Are you pregnant with twins? If so, you may be at risk for Twin to Twin Transfusion Syndrome, a disease of the placenta that can put your babies at risk. In order to obtain the best possible medical care, ask your physician these important questions, provided by The Twin to Twin Transfusion Syndrome Foundation.
Reprinted with permission from Twin to Twin Transfusion Syndrome Foundation. Please visit their site for more information.
Confirm at Initial Ultrasounds (preferably by 10-16 weeks)
1. Is the placenta monochorionic?
TTTS only occurs in identical twins with a single, shared monochorionic placenta. Placental type can be determined as early as 6 weeks of pregnancy.
2. Are the babies the same gender?
Monochorionic twins are identical, so by definition they should be of the same sex, and will carry a risk for TTTS.
3. Can you see the dividing membrane?
The ‘dividing membrane’ is formed by the two amniotic sacs of the twins meeting in the middle of their placenta. A thin, wispy membrane confirms that the twins are monochorionic. A thick, easy to see dividing membrane is seen when the twins have separate placentas. Inability to see the membrane at all does not always mean same sac (monoamnionic) twins. For instance, in TTTS the membrane may be ‘shrink wrapped’ around a donor baby who lacks amniotic fluid, and further pressed around the donor by the excess fluid in the recipient.
4. Is the placenta implanted on the anterior or posterior surface of the womb?
Laser surgery may be performed on placentas in either location, but the anterior location presents more challenges. Depending on the doctor’s technique, the twins will have a greater risk of still having open connections with anterior placentas. Placentas that wrap around 3 surfaces (anterior, fundal, and posterior) may also be difficult to operate upon.
5. Do the twins’ umbilical cords each have the normal 3 blood vessels, or does one of them have 2 vessels?
Identical monochorionic twins should, by definition, be the same in every way. It is not uncommon for the twins (both TTTS and non-TTTS) to share their single placenta unequally. This is the most common reason for size differences, which can be more than 20%. The smaller twin will have the smaller placenta, and its umbilical cord may have only 2 blood vessels in it.
6. Are the umbilical cords fully attached to the placenta?
Identical monochorionic twins can be more than 20% different in size. Similar to the 2 vessel umbilical cord, the umbilical cord may not insert into the placenta itself, but into the membranes that surround the baby and signify a smaller placental share for that twin. This is called a velamentous cord insertion.
Questions to Ask at Weekly Ultrasounds (16 weeks up until delivery)
7. What is the largest vertical pocket of amniotic fluid in each baby’s sac?
In normal twins, the deepest pocket of amniotic fluid should be around 3-8cm. When the fluid is greater than 8cm (polyhydramnious) and less then 2cm (oligohydramnios), the babies have Stage I TTTS. The fluid level differences are distressing to see, but are the findings most likely to change with treatments such as horizontal rest and nutritional supplements. You can determine the severity of TTTS to some degree, by watching what these numbers are, and how much they vary from the normal range. This information can help you to know when treatment may be needed and why, and gives you a tool to help make these decisions.
There are varying opinions as to the number where an amniocentesis should be done. Some experts are wary about putting a needle into the uterus, there are some risks, and so it should be done for a good reason. In TTTS pregnancies genetic abnormalities are extremely rare, so it does not make sense to do an amniocentesis for genetic reasons alone. It may also not make sense to do amnioreductions of small volumes (less than a liter), which is often the case if the deepest pocket measures 8-9cm or less. In higher stages of TTTS (III-IV), placental laser surgery is becoming the preferred treatment. Here the excess amniotic fluid is actually required to perform the operation, and should not be removed until the surgery itself. TTTS after the laser cutoff (over 25 weeks of pregnancy) will be treated with amniocentesis when necessary.
8. Can you see the urinary bladder of the donor baby?
The baby’s bladder is visible on ultrasound when it contains urine. Urine is the main source of amniotic fluid. If it cannot be visualized within 30 minutes, or if the donor baby has no or little amniotic fluid, its blood volume may be too low (from transfusion into the recipient) to perfuse the kidneys enough to urinate. Recipients always have larger than normal bladders in TTTS. If the ultrasound finds a visible bladder and a 2cm or more pocket, this much better news for the donor. These findings will help give you some perspective on the donor’s status and the seriousness of TTTS.
9. What are the weights of the babies in grams? (ask for an update every 2-3 weeks)
The relative size differences between monochorionic twins with TTTS (or in general) are best calculated with grams (typically 3 digits) rather than ounces (3 digits rounded to 1 or 2). The percent difference is calculated by taking weight difference in grams, and dividing that number by the weight of the larger baby. If the weight discordance is 20% or more, it is considered significant. The most likely cause of the discordance in monochorionic twins is unequal sharing of their single placenta. The smaller a placenta portion, the less nutrients are delivered to that baby. Small placentas are often associated with two vessel or velamentous umbilical cords, and Doppler flow abnormalities. Since the twins’ shares of the placenta are fixed from the beginning of the pregnancy, and cannot be improved upon, nutritional supplementation and horizontal rest may help maximize the supply of nutrients to the smaller twin and help it thrive.
Continue reading: Important Questions 10-15
