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Complications of the Umbilical Cord and Fetal Membranes

The umbilical cord and fetal membranes are vital to the healthy growth and development of your unborn baby. Usually, pregnancy proceeds without complication. Sometimes, however, problems can arise with these structures, which can cause concerns for both mother and baby.

Umbilical cord complications

Single umbilical artery

The umbilical cord normally contains two umbilical arteries and one umbilical vein, which carry blood between the placenta and the unborn baby. Some unborn babies have only one umbilical artery. While this usually does not pose a problem to the developing baby, about 30% of infants with only one umbilical artery have some sort of congenital abnormality such as cleft lip, heart conditions, or chromosomal abnormalities.

Velamentous insertion and vasa previa

Usually the umbilical blood vessels run from the placenta, protected within the umbilical cord, to the baby. However, in 1% to 2% of pregnancies, a condition called velamentous insertion of the umbilical cord can occur. In this condition, the blood vessels travel, unprotected, across the fetal membranes before they come together into the umbilical cord. This condition may be associated with low birth weight, premature birth, and various congenital abnormalities. Velamentous insertion can cause hemorrhage from the baby during childbirth, after the fetal membranes have ruptured. If velamentous insertion is suspected, you may be advised to have a caesarean section to avoid the chance of rupture.

Vasa previa is a complication of velamentous insertion where the umbilical blood vessels cross the fetal membranes and pass through the space between the unborn baby and the cervix. This is a very serious condition because once the fetal membranes rupture, the exposed blood vessels can tear, causing massive bleeding from the baby. This causes the baby’s heart rate to slow down, and puts him in grave danger. If you have vasa previa with significant vaginal bleeding, you will need to have a caesarean section in an effort to save the baby’s life.

Fetal membrane complications


This is an infection of the fetal membranes and amniotic fluid, which may be associated with infections in the mother and baby. The symptoms of chorioamnionitis include fever, increased heart rate in the mother or unborn baby, a tender or painful uterus, and foul odour of the amniotic fluid. Chorioamnionitis can result from prolonged membrane rupture and long labours. The condition is diagnosed, prior to labour, with blood tests and amniocentesis, and during labour with monitoring. If you develop chorioamnionitis during pregnancy, you will be given antibiotics and the baby will be delivered as soon as possible.

Disorders of the amniotic fluid volume

Usually, the volume of amniotic fluid in the uterus reaches about 1 L (1 quart) by 36 weeks of pregnancy, and it decreases significantly after childbirth. There are two types of problems that can occur with regard to the volume of amniotic fluid:

  • Polyhydramnios is over 2 L (2 quarts) of amniotic fluid in the uterus. This condition is quite common in women with diabetes. The causes of polyhydramnios are not well-known. The condition can be diagnosed with ultrasound. Polyhydramnios is associated with higher rates of congenital and chromosomal abnormalities, placental abruption, premature birth, death of the unborn baby, and postpartum hemorrhage. Sometimes amniocentesis is used to remove some of the amniotic fluid.
  • Oligohydramnios is too little amniotic fluid. Again, its cause is not well known. Oligohydramnios is rare in early pregnancy, but when it does occur, there is an increased risk of miscarriage, fetal growth restriction, placental abruption, premature birth, musculoskeletal abnormalities such as clubfoot, an abnormality of the lungs called pulmonary hypoplasia, and stillbirth. Because the level of amniotic fluid in the uterus decreases somewhat after 35 weeks of pregnancy, oligohydramnios is more common during that time. Oligohydramnios in late pregnancy is associated with higher rates of fetal distress and caesarean section. Oligohydramnios can be treated by infusing a fluid called crystalloid into the uterus to replace the missing amniotic fluid.

Nicolette Caccia, MEd, MD, FRCSC

Rory Windrim, MB, MSc, FRCSC