HY lecture notes:
Cardiotocography = colloquially known as fetal heart rate monitoring; cardiotocograph is a machine used to measure fetal heart rate + uterine contractions simultaneously.
Accelerations = normal fetal well-being = fetal HR increases 15-20 bpm for 15-20s; this occurs ~2-3 times every 20 minutes.
Decelerations = fetal bradycardic events.
Early decelerations = fetal head compression; results in fetal vagal stimulation and concurrent bradycardia in the same y-axis on the fetal heart tracing; not associated with fetal distress and are reassuring.
Early decel –> uterine contraction + fetal bradycardia occur in the same y-axis / vertical plane.
Variable decelerations = fetal cord compression; literally variable in relation to fetal distress vs non-distress; often associated with premature rupture of membranes; compression of cord initially causes compression of umbilical artery within the cord, leading to the fetal bradycardia, followed by a rebound of the fetal heart rate as the compression on the cord abates with the relaxation of the uterus.
Variable decel –> no relation between uterine contractions and fetal bradycardia.
Q on one of the obgyn forms has amnioinfusion as the answer for variable decels. Patient was 4-cm dilated. Point I make to the student in this lecture is that, no, you are not expected to go into the 2CK knowing all about amnioinfusion; it’s more about eliminating answer choices –> i.e., you can eliminate other answers, like forceps delivery, because you can’t attempt delivery unless mother is fully dilated at 10 cm.
Late decelerations = fetal hypoxia / uteroplacental insufficiency; always non-reassuring; fetal hypoxia –> sensed by fetal chemoreceptors –> fetal autonomic response causing increased BP –> fetal baroreceptors activate –> increase parasympathetic outflow –> decreased HR
Late decel –> fetal bradycardia occurs just after the uterine contraction.
Tx for variable and late decels = change maternal position to left-lateral decubitus (takes pressure off maternal inferior vena cava –> increases venous return –> increased cardiac output –> increased placental perfusion –> mitigation of any fetal hypoxia); stop all oxytocin; give O2.
C-section done for continued non-reassuring FHR tracings, but not an instant answer.
Normal FHR is 110-160 bpm.
If the FHR tracing is a straight-line of zero slope:
If within the normal range –> answer = fetal sleep state.
If tachycardia –> answer = maternal fever.
Two good articles on decels:
