CLINICAL TOOL
Twin Surveillance & TTTS/sFGR Calculator
Clinical tool to track twin growth discordance, identify Twin-Twin Transfusion Syndrome (TTTS), and stage selective Fetal Growth Restriction (sFGR) in monochorionic twins.
About this page
This is a clinician-reviewed evidence brief, not an interactive calculator. It summarises the guideline logic our subspecialists apply when managing these cases every day. For a case-specific assessment, request a consultation or refer your patient.
Clinical Purpose
To calculate inter-twin weight discordance and apply the Quintero staging system for TTTS and the Gratacos classification for sFGR in monochorionic diamniotic (MCDA) twin pregnancies.
Inputs
- Chorionicity (MCDA, DCDA)
- Estimated Fetal Weight (EFW) for Twin A and Twin B
- Deepest Vertical Pocket (DVP) for Twin A and Twin B
- Bladder visibility for donor twin
- Umbilical Artery Doppler patterns (positive, absent, reverse)
Formula & Guideline Source
ISUOG Practice Guidelines: role of ultrasound in twin pregnancy (2016).
Limitations
Quintero staging does not strictly correlate with prognosis, as disease can rapidly progress or regress. Frequent serial ultrasounds (every 2 weeks) are mandatory for MCDA twins.
FAQ
How is weight discordance calculated?
Weight discordance = ((EFW of larger twin - EFW of smaller twin) / EFW of larger twin) × 100%. A discordance > 20-25% is generally considered clinically significant.
What defines Stage I TTTS?
Stage I TTTS is defined by the oligohydramnios-polyhydramnios sequence (DVP < 2cm in the donor sac and DVP > 8cm in the recipient sac) with visible bladders in both twins and normal Dopplers.
References
- Khalil A, et al. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound Obstet Gynecol. 2016.
- Quintero RA, et al. Twin-twin transfusion syndrome: standardisation of ultrasound diagnosis and staging. J Matern Fetal Med. 1999.