In utero laser ablation of blood vessels treats rare condition
Gwynne D. Koch
Vasa previa, a rare condition in which placental blood vessels block the birth canal and can rupture during labor, occurs in about one in every 2500 to 5000 pregnancies. The condition typically is managed by hospitalizing the patient for the last two months of pregnancy and delivering the baby at 35 to 36 weeks via elective cesarean section.
However, a recent case report suggests that a minimally invasive laser technique may provide an alternative treatment option. According to Dr. Rubén A. Quintero, director of the Division of Maternal-Fetal Medicine at the University of South Florida in Tampa, the risk of fetal death may be reduced substantially if the blood vessels are obliterated in utero.
The vessels supplying blood to the fetus normally are embedded in the placenta or the umbilical cord. In this case, the 37-year-old patient had an abnormal placenta with one larger and one smaller lobe linked by two exposed vessels crossing over the opening to the birth canal. Exposed vessels in that position can tear when the amniotic membranes rupture, or they may be compressed between the fetus and the walls of the birth canal during labor, cutting off oxygen to the fetus.
An ultrasound image captured using combined color and pulsed Doppler shows an artery and a vein crossing over the internal cervical opening, an abnormal arrangement indicating a rare condition known as type II vasa previa (left). A postoperative ultrasound image shows the lack of blood flow through the obliterated vessel (arrow) following a novel in utero laser ablation procedure (right). Reprinted with permission of The Journal of Maternal-Fetal and Neonatal Medicine.
At 22.5 weeks of pregnancy, the patient was given local anesthesia. With ultrasound guidance, Quintero inserted an endoscope housing a laser fiber through the abdominal wall and into the uterus, avoiding the placenta and the fetus. Using the 25-W, 1094-nm emission generated by an Nd:YAG laser from Surgical Laser Technologies (now PhotoMedex Inc.) of Montgomery, Pa., operated in continuous mode, he successfully photocoagulated the blood vessels connecting the two placental lobes. YAG lasers are used in fetal surgery because they can function in amniotic fluid.
Because there are two types of vasa previa, an accurate diagnosis of the condition is critical before proceeding with the treatment. In type I, the umbilical cord is abnormally inserted into the fetal membranes, not into the placenta. In type II, vessels joining two placental masses -- a main placental mass and a smaller accessory lobe -- cross over the cervix. Laser treatment is feasible only for type ll, and only if the umbilical cord inserts into the larger lobe. Laser ablation of vessels in type I would result in the death of the fetus.
The condition can be diagnosed on a routine ultrasound examination by assessing the area over the cervix with color and pulsed Doppler. Color Doppler is used to identify the blood vessels, and pulsed Doppler is necessary to document that the vessels have a fetal heart rate. Diagnosis of type II vasa previa can be confirmed with an endoscopic assessment of the amniotic cavity.
Laser ablation could eliminate prolonged hospitalization and the obligatory cesarean section, enabling the pregnancy to progress to term with a vaginal delivery. Further work is required to determine the risks and benefits of the technique. Potential risks include ruptured membranes, miscarriage, preterm delivery, neurological damage and fetal death.
According to Quintero, the next steps will be to determine the optimal time for the surgery, to refine some aspects of the surgical technique and to propose an international study to compare the current management strategy with the laser treatment.
The Journal of Maternal-Fetal and Neonatal Medicine, December 2007, pp. 847-851.
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