Results
4 patients in the study group as the 1st, and 7th to 9th, had inconclusive ultrasonic results for vasa previa at 23-25w of gestation, and still had suspicious ultrasonography diagnoses at 31-33w since the interpretation for vasa previa existence varied among ultrasonologists. 6 ones as the 2nd to 5th, 10th and 11th had no signs of vasa previa in ultrasonic scanning at 23-25w, however, detected of naked previa vessels once by a certain ultrasonologist at 31-33w, whilst another ultrasonologist couldn’t confirm that in subsequent scanning. 2 patients as the 6th and 12th, had been diagnosed by ultrasonography as vasa previa at 23-25w, but previa vessels couldn’t be reconfirmed by ultrasonography at 31-33w.
Maternal demographics, sonographic findings including placental position, umbilical cord insertion and ultrasonographic judgement of potential vasa previa for the study group are given in Table 1.
In the 12 patients enrolled into the study group with suspected vasa previa but inconclusive ultrasonic results, MRI demonstrated vasa previa in 11. The 12th patient had been excluded of vasa previa by MRI.
6 patients from 1st to 6th, had been identified as TypeⅠvasa previa in MRI scanning. The 1st patient’s previa vessels just plastered to the fetal scalp (Figure 1). Velamentous portion of the 2nd patient was tiny and entering the lower pole of the low-lying placenta (Figure 2). 3rd patient’s cord clearly diverged into velamentous form just before entering placenta, and at the same level of fetal lips as the fetus was facing down (Figure 3). From 4th to 6th patients, MRI also showed mangrove umbilical vessels without Wharton’s jelly inserting placenta. The 4th patient’s velamentous insertion was in a so large scale of mangrove form, that almost like a parachute (Figure 4). In both 5th and 6th patients, fetal heads were so low that compressed the previa vessel (Figure 5 & Figure 6).
The 7th patient was classified into Type Ⅱvasa previa. MRI clearly displayed the mangrove bridge vessels connecting placental major and succenturiate lobes, and one of the vessels overlying the cervix (Figure 7).
4 patients from 8th to 11th, were demonstrated as Type Ⅲ vasa previa by MRI with boomerang vessels beyond the edges without placental mass protection. The 8th patient’s previa boomerang vessels formed a transverse V shape (Figure 8). Previa vessels in the 9th and 10th patients were close to the uterine lateral walls (Figure 9 & Figure 10). In the 11th patient, the boomerang vessel was slightly compressed by the fetal head (Figure 11).
MRI had excluded 12th patient of vasa previa diagnosis at 33 weeks of gestation, as the mangrove bridge vessels connecting placental major and succenturiate lobes, previously adjacent to the cervical internal orifice, had moved away from the cervix a little laterally and upward, because the lower uterine segment gradually formed and extended (Figure 12). And this phenomenon had been proved by pathology examination showing naked mangrove vessels away from the amnion split.
MRI findings including placental position with morphology, vasa previa types and directions, also pregnancy outcomes and pathology examinations of the study group are summarized in Table 2.
In the control group, MRI had excluded vasa previa in all the 51 patients.
Placentas from the study and control groups were checked to confirm the existences of vasa previa immediately at delivery, and postoperatively by macroscopic examination before pathological sectioning. Pathology examination showed no vasa previa was missed in MRI diagnosis, and all the vasa previa running courses were coincided with directions displayed in MRI.