Mechanism of labor in first and second stage of labor
The mechanisms of labor refer to the physiological changes and processes that occur during the first and second stages of labor. Here’s an overview of the mechanisms involved in each stage:
First Stage of Labor: The first stage of labor is the longest and can be further divided into three phases: early, active, and transitional.
- Early Labor: During this phase, the cervix starts to efface (thin out) and dilate (open). Contractions become regular, but they are typically mild and occur at longer intervals (around 5-20 minutes apart). The mechanism involved in this phase includes:
- Cervical Effacement: The cervix gradually thins out and prepares for dilation.
- Cervical Dilation: The cervix begins to open up, usually reaching around 3-4 centimeters in dilation.
- Active Labor: In this phase, contractions become more intense and frequent, occurring approximately every 3-5 minutes. The mechanisms involved include:
- Continued Cervical Dilation: The cervix continues to dilate, reaching around 7-8 centimeters.
- Descent and Engagement: The baby’s head moves down into the pelvis and engages in the optimal position for birth.
- Rupture of Membranes: The amniotic sac may rupture, leading to the release of amniotic fluid (commonly referred to as the “water breaking”).
- Transitional Labor: This is the final phase of the first stage and involves rapid cervical dilation and descent of the baby’s head. The mechanisms include:
- Complete Cervical Dilation: The cervix dilates fully to around 10 centimeters.
- Intense Contractions: Contractions become strong, frequent, and closer together, lasting around 60-90 seconds.
- Fetal Descent: The baby’s head descends further into the birth canal.
Second Stage of Labor: The second stage of labor begins when the cervix is fully dilated and ends with the birth of the baby. The mechanisms involved in this stage include:
- Maternal Pushing: The mother actively pushes during contractions, using her abdominal muscles and diaphragm to push the baby through the birth canal.
- Fetal Descent and Rotation: The baby continues to descend through the birth canal, rotating to the optimal position for delivery.
- Crowning: The baby’s head emerges at the vaginal opening, referred to as crowning.
- Birth: The rest of the baby’s body follows, and the baby is born.
It’s important to note that every labor experience can vary, and the mechanisms may differ depending on individual circumstances and the specific progress of labor.
CTG Monitoring During Pregnancy
Antenatal and intrapartum CTG (Cardiotocography) are two types of monitoring used during pregnancy and labor to assess the well-being of the fetus. Let’s discuss each of them separately:
- Antenatal CTG: Antenatal CTG, also known as antepartum or fetal surveillance, is performed during pregnancy to monitor the fetal heart rate and uterine contractions. It helps in assessing the fetal well-being and detecting any signs of distress or abnormalities.
During an antenatal CTG, two sensors are placed on the mother’s abdomen. One sensor measures the fetal heart rate, while the other sensor detects uterine contractions. The data collected is then recorded and analyzed for patterns and variations.
Interpretation of an antenatal CTG involves assessing the following parameters:
a. Baseline Fetal Heart Rate: The average heart rate of the fetus over a specific period. A normal baseline heart rate typically ranges between 110-160 beats per minute.
b. Variability: Variability refers to the fluctuations in the fetal heart rate around the baseline. It indicates the autonomic nervous system’s control over the fetal heart rate and is a good indicator of fetal well-being. Normal variability is considered a sign of a healthy, oxygenated fetus.
c. Accelerations: Accelerations are temporary increases in the fetal heart rate, usually associated with fetal movement. They are a positive sign and indicate a responsive, healthy fetus.
d. Decelerations: Decelerations are temporary decreases in the fetal heart rate. They can be early, late, or variable, each indicating different potential causes. Decelerations can be benign or indicative of fetal distress, and their pattern and timing are crucial for interpretation.
Overall, the antenatal CTG helps identify any deviations from normal fetal heart rate patterns and assists in determining if further intervention or monitoring is necessary.
- Intrapartum CTG: Intrapartum CTG, also known as electronic fetal monitoring (EFM), is performed during labor to continuously monitor the fetal heart rate and uterine contractions. It provides information about the well-being of the fetus during the intense process of childbirth.
Similar to antenatal CTG, two sensors are placed on the mother’s abdomen to measure the fetal heart rate and uterine contractions. Intrapartum CTG helps healthcare providers assess the fetal response to labor and identify any signs of distress or complications.
Interpretation of intrapartum CTG involves analyzing the same parameters as the antenatal CTG, including the baseline heart rate, variability, accelerations, and decelerations. Additionally, healthcare providers also consider the progress of labor, uterine contractions, and maternal well-being to make decisions regarding the management of labor and potential interventions.
It’s important to note that the interpretation of CTG readings requires clinical expertise, and any concerns or abnormalities identified should be discussed with a healthcare professional. They will consider the specific context of the pregnancy, labor, and the overall well-being of both the mother and the fetus to make appropriate decisions regarding further assessment or intervention.
Causes of abnormal CTG in labor
Abnormal CTG (Cardiotocography) readings during labor can indicate potential issues with the fetus’s well-being. Several factors can contribute to abnormal CTG patterns. Here are some common causes:
- Fetal distress: This is a significant concern and can be caused by insufficient oxygen supply to the fetus, resulting in abnormal heart rate patterns.
- Uterine hyperstimulation: Overstimulation of contractions, often due to the excessive use of oxytocin or other labor-inducing medications, can cause abnormal CTG patterns.
- Fetal hypoxia: Inadequate oxygen supply to the fetus can occur due to various reasons, such as placental insufficiency, umbilical cord compression, or maternal hypotension.
- Maternal factors: Certain maternal conditions can affect the fetal oxygen supply and lead to abnormal CTG readings. These include maternal hypotension, hypertension, diabetes, preeclampsia, and maternal drug use.
- Fetal anomalies: Structural or genetic abnormalities in the fetus can cause abnormal CTG patterns. These anomalies can affect the fetal heart rate and variability.
- Maternal medication: Certain medications administered during labor, such as opioids, may influence the fetal heart rate and result in abnormal CTG readings.
- Fetal sleep cycle: Fetal sleep cycles can cause temporary decelerations in the heart rate, leading to abnormal CTG patterns. These are usually considered normal if they resolve quickly.
- Fetal movement: Sudden fetal movements can sometimes cause temporary accelerations or decelerations in the heart rate, resulting in abnormal CTG patterns.
- Incorrect CTG placement: Improper placement of the CTG device on the mother’s abdomen can lead to inaccurate readings and give the appearance of abnormal patterns.
It’s important to note that abnormal CTG readings are not always indicative of a severe problem. Further assessment and evaluation by healthcare professionals, such as additional monitoring, clinical examination, or additional tests, may be required to determine the cause and decide on appropriate management.
