Growing baby in a lab
In vitro refers to processes taking place in a test tube, culture dish, or elsewhere outside of a living organism. During IVF, this is precisely what happens. After retrieval, the fertility specialist combines the egg with a sperm sample in the lab. If fertilization is successful, an embryo will be created. However, the embryo needs a little more time to grow before being transferred back into the woman’s uterus to implant.
The Day 3 approach
A normally growing embryo will have 6-10 cells on Day 3 and can be transferred into the uterus at this stage. However, research shows waiting until Day 5 is more likely to result in successful implantation. In a recent study, good quality Day 5 embryos had 161% increased odds of live birth, far surpassing Day 3 contenders. In addition to being less successful overall, Day 3 embryos often do not qualify for preimplantation genetic testing (PGD) due to the limited number of cells present. This means the patient cannot test for genetic issues early on, and the embryo transferred could have a chromosomal abnormality or other problem.
Waiting for Day 5
Although statistics vary, patients who wait just 2 days longer are thought to have increased chances of pregnancy. At this stage, the embryo now consists of 70-100 cells and is thought to be stronger. Since there are more cells, the embryologist can take a closer look at the embryos using an embryo grading system to identify the strongest contender. The main disadvantage of a Day 5 approach applies to patients with fewer good-quality embryos. In this scenario, the body may provide a more hospitable environment than the lab for the embryo to develop in. When quality is a concern, Day 3 may be preferred.
Other advantages and disadvantages
Since Day 3 embryos are less likely to implant, the doctor may want to transfer more than 1 embryo at this stage. This means multiples are possible. The patient should consider this possibility if Day 3 is selected. Some women prefer Day 5 since the timing matches the natural process of pregnancy when the embryo would normally implant. Although patients should always double-check with the fertility clinic, many women will be happy to know Day 3 and Day 5 transfers typically cost the same. However, the price could increase if additional tests, such as PGD, are added to a Day 5 embryo transfer.
Choosing the right day
Although both Day 3 and Day 5 embryos have the potential to result in pregnancy, there may be a slight advantage to choosing a Day 5 transfer. Each case is unique, and the fertility specialist can advise on the preferred approach after considering factors such as age and egg quality. Whether a patient chooses Day 3 or Day 5, IVF is a great way to build a family.