What is Late Decelerations?
Late decelerations refer to a certain type of slow down in a baby’s heart rate while a woman is in labor. This is usually due to reduced blood flow to the placenta, the organ that provides oxygen and nutrients to the baby during pregnancy. These heart rate decelerations could point to the baby not getting enough oxygen.
So, what is a late deceleration exactly? It is recognized visually as a slow decrease in the baby’s heart rate, generally happening after the mother’s contraction. This slow decrease would take 30 seconds or more to reach its lowest point. The timing of these decelerations usually lines up with the mother’s contractions. So, the starting point, the lowest point, and the return of the decreased heart rate follow the start, peak, and end of a mother’s contraction.
Generally, late decelerations are mild, with a slow start and gradual return to the normal heart rate. The common cause for a late deceleration is a situation called uteroplacental insufficiency. This is when the placenta doesn’t work as well as it should in supplying the baby with the needed oxygen and nutrients.
What Causes Late Decelerations?
The main cause of late decelerations is usually not getting enough blood flow to the placenta. This means the fetus isn’t getting as much blood and oxygen as it needs to.
There are several conditions that might affect the mother or the baby and cause late decelerations. These include the mother being dehydrated, anemic, low oxygen levels, low blood pressure from pain relief during labor, a sped-up uterus, and the separation of the placenta from the womb.
Any condition that leads to reduced blood flow to the placenta and the baby can cause late decelerations. In other words, if anything restricts the blood supply to the placenta, it can lead to late decelerations.
Risk Factors and Frequency for Late Decelerations
Late decelerations are quite often seen and are associated with a condition called uteroplacental insufficiency.
Signs and Symptoms of Late Decelerations
A late deceleration is a visual drop in the baby’s heartbeat that generally happens after a uterine contraction during labor. This means the deceleration – the start, lowest point, and return – overlaps with the contraction’s beginning, peak, and recovery.
Testing for Late Decelerations
If a baby’s heart rate slows down after a contraction – this is known as a ‘late deceleration’ and can be a sign of distress. If these late decelerations continue to occur consistently, it’s critical that further tests are carried out to find out what’s causing them and to ensure the baby isn’t suffering from a condition called ‘fetal acidemia’, which is an abnormal level of acid in the baby’s blood.
To ascertain the severity of a baby’s oxygenation status (how much oxygen is reaching their tissues), one method used is the three-tier fetal heart rate tracing system. This system breaks down as follows:
Category I – means the baby’s heart rate is between 110 to 160 beats per minute, with moderate variability (changes between 6 to 25 beats per minute). There may or may not be increases in heart rate or early decelerations, but importantly there are no late or variable decelerations.
Category III – is identified by a pattern of no variability in the baby’s heart rate, along with frequent late and/or variable decelerations (rapid drops in heart rate), a slower-than-normal heart rate, or a ‘sinusoidal pattern’, which is a specific type of abnormal heart rhythm.
Category II – encompasses any heart rate patterns which don’t fit into Category I or III.
It’s essential to look at the complete picture of the baby’s heart rate, which includes checking for ‘tachysystole’ (excessively frequent contractions), variability (fluctuations in heart rate), and accelerations (increases in heart rate).
The results of this assessment will lead to categorisation into I, II, or III as outlined above. If variability and accelerations are both present, it generally suggests the baby is not suffering from acute fetal acidemia. However, if variability and accelerations are absent and there are ongoing late decelerations, immediate attention is required. This could indicate the baby isn’t getting enough oxygen, which can lead to ‘metabolic acidosis’ (a build-up of too much acid in the body).
It’s also crucially important to check the mother’s health. This involves constant monitoring of her vital signs including heart rate, respiration rate, temperature and blood pressure, ensuring she is well-hydrated, is not losing too much blood, and is not suffering any adverse effects from recent medication or epidural anesthesia. It’s also crucial to address any low blood pressure immediately.
Treatment Options for Late Decelerations
The main aim of managing late decelerations, which are signs of distress in the baby’s heart rate during labor, is to:
* Restore blood flow from the uterus to the placenta by addressing the root cause
* Increase the level of oxygen (PO2) the baby’s receiving
* Avoid or correct a state of too much acid (acidemia) in the baby’s blood
Doctors start to take steps to prevent acidemia and reduce risks to the baby’s health immediately after they’ve figured out what’s causing the late decelerations. Here’s what those steps often include:
* Repositioning the mother to her left side, right side, or in a knee-chest position. This helps to relieve pressure on a large vein in her body, the vena cava, from the weight of the pregnant uterus. This results in better blood flow back to her heart and more blood being pumped to the uterus and placenta.
* Giving the mother fluids through a vein (intravenous hydration). This is especially important if low blood pressure is a result of epidural anesthesia. The extra fluids, or sometimes medication given by the anesthesiologist, can help to raise her blood pressure. When her blood pressure gets better, her blood can carry more oxygen, and blood flow to the uterus and placenta is increased.
* Giving the mother extra oxygen (administering supplemental oxygen): there isn’t a clear consensus on whether this works. While some studies suggest that extra oxygen can reduce decelerations and better oxygenate the baby, other studies conflict with these findings. However, additional oxygen is usually given when there are concerns about the baby’s heart rate.
* Stopping uterotonics: These are medications to induce labor or increase contractions. By stopping them, the uterus can relax, and this leads to improved blood flow between the uterus and the placenta. Other medications that relax the uterus (tocolytics) can also be used to reduce the frequency of contractions and boost uteroplacental blood flow.
* Urgent vaginal delivery with tools or cesarean (C-section) delivery: If the baby’s heart rate isn’t improving despite these measures, and there are continued late decelerations and loss of variability (changes in the heart rate), doctors may need to take quick action to deliver the baby.
What else can Late Decelerations be?
There are several potential causes for certain complications that can occur during pregnancy. These include:
- Increasing fetal acid levels
- Compression of the umbilical cord inside the womb
- Poisoning affecting either the mother or the fetus
- Entanglement of the umbilical cord around the baby’s neck
- Low level of amniotic fluid (oligohydramnios)
- Mother’s pushing efforts during the second stage of labor
- Prolapse of the umbilical cord (when the cord comes out before the baby)
- Abnormal acid levels in the uterus
- Excessive rapid contractions of the uterus (uterine tachysystole)
What to expect with Late Decelerations
Repeated occurrences of late decelerations, a medical term referring to a slow-down in the baby’s heart rate during labor, can be dangerous if not quickly checked. It’s vital to assess both the baby’s heart rate pattern and the mother’s health.
It matters how much the heart rate changes and whether there are increases, called accelerations. Finding out and treating the reason for these late decelerations is crucial. If the baby’s heart rate continues to drop with little or no change and does not improve with methods used to help them inside the womb, then quick actions must be taken to deliver the baby.
Possible Complications When Diagnosed with Late Decelerations
If a baby’s heart rate decreases suddenly and does not return to normal quickly (a situation known as Category III), it could lead to severe health issues or even death for the baby if not evaluated and treated immediately. The problems linked with Category III situations include a high risk of the baby having a low APGAR score (a quick assessment of the baby’s physical health condition at birth), a dangerously low level of acidity in the baby’s blood in the umbilical cord, a higher risk of needing to be admitted to the neonatal intensive care unit after birth, a brain disorder causing difficulty with bodily movements and coordination (neonatal encephalopathy), and cerebral palsy.
Possible Risks:
- High risk of low APGAR score
- Risk of low acidity in the baby’s blood in the umbilical cord
- Increased likelihood of needing neonatal intensive care
- Neonatal encephalopathy – a brain disorder damaging physical coordination
- Possible risk of cerebral palsy
