In Spain, Law 14/2006 regarding Assisted Human Reproduction allows to transfer a maximum of 3 embryos.
The greater the number of embryos transferred, the higher the chances for embryo implantation to occur. However, it may also rise the multiple birth rate—twins or triplets—, with the subsequent risks this type of pregnancy involves both for the mother and the babies.
When making the decision of how many embryos to transfer, the following aspects should be taken into consideration:
- Egg quality
- Embryo quality
- Endometrial receptivity
- Uterine malformations
- Maternal age
- Previous failure with other fertility treatments, e.g. implantation failure, recurrent pregnancy loss, etc.
- Female factor infertility
Keeping in mind these factors altogether, among others, and medical instructions, a couple is ready to make up their minds regarding how many embryos they want to transfer. Such decision must be reached according to the couple’s own particular situation and always with the same goal: achieving a pregnancy without problems.
Thus, if there was a case in which embryo quality is not too high, it is understood that chances for embryo implantation to take place will shrink. In this sense, we can only expect that, if it is a 2-embryo transfer, just one of them is able to implant or even none of them, taking therefore for granted that the odds for both embryos implanting is too low due to their poor quality.
Guidelines by the SEF
In this area, the Spanish Society of Fertility (referred to as SEF, its initials in Spanish) has established some guidelines, although each case requires an individual approach:
- Women over 30: ideally, a single embryo transfer; 3-embryo transfers should be avoided.
- Women aged 30 to 37: single or two embryo transfer depending on embryo quality; three embryo transfer are only indicated after 3 failed IVF cycles.
- Women over 38: preferably, a two embryo transfer; only in cases of poor quality will be a three embryo transfer recommended.
- Egg donation: when donor eggs are used, they are more likely to be high quality eggs; therefore, one can only expect a better embryo quality, and subsequently greater odds for implantation. That’s why there is a preference for single or two embryo transfers, by no means is a three embryo transfer advisable.
Advances in assisted reproductive technology
Nowadays, experts in the field of reproductive medicine has reached an agreement by which the goal of every fertility treatment must be performing a single embryo transfer of high quality. This way, success rates increase because of using a high quality embryo, but at the same time we erase the risk of multiple births.
Advances in assisted reproductive technology (ART), as well as improvements made on post-thaw embryo survival rates, make it possible for assisted conception to take a step forward and get closer to its goal. Nevertheless, the effectiveness of fertility treatments and the pressure on the part of professionals and/or patients prove that there is still a lot to be done.
Risks of multiple births
For couples who have been trying to conceive for a long time, the desire to have a baby is so strong that sometimes they find shelter in the fact that chances of getting pregnant increase if more than a single embryo is transferred. The problem is, most of them do not take into account the risk of multiple births it entails. In fact, many women have a preference for this type of pregnancy.
When, on the one hand, a woman is given a pregnancy success rate of 40% with a two embryo transfer which risk of multiple birth reaches 30% and, on the other hand, lower chances of getting pregnant, but free from the risk of multiple births, most women might go for a two embryo transfer. This is because the desire to have a baby is so strong that the perception of the risk becomes blurred.
Not only the likelihood of preterm birth is higher with multiple births, but also it may lead to extreme prematurity. Besides, this type of pregnancy is linked to premature rupture of membranes (PROM)—i.e. breakage of the amniotic sac—, gestational diabetes, high blood pressure, and other side effects associated with pregnancy, such as anemia. On the other hand, there is a higher chance of having a cesarean section or C-section with twins, and miscarriage is more likely to occur as well.