Case
Our case was a 36-year-old Asian women, gravida 2 para 0. Before 32 weeks of gestation, the patient had gone to the local clinical institute as scheduled for prenatal examinations. Everything went smoothly during her process of pregnancy by then. At 33 weeks of gestation, the patient was found low lying placenta in that local institute by ultrasonography, and was referred to our hospital, a municipal tertiary institute.
An ultrasonography Specialty Register gave the transabdominal ultrasonic scan initially, and described as follows, “The placenta locates at the anterior wall of the uterine cavity, the distance between the placenta lower margin to the cervical internal os is 18mm. The insertion site of the umbilical cord is at the posterior wall of the uterine cavity, several vessels supported only by membranes insert into the placenta edges, including one vessel goes along the interior surface of the uterine fundus entering the placenta upper pole, and another vessel goes along the lower uterine segment entering the placenta lower pole near the cervix”(Figure.1 a ). Though a little puzzled as the insertion site of the umbilical cord and the placenta location were at posterior and anterior walls respectively, the diagnosis was obviously vasa previa. According to the guidelines, we should accomplish the cesarean section at 34 to 35 weeks[5].
However, the patient insisted on obstetricians’ reconsidering possibility of vaginal delivery since the vessel entering the placenta lower pole didn’t go exactly over the cervical internal os. 3 days later, we offer second time of ultrasonic examination. This time, an ultrasonography Consultant gave both transabdominal scan and transvaginal gray scale with color Doppler, and described as follows, “Yes, the umbilical cord insertion is at posterior wall and the placenta locates at the anterior wall. But no obvious sign of vessel overlying the cervix”. That result might overturn the previous diagnosis of vasa previa. So should we still schedule the cesarean section at 34 weeks of gestation?
In order to further understand the relationship between the patient’s umbilical cord and placenta, we referred her to MRI scan. The radiologists didn’t give any confirmation about umbilical vessels, because they’re usually specialists focusing on diagnosis of placenta increta, since vasa previa identification is commonly in sonographers’ field. But our obstetricians found a isolated vessel supported only by membrane going along the lower uterine segment and entering placenta lower pole near the cervix, just as the ultrasonography Specialty Register had described(Figure.1 b and c ). The umbilical cord truly inserted at posterior wall of the uterine cavity, and Wharton’s jelly lost from there with a great number of isolated vessels traveling through membranes connected to the anterior wall placenta(Figure.1 c and d ).
At first, we considered there might be a very tiny placenta at the posterior wall and then connected by naked vessels to the much larger succenturiate lobe at the anterior wall. Immediately, an obstetric Specialty Register pointed out there was hardly any space for placental tissue existing between the amnion and the uterine muscle at posterior wall. Ultimately, we got the conception that it was a special “parachute” type of placenta, with no placental tissue at the posterior wall, just several isolated vessels diverging from umbilical posterior wall insertion site, like strings connecting to the parachute canopy, to the anterior wall placenta.
We performed a cesarean section at 34 weeks and 3 days of gestation. At the time of surgery, the incision at lower uterine segment was gradually and carefully deepened until the decidua reached. Then rapidly cut through the placenta that covered the lower anterior wall of the uterine cavity, and got the fetus out immediately. A healthy female fetus was delivered with Apgar scores 9,10 and birth weight 2450g. The placenta was sequentially checked to confirm diagnosis of vasa previa on the spot at delivery, and postoperatively by pathology gross examination(Figure.1e ) before pathological sectioning. The postoperative course of the patient and the infant was uncomplicated and they were discharged 3 days later in a healthy condition.