Learning you’re pregnant with two little ones instead of one can be exciting news. But, twin pregnancies are marked by certain risks that typically don’t impact a single fetus. One such complication is twin-to-twin transfusion syndrome (TTTS), which occurs when both fetuses share the same placenta and the blood flow between the two becomes unequal.
“Each of the fetuses have blood vessels that project out from where the cord inserts. In this particular type of placenta, blood vessel connections within the placenta allow blood to flow between the two fetuses. This is a normal physiologic event, and as long as the amount of blood that is going back and forth is normal or equal, then the world is a happy place,” explains Michael Bebbington, MD, a Washington University Maternal-Fetal Medicine specialist, surgeon, and the Director of the Fetal Care Center at Barnes-Jewish Hospital and St. Louis Children’s Hospital. “But, if that blood flow becomes unequal and there’s more going in one direction than the other, that’s when TTTS develops.”
The most common way for TTTS to be diagnosed is via ultrasound. From 16 weeks on, moms with monochorionic twin pregnancies should have an ultrasound evaluation to look for any early signs of TTTS. Typically, the first sign is a difference in the amount of fluid surrounding each of the twins.
“The one twin who is giving blood away, or what we call the donor, starts to develop a decrease in the amount of amniotic fluid. The other twin that’s receiving the extra blood, or the recipient, develops increased amounts of amniotic fluid. That’s usually the ultrasound criteria for defining the earliest stage of TTTS,” says Dr. Bebbington.
Why Both Fetuses Are at Risk
With TTTS, both fetuses are put in danger. The donor fetus becomes blood volume depleted and starts to shunt what blood is coming in to the central part of the body, which decreases the amount of blood perfusing to other parts of the body. As blood flow to the kidneys lessens, the fetus is unable to properly process urine—which is what produces amniotic fluid.
When the condition gets to the stage two, the volume depletion is so rapid that any urine being made is reabsorbed into the body. None of it makes it to the bladder. The bladder becomes invisible, and the amount of amniotic fluid just continues to decrease.
The co-twin is experiencing the opposite problem, with too much blood entering the body. The recipient fetus compensates by increasing renal perfusion and the amount of urine, and thus the volume of amniotic fluid increases as well.
“In more serious cases, that amniotic fluid can distend the uterus considerably, making mom very uncomfortable and increasing risk for preterm labor and preterm rupture of the membranes,” warns Dr. Bebbington. “In its untreated form, it’s a condition that is associated with a very, very high perinatal morbidity and mortality, with mortality rates up to 85%, all as a result of extreme prematurity.”
Fortunately, fetal surgery for TTTS is an intervention that has proven success rates.
Laser Technology Is Reversing Mortality Rates
Currently, the technique used is laser surgery—using an endoscope that is inserted through the maternal abdomen, through the wall of the uterus, and into the sac of the recipient twin.
Surgeons map the placenta to locate where the blood vessels from the two fetuses overlap—what is called the vascular equator. “With the scope going from one side of the placenta to the other, we can identify where the connecting points are. We then use an operative fetus scope that has a side port to insert a 600 micron laser fiber,” informs Dr. Bebbington. “Wherever there are connections between the circulations, we use the laser energy to clot the blood at those connections. The final step of the surgery is to use the laser to draw a line and ‘connect the dots’ so to speak.”
At the end of the procedure, the fetuses are no longer transfusing blood back and forth. The placenta has been separated into two parts, one for each fetus. “Then, we let Mother Nature correct the physiology gradually. As the transfusion process is stopped, the fetuses can recover,” adds Dr. Bebbington.
In experienced hands, the surgery can result in an approximate 86% overall survival rate and about 72-74% survival of both twins. Future pregnancies are unaffected as long as the mother doesn’t have another set of monochorionic twins.
Time Is of the Essence
In order to prevent severe complications, Dr. Bebbington advises monochorionic twins be monitored very closely with ultrasound surveillance at least every two weeks. He also stresses that families be referred to a fetal care center at the first sign of any discordance in the amount of amniotic fluid.
“Even if they don’t need surgery right away, early interference affords me the chance to sit with the family to explain what’s going on and what potential interventions we can offer when it gets to the point where an intervention is needed,” shares Dr. Bebbington. “I just want parents to know, this surgery is game-changing. We really have an opportunity to make a huge difference with early referral and with timely intervention. We can have a significant impact on pregnancy outcomes.”
**To listen to an interview with Dr. Michael Bebbington, Washington University Maternal-Fetal Medicine specialist, surgeon, and Director of the Fetal Care Center, a partnership between Barnes-Jewish Hospital, St. Louis Children’s Hospital and Washington University Physicians, follow this link: https://radiomd.com/stlouischildrens/item/39782