For anyone trying to get pregnant, successful embryo implantation is the end goal. If you’re undergoing fertility treatments, you’ve probably realized that the implantation process is complicated. There are a lot of factors in play that all have to line up just right for implantation to succeed. This article will demystify the process by giving you in-depth information on what implantation is, what factors are important for successful implantation, and what your IVF implantation timeline could look like.
In vitro fertilization (IVF) is one type of assisted reproductive technology (ART), and it involves harvesting viable eggs that are fertilized outside the body and then transferred to the lining of the uterus for implantation. An IVF cycle has these 5 main steps:
Embryo implantation is the process by which a fertilized embryo or blastocyst attaches itself to the endometrium and pregnancy begins. There are two major factors to creating the proper uterine environment for successful implantation.
First, the embryo needs to be of good quality and the right maturity. With IVF, you have a lot more control over this part. Once your eggs are retrieved and fertilized, an embryologist monitors your embryos to ensure they’re developed enough for transfer, and that they are of sufficient quality to implant successfully.
Second, the endometrium must be receptive. Receptivity is achieved when the endometrium reaches a thickness of 7-10 mm and has a trilaminar appearance. In the early stages of IVF treatment, your fertility specialist might recommend doing what is called a mock cycle and an endometrial receptivity test to determine your receptivity. If your receptivity isn’t ideal, they may adjust your embryo transfer timing.
If all the conditions are met, implantation occurs between days 20 and 24 of a typical 28-day menstrual cycle. In an IVF cycle, it happens 6-10 days after egg retrieval, and 1-5 days after embryo transfer.
It’s important to remember that even though IVF can overcome a lot of barriers to getting pregnant, the embryo still has to attach itself to the endometrium on its own. Even if you’ve done everything right, there is a chance that the implantation might fail.
While embryo implantation is the last step in becoming pregnant, it’s important to understand the basic timeline of your IVF treatment. The following are the stages you’ll move through:
Once you decide fertility treatment is something you wish to pursue, you’ll meet with a reproductive endocrinologist who will go over your medical history and any diagnosis you or your partner might have that could impact your fertility.
Before the treatment starts, you will undergo blood work, fertility testing (both male and female), an ultrasound, and infectious disease screening. Your fertility specialist will use your test results and medical history to design a treatment protocol personalized to your needs.
Most IVF cycles are done with injectable hormones to stimulate follicle growth so that multiple eggs can be retrieved in one cycle. Your fertility specialist will use blood work and ultrasounds to monitor your follicle and egg development, as well as your hormone levels. This is the part of your implantation timeline that is the most time consuming, as it can involve daily cycle monitoring appointments at your fertility clinic.
When your fertility specialist is satisfied with the growth of your eggs, they’ll administer a hormonal shot that causes your eggs to mature. This is frequently referred to as the trigger shot. You will be scheduled for egg retrieval 36 hours later. Once the retrieval procedure is done, your eggs will be fertilized in a lab and monitored by an embryologist.
Once your embryos are adequately matured, and you’ve decided which to implant, you will be scheduled for your embryo transfer procedure. This is a short procedure where the embryo is injected into your uterus using a catheter and ultrasound.
Two weeks after your transfer, you will return to your fertility clinic to do a pregnancy test. It is necessary to wait two weeks because that is how long it takes for the pregnancy hormones to reach a stable enough level to provide reliable results. Testing at home during the two weeks is likely to give you false positive or negative results.
IVF with frozen embryo transfer is similar to IVF with fresh embryo transfer. The biggest difference is that there is no need to go through the process of stimulating follicle growth and retrieving eggs for fertilization. Instead, you move directly to preparing your uterine lining to receive developed embryos.
At the start of your menstrual cycle, your fertility specialist will do baseline blood work and ultrasound testing to determine if you will need medication to boost your estrogen levels.
At around the midpoint of your menstrual cycle, your fertility specialist will do an ultrasound to check the thickness of your endometrium. If it’s less than 7 mm thick, you will continue estrogen treatment until it reaches the necessary thickness.
Once your endometrium has reached an appropriate thickness, your embryo will be thawed and you’ll undergo the embryo transfer process during your window of implantation (WOI).
The window of implantation is when the endometrium (the mucous tissue that lines the inside of the uterus) is most receptive to the embryo implanting. Typically, this happens between days 19 and 21 of an average menstrual cycle. It varies for each person, of course, but the fact that there is a window – and that it is a relatively short one – does not.
During the WOI, a mix of hormones are created to encourage the embryo and endometrium to synchronize. It’s crucial that the embryo be transferred during this window to maximize the chances of a successful implantation. This is true for both frozen embryos and fresh ones. An endometrial receptivity test will tell you when exactly your WOI occurs.
One of the causes of implantation failure is the lack of synchronization between the embryo and endometrium. This happens when the WOI occurs before or after the average timing in a 28-day menstrual cycle. Up to 30% of fertile women have a nonstandard window of implantation. This makes endometrial receptivity testing an important consideration in your IVF cycle. For women who’ve already experienced implantation failure or who only have a small number of viable embryos for IVF, ORA™ (Optimal Receptivity Analysis) can help with understanding your endometrial receptivity and identifying your individual WOI.
