In Vitro Fertilization (IVF)
Medically reviewed by Norbert Gleicher, MD, FACOG, FACS - Written by CHR Staff - Updated on Nov 15, 2014
IVF & Twins
Practically every fertility treatment including In Vitro Fertilization (IVF) increases the risk for multiple births. Depending on the fertility treatment, multiples can represent anywhere from approximately 5 to 35 percent of deliveries. The reason is simple: in 99 percent of natural menstrual cycles, only one egg is released from the ovary. The natural prevalence of multiple births is only around one percent, with a large majority of those instances being twin births. Since fertility treatments turn a single-egg cycle into a multiple-egg procedure with ovarian stimulation, the ovaries release more than one eggs, and more than one can be fertilized, potentially resulting in a multiple birth.
The likelihood of twins and higher-order multiple births depends somewhat on the degree of control that physicians have over how many eggs are fertilized and how many are implanted in the uterus. For example, intrauterine insemination (IUI) with ovarian stimulation has a higher risk of twins and high-order multiples than IVF with one or two embryos transferred, because in an IUI cycle, the physician does not have much control over how many eggs will fertilize and implant in the uterus.
Attitudes toward twin births as a result of IVF have been going through a significant change in the past few years. Specifically, more and more colleagues (especially physicians in Europe, but increasingly in the US as well) opt for single embryo transfer (SET) to eliminate twin or higher-order multiple pregnancies in IVF cycles. In 2010, the government of Quebec, Canada, even enacted a law requiring SET in all but a handful of special cases. A recent article in the online magazine Slate (which quoted Dr. Gleicher, CHR's Medical Director), the writer explained that this government intervention in Quebec resulted in a reduction in IVF pregnancy rates from 42 percent to 32 percent, a nearly 25% drop. At CHR, we feel that this trend poses a threat to the individual patient's right to self-determination, and take a more balanced approach.
Managing IVF and Multiple Birth Risk
Increasingly successful infertility treatments have resulted in an increase in multiple births. Quite rightly, the lay public and medical community have identified this as a major problem. (Remember the Octomom?!) Dr. Gleicher was in the vanguard of efforts to reduce multiple births, when he, in a 2000 study in the prestigious New England Journal of Medicine, found the risk for high order multiples (triplets or more) with intrauterine inseminations (IUI) to be uncontrollable and suggested that patients be taken earlier into in vitro fertilization (IVF) (Gleicher et al. N Engl J Med 2000;343:2-7).
Amongst all infertility treatments, IVF gives us the best control over an increased risk for multiples because we (that is, patient and physician) decide how many embryos to transfer into the uterus. The more embryos are transferred, the higher the risk of multiples will be, though the age of the mother also plays a significant role. As the utilization of IVF in infertility has increased over the last decade, so has our ability to reduce risks of multiple births.
Balanced Approach to IVF Pregnancy
CHR has always placed a priority on achieving high clinical pregnancy rates without exposing patients to risk of high order multiples. Many patients bear witness to CHR's conservative embryo transfer policy, even if, at times, it has taken efforts and strong arguments to convince them of the wisdom of such an approach. CHR's embryo transfer policy has always been based on the acceptance of twins and avoidance of triplets or even higher-order multiple births. Everybody agrees that singletons represent the lowest risk pregnancy and that, with increasing order of pregnancy (i.e., the number of babies in a single pregnancy), the risk to babies and mothers increases. We've always felt that the additional risk of twinning was minor enough to be more than made up by the benefits a twin pregnancy bestows on an infertile couple, who, quite frequently, want more than one child and for whom having twins is a definite option.
Until recently, most of our colleagues agreed with us. More recently, first starting in Europe but now also in the U.S., an increasing number of colleagues have started to argue that even twins are an unfavorable outcome of infertility treatments, something to be avoided at all cost. To this end, many infertility physicians have started advocating for "elective" single embryo transfer (eSET). We strongly disagree! Our disagreement with many of our colleagues is based on hard statistical facts, which can be summarized this way:
The sudden antipathy towards twin delivery stems from the fact that perinatal risk (risks related to the baby) and maternal risk (those related to the mother) in a twin pregnancy are somewhat higher than in a singleton delivery. But so are the benefits! Most fertility patients want to have more than one child, and for many of them, having twins in just one cycle of IVF is a faster and more economical way to achieve that goal than going through two or more cycles of IVF with one singleton pregnancy each. Yet, this is usually ignored by our colleagues.
Furthermore, in all of the literature claiming the superiority of eSET, researchers are comparing risks of one twin pregnancy to one singleton pregnancy. This, in our opinion, is a flawed comparison, because one twin pregnancy brings two children to the couple, while one singleton pregnancy brings one baby. For a statistically sound comparison, one twin pregnancy must be compared to two singleton pregnancies, and when this is done, there is no significant difference in perinatal and maternal risks in twin and singleton pregnancies.
Risk/benefit calculations form the basis of all decision making in medicine, since nothing in medicine is completely risk-free. Patients and physicians, once risks and possible benefits of a medical intervention are known, make a decision. What level of risk a person is willing to take to achieve a certain benefit, of course, varies between individuals. In other words, patients have an absolute right to take more or less risk, depending on what their desires are and what their risk tolerance is.
For those who want to read more on the topic, CHR physicians have published many articles in peer-reviewed medical journals on this topic of IVF and twins. Here is a short list:
- Gleicher N. Eliminating multiple pregnancies: an appropriate target for government intervention? Reprod Biomed Online 2011; In press.
- Gleicher N, Oktay K, Barad DH. Patients are entitled to maximal IVF pregnancy rates. Reprod Biomed Online 2009;18(5):599-602.
- Gleicher N, Barad DH. Arguments against elective single-embryo transfer. Expert Rev Obstet Gynecol 2008;3(4):481-6.
- Gleicher N, Barad DH. Twin pregnancy, contrary to consensus, is a desirable outcome in infertility. Fertil Steril 2008;91(6):2426-31.
- Gleicher N. Is it time to limit IVF transfers to one embryo? Contemporary Obstet Gynecol 2004;49:73-81.
- Gleicher N et al. Reducing the risk of high-order multiple pregnancy after ovarian stimulation with gonadotropins. New Engl J Med 2000;1:2-7.
Norbert Gleicher, MD, FACOG, FACS
Norbert Gleicher, MD, leads CHR’s clinical and research efforts as Medical Director and Chief Scientist. A world-renowned specialist in reproductive endocrinology, Dr. Gleicher has published hundreds of peer-reviewed papers and lectured globally while keeping an active clinical career focused on ovarian aging, immunological issues and other difficult cases of infertility.