Continued from Page One: Questions 1-9
10. Are the Doppler ultrasound studies normal for both babies?
The Doppler ultrasound demonstrates how blood is flowing through the umbilical cords and placentas of the babies. It shows how well their hearts are pumping the blood by color (similar to taking a blood pressure which uses sound to determine systolic and diastolic numbers). In TTTS, Doppler is used to study blood flow through the umbilical cords, through the middle cerebral artery to detect anemia in the donor, and in and around the recipient’s heart to detect stress or heart failure.
Common abnormal Doppler studies in donor twins include absent diastolic flow in the umbilical cord (blood moves forward only when the heart is contracting), and reverse diastolic flow in the cord (blood moves back toward the heart when the heart relaxes). These studies are influenced by both the size of the transfusion and smaller sizes of a twin’s placenta share. Reverse diastolic flow is much more dangerous, and requires urgent decision making regarding laser surgery or delivery, if feasible at the gestational age. Doppler studies are considered a routine part of monitoring complicated monochorionic twin pregnancy from about 15 weeks onward.
11. Is the heart of the recipient baby thickened or enlarged?
When the recipient baby’s cardiovascular system is overloaded by a transfusion from the donor, it will show thickening and an increase in size. Here, laser surgery is the only option to stop the transfusion and reverse these TTTS signs (considered stage III). Hearts that are considered ‘in failure’ are also enlarged and thickened, but they are also noted to be poorly contracting. These findings are reversible after laser surgery.
12. Does the recipient baby have any signs of hydrops?
Eventually a transfusion-related severely stressed heart will fail, and the baby’s body fills up with water (edema) to become hydropic. This is stage IV TTTS.
Hydrops is reversible only with laser surgery. Stage IV TTTS babies can survive and be healthy, even after having hydrops, with proper treatment.
13. How long is my cervix by ultrasound, and it is showing any signs of funneling or thinning?
It is now clear to us, that as much as one-fourth of all the lost babies, as well as babies who survived with disabilities after TTTS, did so because of problems (i.e., abnormal shortening) with the mother’s cervix. Doctors only began routine measurement of the mother’s cervix in multiple pregnancy in 2000. A normal cervix should be more than 3.5cm long without signs of funneling (opening of the upper cervix closest to the baby, rather than at the vagina). A short cervix (< 3.0cm), especially with funneling, is called cervical insufficiency and almost ensures a premature delivery. Cervical insufficiency can be fixed by shoring up the cervix with a stitch (cerclage). Cerclage is performed in some centers in TTTS cases up to 25 weeks, and hospitalization for the duration of pregnancy if it is after 25 weeks.
A word of caution: there are doctors and centers that do not perform cerclage under any circumstances, for whatever reason, so be sure to ask what they do if your cervix gets short under their care. Conversely, there are other doctors who are convinced that they have had better outcomes and healthier babies for their TTTS patients, since incorporating cervical ultrasound, and cerclage when necessary, to their TTTS treatment protocols. So, it is crucial to have your cervix looked at every scan since increased amniotic fluid adds to the burden on the cervix. You should always have the cervix checked immediately before traveling to another center (especially by air) for treatment.
14. Is the smaller baby growing at the same rate?
When monochorionic (single placenta) twins are 20% or more different in size, it is considered significant. The most likely cause for this discordance is unequal sharing of the placenta. Although a size difference can be detected even in the first trimester, this difference can become extreme (> 40%) by mid pregnancy in cases of extreme unequal sharing of the placenta (e.g., the smaller twin has less than 25% of the placenta). However, in the third trimester the babies are having their greatest weight gain, which must be supported by a normal placenta and supply of nutrients from the mother. A twin can actually ‘run out of placenta,’ so monitoring of their rate of growth and difference between their weights is crucial. When a monochorionic twin stops growing, the babies need to be delivered (i.e., better off out than in) or this baby will be become harmed. The monochorionic placenta can be analyzed after birth to determine the twins’ relative shares.
15. What is the fundal height measurement?
Doctors have long used a centimeter tape to measure the distance from the top of the public bone to the top of the pregnant uterus. In a singleton pregnancy, height in centimeters should equal the weeks of gestation, and then grow appropriately at subsequent visits. In normal multiple pregnancy, roughly 3 to 4cm is added to the number of weeks. This test can be used to find babies that are not growing enough (a low value indicates intrauterine growth restriction – IUGR), or growing too much (like babies of mothers with gestational diabetes). In monochorionic twins at risk for TTTS, an abnormally high fundal height value may be the first (and most common) sign of TTTS – polyhydramnios or too much amniotic fluid. It can be especially important for women having a difficult time getting ultrasounds weekly, or not being told the largest vertical pocket at the ultrasounds they have. You can get this measurement from a qualified nurse or midwife, if they are the only ones available to you. When TTTS is diagnosed, ultrasounds are then used in lieu of fundal height, because the scan provides more specific information on the babies and mother’s cervix.
Reprinted with permission from The Twin To Twin Transfusion Syndrome Foundation.