What are the risks of a twin pregnancy?
Women with twin pregnancies have increased risks in general compared to women carrying a single fetus. In particular, women pregnant with twins are at increased risk for preterm birth. On average, women with twins deliver around 36 weeks of pregnancy. This is mostly due to spontaneous preterm labor, which is defined as contractions and cervical change before term, or at less than 37 weeks of pregnancy. Other complications, such as preeclampsia or gestational diabetes, both of which are more common in women with twins, can occur as well. These risks are increased even further when women have triplets, quadruplets or higher.
How and when are twins delivered?
There are numerous things to consider when planning the delivery of a twin pregnancy. Many women assume that because they are having twins, they MUST have a cesarean delivery. Although this is largely the most common way twins are delivered, vaginal delivery is an option in certain situations. If the babies are close to term, and the presenting (first) twin is head down, a vaginal delivery may be considered. In this situation, it is important to understand that the second twin may have to be delivered breech, or rarely by cesarean section (even after successful vaginal delivery of the first twin). The ideal situation for a twin vaginal delivery is if both twins are headfirst in an otherwise uncomplicated twin pregnancy.
Overall, vaginal delivery of a twin pregnancy requires special precautions. An epidural may be recommended, to ensure that pain is well controlled prior to needing to perform a breech delivery of the second twin, and your delivering obstetrician must be comfortable with vaginal breech delivery. Monitoring of each twin is especially important, so if this is not able to be achieved cesarean delivery may be recommended. There are some circumstances, such as fetal size, position, or presentation that may deem vaginal delivery unsafe; therefore care must be individualized between the patient and her obstetrician when planning a vaginal delivery.
While spontaneous preterm labor is more common in women with twins than in women with a singleton pregnancy, many women still require induction of labor or cesarean delivery prior to the spontaneous onset of labor. To reduce some of the increased risks associated with twins as a pregnancy progresses, delivery is often planned prior to the estimated due date. Timing of delivery depends on many factors, including the type of twins (see above). Ideally, if the mother is healthy and both babies are growing appropriately, delivery is recommended between 38 weeks 0 days to 38 weeks 6 days for dichorionic-diamniotic twins, to as early as 34 weeks 0 days to 37 weeks 6 days for monochorionic-diamniotic twins. Delivery for monochorionic-monoamniotic twins is frequently planned between 32 weeks 0 days to 34 weeks 0 days. If any complications arise for either the mother or one or both babies, an even earlier delivery may be necessary.
It is important to balance the risks of prematurity with the risks of continuing the pregnancy, and these risks should be discussed with your obstetrical provider. Additionally, it is important to ask about the type of neonatal care unit available at the facility where you plan to deliver, as each hospital has a different level of neonatal care. Oftentimes women are transferred to a facility equipped with a Level III or IV Neonatal ICU (NICU) and Maternal-Fetal Medicine specialists if a preterm birth appears probable.
What about twins and IVF?
Many women undergoing IVF may be tempted to “just go for twins” or beyond. Some women feel that they are investing a large sum of money and would rather “get it all over with in one pregnancy”. Others who have had unsuccessful IVF attempts feel that transferring more than one embryo may increase the odds that they carry at least one to delivery. Based on the risks as discussed above, the most recent recommendations are to transfer only one healthy embryo at a time. Occasionally, embryonic division (creating twins) can still occur even when one embryo is transferred.
If twins, triplets, or beyond occur, fetal reduction (from 4 to 3 fetuses, 3 to 2, etc.) may be offered, but is often not a valid option for some mothers. By limiting the number of embryos transferred per cycle, these risks are reduced. In some countries, transfer of more than one embryo has been outlawed, and in some states, state-provided IVF insurance coverage only covers single embryo transfer. According to the most recent Society for Assisted Reproductive Technology guidelines, if more than one embryo is to be transferred, the patient must be thoroughly counseled about the risks of multi-fetal pregnancies, and transfer of more than 2 embryos should not even be considered in patients younger than age 38, as long as they have a reasonable chance of successful pregnancy. These numbers depend upon a woman’s age, history, and potential for future success.
For any woman considering multiple embryo transfer, a thorough consideration of the pros and cons of carrying twins or more must be undertaken. Early prenatal care should be encouraged for anyone with twins to establish a sound plan of care throughout pregnancy.