In Vitro Fertilisation (IVF) is a process where eggs are taken from the ovaries and fertilised outside the body.
The fertilised eggs grow into tiny balls of cells called embryos. One (or less commonly two) embryos that look healthiest are selected to be placed in the uterus (womb). If an embryo successfully attaches (implants) to the uterus, a pregnancy will start. From this point onwards the pregnancy continues as usual.
IVF is used by couples experiencing infertility. It can overcome a number of different barriers to pregnancy. It can also be used with donor sperm and eggs, or when using a surrogate.
Vocabulary
To make this article as easy as possible to read, the words women and mother are used in reference to people with biologically female reproductive organs at birth. Transgender and Intersex people’s IVF opportunities will depend on their reproductive organ and hormonal status.
A surrogate is a woman who carries a pregnancy and gives birth on behalf of someone else. The child is then passed to its parents.
Why is IVF needed?
Many people experience difficulties in conceiving a child. About one in six UK couples find themselves unable to conceive after a year of trying. This is called infertility. Single-sex couples may also use IVF treatment to conceive.
Often there is a mix of different causes for infertility. It’s not uncommon for couples to find that there are causes from both partners. Or sometimes it is not possible to identify the cause; this is called ‘unexplained fertility’.
There are a variety of possible treatments for infertility – see our article Female Infertility for more detail about the causes and treatments of infertility in women. Often women will have tried other simpler treatments before they consider IVF.
IVF is an important fertility treatment because it can overcome many common barriers to pregnancy. It has led to many successful pregnancies, but it is also a difficult and lengthy process with no guarantee of success.
Who is IVF for?
In Vitro Fertilisation (IVF) treatments are able to help in a variety of different situations.
Most commonly, IVF is used to help women whose infertility is caused by their eggs not being released from their ovaries, or where the fallopian tube that guides the egg to their uterus is missing or blocked, or to help men who are not able to produce enough quality sperm.
Because of how it works, IVF also provides the opportunity to use donated eggs or sperm. This is useful for same-sex couples, or couples where either the eggs or sperm are not available.
IVF can also be used alongside surrogacy. Surrogacy is necessary if the parent(s) do not have a uterus able to safely carry the pregnancy (e.g. if it has been removed, or is damaged). Surrogacy may also be used if health problems would make it dangerous for the mother to carry the pregnancy themselves.
A special use of IVF is to check embryos for inherited conditions. Some couples know that they carry genes for serious medical conditions that they could pass on to their children. By using IVF, they can select embryos that have not inherited these genes, so that their children will not have the condition.
Finally, a more recent use for IVF treatments is to save eggs or sperm for later use. For example, some people with cancer choose to ‘freeze’ their eggs or sperm before starting their cancer treatments if those treatments carry the risk of causing infertility.
Step 1: Growing and collecting the eggs
During a normal menstrual cycle, one mature egg is released from an ovary into the fallopian tube each month. This is called ovulation. Hormones control this process, preventing too many eggs from growing and being released. But for IVF, more than one egg will be needed. The woman (or egg donor) has to go through a special process to make this possible.
Each egg develops inside a structure called a follicle, which nurtures the egg and releases hormones including oestrogen. The hormone follicle stimulating hormone (FSH) is used by the body to tell the ovaries to grow the follicles.
In IVF, the woman takes injections of a large amount of FSH. This boosts the hormone’s levels beyond those found during a normal menstrual cycle. This leads to many more follicles developing than usual. The follicles can be seen using ultrasound imaging, so that their development can be tracked.
Normally, the release of oestrogen from the follicles triggers the pituitary gland to increase levels of luteinising hormone (LH), signalling to the ovaries that it’s time for ovulation. But in IVF, it’s important that the mature eggs stay in the ovary to be collected! Drugs are used to prevent this LH signal, so that the eggs continue to develop and stay in the ovary.
But there’s one more problem: without LH, the eggs won’t fully complete their maturation. And so, when the time is right, another hormone is given to increase levels of LH and get the eggs ready for collection. This is usually done using human chorionic gonadotrophin (hCG) or gonadotrophin releasing hormone (GnRH).
When everything is ready, the eggs are collected directly from the ovaries in a small surgical procedure.
Step 2: Fertilising the eggs
The eggs are usually mixed with the sperm in a dish in the laboratory. But sometimes there is a problem with the sperm and they might need a little help. In this case, a selected sperm can be injected directly into the egg.
Step 3: Choosing an embryo
After fertilisation, the eggs are grown for three to five days. By this time each fertilised egg should have divided to become a little ball of cells. It is now called an embryo.
The embryos are checked to make sure they are growing properly. The healthiest looking embryo(s) is then chosen for implantation into the uterus. Doctors use the expression ‘returning’ the embryo, although it doesn’t have to be implanted into the same woman as the egg came from.
But first during this step, there are some ethical questions to consider.
DNA testing and embryo selection
It is possible to do DNA testing on the embryos. This means it is possible to find out all sorts of things about them. But is it ethical to test them in this way? How would the information be used?
When, and for what reasons, is it ethical for people to choose one embryo over another?
In the UK, it is illegal to test an embryo for DNA linked to things like sex, height, hair colour, or intelligence.
But it is legal to test for chromosomal problems including Down’s Syndrome. It’s also legal to test for serious inherited medical conditions. This means that parents who know they carry genes for a serious condition can select an embryo knowing that the child will not suffer from it.
In addition to DNA testing, there are also ethical questions about whether it is acceptable that unused embryos are destroyed. Different countries have different rules about embryo testing and destruction. What do you think? Where would you draw the line?
Step 4: Transferring the embryo to the uterus
Before the embryo is returned, the woman is given hormones like progesterone to prepare the lining of her uterus for the embryo to implant (attach).
In the UK, it’s normal practice that only one embryo is returned to the uterus especially in younger women, although sometimes two are returned. Returning two (or more) embryos increases the chances of a pregnancy, but it comes with the risk of both embryos developing and causing a twin pregnancy. Twin pregnancies are more dangerous for both mother (or surrogate) and child, so it’s best to avoid this if possible.
If the embryo successfully implants then it will start growing a placenta, which will send hormonal signals to the mother to let her body know that it is there. The pregnancy will then continue in the normal way. The hormonal signal from the embryo’s developing placenta can also be picked up by pregnancy tests, which are used to confirm the pregnancy.
You can find out more about implantation, pregnancy tests, and what happens next in our article Hormones in Pregnancy and Lactation.
Difficulties and side-ffects from treatment
Using Follicle Stimulating Hormone (FSH) to encourage follicle growth can sometimes work too well, so that the ovaries grow too many follicles. If this happens, the ovaries become enlarged and leak fluid into the abdomen. This can cause pain, swelling, nausea and vomiting. This usually goes away without treatment, but in particularly bad cases it might be necessary to drain fluid from the body.
An important difficulty of any fertility treatment is the complex emotional rollercoaster that couples can experience. Infertility can have long term impacts on the mental health of women and their partners, and on their relationships.
IVF in particular can be very emotionally stressful because it takes a long time to complete (six to eight weeks for each attempt). It involves many visits for monitoring and procedures, and many injections and medications. And all this with no guarantee of success. But of course, IVF also offers an opportunity for many couples who have struggled with infertility to be able to have children.
Fertility counselling is recommended to people making difficult decisions about what treatments to try, especially if considering the use of donor egg/sperm or surrogates. Counselling can be of help before, during, and after treatment, as the emotional impact can be long-term.
Chances of success
Most rounds of IVF fail, so multiple rounds might be necessary. But there is still no guarantee of a successful pregnancy and live birth.
The age of the woman providing the eggs makes a big difference to the chances of success. In 2021, for women under 35 years old who used their own eggs, nearly one in three embryo transfers resulted in a live birth. But for women over 44 years old, it was less than one in twenty.
Knowing the average chances of success helps the NHS plan IVF care. But infertility is complex, and averages only tell us part of the story. The chance of success can vary a lot between different people.
For this reason, doctors consider many different factors when estimating an individual’s chances of success, including their health and reasons for infertility. When taking these factors into account, their personal chances might be higher or lower than the above averages would suggest.
