As an IVF specialist, the commonest question patients ask me is - How many embryos should I transfer ? While IVF technology today is very good at making embryos in the IVF lab, we still cannot control the process of embryo implantation. This means that most of the embryos we transfer do not become babies - which is why the success rate of most IVF treatment cycles is still about 40% per cycle.
I tell patients that if the technology was perfect, we would transfer 2 embryos for every patient ( most infertile couples are very happy to have twins so they can complete their family at one stroke); or just 1 for the minority who wanted to have only one baby. However, because the technology is still not perfect, deciding how many embryos to transfer is always a heart-wrenching decision.
As is usual with most of life's decisions, there is a price you pay for every decision you make - and every couple needs to weigh the risks and benefits of this tough choice. ( In countries which allow doctors to transfer only 2 embryos by law, the decision is much simpler, because there is no choice available !)
We know that the chances of pregnancy are proportional to the number of embryos we transfer - the more the number of embryos transferred, the greater the chances. However, just as the chances of success rise, so does the risk of multiple pregnancy. High order multiple births can be a major complication, because of the risks of prematurity, so we would like to select the optimal number of embryos to transfer , which would ensure a pregnancy, without risking a high-order multiple birth.
Since the chances of implantation depend upon a number of biological variables which are hard to quanitfy, we use the following guidelines to help our patients make this difficult decision.
The variables we need to consider include:
1. Age of the woman and ovarian reserve
2. Quality of the embryos ( Grade)
3. Day of transfer ( Day 2, 3 or 5)
4. Number of failed IVF attempts
5. Fertility history
6. Endometrial receptivity
7. Financial and real-life constraints
8. Patient preference
9. Use of donor eggs/ donor embryos
10. Quality of the clinic ( overall success rate)
Such a large list of variables ( many of which are "soft" and subjective")explains why this is such a difficult decision.
This is how we approach this problem in our clinic.
For young patients ( less than 30) , who are doing their first IVF cycle, we suggest they transfer 2 embryos if these are Grade A embryos on Day 3. If the patient is between 30-38, we add one more, so we transfer 3. For patients more than 38, we suggest 4, as the risk of a multiple pregnancy decreases as a woman gets older. For women more than 40, we are happy to transfer as many embryos as they get.( Of course, if they are using donor eggs or donor embryos , then we need to re-do the calculations). If the embryo quality is poor ( Grade C or less) , we add one more. If the endometrium is poor, we add one more embryo ( as the chances of implantation go down if the uterine lining is poor). For patients who have failed IVF cycles elsewhere, we transfer one more embryo. If the patient opts for a Day 5 ( blastocyst ) transfer, we reduce the number by one. This algorithm gives us a rough rule of thumb as to how may embryos to transfer, which tries to factor in all the key variable which can affect embryo implantation. What I like about it is that it allows us to choose a number which is individually tailored for each patient,
However, we always let the patient make the final decision. For example, if a patient says that it's her last IVF cycle, because of financial constraints, and she wants to transfer more embryos, we will do this.
In the final analysis, we feel that the patient should make their own decision, since they suffer the consequences of whatever decision they make. I suggest to patients that they take what I call the "path of least regret". It's often a question of choosing between the lesser of two evils : not getting pregnant; or having a high order multiple. Many patients prefer transferring more embryos, and are willing to consider the option of selective fetal reduction in case they have a high order multiple. In this sense, a high order pregnancy is a "manageable complication" . Others would start a fresh cycle rather than countenance a reduction. Since this is such a personal decision, it's best if couples make it for themselves, so that they have peace of mind they did their best.
Most of the time, this system works well and we have a high pregnancy rate and many satisfied patients. However, whenever a patient does not get pregnant, we always wonder - Maybe if I had transferred one more embryo, she might have conceived ? And conversely, when she has a triplet pregnancy, we kick ourselves for transferring too many embryos ! Being an IVF specialist can be stressful !