Multiple pregnancies are a potential problem for the children and the parents but they have been hard to avoid with IVF. Traditionally, the success of IVF has hinged upon availability of more than one embryo for transfer. Currently about 30% of IVF pregnancies are twins or higher-order multiple gestations (triplets or greater), and about half of all IVF babies are a result of multiple gestations. Despite widespread concern about the health risks of multi-fetal pregnancies, single embryo transfers account for a small fraction of all embryo transfers performed nationally. This anomaly reflects a deep split between the “party line” embraced by the CDC and SART and the widespread preference for twins among infertility patients.
Most twins are fraternal, i.e. they arise from 2 different embryos and have separate placentas. Identical twinning occurs in 1.5% to 4.5% of IVF pregnancies and occurs when a single embryo splits into two. IVF twins deliver on average three weeks earlier and weigh 1,000 gm less than IVF singletons. While IVF singletons are smaller than non-IVF singletons, IVF twins do as well as spontaneously conceived twins. Triplet (and greater) pregnancies deliver before 32 weeks (7 months) in almost half of cases.
The most important maternal complications associated with multiple gestation are preterm labor and delivery, pre-eclampsia, and gestational diabetes. Prematurity accounts for most of the risks associated with multiple gestations. Poor fetal growth and discordant growth among the fetuses also result in perinatal morbidity and mortality. Multi-fetal pregnancy reduction (where one or more fetuses are selectively terminated) reduces, but does not entirely eliminate, the risk of these complications.
Fetal death rates for singleton and twin pregnancies are 4.3 per 1,000 and 15.5 per 1,000, respectively. Identical twins that share the same placenta have additional risks. Twin-twin transfusion syndrome may occur in up to 20% of identical twins resulting in excess or insufficient amniotic fluid. Twins sharing the same placenta also have a higher frequency of birth defects compared to fraternal twins. Twins sharing the same placenta appear to occur more frequently after blastocyst transferalbeit it has not been our experience to date.
Obstetrical complications, such as placenta previa, placenta abruption and postpartum hemorrhage are more common in multi-fetal pregnancies.
The major lifelong consequences of prematurity include cerebral palsy, blindness and chronic lung disease. It is unclear to what extent multiple gestations themselves affect neuro-behavioral development in the absence of these complications. Rearing of twins may generate physical, emotional, and financial stresses, and the incidence of maternal depression and anxiety is increased in women raising multiples. At mid-childhood, prematurely born offspring from multiple gestations have lower IQ scores, and multiple birth children have an increase in behavioral problems compared with singletons. It is not clear to what extent these risks are affected by IVF as such.
While most consumers and reproductive endocrinologists agree with the goal of avoiding triplets and higher order multi-fetal pregnancies, many patients not only accept, but in fact desire, twins. Thus a major discrepancy has evolved between the avowed goals of patients and public health officials such as the CDC. The reasons why patients desire twins despite knowledge of the above risks is grounded not in ignorance but in valid reasoning. Since most patients have no insurance to cover the cost of IVF, getting twins seems like a bargain. The added obstetrical and pediatric expenses, on the other hand, are usually covered benefits under their health insurance policies, so they are of more concern to epidemiologists and economists than to subscribers. In Europe, where IVF is a covered benefit, clinics and patients are under intense government pressure to accept transfer of single embryos.
Age is another valid reason why so many consumers hope for twins. For many women in their late 30s and early 40s, it may be possible to establish one pregnancy through IVF but repeating that feat a couple of years later may prove impossible (What is Age Factor?). Finally, single embryo transfer is the only strategy that reliably reduces IVF twin rates but most patients are unwilling to accept the reduction in live birth rate resulting from a single embryo transfer. The recent advances in PGD (pre-implantation genetic diagnosis) allows patients to achieve a high live birth rate through transfer of a single genetically normal blastocyst-stage embryo while avoiding the risks of twins and higher order deliveries.
Where does the Alta Bates IVF Program stand on this issue? We are proud of the progress we have achieved in lowering the rate of triplets, but when it comes to twins we remain sympathetic towards our patients' preference for twins as a reasonable family-building approach. This policy is consistent with both patient autonomy and the fact that so many of the women we see fall into the older age group (as you can see in the graph below depicting age distribution in the entire U.S. and in our program).
As the graph below illustrates the frequency of multi-fetal births, portrayed as the area between the blue and red curves, markedly declines with the woman’s advancing age.