Longitudinal Doppler references for monochorionic twins and comparison with singletons.

Area of Science:

• Perinatal Medicine
• Fetal Ultrasound
• Maternal-Fetal Medicine

Background:

• Monochorionic (MC) twins share a placenta, leading to unique physiological adaptations.
• Existing Doppler reference charts are primarily based on singleton pregnancies, potentially misrepresenting MC twin development.
• Accurate reference charts are crucial for monitoring fetal well-being in MC twins.

Purpose of the Study:

• To create 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.
• To compare these MC twin-specific references with established singleton charts.
• To highlight the distinct physiological parameters in uncomplicated MC twin pregnancies.

Main Methods:

• Retrospective analysis of 150 uncomplicated MC twin pregnancies (2010-2018).
• Serial Doppler assessments (UA-PI, MCA-PI, MCA-PSV, DV-PI) performed fortnightly from 20 to 37 weeks gestation.
• Advanced statistical modeling (multilevel models, quantile regression) used to generate centile curves.

Main Results:

• Longitudinal reference centiles (3rd-97th) for UA-PI, MCA-PI, MCA-PSV, and DV-PI in MC twins were established.
• MC twins demonstrated higher UA-PI and lower MCA-PI/PSV medians compared to singletons.
• DV-PI medians were similar to singletons, but upper centiles were higher in MC twins.

Conclusions:

• This study provides the largest dataset of MC twin-specific Doppler references to date.
• The findings underscore significant physiological differences between MC twins and singletons.
• MC twin-specific charts are essential for accurate interpretation of fetal Doppler assessments in these pregnancies.