Expert advice Q&A
 What is velamentous cord insertion?
 The umbilical cord joins the baby to his or her placenta. The average cord is about 50cms long, and as thick as the base of an adult finger. It comprises a twisted rope of three blood vessels (two arteries and a vein), surrounded by a firm jelly-like substance called 'Wharton's Jelly', and covered by a layer of amniotic membrane. At the point where the cord meets the placenta, this tough membrane spreads out, covering the surface of the placenta, and extending beyond to form the inner of the two membranes that enclose the amniotic fluid - the so-called 'bag of waters'.
The baby's umbilical cord is normally firmly attached to the centre of the placenta. From here, the blood vessels in the cord spread out, branching many times to reach each part of the placenta. The tips of these blood vessels are buried within the tissue of the placenta. This is the 'interface' between the mother's and the baby's circulations, where the exchange of oxygen and nutrients, and carbon dioxide and waste products, takes place.
Occasionally, the umbilical cord may be attached to the side of the placenta. This is interesting because it's unusual, but generally poses no problems for either mother or baby.
Even more rarely, the insertion of the cord is described as 'velamentous'. This is when the Wharton's Jelly (mentioned in the first paragraph) does not cover the whole length of the cord, stopping short a few inches of the placenta. The arteries and vein of the cord therefore spread out before they reach the cord so that, instead of forming a firm rope, the three vessels can be seen wriggling their independent way through the amniotic membrane to the placenta. More often than not, nobody is aware that there is a velamentous cord insertion until after the placenta is safely delivered. A comment may be made in the mother's notes, and the placenta may be shown to any passing midwifery students - but generally neither mother nor baby come to any harm or inconvenience.
However, an undiagnosed velamentous insertion may sometimes cause problems. Firstly, the cord vessels may start to tear as 'controlled cord traction' is being used to remove the placenta (the usual way of delivering the placenta in UK hospitals). This may delay delivery of the placenta, since the midwife can no longer pull on the cord. If things are not managed well at this point, the mother may be at increased risk of bleeding, because the placenta has come away from the wall of the uterus, but the uterus cannot yet clamp down to stop the bleeding from the placental site.
Forewarned by the knowledge that your cord has a velamentous insertion, the midwife attending the birth of your baby may feel that 'active management' of the delivery of the placenta should be avoided. This means that the placenta will not be pulled out following separation. Instead, it will be left to separate in its own time (so you would not be given the usual injection) and then you will be asked to push it out, usually whilst squatting, or sitting on a bedpan. I recommend that you talk this over with your midwife or obstetrician some time in pregnancy, since not everybody would agree with this course of action.
Secondly, the cord vessels of a velamentous insertion may be at risk of rupturing during labour if they run across, or close to, the internal opening of the cervix. The blood vessels may tear as the cervix starts to open, or may be torn as the midwife or doctor artificially breaks the waters to either start labour, or speed up contractions once labour has started. Although this is a very, very rare situation, it is obviously very serious, since it is the baby who would be losing blood. He or she would have to be immediately delivered, either by caesarean section or forceps, and would probably need a blood transfusion in order to survive.
I do not know of any link between problems with the baby's development and a velamentous cord insertion. However, I have read that the incidence of velamentous cord insertion is much higher in IVF pregnancies than naturally conceived pregnancies.
Answer provided by Hannah Hulme Hunter
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