Management of Monochorionic Twin Pregnancies

Initial Assessment and Surveillance

The American College of Obstetricians and Gynecologists recommends ultrasound surveillance every 2 weeks starting at 16 weeks of gestation until delivery to screen for twin-twin transfusion syndrome (TTTS) and other complications in monochorionic twin pregnancies 1
Establishing chorionicity and amnionicity by first-trimester ultrasound (10-13 weeks of gestation) is critical to identify monochorionic pregnancies, which carry a 2-fold higher perinatal mortality compared to dichorionic twins 1, 2
Monochorionic twins share a single placenta with vascular anastomoses present in >95% of cases, predisposing them to unique complications 2

The Society for Maternal-Fetal Medicine recommends maximum vertical pocket (MVP) measurement in each amniotic sac, visualization of urine-filled bladder in each fetus, and umbilical artery Doppler studies every 2 weeks starting at 16 weeks of gestation 1, 3, 4
Middle cerebral artery (MCA) peak systolic velocity (PSV) Doppler should be started at 16 weeks to screen for twin anemia-polycythemia sequence (TAPS) 1, 2
TTTS is diagnosed when MVP <2 cm in one sac (donor twin with oligohydramnios) AND MVP >8 cm in the other sac (recipient twin with polyhydramnios) 3, 4
TAPS requires MCA-PSV >1.5 multiples of the median (MoM) in the donor twin AND <1.0 MoM in the recipient twin, OR an intertwin difference >0.5 MoM 1, 2

The American College of Obstetricians and Gynecologists recommends expectant management with at least weekly fetal surveillance for asymptomatic stage I TTTS patients 1
Fetoscopic laser surgery is the standard treatment for stage II-IV TTTS and all patients should be referred to a fetal intervention center 1
For TAPS, stage I can be managed with close monitoring, while stage II or higher requires mandatory referral to a specialized fetal care center for laser therapy evaluation 1, 5

The American College of Obstetricians and Gynecologists recommends delivery at 34-36 weeks of gestation for uncomplicated monochorionic-diamniotic pregnancies 1, 2
After successful laser therapy with both twins surviving, delivery should occur at 34-36 weeks of gestation 1
After single fetal demise post-treatment, the surviving co-twin should be delivered at 39 weeks (full-term) to avoid complications of prematurity unless other indications for earlier delivery exist 1, 2

High-risk features such as velamentous cord insertion, intertwin membrane folding, and umbilical artery Doppler abnormalities warrant more frequent surveillance 3, 4
The dynamic nature of TTTS necessitates consistent biweekly surveillance throughout the second and third trimesters until delivery 3, 4