The use of fertility promoting medications has increased the occurrence of twins, triplets, etc. because they work by causing the ovary to develop and ovulate more than one egg at a time. Alternatively, in in vitro fertilization, after the fertility medication is taken, eggs are removed, fertilized in the laboratory, and after a few days, the fertilized eggs (now called embryos) are returned to the woman’s uterus. Usually more than one embryo is transferred and thus the risk for twins in increased. To get an idea about how significant this problem is, the Society for Assisted Reproductive Technologies reported data for 2009 which lists 39,465 cycles of IVF performed for women under the age of 35. The pregnancy rate (live birth rate) for this group of women was 41.4% which means 16,338 women delivered at least one child. For those who delivered a child, 32.9 % had twins (5375 sets of twins) and 1.6 % had triplets or more(261 sets of triplets or more). The average number of embryos transferred for this group of women was 2.1.
Multiple Gestations (termed high order multiple pregnancies or HOMP) increases the risk to both mother and child(ren). Premature births, far more common with multiple gestations, also increase the likelihood of long term health and developmental issues as well. The more fetuses, the greater the risk.
The American Society for Reproductive medicine (ASRM) has actively been advocating for the transfer of fewer embryos so that fewer multiple pregnancies will occur. Their results have been successful yet most couples prefer to have more than one embryo transferred at a time. Part of the reason for this is the desire to be pregnant and part is the cost of IVF. Transferring more than one embryo at a time does increase the overall chance of have a child. For young patients with high quality embryos, transferring more than two does not appreciably increase the chance of having a child but it does increase the risk for twins and triplets. Thus the compromise has been to transfer two embryos where the embryos appear under light microscopy to be healthy. The price for the improved pregnancy rate is the higher incidence of twins and triplets. Physicians and scientists have been trying to find a way to tell which embryo is the best, but so far these attempts have been largely unsuccessful. Therefore, until a better method can be found, the option for the highest chance of having a child in IVF is to transfer more than one embryo at a time. The overall number transferred is tempered based upon the visual quality of the embryos, the clinical situation and the age of the women producing the eggs. ASRM guidelines suggest that for women between the ages of 35 and 37, two or three embryos can be transferred, for women ages 38 to 40, 3-4 embryos, and for women 41 and older, up to 5 embryos can be transferred.
Could there be options to try to limit the occurrence of twins and triplets? One thing to keep in mind is that the use of “injectable” infertility drugs (FSH based medication) has a higher chance of resulting in triplets, quads, etc. than does IVF because the number of oocytes released cannot be controlled. Thus, for some women, if simple therapies such a clomiphene citrate (Clomid) do not work, IVF is safer than the more traditional approach using “injectable” fertility drugs, paired with Intrauterine Insemination (IUI).
One approach to the problem of twins, triplets, etc,) is to perform fetal reductions once the pregnancy has been established. This procedure is performed in the first trimester by injecting a lethal substance into one or more of the fetuses. The body then will remove the fetus and the living fetus can continue to develop to term. The estimated pregnancy loss of all fetuses from the procedure itself is about 5%. Many couples find the thought of a pregnancy termination unimaginable given how hard they have worked for the pregnancy and their desire to be parents. So is there an alternative?
Freezing of human tissue is called cryobiology and it provides a very reasonable method to limit the occurrence of HOMP when used in conjunction with IVF. Many IVF programs have found that the chance of pregnancy is about the same for fresh embryo transfers versus frozen embryo transfers. This means that a couple would not appreciably sacrifice their chance of conceiving if they chose to transfer only one embryo and freeze the remaining viable embryos. This alternative approach has some downsides. From the perspective of the IVF center, single embryo transfer (SET) lowers their overall national statistics which many couples use to choose an IVF program for services. While this is less than an admirable aspect of the infertility business, it nonetheless does exist. In the future, we look to ASRM to correct the reporting so that couples can get a more accurate picture of the success of the various IVF programs. Another downside is the extra cost of freezing, in terms of time and money, and then doing a frozen embryo transfer. The issue of time can be justified on the basis of safety for the children that result from the IVF procedure since almost all maternal and fetal complications increase with increasing number of fetuses. Some states have mandatory insurance coverage, so for couples living in these states, the extra cost is not born by them. For example, in Illinois, for couples whose employers meet the criteria of the Family Building Act (1991), they are provided with coverage for 4 cycles of IVF where a cycle is the retrieval and not the transfer. That means that a couple could have more than one chance to conceive from a single retrieval.
In summary, IVF has given many couples a chance to biologically have their own child, but the risk from IVF has been high order multiple pregnancies. Since IVF has become more successful, the number of embryos needed to be transferred could be reduced, thus reducing the risk of HOMP. The use of cryobiology in the form of freezing embryos allows for a further reduction in this risk, without an appreciable overall loss of having a child.