Abstract
ObjectivesTo construct monochorionic (MC) twin-specific longitudinal Doppler references for umbilical artery pulsatility index (UA-PI), middle cerebral artery (MCA) PI and peak systolic velocity (PSV) and ductus venosus (DV) PI derived from a strictly selected cohort of uncomplicated MC twins. The secondary aim of the study was to compare our findings with singleton reference charts.MethodsA retrospective evaluation was made of all consecutive uncomplicated MC twin pregnancies referred to our Unit from 2010 to 2018. Fortnightly serial examinations were performed of UA-PI, MCA-PI, MCA-PSV and DV-PI, according with the clinical protocol, from 20 to 37 weeks of gestation. We included cases with at least four ultrasound examinations, delivery at our hospital and complete neonatal follow up. A two-step method was used to trace the estimated centile curves: estimation of the median was performed with appropriate fractional polynomials by a multilevel model and estimation of the external centiles through the residuals (quantile regression). The comparison with singletons was made by plotting the references derived from the present study on the referred charts commonly used for singletons.ResultsThe study group comprised 150 uncomplicated MC twin pairs. Estimated centiles (3rd, 5th, 10th, 50th, 90th, 95th, 97th) of UA-PI, MCA-PI, MCA-PSV and DV-PI in function of the gestational age are presented. The comparison with singletons showed substantial differences, with higher UA-PI and lower MCA-PI and PSV median values in MC twins. Median DV PI values were similar to the values for singletons, while the upper centiles were higher in MC twins.ConclusionsThis study sets out MC twin-specific longitudinal references for UA-PI, MCA-PI, MCA-PSV and DV-PI derived from the largest series of uncomplicated MC twin pregnancies presently available. The comparison with singleton reference values underscores the deviation from physiology that is intrinsic to these unique pregnancies and supports the need for MC twin-specific charts.
Highlights
Doppler ultrasound investigation of umbilical and fetal circulation is widely used for fetal surveillance in high risk pregnancies, with proven efficacy for identifying fetal compromise and improving pregnancy outcomes [1,2]
Median ductus venosus (DV) pulsatility index (PI) values were similar to the values for singletons, while the upper centiles were higher in MC twins
This study sets out MC twin-specific longitudinal references for umbilical artery pulsatility index (UA-PI), middle cerebral artery (MCA)-PI, MCA-peak systolic velocity (PSV) and DV-PI derived from the largest series of uncomplicated MC twin pregnancies presently available
Summary
Doppler ultrasound investigation of umbilical and fetal circulation is widely used for fetal surveillance in high risk pregnancies, with proven efficacy for identifying fetal compromise and improving pregnancy outcomes [1,2]. Additional consideration is necessary for monochorionic (MC) twins who have interdependent circulations deriving from placental vascular anastomoses which may give rise to specific Doppler waveforms In comparison to both dichorionic (DC) twins and singleton pregnancies, MC pregnancies are at higher risk of severe complications such as intrauterine growth restriction (IUGR), intrauterine fetal demise, severe congenital anomalies, neurological impairment, perinatal and neonatal morbidity and mortality [13,14,15,16,17,18]. In 2014, a prospective multicenter cohort study in Ireland reported the longitudinal references for umbilical artery (UA) pulsatility index (PI) and resistance index (RI), middle cerebral artery (MCA) PI and peak systolic velocity (PSV) and cerebroplacental ratios (CPR) derived from 508 DC and 110 MC twin pregnancies from 24 to 38 weeks of gestation They found that both in DC and MC twins, UA-PI and UA-RI appeared to be higher than in singletons, while MCA-PI, MCA-PSV and CPR appeared lower [12]
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