Birth defects, or anomalies, occur more frequently in pregnancies with monochorionic twins than with other pregnancies. Monochorionic twins are identical twins who share one placenta. This occurs in approximately 70 percent of pregnancies with identical twins.
For Patients
- What is AMT?
Birth defects, or anomalies, occur more frequently in pregnancies with monochorionic twins than with other pregnancies. Monochorionic twins are identical twins who share one placenta. This occurs in approximately 70 percent of pregnancies with identical twins.
Twins in general are more likely than pregnancies with a single baby to face challenges in development and delivery. The chances for birth defects and other problems are increased even more for monochorionic twins.
- Concerns With Monochorionic Twins
Low Birth Weight
Birth weight is a factor for nearly all monochorionic twins. The risk of low birth weight is four times higher than in pregnancies in which each baby has their own placenta.
Weight Discrepancies Between Twins
Significant weight differences between the two babies is common among monochorionic twins. When there are not enough nutrients for one or both babies to develop at a normal rate, intrauterine growth restriction (IUGR) can occur.
Amniotic Fluid Problems
Different levels of amniotic fluid can affect monochorionic twins. Twins deprived of a blood supply will produce too little amniotic fluid, a condition known as oligohydramnios. This condition limits their bladder size and ability to move, among other consequences. A larger than normal blood supply will result in excess amniotic fluid, or polyhydramnios. This condition can lead to an enlarged bladder and the possibility of hydrops (excess fluid).
Umbilical Cord Entanglement or Compression
Umbilical cords are the lifeline to blood and nutrients for all babies in the womb. If the cord gets flattened or bent, the supply line for the babies can be damaged or cut off altogether, affecting fetal development and increasing the risk of death. Cord entanglement or compression is a risk for all monochorionic-monoamniotic twins who share space in a single amniotic sac.
TTTS and TRAP Sequence
Twin-to-twin transfusion (TTTS) and twin reversed arterial perfusion (TRAP) sequence are two life-threatening conditions that may develop in rare circumstances. Both are caused when the babies have different levels of blood supply. If TTTS is not detected and treated, it is likely to result in the loss of both babies. In TRAP sequence, one twin will not survive because it lacks a developed heart and brain structure.
The specialized services provided by physicians at Fetal Care Center Dallas address the serious nature of these and other conditions that may impact the health of monochorionic twins. Our goal through treatment of identical twins who share a placenta is to promote the health and survival of both babies whenever possible.
- Prenatal Diagnosis Of Monochorionic Twins
Diagnosis of a monochorionic twin pregnancy is typically made during a routine ultrasound when the placenta and amniotic sac are visible. The ultrasound will show a single placenta and two babies with one, thin dividing membrane between them.
Additional maternal and fetal testing may be performed to screen for anomalies such as TTTS and TRAP sequence. Our staff uses fetal echocardiography to evaluate your babies’ hearts and blood vessels by assessing the flow of blood between the twins. To monitor the size of your babies, along with their blood supply and amniotic fluid, we will perform testing and ultrasounds throughout your pregnancy.
- How We Treat Anomalies Of Monochorionic Twins
Caring for pregnancies with monochorionic twins varies depending on the condition of the babies.
Amniotic Fluid Issues
If excessive amniotic fluid is a concern, our maternal fetal medicine physicians may perform an amnioreduction to reduce the amount of amniotic fluid. With amnioreduction, a small needle is introduced into the amniotic sac containing the extra fluid under ultrasound guidance.
Amniotic fluid is then removed until the fluid levels return to normal. This will help you feel more comfortable by decreasing abdominal pressure. The procedure will also help equalize blood flow between your twins and reduce your chance of premature labor. In rare cases, it can stop the progression of the TTTS or even reverse it.
Cord Entanglement
In the case of cord entanglement, our physician may recommend delivery of your twins as soon they are mature enough to survive — as early as 24 weeks. You will be closely monitored by our maternal-fetal medicine physicians to help determine the optimal time to deliver your twins. Corticosteroid medications may need to be administered to accelerate lung development in your twins to help promote their survival outside of the womb.
Laser Surgery for TTTS
For severe cases of TTTS, our fetal surgeons are skilled in the use of a definitive surgical technique to disconnect part of the blood supply between the twins. During the minimally invasive procedure, a small scope with a camera is inserted into the uterus to view the abnormal blood vessel connections between your babies. A laser fiber is then inserted alongside the camera to stop the flow of blood between the babies.
TRAP Sequence
If you are far enough along in your pregnancy, delivery of your healthy twin may be recommended. In other cases of TRAP sequence, highly specialized prenatal treatments may be done to stop the extra pumping between your twins. Radiofrequency ablation is an advanced technique performed within the womb by surgeons at Fetal Care Center Dallas. RFA is usually performed between 17 and 24 weeks of pregnancy.
The procedure uses heat energy to stop the flow of blood to the umbilical cord of the underdeveloped twin. RFA has been shown to be a very successful approach to treatment, with a 90 percent or higher survival rate for the normal twin, when delivery takes place at least 35 weeks into the pregnancy.
- Long-Term Outlook For Monochorionic Twins
The prognosis depends largely on the types of complications caused by the monochorionic pregnancy as well as when delivery occurs. Low-birth-weight babies have an increased risk of cerebral palsy, mental deficits or other problems. Babies born closer to term, around 32+ weeks, may face feeding and breathing problems but they nearly always survive.
The staff at Fetal Care Center Dallas is available every step of the way to offer guidance and counseling to families and groundbreaking treatments for babies when birth defects arise.