How does ICSI increase IVF success?

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The traditional IVF approach is to allow this meeting to take place ‘naturally’, albeit in a laboratory dish: the woman’s egg is placed in a special culture medium with a prepared semen sample containing thousands of sperm. The fittest sperm fertilises the egg, mimicking what would normally happen in the woman’s reproductive tract.

As its name suggests, ICSI is far more precise. Rather than leaving the egg and sperm to meet on their own accord in a laboratory dish, this technique allows us to directly inject a single sperm into a woman’s egg, thereby overcoming any issues that may be getting in the way of a sperm and an egg meeting and coming together naturally. Here, we consider some of the reasons why ICSI may be considered during IVF and what specific fertility problems it can help overcome.

Who is ICSI suitable for?

When a couple is experiencing difficulties getting pregnant, it can be easy to focus solely on the woman’s fertility. However, a male factor contributes to infertility in approximately 40% of couples who fail to conceive.1 ‘Male factor infertility’ typically involves an alteration in the number, shape and/or movement of the man’s sperm, all of which can affect the sperm’s ability to fertilise an egg the natural way. ICSI is most commonly used to help overcome these types of sperm-related issues.

ICSI may also sometimes be offered if a woman has very few eggs available (e.g. due to age). In this case, ICSI is used to increase the chances of successful fertilisation, thereby lowering the risk that the woman runs out of eggs before she achieves a successful pregnancy through IVF.

ICSI may also be recommended if one or more previous standard IVF cycles were not successful due to failed fertilisation, or if the reason for cycle failure is unclear but a sperm-related issue is suspected despite a normal semen analysis.2

A checklist for fertile sperm

If your doctor suspects male factor infertility could be affecting your chances of pregnancy, they will usually suggest a semen (sperm) analysis. This is the main method used to test male fertility. During the analysis, a number of different factors that could be affecting your ability to conceive naturally are studied, including:

  • The volume of semen, which needs to be sufficient to transport sperm into the female reproductive tract
  • The sperm concentration and total sperm count, which affect the likelihood that enough sperm will reach the egg in order for one to fertilise it
  • The physical shape of the sperm, as abnormally shaped sperm can have difficulty swimming to the egg or penetrating the egg’s outer layer
  • The motility of the sperm (i.e. how well it can swim) – if large numbers of sperm in the sample are ‘weak swimmers’, then a natural pregnancy will be more difficult to achieve.

Your specialist might also recommend additional testing for:

  • Sperm DNA damage or fragmentation: sperm with damaged or fragmented DNA have a reduced chance of fertilising an egg
  • Sperm antibodies, which if present, can attack and impair sperm function.

Depending on your results, your doctor may then order follow-up tests to make sure the results are accurate and/or to see if anything else is preventing the semen from doing its job.

Once the tests are complete, your specialist will discuss your results with you and explain what your options are, including whether ICSI is likely to increase your chances of successful fertilisation and the overall success of your IVF treatment cycle.

Success rates with ICSI

Because of ICSI, many previously infertile men now have a good chance of fertilising eggs with their sperm. With some couples, pregnancy rates as high as 45% have been achieved with ICSI.3 However, rates this high are not always possible because of other factors, including age and egg quality.

The fertilisation of an egg and its subsequent development into a growing embryo is a complicated process, and there are many reasons why IVF may not be successful, even with the assistance of ICSI. To aid our success rates at Newlife IVF, we:

  1. Ensure an egg is suitable for fertilisation prior to ICSI: Using polarised light microscopy, we assess a structure inside the eggs called a ‘spindle’. We call this ‘egg spindle visualisation’. This allows us to identify if an egg is at a certain stage of development (called metaphase II) and therefore, in optimal condition for fertilisation via ICSI.
  2. Select the healthiest-looking sperm for ICSI: If the genetic information in the sperm has been damaged, or if the sperm is unable to use its DNA correctly, then there is a risk that development of the embryo will fail, even if it has been successfully fertilised via ICSI.4 A number of factors can increase this risk, such as smoking and older age.5,6 It’s not currently possible to know if the sperm we choose for ICSI is completely free of genetic defects. However, by using an advanced imaging system with an extremely high-powered microscope, we are able to study the structure of individual sperm, helping us to select the optimum sperm to inject into an egg. Sometimes, we may also use another technique, called intracytoplasmic morphologically selected sperm injection (IMSI), to help us pick out a healthier sperm based on its shape. A DNA test can also provide us with more details about sperm quality.
  3. Assess the best position to inject the sperm into the egg: Our extremely high-powered microscope also allows us to very precisely inject the selected sperm into the egg, such that we avoid an important structure inside the egg called the spindle. Research has shown that injecting eggs away from the spindle results in higher fertilisation rates and better embryo quality.

Are there any risks with ICSI?

As with any medical procedure, ICSI carries both potential benefits and risks. While complications are uncommon, some risks specific to ICSI include:

  • Damage to the woman’s egg: Though the risk is low, the process of preparing the egg and inserting the needle can cause structural damage to the egg
  • Genetic inheritance of male infertility: If ICSI is used due to a genetic issue on the Y chromosome, there’s a possibility that a male child could inherit the same condition.

Your fertility specialist will only recommend ICSI if the potential benefits outweigh the risks for your individual situation. It’s important to discuss these factors in the context of your personal circumstances.

What is the cost of ICSI?

ICSI is offered as part of an IVF cycle. Please visit our IVF fees page for more detailed information about the costs involved.

Still have questions?

If you are concerned about the possibility of male factor infertility or would like more information about the role of ICSI in an IVF treatment cycle, you can make an appointment with one of our fertility specialists by calling Newlife IVF on (03) 8080 8933. You can also book online via our appointments page.

References

  1. Agerwal A et al. Reprod Biol and Endocrinol. 2015;13:37–46. ↩
  2. Palermo GD et al. Sem Reprod Med. 2015;33:92–102. ↩
  3. Palermo GD et al. Sem Reprod Med. 2009;27:191–201. ↩
  4. Colaco S & Sakkas D. J Assisst Reprod Genet. 2018;35:1953–1968. ↩
  5. García-Ferreyra J et al. Clin Med Insights. Rep Health 2015;9:21–27. ↩
  6. Zini A & Sigman M. J Androl 2009;30:219–229. ↩

Improving your fertility – top tips for men

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The most common fertility issues males encounter include a physical obstruction to the passage of sperm (the sperm simply can’t get to the woman’s egg), problems with sperm production or function (a low sperm count or large numbers of sperm with abnormal shape or movement), functional issues (such as impotence) and hormonal problems (which may impact the production of sperm and/or your libido).

Male factor infertility is more common than you may think – it plays a role in over a third of cases where couples can’t conceive, and affects one in 20 men.1,2

However, beyond a specific medical or physical problem, there are also certain diet and lifestyle changes you can make as a man to improve your overall fertility and chances of conceiving. This is because what we eat and how we live can actually have a big impact on our sex hormones and sperm quality, as well as our libido (sexual drive).

Below, we describe some adjustments you can make to your daily routines to help improve your fertility and overall reproductive health.

Exercise regularly

male in exercise shirt and headphones smiling with waterfront in backgroundNumerous studies have shown that exercise can boost testosterone levels.3 Testosterone is the key male sex hormone that regulates fertility. It is mainly produced in the testicles and is linked to both the development of sperm and sexual function.

It’s also important to be aware that exercising too much can sometimes have the reverse effect and lead to a reduction in testosterone levels. Taking zinc supplements can help mitigate this effect; however, in general you should aim to exercise regularly but not excessively.

Quit smoking

We all know that smoking is bad for our health but what many men don’t know is that smoking can affect every stage of the reproduction process in men. This includes the development of the DNA (genetic material) in sperm, as well as the production of important reproductive hormones. Men who smoke may also experience difficulties in getting and maintaining erections because smoking can cause damage to the small blood vessels that supply the penis with blood.

There is now extensive evidence that smokers are more likely to have fertility problems and take longer to conceive than non-smokers.4,5,6 Therefore, the best way to improve your chances of conceiving is to quit smoking. It’s well established that smoking decreases quality of life and shortens lifespan.  As a motivator, think about the child you are hoping to create and how much quality time you hope to spend with them in the future.

Reduce your alcohol intake

Excessive alcohol consumption can harm sperm count, shape and motility (i.e. how well the sperm can ‘swim’).

Studies have found increased sperm abnormalities in men who drink more than three-and-a-half standard drinks per day.7,8 Alcohol can also disrupt testosterone levels and even turn the testosterone precursor chemicals into oestrogen, leading to increased oestrogen levels (and the dreaded ‘man boobs’!).9 Therefore, reducing or even ceasing alcohol intake can improve your reproductive health.

Stop taking recreational drugs or steroids

Taking certain drugs, both legal and illegal, can affect your fertility. The main ones are:

  • Anabolic steroids – often taken to reduce fat and increase muscle mass, these drugs can actually lead to testicular shrinkage and interfere with the hormones that affect sperm production.
  • Marijuana – the psychoactive ingredient in marijuana, THC, can disrupt testosterone production, leading to a lowered libido as well as reduced quantity and quality of sperm.
  • Opioids – both prescription opioids (for treating pain and addiction) and illegal narcotics (such as heroin), can impact male fertility by affecting testosterone levels.
  • Testosterone – replacement testosterone can impair sperm production by blocking the hormonal signals that tell the testicles to make testosterone.

Manage your stress levels

High stress levels, particularly ongoing, can have a negative impact on your fertility by interfering with certain hormones. It is thought that stress may activate steroid hormones involved in the metabolism of proteins, fats and carbohydrates, which may, in turn, affect testosterone levels and the production of sperm.10,11

Get enough sleep

Sleep may be just as important for fertility as other bedroom activities (!), according to a growing body of research. A recent study suggests that 7–8 hours of sleep a night is the ideal, while too little or even too much sleep can reduce your chances of conceiving.12

Eat a healthy diet

A healthy, balanced diet is essential for your overall health. But did you know that choosing the right foods can enhance sperm function and, in turn, your fertility? Nutrients that can improve the quality of your sperm include:

  • Vitamin D (tuna, salmon, cheese, egg yolk)
  • Vitamin E (vegetable oils, nuts, seeds, green leafy vegetables)
  • D-aspartic acid (oysters, avocado, asparagus, oat flakes)
  • Omega-3 fatty acids (mackerel, chia seeds, walnuts, plant oils)
  • L-arginine (pumpkin seeds, turkey breast, chickpeas, seaweed).13,14,15,16

It’s also important to keep your weight in check, as being overweight can reduce your fertility by affecting sperm and leading to hormonal changes.17

The bottom line

If you or your partner are having difficulties conceiving, there are a number of steps you can take as a man to improve your fertility and overall health, thereby maximising your chances of having a baby. Seeking professional help to rule out a specific physical or medical problem is also prudent. At Newlife IVF, we conduct both male and female fertility testing, including the highest quality semen analysis currently available in Victoria.

To make an appointment with one of our fertility specialists or to get a second opinion, call Newlife IVF on (03) 8080 8933. Alternatively, you can book online via our appointments page.

Further reading

References

  1. Hirsh A. BMJ. 2003;32:669. ↩
  2. Winters BR, Walsh TJ. Urol Clin North Am. 2014;41:195­–204. ↩
  3. Kumagai H et al. J Clin Biochem Nurt. 2016;58:1:84–89. ↩
  4. Mitra et al. Syst Biol Reprod Med. 2012;58: 255–262. ↩
  5. Al-Turki HA et al. Urol Ann. 2015;7:63–66. ↩
  6. Cui X et al. Mol Med Rep. 2016;14:753–761. ↩
  7. Jensen TK et al. BMJ Open. 2014;4:e005462. ↩
  8. Martini AC et al. Fert Ster. 2004;82:374–377. ↩
  9. Emmanuele MA et al. Alcohol Health Res World. 1998;22:195–201. ↩
  10. Ragni G, Caccamo A. Acta Eur Fertil. 1992;23:21–23. ↩
  11. IIacqua A et al. Reprod Biol Endocrinol. ↩
  12. Liu MM et al. Med Sci Monit. 2017;23:1842–1848. ↩
  13. Blomberg JM et al. Hum Reprod. 2011;26:1307–1317. ↩
  14. Sedigheh A et al. Int J Reprod Biomed. 2016;14:729–736. ↩
  15. Topo E et al. Reprod Biol Endocrinol. 2009;27:120. ↩
  16. Safarinejad RM. Asian J Androl. 2012;14:514–515. ↩
  17. Martini AC et al. Fert Ster. 2010;94:1739–1743. ↩

If not IVF, then what? Fertility treatments explained

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In vitro fertilisation (IVF) is the most widely known fertility treatment, but it is not the only option available to help couples with fertility issues. This is due to the fact that there are many different reasons why an individual or couple may be experiencing fertility problems and treatment should be tailored accordingly. Thus, fertility treatment actually encompasses quite a wide range of methods, each of which can help people to overcome specific challenges and ultimately, conceive. We explain the different options below, including when they might be suitable.

First-line treatments

Ovulation induction

Ovulation induction may be recommended for women who are not ovulating regularly or who are not ovulating at all, and is commonly used for those suffering from polycystic ovarian syndrome (PCOS).

As its name suggests, ovulation induction involves the woman taking medication to increase the level of follicle-stimulating hormone (FSH) that causes ovulation. These medications may be in the form of tablets (clomiphene or letrozole) or direct injections of FSH. This stimulates the growth of ovarian follicles (fluid-filled sacs containing an egg). Once the follicles are large enough, another hormone is then given to release the egg from the follicle. Couples are advised to have intercourse at this time to increase their chances of conceiving.

Intrauterine insemination (IUI)

Intrauterine insemination (also known as artificial insemination) may be considered when a couple has difficulty having intercourse. It may also be appropriate for women with scarring or defects of the cervix that prevent sperm penetration, and for men with mild reductions in either sperm count or sperm motility (i.e. sperm that don’t move properly) where concentrating the semen sample and placing it in the uterus is likely to be of benefit. IUI may be used in combination with medications that stimulate ovulation – this combination can increase the chance of pregnancy in some cases.

During a treatment cycle, patients are monitored closely with blood tests and ultrasounds. At the time of ovulation, sperm are placed directly through the woman’s cervix and into her uterus (womb) using a long, thin plastic tube that is similar to a straw (hence, the name artificial insemination).

Laboratory treatments

In vitro fertilisation (IVF)

IVF is a form of assisted reproductive technology (ART) in which eggs are retrieved from the body of a woman and combined with sperm outside the body to achieve fertilisation. If this is successful and the fertilised egg continues to develop into an embryo, it is transferred back into the uterus (womb) in the hope that it will implant and grow, thereby achieving a pregnancy.

Intracytoplasmic sperm injection (ICSI)

ICSI is a technique where a single sperm is directly injected into an egg to achieve fertilisation. This technique may be recommended when the male partner in a couple has been diagnosed with fertility issues such as low sperm count, abnormal sperm morphology (shape) or motility (movement), has had a previous vasectomy or an unsuccessful vasectomy reversal. The ‘best’ sperm – based on size, shape and movement – is selected for the ICSI procedure.

Sperm retrieval procedures

Some men have no sperm in their semen (a condition known as azoospermia) due to a sperm production problem or a blockage that prevents the sperm from getting into the semen. These men may need to have sperm taken directly from the testis or the epididymis (a coiled tube that stores sperm and transports it from the testis).

  • Testicular sperm aspiration (TESA) is done by inserting a needle into the testis and taking a small amount of material from the seminiferous tubules – a network of tiny tubes where sperm is produced. The procedure is done using local anaesthesia in an operating theatre.
  • Percutaneous epididymal sperm aspiration (PESA) can be an option for men who have obstructive azoospermia from a previous vasectomy or infection. Under local anaesthesia, a small needle is inserted into the epididymis to extract sperm. PESA is also usually performed in an operating theatre.
  • Microdissection TESE (microTESE) may be used for men who have a sperm production problem. This procedure is done under general anaesthetic. The testis is first opened with a small incision, then an operating microscope is used to identify the seminiferous tubules most likely to contain sperm and take tissue samples from them.

Pre-implantation genetic testing (PGT)

PGT is a way to reduce the risk of an individual or a couple passing on a specific genetic or chromosomal abnormality to their child. It may also be used to check for genetic problems in older women (e.g. over the age of 38 years), women who have experienced several miscarriages, or cases of repeated IVF failure.

In PGT, embryos are produced through the usual IVF process and then cells taken from the embryo are tested for genetic conditions. If the embryo is unaffected, it is then transferred to the woman’s uterus.

Egg or sperm freezing

There are two main reasons for freezing eggs. Some women need to freeze their eggs for medical reasons such as impaired ovarian function or impending chemotherapy or radiotherapy for cancer. Other women choose to freeze their eggs because they want to give themselves the option to have children in later years.

A man may be advised to freeze his sperm if he is about to undergo treatment for cancer, or if he has decided to have a vasectomy but may potentially want to have children later on. Men also can freeze sperm prior to either IUI or IVF if they cannot be present on the day scheduled for the respective ART procedure.

Donor treatments

Donor insemination

Donor insemination may be used as part of IVF for a single woman or for women in a same-sex relationship. The process is the same as artificial insemination, but the sperm used is from a donor rather than a male partner.

Donor insemination may be considered when the male partner does not produce sperm (or the sperm is abnormal) or when there is a high risk of the man passing on an illness or abnormality to a child.

Donor eggs

Donor eggs may be an option when a woman is unable to produce eggs or her eggs are of a low quality. This may be due to age or premature ovarian failure (a condition in which a woman stops producing eggs earlier than usual).

Donor eggs may also be appropriate in cases of recurrent miscarriage or if there is a high risk of the woman passing on an illness or abnormality.

Donor embryos

In some cases, some people choose to donate frozen embryos they no longer need. Treatment using these donated embryos may be suitable for a person or a couple who need both donor sperm and donor eggs.

What is the best option for you?

If you would like advice about the next steps to take on your fertility journey, you can make an appointment with one of our fertility specialists by calling Newlife IVF on (03) 8080 8933 or by booking online via our appointments page. We’ll complete a comprehensive assessment before explaining the options available to you and your partner.

What influences your chance of IVF success?

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The first baby conceived by this method was born in 1978, paving the way for a new era in how babies could be conceived and thus helping to address a range of fertility issues. Since then, the methods and technology used in IVF treatment have significantly improved, success rates have risen, and millions of babies have now been born worldwide using IVF.

IVF may be suitable if you would like to conceive but you or your partner have fertility problems, or perhaps because you want to avoid passing on inherited genetic disorders to your children. Whatever the reason, opting for IVF is a big decision so it is important to understand the factors that may influence the outcome of the procedure.

The likelihood of you having a baby via IVF can be affected by a number of factors – some that you cannot change, such as your age or particular types of fertility problem, and some that are modifiable. Modifiable factors can be medical or lifestyle related. Here, we will explore some of the most important factors that could affect your chances of conceiving with IVF.

Age

Age is well recognised to be one of the most influential factors in predicting IVF success. This is because as a woman ages, both the quantity and quality of her eggs declines.1 IVF technology in the setting of low numbers of eggs and/or poor-quality eggs is much less successful.2

If you receive donor eggs from a younger woman, you can expect to have nearly the same chance of success as women of the age of your donor. This is because younger eggs tend to be of better quality.2

Chromosomal abnormalities (problems with the DNA-containing structures in cells) are one of the major factors contributing to IVF failure and are the reason behind most miscarriages. These abnormalities increase as we age, and at a faster rate in women – by your mid-40s, as many as 75% of the chromosomes in your eggs are likely to have abnormalities.1

Our recommendation is to start IVF sooner rather than later (there is no lower age limit for IVF treatment). Everyone’s body is unique so a comprehensive medical assessment can give a better indication of your chances of conceiving with IVF than your age alone. IVF has been used successfully to help women at all stages of their reproductive life, but it is important to understand that each case is different.

Previous pregnancy or miscarriage

If you’ve previously been pregnant, the likelihood of you having a baby during your IVF treatment may be increased – IVF is recognised as being more effective in women who have previously been pregnant and/or had a live birth.3 On the other hand, if you have had a miscarriage, your chances of success with IVF may be reduced. If you have experienced recurrent miscarriages (three or more pregnancy losses), you might have a particular fertility issue where IVF may not help.

We can help you narrow down the probable causes of pregnancy loss and provide recommendations on the most appropriate course of action.

Type of fertility problem

IVF can be a good option for couples having trouble conceiving as a result of certain fertility problems, such as low numbers of sperm, issues with ovulation, endometriosis or blockages of the fallopian tubes. However, IVF does not work well for everyone.

Some fertility problems respond less well to IVF, including:

  • Poor ovarian response: Sometimes the ovaries do not respond well to fertility medications and therefore can’t produce the multiple eggs that make IVF more effective. This can occur if your ovarian reserve (number of eggs in your ovaries) is low or if they are not responding to the IVF treatment. If this is the case, IVF with your own eggs may not be the best option and you may wish to opt for donor eggs.
  • Duration of infertility: Statistically, couples that have been infertile for longer are less likely to have a baby with IVF.4 If you and/or your partner have had problems with fertility for several years, a health assessment will be necessary to determine whether IVF is suitable for you.
  • Dual infertility: If both you and your partner have fertility problems, the chance of success with IVF may be lower. Male infertility can be challenging to address with IVF, because sperm of impaired quality do not fertilise eggs at the same rates as normal sperm. Careful testing of both partners can give a better idea of whether IVF is the right option for you.
  • Fibroid tumours: Benign fibroid tumours (tissues that grow in and around the wall of the uterus, or womb) are very common, and usually don’t interfere with becoming pregnant. Sometimes, however, they can make it difficult for the embryo to implant and grow properly. These cases can usually be surgically corrected, allowing pregnancy to occur.
  • Uterine abnormalities: Congenital uterine anomalies (i.e. problems with the uterus that develop before you are born) can reduce the chance of a successful pregnancy. Outcomes vary from woman to woman, depending on the type of abnormality, so it is important to have a full health assessment to determine the specific abnormality.

Each case is different, so it is important that you undergo an in-depth consultation and careful testing in order to understand whether IVF is the right option for you.

Lifestyle factors

Lifestyle factors such as nutrition, smoking, and alcohol consumption can affect you and/or your partner’s fertility. Even though many factors influencing IVF success are out of your control, you may be able to improve your chances by understanding and addressing the following factors.

Obesity and nutrition

Being overweight or obese can have an impact on your fertility. Obesity (BMI 30 to 35) has been linked to miscarriage following IVF, and is also associated with reduced pregnancy rates in women and lower sperm quality in men.5 It is thought that an increase in leptin (the hormone secreted by fat tissue) can affect menstruation, in turn leading to worse IVF outcomes.

The ‘Mediterranean diet’, which consists of a high intake of vegetables, legumes and vegetable oils, and a low intake of fast food, has been linked to a higher pregnancy rate and may potentially improve the chances of pregnancy after IVF.6 This could be due to the presence of linoleic acid in vegetable oils, which may be beneficial for the implantation of the fertilised embryo.

Smoking and alcohol

You and/or your partner should quit smoking if you’re considering IVF. Smoking can cause damage to the sperm’s DNA and can affect the reserve of eggs and their ability to become fertilised.7 Smokers often require twice as many IVF cycles to conceive than non-smokers.8 You can also be affected by second-hand smoke – fertility is reduced in women exposed to cigarette smoke from their partners smoking at home.9

Drinking alcohol can also reduce your chances of IVF success, as it affects pregnancy and miscarriage rates. Just one can of beer per day before week 1 of the sperm or egg collection has been linked to reduced IVF success.10 Drinking alcohol when you’re trying to conceive – whether through IVF or not – is not recommended. This is because alcohol can cross the placenta and affect the development of your baby, potentially leading to problems such as fetal alcohol syndrome, stillbirth or physical disabilities.

During an IVF cycle, you should focus on eating healthy, balanced meals. Maintaining a healthy weight is extremely important, and your BMI range should ideally be between 19 and 30 before attempting IVF.Consider reducing your alcohol intake, and if you or your partner smoke, quitting is the best option.

Deciding whether IVF is right for you

When considering your fertility, there is no one-size-fits-all approach. As with all aspects of fertility care, the best decision for you is the one that is personalised to your individual situation.

For more information about IVF, please visit our IVF page. And if you would like to discuss your options with one of our fertility specialists, please call Newlife IVF on (03) 8080 8933 or book online via our appointments page.

References

  1. van Loendersloot LL et al. Hum Reprod 2010;16:577–589.
  2. Sabatini L et al. Reprod Biomed 2008;17:10–19.
  3. Nelson SM, Lawlor DA. PLoS med 2011;8:e1000386.
  4. Roberts S et al. Health Technol Assess 2010;14:1–237.
  5. Fedorcsak P et al. Acta Obstet Gynecol Scand 2000;79:43–48.
  6. Vujkovic M et al. Fertil Steril 2010;94(6):2096–2101.
  7. Frins S et al. Reprod Biol and Endocrinol 2015;13:134.
  8. Younglai EV et al. Arch Environ Contam Toxicol 2002;43:121–126.
  9. Zenzes M et al. Mol Hum Reprod 1998;4:159–165.
  10. Klonoff-Cohen H et al. Fertil Steril 2003;79:330–339.