Umbilical cord inserting into the membranes of the placenta rather than onto
the placental mass (1-11). The vessels are unsupported by either the umbilical
cord or placental tissue. The vessels traverse the fetal membranes between the
amnion and chorion prior to inserting into the placenta. The umbilical vessels
separate from each other and course between the amnion and chorion before
reaching the placenta.
Common (1.1% of singleton births and 8.7% to 16% of twins deliveries) (1).
In cases of monochorionic twin placentation, the frequency increases when the
placentas are fused. The incidence of velamentous insertion is higher in early
pregnancy: 33% between 9th and 12th weeks and 26% between
13th and 16th weeks (11).
Several theories have been proposed including (1,11):
fixation of the yolk sac to the chorion at a site which is distant from the
definitive placental site.
of the body stalk to a region of proliferating trophoblast other than the
decidua basalis (this theory propose that the umbilical cord arises from the
chorion which is very vascular).
primary implantation due to obliquity of the embryo during implantation.
(umbilical cord implants normally but becomes abnormal due to central atrophy
and unidirectional lateral growth of the chorion frondosum).
Marginal cord insertion
Velamentous cord insertion
- Fetal exsanguination due to
rupture vasa previa (mortality > 50%) (1,2). Vasa previa occurs when
the vessels traverse the fetal membranes below the presenting part.
- Intrapartum hemorrhage.
- Fetal bradycardia.
- Twin-to-twin transfusion
- Small for gestational age
infants with a velamentous insertion of the cord is estimated to be 7,5%
(5). In twin pregnancies, the twin with the velamentous cord insertion has
a lower mean birth weight than the unaffected co-twin (5).
- IUGR (7.5%) (5-7).
- Congenital fetal anomalies
(5.9% - 8.5%) (5,8) (esophageal atresia; obstructive uropathies,
congenital hip dislocation; asymmetrical head shape; spina bifida; ventricular
septal defects; single umbilical artery; bilobed placenta; trisomy 21).
- Preterm delivery (up to
- Low birth weight, small for
gestational age fetus (7).
umbilical artery (10).
- Careful scan to rule out
- Follow up scans to exclude
- Caesarean section prior to
onset of labor or cervical dilatation.
- Benirschke K, Kaufmann P.
Umbilical cord and major fetal vessels. In: Benirschke K, Kaufmann P
(Eds): Pathology of the human placenta. 2nd Ed. New York, Spriner-Verlag, 1990:220.
- Quek SP, Tan KL. Vasa
Previa. Aust NZJ Obstet Gynecol 1972;12:206.
- Kouyoumdjian A. Velamentous
insertion of the umbilical cord. Obstet Gynecol 1989;56:737-742.
- Paavonen J, Jouttunpaa K,
Kangaslucoma P et.al. Velamentous insertion of the umbilical cord and vasa
previa. Int J Gynaecol Obstet 1984;22:207-211.
- Bjoro K Jr. Vascular anomalies
of the umbilical cord. I. Obstetrical implications. Early Hum Dev
- Scott JM, Jordan JM.
Placental insufficiency and small for dates baby. Am J Obstet Gynecol
- Rolschau J. The
relationship between some disorders of the umbilical cord and intrauterine
growth retardation. Acta Obstet Gynecol Scand 1978;72(Suppl):15.
- Robinson LK, Jones KL,
Benirschke K. The nature of structural defects associated with velamentous
and marginal insertion of the umbilical cord. Am J Obstet Gynecol
- Brody S, Frenkel DA.
Marginal insertion of the cord and premature labor. Am J Obstet Gynecol
- Pretorius DH, Chau C,
Poelyler DM et.al. Placental cord insertion visualization with prenatal
ultrasonography. J Ultrasound Med 1996;15:585-593.
- Monie IW. Velamentous
insertion of the cord in early pregnancy. Am J Obstet Gynecol