Introduction
Monochorionic diamniotic twins are high risk pregnancies that can be complicated (9-15% of all cases) by twin-to-twin transfusion syndrome (TTTS) 1-3. This severe condition can lead to polyhydramnios in the recipient twin, premature delivery and poor perinatal outcome 4, 5. Currently, TTTS remains a challenge in modern fetal medicine and in the absence of treatment perinatal mortality is extremely high (>80%)6, 7.
Management of TTTS has evolved considerably over the last decades1-7. Presently, the fetoscopic laser ablation (FLA) of the superficial placental anastomoses is the most common treatment strategy. Many studies compared between amnioreduction (AR) of excess amniotic fluid with FLA strategies and most concluded that FLA is the optimal TTTS treatment, since it resulted in higher survival rate and less neurological complications at six months of age8-11. However, the FLA procedure is limited to weeks 16-26 of gestation 12 and is heavily hindered by anatomical restrictions such as anterior placenta. Moreover, the incidence of neurodevelopmental impairment in TTTS survivors treated with FLA is still high 8. Thus, no single treatment seems to be associated with a clearly improved survival13.
The amniotic fluid volume increases progressively throughout a normal singleton pregnancy; from 200 to 300 mL in week 16 to 1400 mL in week 40 14, 15, while maintaining a linear relationship between amniotic pressure and gestational age 16-18. A similar tendency exists in normal twin pregnancy. However, it has been noted that amniotic pressure in most cases of polyhydramnios and TTTS is higher than in case of an uncomplicated gestations and it significantly falls with the amniotic fluid drainage 19-23. A comprehensive literature search did not reveal a consensus regarding the volume and rate of amniotic fluid removal, as well as the intrauterine pressure during the procedure. As a result there is neither a commonly accepted treatment protocol, nor indicators for interruption of amniotic fluid drainage. The clinical threshold to terminate the procedure is subjective and based on the clinical experience.
In the present study we implemented a controlled AR procedure and measured the relationship between amniotic pressure, volume removed and blood flow of each twin during the procedure. We also analyzed the long-term neurodevelopmental outcome of children born following a pregnancy complicated by TTTS whose mothers underwent the controlled AR.