Overview of Tocolysis
Tocolysis is a procedure in pregnancy used to delay preterm labor or early delivery. It involves the use of certain medications to lessen the contractions of a mother’s uterus. In doing so, the procedure seeks to reduce risks to the baby. The overall goal of tocolysis is to push the pregnancy into a window of two to seven days further along, not to bring the pregnancy to full term. This little extra time is valuable as it provides the opportunity for doctors to transfer the mother to a hospital that offers high-level maternity care, to give the baby steroids to help with lung development, and also to check and, if needed, treat the mother for group B streptococcus (a common infection that can be harmful to newborns).
The key point to understand is that tocolysis doesn’t aim to prolong pregnancy until full term. Instead, the focus is to afford that critical ‘window’ of extra time to engage health measures that can make labor and delivery safer for both mother and baby.
To clarify though, as of now, the United States Food & Drug Administration (FDA) hasn’t officially approved any medication specifically for use in tocolysis. So, all the medications used in this procedure are off-label, meaning they aren’t officially recognized for this use, but have shown promise and are considered effective. They should be used in situations where doctors decide that they’re necessary.
Historically, two drugs, ritodrine and terbutaline, had been used for this purpose. Though ritodrine was taken off the approved list in the US due to potential heart risks to mothers, it’s still in use in some countries. Terbutaline was also suggested for this use in 1987, however, it was taken off the list in 2011 and reclassified from a Pregnancy Class B drug (safe in animal studies but not enough human studies) to a Class C drug (not proven safe in animal or human studies).
Anatomy and Physiology of Tocolysis
The process of slowing down and weakening contractions in the womb is called tocolysis. It specifically targets the activity of the myometrium, a type of smooth muscle found in the uterus. This type of muscle is responsible for the contractions that enable childbirth.
These contractions start naturally, without needing any kind of stimulation from nerves or hormones. They begin when there’s a change in the electric charge on the surface of the cells in the uterus. This change opens special channels in the cells, allowing calcium to flood in. The calcium then binds with a protein called calmodulin. This new combination activates an enzyme that attaches phosphate molecules to another protein called myosin.
Myosin plays a crucial role in muscle contraction. The addition and removal of phosphate molecules cause the myosin to continuously interact with another protein called actin. This back-and-forth motion is what leads to the muscle contractions in the uterus.
Normally, women start going into labor around the 40th week of pregnancy. However, some conditions can kickstart labor earlier than expected. These early contractions can be triggered by an imbalance of proinflammatory and anti-inflammatory proteins in the body. Other causes can include excessive stretching of the uterus, stress, infection, problems with the blood vessels, and aging of the uterine lining. If contractions start too soon, it can put the baby at a high risk because they may not be developed enough to survive outside the womb.
Why do People Need Tocolysis
When a woman goes into labor before her 37th week of pregnancy, it is called preterm labor. As per medical standards, preterm labor is diagnosed when contractions, or episodes of belly tightening, occur more than four times within a 20-minute span. Contractions at this stage can bring about changes in the cervix, a part of the woman’s reproductive system, which can lead to early delivery. However, it is tough to predict if preterm labor will result in a preterm delivery.
Medical professionals use a method called tocolysis to delay labor in women who are less than 34 weeks pregnant. This method uses drugs to relax the womb and slow down or stop the contractions. However, these drugs should not be used as prevention, since it has not been shown to decrease health problems in newborn babies.
Tocolysis is also used in certain other situations, besides preterm labor. For example, during an external cephalic version – a procedure used to turn a baby from a head-up to a head-down position before labor begins. In this case, a drug called terbutaline is often used. This drug can be given through the skin or directly into a vein, half an hour before the procedure begins.
Another instance where tocolysis can be used is during a condition called uterine tachysystole, where the pregnant woman experiences more than five contractions in 10 minutes over the course of 30 minutes. In such cases, drugs like terbutaline can be used to quickly stop the contractions.
When a Person Should Avoid Tocolysis
The ACOG Practice Bulletin 171 outlines certain situations where a particular medical procedure may not be advisable. These include:
- When pregnancy is beyond 34 weeks
- If the baby has unfortunately passed away in the womb (intrauterine fetal demise)
- In case the baby has a fatal birth defect (lethal fetal anomaly)
- If the baby’s health in the womb is not stable (nonreassuring fetal status)
- Severe forms of high blood pressure in pregnancy (preeclampsia or eclampsia)
- In case the pregnant mother is bleeding severely and her overall health condition is unstable
- When the mother has an infection in the womb (chorioamnionitis)
- When the water around the baby breaks prematurely before the time of birth (preterm premature rupture of membranes), unless there’s no maternal infection and there’s a need for transport or steroid treatment
- Specific situations where medication to stop labor (tocolytic agents) is not safe.
There are also relative situations where the procedure might not be a good idea such as if the cervix is already more than 5 cm dilated, if the mother has heart disease, hyperthyroidism, uncontrolled diabetes, minor abruptio placentae, stable placenta previa, and if the baby is not growing well in the womb. Studies have shown that delaying birth with medication (tocolytics) is not beneficial if there are problems with the placenta. Another possible situation where the procedure might not be a good idea is if the baby is too small for the gestational age. This can vary on a case by case basis, but smaller babies may need help breathing (ventilation) after delivery.
Equipment used for Tocolysis
Tocolysis is a process used to stop the uterus from contracting too much. Different medications are used to achieve this depending on the mother’s health history, how far along the pregnancy is, and cost considerations. There isn’t one recommended medication for this according to the American College of Obstetrics and Gynecology (ACOG), but nifedipine and indomethacin are often used. Sometimes, using a combination of medications might be more effective than one alone. Repeating this treatment isn’t recommended. Here are some of the types of drugs used for this:
- Beta-Adrenergic receptor agonists
- Calcium channel blockers
- Magnesium Sulfate
- Nonsteroidal anti-inflammatories
- Oxytocin inhibitors
Beta-Adrenergic receptor agonists work by targeting a specific receptor, leading to muscle relaxation. Common drugs in this category include terbutaline, hexoprenaline, and ritodrine. However, these may have risks like heart complications for the mother and potential development of asthma in the child.
Calcium channel blockers stop calcium from entering the uterine smooth muscle, which in turn affects the muscle’s ability to contract. The most common drug in this class is nifedipine. However, while it’s mostly safe, it can cause side effects such as headaches, dizziness, and hypotension (low blood pressure). It’s especially crucial for women with pre-existing cardiac conditions to be careful when using nifedipine.
Magnesium sulfate affects uterine contractions in a yet unclear mechanism, possibly by inhibiting the entry of calcium into the muscle. It also has effects on blood vessels in the uterus. While it’s often used for specific protective measures, it’s important to note that its effectiveness is still up for debate. Side effects can include blurred vision, and reduced cardiac contractility (heart muscle’s ability to contract).
Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the production of compounds that can cause inflammation and pain. However, some NSAIDs, like indomethacin, may have side effects and risks such as gastrointestinal bleeding and kidney effects. After 32 weeks of pregnancy, they can cause premature closure of a critical vessel in the baby, so they’re not advised.
Oxytocin inhibitors work by blocking the effects of oxytocin, a hormone that increases contractions. Medications in this group include atosiban and retosiban, but these are not approved for use in the United States.
Besides these tocolytic agents, nitroglycerine has also been tried for effectiveness in stopping premature labour. This medication works by preventing contractions from proceeding. Although it has fewer side effects compared to some of the aforementioned drugs, it is not typically recommended for this purpose.
How is Tocolysis performed
Maintenance tocolysis is the medical term for continuing treatment aimed at delaying labor beyond 48 hours. Usually, doctors administer medications for about 48 hours to help the patient through what’s called a ‘steroid window,’ This period enables her to be safely transferred to a specialized hospital if need be. However, the American College of Obstetricians and Gynecologists (ACOG) does not have an official position on continuing this treatment beyond the 48 hours.
Current studies and evidence do not show that certain types of drugs, including beta-adrenergic receptor agonists, calcium channel blockers, COX inhibitors, or magnesium sulfate, are effective for prolonging this labor-delaying treatment. However, some preliminary evidence suggests that two types of hormone-related medications, progesterone and hydroxyprogesterone caproate, might be useful for continuing this kind of treatment.
These hormones might be used in patients who have experienced preterm labor in the past, even though they are not officially classified as drugs that delay labor. However, it’s always the doctor’s call based on each patient’s medical history and current healthcare situation.
Possible Complications of Tocolysis
Potential issues that can occur from tocolysis, which is a treatment used to delay labor, largely depend on the certain medication used. It’s important to note that these drugs do not guarantee that they can extend the duration of labor. So, sometimes, healthcare providers might need to switch out these medications in order to successfully calm the uterus.
What Else Should I Know About Tocolysis?
Tocolysis is an important treatment because it can postpone childbirth, giving doctors more time to do procedures that can assist the newborn. The World Health Organization (WHO) has shown that delaying delivery by up to 48 hours can be beneficial. This delay allows doctors to administer drugs known as antenatal corticosteroids. These drugs can help the lungs of babies who are born early (premature neonates) to mature more fully.
However, there’s ongoing discussion on the benefits of tocolysis in reducing severe newborn illnesses. It’s important to note that tocolysis doesn’t tackle the main issue of why a baby might be born prematurely, but it provides crucial time for doctors to help improve the baby’s health outcomes.
