Confirm at first ultrasound (hopefully by 12 weeks)
- Is the placenta monochorionic? TTTS, including TAPS, has been extremely rarely reported in dichorionic separate placentas that fuse. It is crucial parents understand that. However, TTTS, including TAPS occurs predominately with identical twins or higher multiples with a single, shared monochorionic placenta and is our focus. Placental type can be determined as early as 6-8 weeks of pregnancy.
- Are the babies the same gender?
Monochorionic twins are identical, so by definition they should be of the same sex.
- Can you see the dividing membrane?
The dividing membrane is formed by the two amniotic sacs of the twins which meet in the middle of the placenta. A thin membrane confirms that the twins are monochorionic with what looks like a “T” where the membrane attaches to the placenta. A thicker membrane is seen in dichorionic twins with a triangle at the base of the dividing membrane. Occasionally, the membrane is hard to see either because TTTS is present, with the membrane wrapped around the donor, or the ultrasound machine may have poor resolution. With the latter, it may be identified with a higher resolution ultrasound machine. Make sure the ultrasound is only with MFM specialist.
- Is the placenta anterior or posterior? 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 continued connections with anterior placentas. Placentas that wrap around 3 surfaces may also be difficult to operate on, but they can depending on the expertise of your surgeon which varies widely.
- Do the cords have 3 vessels or 2? Umbilical cords normally have 3 blood vessels. Having only 2 vessels can contribute to a size difference between the babies. MC twins, by definition, should 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.
- Where did the cords implant into the placenta?
The cords can attach to the placenta centrally, marginally (on the edge creating less placental share) and velamentous (not inserting into the placenta itself, but into the membranes that surround the baby. In addition to having an umbilical cord with 2 blood vessels, cord insertion can contribute to a significantly smaller placental share for that twin.Ask at weekly ultrasounds (starting at 16 weeks through delivery)
- What is the deepest vertical pocket of amniotic fluid for each baby?
In normal twins, the deepest pocket of amniotic fluid should be around 2-8cm. 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. Laser surgery is typically not offered at this stage.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 amnioreduction 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. One reason could be a situation where donor baby has a very small share of the placenta and is at risk if laser were done. In TTTS pregnancies genetic abnormalities are extremely rare, so it does not make sense to do an amniocentesis for genetic reasons. 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 (II-IV), placental laser surgery is 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 (up to 28 weeks of pregnancy in some centers) will be treated with amniocentesis when necessary.
- Is the bladder visible in 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.
- What are the weights of the babies in grams? (every 2 weeks)
The relative size differences between MC 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 MC 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.
- Are the babies growing at the same rate or is there a significant difference?
When MC twins are 20% or more different in size, it is considered significant. 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 MC twin stops growing, the babies need to be delivered (i.e., better off out than in) or this baby will be become harmed. The MC placenta can be analyzed after birth to determine the twins’ relative shares.
- Are the umbilical cord and the middle cerebral artery Doppler studies normal for both babies? Is the placenta thicker and paler on one side? Is there a starry sky pattern on the livers?
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, MCA, to detect anemia in the donor-polycythemia in the recipient (TAPS), and in and around the recipient’s heart to detect stress or heart failure. The MCA Dopplers can determine if the babies have TAPS, a form of TTTS. Dopplers help to stage TTTS (stage III), including TAPS (stage 3-4) and SIUGR (stage 2-3) and the well-being of the healthy TRAP twin.
Common abnormal Doppler findings 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 in the cord are considered a routine part of monitoring complicated MC twin pregnancy from about 15 weeks onward, but MCA dopplers can be more difficult to get. The only way to diagnose or rule out TAPS is through the MCA doppler and you must fight for them at every ultrasound.
If the flow or measurements are not normal, ask what the flow and measurements are. Having one side of the placenta thicker and paler could be a sign of TAPS in an anemic donor baby. Having a starry sky pattern on a liver could be a sign of a TAPS in the polycythemic recipient baby.
- Is the heart of the recipient baby enlarged or thickened?
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). This also affects the staging of TAPS and SIUGR and intervention for TRAP.Hearts that are considered in failure (stage IV) are also enlarged and thickened, but they are also noted to be poorly contracting. These findings are reversible after laser surgery. Many centers perform fetal echocardiograms to verify and characterize the type if heart abnormalities if present.
- Does the recipient baby show hydropic (edema) changes?
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. With TAPS, it would be the donor that could have edema and hydrops due to extreme anemia. With TRAP it could be seen in an overloaded cardiovascular system of the healthy baby if the other twin is more than 50% his or her size.
- What is the fundal height?
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 selective intrauterine growth restriction ( SIUGR), 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. The fundal height measurement 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. Please call us if this is your situation so we can help you.
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.
- How long is your cervix by ultrasound and is it showing any signs of funneling or thinning?
It is now clear, that as many as 25% 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 began routine measurements 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 26 weeks, and hospitalization for the duration of pregnancy if it is after 26 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. Please call us and we will help you get to a doctor that will do a cerclage if you are able to travel.
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, please get second opinion and call us if you are having trouble. It is crucial to have your cervix checked 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 laser center (especially by air) for treatmentmax
