Gestational Age at TAPS Diagnosis
Twin anemia polycythemia sequence (TAPS) is most commonly diagnosed at a median gestational age of 23.7 weeks, though it can present anytime from 15 weeks through the third trimester. 1
Timing of Diagnosis Based on Registry Data
The largest international cohort study provides the most definitive data on when TAPS is typically identified:
- Median gestational age at antenatal diagnosis: 23.7 weeks (interquartile range 9.7-28.8 weeks) 1
- Range of diagnosis: 15.1 to 35.3 weeks of gestation 1, 2
- 88% of cases are diagnosed prenatally when systematic surveillance is performed 1, 2
This data comes from an international registry of 249 cases of spontaneous TAPS, representing the highest quality evidence available on diagnostic timing. 2
Clinical Context: When TAPS Can Develop
TAPS can occur at any time during the second or third trimesters, distinguishing it from twin-twin transfusion syndrome which typically presents earlier:
- Disease onset can begin as early as the beginning of the second trimester (around 15 weeks) 2
- Cases have been documented continuing through the end of the third trimester (up to 35+ weeks) 1, 2
- The Society for Maternal-Fetal Medicine confirms TAPS "can occur anytime in the second or third trimester" 1
Surveillance Implications
Given this wide diagnostic window, the American College of Obstetricians and Gynecologists recommends:
- Begin MCA-PSV Doppler screening at 16 weeks of gestation for all monochorionic twins 3
- Continue surveillance every 2 weeks throughout pregnancy until delivery 3
- More frequent monitoring is indicated when clinical concern arises 1
This systematic approach is critical because TAPS is unlikely to be detected prenatally without MCA-PSV evaluation, especially at earlier stages when the disease may be asymptomatic. 1, 3
Post-Laser TAPS Timing
For iatrogenic TAPS following fetoscopic laser surgery for TTTS, the timing may differ and progression can be more rapid, requiring particularly vigilant surveillance in the weeks following intervention. 1, 3