Late decelerations would be a waveform decelerating gradually and returning gradually to baseline from onset to lowest point of the deceleration (nadir )>30 seconds.
When late decelerations occur?
It is caused when fetal chemoreceptors are activated when there is a drop in oxygen levels in the fetal blood, which triggers an auto-contraction of vessels in non vital peripheral areas in order to increase blood flow to vital organs.
Constriction of peripheral blood vessels causes hypertension that stimulates a baroreceptor mediated vagal response which slows the heart rate. Deceleration occurs at a later time in relation to contraction due to this two-step process.
Etiologies of Late Decelerations:
- Excessive uterine contractions
- Maternal hypotension
- Maternal hypoxemia (asthma, pneumonia)
What Do Late Decelerations Look Like?
Decelerations do not occur before contractions as they do during variable decelerations. There is a sudden decrease in fetal heart rate associated with variable deceleration. Usually after the contractions stop, the heart rate of the fetus does not return to baseline for a while; this contrasts markedly with decelerations that occur rapidly during labor. Unlike variable decelerations that look like an upside-down mountain, late decelerations appear as a “U” or “W” shapeThere are usually fewer abruptness and less pointedness.Gradually, your heart rate returns to its baseline over a period of time.
Why Are Late Decelerations Dangerous?
Decelerations that occur late indicate insufficiency in the placenta, and this is potentially dangerous.During pregnancy, the placenta serves as the fetus’ life line from the mother. Blood and oxygen travel from the mother’s uterus into the placenta and down the umbilical cord to the fetus. If placental blood flow is disrupted, the new fetus suffers by losing nutrients, oxygen, and blood. Below is a diagram of placental blood flow.In the case of a disruption of blood flow, the fetus could suffer severe harm.
What Conditions Cause Late Decelerations?
Several dangerous conditions can lead to late decelerations. These are a few examples:
- Placental abruption.
- Maternal diabetes.
- Gestational hypertension.
- Maternal anemia.
- Maternal sepsis.
- Post-term pregnancy.
- Hyper-stimulated uterus.
Can Recurrent Late Decelerations Be Corrected?
Sometimes, but it depends. When blood pressure is too low or uterine contractions are too intense, repeated late decelerations may be experienced with moderate variability between them. A reduction in contractions or an increase in blood pressure are usually sufficient to resolve these conditions. It may be necessary to reduce the contractions or increase blood pressure in order to correct these conditions.Reduce Pitocin, provide intravenous fluids, or adjust the position of the mother, In order to give birth to a healthy baby.
However, measures to improve blood flow and oxygen may not be successful in treating some conditions, including diabetes, high blood pressure, and IUGR. If the lack of oxygen continues, the fetus may develop acidosis and suffer injury.As a result of an inadequate supply of oxygen to the fetus, there may be late decelerations, no rapid decelerations or bradycardia (low pulse below 60 beats per minute).It is not a good idea to wait until this kind of emergency happens to seek medical attention.
Possible complications of late decelerations?
- Insufficient scores for appearance, pulse, grimace, activity, and respiration (APGAR).
- A greater chance of being admitted to the neonatal intensive care unit after delivery.
- Cerebral palsy.
- Neonatal encephalopathy.
What are Variable decelerations?
Decelerations observed in the early months of pregnancy are called variable decelerations because they first develop and then gradually slow down. An umbilical cord that is temporarily compressed can cause variable decelerations. Labor is typically characterized by this phenomenon. A baby’s oxygen and other essential nutrients are provided by blood flowing steadily through the umbilical cord.Variable decelerations over and over may indicate that the baby’s blood flow is reduced. It can cause harm to the baby if such a pattern is followed.
The heart rate monitors used by doctors allow them to determine whether variable decelerations pose a problem.In case of severe variable decelerations early in labor, your doctor might suggest a cesarean section. When they are associated with accelerations as well as occurring before delivery, they typically make sense.
Causes of variable decelerations:
Varying decelerations are caused by vagal reflex triggered by head pressure during pushing, as well as cord compression caused by short cords, nuchal cords, entanglement of the body, prolapsed cords, and decreased amniotic fluid.
Late decelerations treatment and management?
An obstetrician will attempt to determine the underlying problem if the pattern of the fetal heart rate appears abnormal. A clinical expert must be able to diagnose whether or not this condition is reversible. To avoid serious consequences for your newborn, they will need to determine the timing of delivery when hypoxia is suspected. However, they should also attempt to prevent delivering your baby prematurely.
A complete fetal heart tracing is required in order to determine your health status. As well as checking the absence/presence of decelerations, your doctor should assess the degree of variability, and immediately address the root cause of late degradations. Please keep in mind that doesn’t mean you will need an immediate intervention like a vaginal birth or Caesarean section.
There is no conclusive evidence that fetal hypoxia is caused by a repeated deceleration, only if the fetal heart trace is normal. That’s the conclusion of the International Federation of Gynecology and Obstetrics (FIGO).
Differential Diagnosis :
- Increasing fetal acidemia.
- Intrauterine umbilical cord compression.
- Maternal/fetal poisoning.
- Nuchal cord entanglements.
- During the second stage of labour, push forward with your efforts.
- Umbilical cord prolapse.
What are early decelerations?
During labor, contractions temporarily interrupt (but repeatedly) the flow of oxygen to the fetus. While most babies can tolerate this oxygen shortage, others cannot.
By measuring the fetal heart rate patterns and the response of their cardiac and central nervous systems to changes in blood pressure and gas levels, we can determine which fetuses are affected.
Monitoring fetal heart rate during pregnancy allows your doctor to identify any unusual patterns that might be caused by an insufficient oxygen supply. This enables them to take immediate and appropriate action to prevent injury caused by hypoxia (an insufficient supply of oxygen for fetal tissues).
Accelerations occur when the fetal heart rate is reduced below 15 beats per minute (bpm) in bandwidth amplitude, and they last longer than 15 seconds.
A fetal heart rate fluctuates according to its baseline interval, frequency, or amplitude, often in conjunction with the contractions occurring in your uterus.