Report from AIUM: Prenatal ultrasound diagnosis averts fetal deaths from vasa previa
Vasa previa, a condition affecting approximately one in 2500 pregnancies, is almost always lethal. Adding vasa previa screening to current obstetrical ultrasound protocols could prevent mortality, according to a study presented Tuesday at the American Institute of Ultrasound in Medicine meeting.
An international group of researchers from Israel, the U.K., and the U.S. compared outcomes and predictors or survival in 155 pregnancies complicated by vasa previa. They found that fetal survival depends mostly on prenatal diagnosis and cesarean delivery at 35 weeks of gestation or earlier if the case warrants the procedure.
"Historically, vasa previa has had a mortality rate of close to 100%," said principal investigator Dr. Yinka Oyelese, an ob/gyn clinician at the University of Medicine and Dentistry of New Jersey (UMDNJ). "It is, however, a preventable obstetric tragedy."
Vasa previa occurs when some fetal vessels that are unsupported by either the placenta or the umbilical cord pass through membranes over the cervix. When these membranes get ruptured, generally at delivery, the fetus may bleed to death.
Ninety-seven percent of infants (59 of 61) from prenatally diagnosed vasa previa pregnancies survived compared with 44% (41 of 94) of those not diagnosed prenatally. Only 3.4% (2) of infants with prenatal diagnosis required blood transfusions compared with almost 59% (24) of surviving neonates born to women without diagnosis.
According to a multivariable logistic regression analysis, the only significant predictors of neonatal survival were prenatal diagnosis (p<.001) and gestational age at delivery (p = .01).
The study by Oyelese and colleagues validates previous findings that showed the prenatal diagnosis of vasa previa to be feasible. Nomiyama et al proved ultrasound can locate the umbilical cord insertion into the placenta in 666 women and diagnosed three vasa previa cases (Ultrasound Obstet Gynecol 1998;12:426-429).
Not all vasa previa cases can be recognized by sonography, however. Abdominal wall scarring, obesity, or an incompletely filled bladder may block the visualization of cord-placenta insertions or that of vessels over the cervix. The condition could be also diagnosed by MR imaging, according to Oyelese.
The study suggested an association between vasa previa and second-trimester low-lying placenta or placenta previa. Findings also suggested an association between in vitro fertilization and vasa previa. Further studies should solidly establish these correlations, he said.
Women belonging to higher risk groups should consider routine transvaginal color Doppler sonography of the region over the cervix if vasa previa cannot be excluded by transabdominal sonography, Oyelese said.
