Fetal Distress

Fetal distress is the term applied to the condition of the fetus who is exhibiting heart rate signs of poor oxygenation. Another synonymous phrase is “fetal intolerance to labor”. Both of these terms emerged with the advent of the electronic fetal monitor (EFM). Until the early 1970’s it was quite difficult to assess the health of the fetus. When the EFM was invented, doctors and midwives had a small window into the womb. It was felt that the fetal heart rate and the patterns created over a period of time printed on paper (much like an adult electrocardigram) could reveal information about the health of the baby. This works to a certain degree. EFMs and the fetal heart rate patterns they produce are very good at telling which babies are healthy. But they are not very good at telling which babies are in distress. More often than not, a baby diagnosed in “fetal distress” is not.

When the uterus contracts, blood flow to the placenta is temporarily reduced or interrupted. For most fetuses, this is not a problem. An appropriate analogy would be the swimmer swimming underwater……..as long as the swimmer comes up for air periodically, one can swim like this for quite a while. The well-oxygenated fetus is like the swimmer who is coming up often enough. The oxygen reserve which most fetuses have is more than enough to last during a contraction of a minute or two.

Both the placenta and the umbilical cord may play a role in true cases of “fetal distress”. The placenta is an organ with a pre-determined lifespan. It is not designed to function for much longer than 9 or 10 months. As it nears the end of its lifespan it becomes clogged with calcium deposits and scar tissue. The placentas ability to function as a respiratory device for the fetus diminishes. The contracting uterus may place an additional stress on the already compromised placenta, and the end result may be decreased oxygenation for the fetus.

Compression of the umbilical cord may decrease oxygen flow to the baby. It seems logical that some compression of the cord is bound to occur since the space inside the uterus is limited. It is also not uncommon for the cord to be looped around the baby’s neck or some other body part. The cord may also get pinched between the baby and part of the mother’s pelvic bone. A particular type of fetal heart rate deceleration seen on EFMs when cord compressions occur is called the “variable deceleration”. Mild to moderate variable decelerations are rarely associated with true fetal distress (though their appearance on the paper read-out of the EFM can be dramatic). However, prolonged severe variable decelerations are like the swimmer who is not coming up for air often enough……over a period of time, there is some oxygen deprivation.