In vitro Fertilization (IVF) is considered the 'big guns' of infertility treatment, but does it always work? Sadly, the answer is no. According to Resolve: The National Infertility Association, women with top chances of IVF success have per-cycle success rates of 40% or higher, while the majority of women have per-cycle success rates of just 20-35%. In other words, the odds of success just aren't that high. There are multiple steps involved in an IVF cycle, and complications may occur at any point in the process. Here we'll take a look at some of the things that may go wrong.

IVF Issues During the Stimulation Phase

Issues with IVF can occur right from the stimulation phase when medications are used to mature multiple eggs (rather than a single egg that is generally produced with each menstrual cycle) and induce ovulation to allow for egg retrieval. There are several different protocols that are used, and each woman's body can respond differently. It is possible too few or too many eggs mature. An over-response with too many eggs means it is possible the egg quality may not be ideal. A poor response to the medications can result in a low number of eggs being retrieved, meaning a slimmer chance of creating embryos that survive to transfer. It is also possible that there are no eggs to retrieve at all.

If the body is overstimulated and estrogen levels become too high, ovarian hyperstimulation syndrome (OHSS) can occur, which can prevent an embryo from being transferred, creating a need for it to be frozen and transferred at a later time when estrogen levels have returned to an acceptable level.

Even if a response to medication is typical, there are additional factors that can complicate the cycle. Hormone levels can be off, and estrogen can be too high, or too low, which can affect how the follicles grow or interfere with other medications, like those meant to suppress ovulation. The presence of cysts, which can sometimes be brought on by the stimulating medication itself, can further delay or derail a cycle as cysts often produce estrogen, which can interfere with the process. Occasionally the body's natural cycle will override and breakthrough bleeding can occur, despite best efforts to delay ovulation and menstruation. Many of these situations can result in a delayed or a canceled cycle. With so many variables, stimulation is a tricky scenario to attempt to control.

IVF Issues During Fertilization

If retrieval is successful and at least one mature egg is retrieved, the sperm will be introduced in the hope that fertilization will occur (or intracytoplasmic sperm injection might be used). Once the sperm has fertilized the egg, the embryo is allowed to grow in a controlled lab setting until it reaches a stage where it can be transferred back to the woman's uterus, or frozen to be transferred at a later date. The time between when the egg is fertilized and when it is transferred back, or frozen, often has a high attrition rate. This attrition combined with a low number of eggs retrieved can mean that no embryos make it to transfer. Even embryos that grow to a point where they are deemed acceptable to be transferred may still be genetically abnormal, and without expensive (and potentially damaging) testing, there is no way of knowing which embryos are the healthiest.

IVF Issues During Embryo Transfer

After progressing through stimulation (without having OHSS) and retrieval with at least one successful embryo, the uterine lining must still be prepared for implantation, and the embryo transferred. Again, medications are used to stimulate to the uterus to grow a lining for the embryo to implant in. Sometimes the hormones used to stimulate the lining to grow don't work, leaving the lining too thin or, on the other end of the spectrum, the lining can also become too thick. Cysts in the uterus can also form, either spontaneously or due to the use of the stimulation medications. A cyst can prevent an embryo from being transferred as it can interfere with implantation.

IVF Issues During Implantation

If a suitable uterine lining is achieved and an embryo transferred, the embryo needs to successfully implant within the lining. This is one of the most mysterious points in IVF as there is little that can be done to assist in implantation; it is simply a waiting game to see if implantation will be successful or not. A blood test will be taken at some point after the transfer (the exact time frame differs from doctor to doctor, but usually between 10 - 14 days after). If the blood test comes back positive for the hormone human chorionic gonadotropin (hCG), implantation has been successful, and pregnancy has been achieved. The level is often monitored every few days for two or three more blood draws to make sure the levels are rising appropriately. If the levels do not increase accordingly, a chemical pregnancy may have occurred, meaning the embryo implanted for a short time, but did not continue to grow. This can happen even with "naturally" achieved pregnancies, but these are often missed because the pregnancy ends before the woman even realizes she was pregnant in the first place. A chemical pregnancy can be a difficult experience because there is often no specific reason to indicate why the pregnancy didn't continue.

There have been amazing advances in reproductive technologies and though there are still limits, IVF is a powerful tool that has helped many women achieve successful pregnancies. Human conception has multiple variables, many of which remain a mystery but knowing what you are up against is a step in the right direction to decide if IVF is for you.