Main Findings
The controlled AR procedure resulted in a relatively high rate of twin survival independently of the gestation week. Moreover, it is objectively more efficient since it revealed positive short and long-term outcomes. The pattern of the amniotic pressure versus the removed fluid demonstrated an apparent exponential relationship with a plateau and represented a logical reason for procedure duration and termination.
The controlled AR procedure was applied to 11 pregnant women with twins diagnosed with TTTS, including severe cases at Quintero stages II and III. In this study group, the procedure was terminated based on amniotic pressure measurements, rather than the removed fluid volume. There were no cases of maternal infection or complications, as well as premature delivery in the 48 hours post procedure.
The overall survival rate was 19/22 (86.4%), which is higher than published outcomes of serial AR interventions 8, 10, 11, 13, 27, 28. It should be noted that the controlled AR procedure was also successful in cases of severe TTTS in patients who were firstly treated at the gestational ages of 17 to 32 weeks, while in published reports AR was recommended only in cases of mild disease or when FLS interventions were unsuccessful 9.
In the present study the amniotic fluid volume removed during the session varied between 700-4500 ml (Figure 1). Presently, there is no consensus regarding the amount removed per session. The published data revealed a wide variety of values from 400 to 7500 mL, which are within 50% to 435% of the mean volume for any given gestational age2, 5, 6, 29, 30. It has been suggested that drainage of a large quantity of amniotic fluid may result in unpredictable changes in blood flow across the vessel connections 31and 1100 ml should be the weekly maximal removed amniotic fluid ensure survival 32. The present study demonstrated that there is no definite volume drainage that predicts the procedure efficiency.
The umbilical artery S/D ratio in uncomplicated twin pregnancy shows close agreement with the normal range for singleton pregnancy33. It is obvious that reduction in amniotic fluid volume decreases the pressure associated with polyhydramnios and leads to increased flow from the placenta to the fetus 34. In the present study, the initial umbilical artery S/D ratio was above the 95th percentile of the normal range in 10 cases and within it in 8 cases. The most noticeable positive effect of the procedure on FVW was observed in the 3 cases of severe TTTS with initial AEDF, but the post-procedure S/D ratio did not reach the normal range for the given week of gestation. Nevertheless, this outcome is in agreement with previous reports on higher fetal mortality in cases of AEDF in either the donor or the recipient (i.e., patients 1, 4, 8)5, 28, 32, 35. The post-procedure S/D ratio changed to be within the normal range in 63.8% of cases, below it in 4 cases (11.2%) and above it in the remaining 9 cases (25%). We did not observe a tendency in the S/D ratio changes due to the procedure. Thus, we assume that post-procedure changes in S/D ratio are related to the cardiovascular system slow adaptation to gradual changes, but unpredictable.
The present results indicate that the pre-drainage amniotic pressure was higher in comparison to the reference range (Figure 2) and are consistent with some published data 20, 36-38. As expected, amniotic pressures always decrease with fluid drainage and the mean difference between pre- and post-procedure pressures was 9.1±5.4 mmHg. The pressure drop had an exponential pattern with a final plateau and further volume removal had no effect, as reported by others20, 22, 39. While one study observed a linear relationship between the removed amniotic volume and the pressure drop22, other studies could not find such a relationship20, 39.
Finally, we also followed for a long-term all surviving twins that their mothers were treated with controlled AR. Analysis of the data revealed that over 2/3 of the twins were neurologically normal, about 1/4 of them demonstrated minor neurodevelopmental impairment and only one child (about 5%) with a cerebral injury.