Methods:
This retrospective cohort study included women with a monochorionic
diamniotic twin pregnancy who underwent laser surgery for the management
of TTTS, between 2012 and 2018 at Baylor College of Medicine in Houston,
Texas and between 2002 and 2017 at the University Of Maryland School Of
Medicine in Baltimore, Maryland. Permission was obtained from
Institutional Review Boards of both institutions (H-19834, H-36458 and
HP-00040715-12). Laser surgery was performed when Quintero stage was II
to IV, or in Quintero stage I associated with symptomatic
polyhydramnios, cervical shortening, or preterm labor.
Laser photocoagulation of placental anastomoses was performed using a
single trocar under either local anesthetic with intravenous sedation,
regional, or general anesthesia. The trocar was introduced
percutaneously using the Seldinger method at one participating
institution, whereas direct trocar entry was used at the other
institution. The placental vascular anastomoses were identified, and
laser was used for photocoagulation under direct fetoscopic
visualization. Amnioinfusion (using Ringer’s lactate or normal saline
solutions) and/or amnioreduction were used at the discretion of the
surgeon(s). After laser surgery, most patients returned to their
referring institutions to continue with their antenatal care.
Absolute intertwin differences in umbilical artery PI was estimated
prior to laser surgery by subtracting the lower pulsatility index (PI)
of the UA of either twin from the PI of the UA of the co-twin, as
previously reported9. TTTS cases were stratified using
a DUAPI cutoff value of 0.4 derived from a receiving characteristic
curve analysis to evaluate double infant survival to 30 days of life. In
order to determine which component of DUAPI is associated with infant
survival, separate ROC curve analyses were done for the UA PI of the
donor and UA PI of the recipient to predict double survival to 30 days
of life in the whole study cohort. Since UA PI changes with gestational
age, correlation analyses were done using spearman’s rho tests to
evaluate the relationship between DUAPI and gestational age at
ultrasonography as well as between UA PI of the donor or the recipient
twin with gestational age at ultrasonography.
Double infant survival and survival of at least one twin to one month of
age was compared between women with a DUAPI ≥0.4 and those with a DUAPI
<0.4 in the whole cohort and then separately in women with
TTTS Quintero stage I or II combined as well as in women with TTTS
Quintero stage III or IV combined. The rationale for this is that
Quintero stages I and II differ only on the visualization of the fetal
bladder of the donor twin; whereas fetal hydrops is the main feature
differentiating stage III and IV. Moreover, besides fetal
echocardiography, there is currently no other method to further stratify
TTTS cases with Quintero stages I or II in order to predict infant
survival prior to laser surgery. We previously reported that among TTTS
with absent or reversed UA EDF, intermittent UA Doppler abnormalities
are associated with higher infant survival when compared to persistent
UA Doppler abnormalities9.
Stepwise backwards conditional regression analyses were performed to
evaluate the association of DUAPI <0.4 and double infant
survival using a DUAPI of ≥0.4 as a reference, adjusted for gestational
age (GA) at surgery, GA at delivery, Quintero stage, selective fetal
growth restriction (sFGR) (estimated fetal weight or birthweight
discordance ≥25% and <10th percentile of one
twin)18, maternal age ≥35 years old,
BMI>35, placental location (anterior, posterior or lateral
with an anterior or posterior component), use of Seldinger method to
place the operative trocar, size of the vascular trocar, participating
center, use of Solomon technique, laparoscopic-assisted procedure,
cerclage and preterm prelabor rupture of membranes (PPROM). These
regression analyses were done in the whole cohort and then separately in
women with TTTS Quintero stage I or II combined as well as in women with
TTTS Quintero stage III or IV combined. To evaluate if the sonographic
components used in Quintero staging are independently associated with
infant survival, a separate regression analysis was performed including
the above-mentioned co-variables in addition to the following ones:
maximum vertical pocket (MVP) >8 cm in the recipient twin,
MVP <2 cm in the donor twin, absent or reversed UA end
diastolic flow (EDF) in either twin, absent or reversed flow during
atrial contraction in the ductus venosus of either fetus, and fetal
hydrops in either fetus defined as the sonographic finding of two or
more of the following: skin edema, ascites, pleural or pericardial
effusion. In the regression analyses evaluating the sonographic criteria
used in the Quintero classification, Quintero stage was excluded to
avoid multicollinearity. Since the MVP cut-off used in the Quintero
classification was not derived from an ROC curve
analysis,7 additional regression analyses were done to
evaluate the association of the MVP of both donor and recipient twins
(as continuous variables) with infant survival adjusting for the
above-mentioned confounders.
Comparisons were done using Pearson Chi-square, Fisher Exact, and
Mann-Whitney U tests. P<0.05 was considered significant. All
statistical analysis was performed using IBM Statistical Package for
Social Sciences (SPSS version 24).