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From OHSU Doernbecher Children’s Hospital
Raphael C. Sun, M.D.
Dr. Sun is a pediatric surgeon at OHSU Doernbecher Children’s Hospital. He provides the full spectrum of pediatric surgery and fetal surgery, as well as complex surgical oncology care and colorectal surgery.
Andrew Chon, M.D.
Dr. Chon is a maternal-fetal medicine specialist at OHSU’s Center for Women’s Health. With advanced training in fetal surgery, he specializes in caring for patients with maternal or fetal conditions that complicate pregnancy.
Twin-twin transfusion syndrome (TTTS) is a serious condition affecting between 10–15% of monochorionic diamniotic twins. TTTS develops from unbalanced blood flow through vascular communications in the monochorionic placenta. Preferential shunting of blood from one twin (donor) to the other twin (recipient) results in hypovolemia with oliguria in the donor fetus, and volume overload and polyuria in the recipient fetus.
These hemodynamic changes lead to the characteristic findings of donor twin oligohydramnios and recipient twin polyhydramnios. The discrepancy is detrimental to both twins. Screening is essential in all monochorionic diamniotic twin pregnancies.
Ultrasound surveillance for monochorionic diamniotic twins starts at 16 weeks of gestation, with TTTS most often diagnosed between 16 and 26 weeks’ gestation. Expectant management of TTTS often results in pregnancy loss. If only one of the fetuses were to die, the surviving twin risks neurological damage (as a result of vascular communications in the shared placenta). The preferred treatment for TTTS is laser photocoagulation of communicating vessels via operative fetoscopy.
Laser photocoagulation is minimally invasive and performed under local and intravenous sedation. During the procedure, surgeons create a 5-millimeter incision on the mother’s abdomen and use a fetoscope to enter the uterus. The aberrant blood vessels along the placental surface are identified and laser photocoagulated. Patients usually spend one night in the hospital following the procedure, continuing the rest of their recovery and pregnancy at home.
After laser surgery, the twins are functionally separated from each other. This cures the TTTS, providing a favorable outcome for many patients (something that is not possible with less ideal management options), says Andrew Chon, M.D., a maternalfetal medicine specialist at OHSU’s Center for Women’s Health. Depending on factors such as TTTS stage, presence of fetal growth restriction and gestational age at surgery, the procedure results in the survival of at least one twin in 85–90% of cases and the survival of both 50–70% of the time.
Laser photocoagulation available at OHSU
As a multidisciplinary fetal care program, OHSU is the only facility in Oregon to offer laser photocoagulation. The means to offer the procedure is a development brought about by the recent expansion of OHSU’s fetal care team and services, including the addition of Dr. Chon, as well as pediatric surgeon Raphael Sun, M.D., who both joined OHSU in 2021. Dr. Chon and Dr. Sun work in collaboration with other members of the Fetal Care Program to provide advanced care for a range of complex fetal disorders. Prior to this expansion, providers had to refer patients out of state for laser photocoagulation. Now, with local care available, patients can recover in their home environment—close to family, friends and their existing medical team.
When to refer
A referral to a maternal-fetal medicine specialist is essential any time an ultrasound reveals the possibility of TTTS. OHSU offers timely evaluation, access to all pertinent providers, and the ability to assess and treat patients in one centralized location. Patients receive follow-up care and monitoring for the duration of their pregnancy, either at OHSU or with their referring provider.
Stages of TTTS
TTTS severity can vary significantly. Staging upon diagnosis informs this severity and allows the fetal surgery team to determine the best course of action. Early diagnosis is ideal in order to achieve the most favorable outcomes. TTTS is diagnosed using ultrasound criteria, with donor twin oligohydramnios (amniotic fluid maximum vertical pocket (MVP) ≤ 2 cm) and recipient twin polyhydramnios (MVP ≥ 8 cm). TTTS is staged using the Quintero staging system, as follows:
- STAGE 1: The fetal bladder of the donor twin remains visible by ultrasound.
- STAGE 2: The bladder of the donor twin is collapsed and not visible by ultrasound.
- STAGE 3: Critically abnormal fetal Doppler studies (in either twin): absent or reversed end-diastolic velocity in the umbilical artery, reverse flow in the ductus venosus, or pulsatile flow in the umbilical vein.
- STAGE 4: Fetal hydrops is present.
- STAGE 5: Demise of either twin.