over health risks and ethical issues. The principal area is generation of artificial gametes from pluripotent stem cells, for in vitro development of human eggs and sperm. This has potential for infertile patients who cannot produce viable gametes, or fertile couples at high risk of transmitting serious diseases to their children. It also has potential for same sex or even single parents, although with obvious ethical concerns. But the science itself takes no account of ethics, and, as Brison noted, this will introduce a completely new set of health concerns. “If we have concerns over health risks associated with conventional IVF, those will be really heightened if we're using gametes produced artificially,” he commented. “The same applies to mitochondrial transfer used to avoid transmission of diseases associated with mitochondrial genes.”

In fact, mitochondrial transfer, for conception of “three‐parent babies”, was first approved in the UK in February 2015, which has created a precedent both for how these new techniques should be monitored and regulated. Under mitochondrial transfer, the baby's mitochondrial DNA comes from a third‐party donor, usually because the mother's mitochondrial DNA includes some genes with deleterious mutations. “The HFEA has required pretty extensive testing in human embryonic stem cell lines before giving the license,” explained Brison, adding that other countries may not be taking as much care. “At least that shows that the HFEA has the framework for that technology to be risk assessed, licensed and then monitored carefully. So in vitro derived gametes from stem cells will go down the same pathway I suspect.”

Yet the whole debate over safety of ART techniques in general still has a long way to go, with scientists such as Scherrer calling for more work on animals to minimize long‐term health risks through development of new culture media and processes. There is at least one point on which all parties do seem to agree at least as far as current techniques are concerned, which is that it will take another 10 or even 20 years to reliably assess the long‐term health outcomes for earlier IVF babies. Hopefully by then techniques will have advanced to the point where many of the earlier risks have been greatly reduced, even if not completely eliminated.