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Magnesium for Preterm Labour (How It Works, Risks, Benefits + More)

Pregnant woman lying on back on bed with arms on stomach.

Table of Contents

Why do hospitals use magnesium for preterm labour? Can magnesium slow or stop early labour contractions? Are there any side effects of taking magnesium during pregnancy or during delivery?

This post will cover everything you need to know about using magnesium to slow preterm labour.

What is preterm labour and why use magnesium to stop it?

premature or preterm labour

Labour is defined as preterm (or premature) if it starts before 37 weeks of gestation. 

As most pregnant people know, preterm labour can put the birth parent and fetus at risk. 

Thankfully, medical professionals can often successfully halt preterm labour. But in 10% of cases, people give birth within the week these early contractions start. 

When contractions start too early, every extra day that medical professionals can delay labour counts. That’s why it’s important to understand how magnesium can help to slow or prevent pre-term labour.

How magnesium slows preterm labour 

Researchers believe that magnesium works to slow preterm labour because of its role in supporting healthy muscles. (With benefits for the heart, exercise, restless legs syndrome (RLS), and chronic pain

Labour and birth depend on muscle function. In fact, birth is only possible because of muscle contractions in the uterus, leading to changes in the cervix. 

At the cellular level, magnesium works by reducing calcium levels and thus inhibiting muscle contraction (since calcium is needed for muscle contraction to occur). When magnesium ushers calcium out of the cells, the uterine muscles relax enough to stall preterm delivery. 

Magnesium is used in hospitals to slow contractions. This treatment may not stop all contractions, but magnesium can delay contractions significantly. The extent to which magnesium can delay preterm labour depends on multiple factors, including (but not limited to) the extent to which the mother’s cervix is dilated when the treatment begins.  

How hospitals use magnesium for preterm labour

hospital IV magnesium for preterm labour

So, how exactly do medical professionals use magnesium when a pregnant person arrives in premature labour?

Hospitals usually rely on intravenous (e.g. drip feed) magnesium for preterm labour. 

The protocol for magnesium drip dosage is to start the treatment with an infusion of 4-6 grams over 15-30 minutes and then continue with 2-3 grams per hour, as needed (maintenance dose). 

It’s important to note that this is a very high dose of magnesium and can only be administered in a hospital setting. For context, the recommended daily intake of magnesium is about 0.4 grams.

Even so, intravenous magnesium may not completely stop preterm labour. However, it can slow the process long enough to make time for other medical interventions. 

How long does magnesium stop labour?

Magnesium can be very effective, but like any medication used to slow uterine contractions, magnesium will not permanently stop preterm labour. However, magnesium treatment can delay infant delivery for at least a few days, allowing enough time for doctors to administer steroids. 

The efficacy of magnesium will depend on how much the mother’s cervix was dilated at the time magnesium was first administered. The sooner, the better. Although delaying labour by a few days may seem insignificant, it is enough time for a round of steroids to improve the infant’s lung function and reduce the possibility of fetal mortality by 40%. In addition, magnesium treatment reduces the likelihood of the child developing cerebral palsy during early delivery. 

Will magnesium delay normal labour or cause late-term pregnancy?

will magnesium delay labour and delivery

If you are not at risk for preterm labour, you might wonder if taking magnesium will prevent you from going into labour at full term. After all, we know that intravenous magnesium slows contractions.

There is no evidence that a daily magnesium supplement may delay a normal pregnancy and lead to late-term delivery. Only very high doses in a hospital setting are shown to slow labour.

The difference is in the dose.

A normal daily supplement may contain about 200mg of magnesium. To slow preterm labour, hospitals administer as much as 6000mg of magnesium intravenously as an initial dose, then 3000mg per hour afterward. So, the initial dose alone is 30x what you’d get from a daily supplement.

Hospital administration of magnesium cannot be compared to normal supplementation.

Taking magnesium during labour for high blood pressure

Magnesium is useful for pregnancy beyond slowing preterm delivery. It is also used to prevent or treat one of the most dangerous complications of pregnancy.

Preeclampsia typically presents itself after 20 weeks of pregnancy. Risk factors include maternal high blood pressure. The cause is largely unknown, although research suggests it may be related to the blood vessels that connect the uterus to the placenta (the organ that brings oxygen from mother to baby). 

There are a variety of complications that can arise from preeclampsia, including seizures, preterm birth or stillbirth, stroke, or damage to the placenta. Women at risk of preeclampsia are closely monitored by their physicians and may be admitted to the hospital. The only way to resolve preeclampsia is to deliver the baby, but this may present a difficult decision if the mother is still early in the pregnancy. 

After diagnosis, doctors may prescribe corticosteroids (to quickly develop the baby’s lung function and maintain the health of the mother), as well as medications to lower blood pressure. It is during this time that magnesium may be administered if the mother is in danger of going into preterm labour. As in cases of preterm labour without preeclampsia, magnesium is delivered intravenously in the hospital and helps to delay delivery for up to two days. 

Magnesium is also used in preeclampsia to reduce the risk of seizures (eclampsia). This treatment is administered throughout the delivery process until about a day after delivery. Once the infant has been born, preeclampsia usually resolves itself in the weeks that follow, though regular checkups remain important. 

Risks and side-effects of using magnesium in pre-term labour

risks of magnesium during premature contractions

The risk associated with intravenous magnesium in preterm labour is low, especially compared to the risks of preterm labour or eclampsia.

Both mother and baby may experience minor side effects when given high doses of magnesium in preterm labour. Yet, only about half the women treated with magnesium report side effects. 

Mothers may experience fatigue and discomfort, sometimes described as “like having the flu” – dry mouth, headache, blurred vision, flushing, nausea, and a feeling of excessive and uncomfortable warmth. It may be challenging to separate these symptoms from those of preterm labour. It’s also generally agreed that the benefits of treatment (slowing preterm labour) outweigh any discomfort.

In hospitals, nurses monitor women to avoid cardiac arrest and respiratory failure – the results of toxically high blood levels of magnesium. If magnesium levels in the blood become too high, the hospital will lower the dose or use calcium gluconate to return blood magnesium levels to normal. 

After being treated with magnesium, babies may experience temporary and mild side effects from the muscle relaxant properties of magnesium. They may appear lethargic, limp, or floppy after delivery. (As do many infants born without intravenous magnesium.) These symptoms disappear quickly because magnesium does not typically stay in the system for more than 24 hours.  

These side effects are associated with very high doses of intravenous magnesium and are not applicable to at-home magnesium supplementation during pregnancy.

Key takeaways on magnesium for preterm labour

We know that magnesium works to slow contractions in preterm labour. It “buys time” for medical professionals to administer steroids and reduces the risk of cerebral palsy development in babies that are born prematurely.

In cases of preeclampsia, magnesium diminishes the likelihood of maternal seizures, protecting the mother and infant. 

Magnesium plays a key role in hospital care for premature labour. It improves health outcomes for both mother and child. 

Should you take magnesium to prevent preterm labour?

Should you take magnesium to prevent premature labour

There’s no substitute for medical care if you’re at risk of preterm labour. If you are concerned about preterm labour, speak to your healthcare provider right away.

If you are not at risk of going into labour early, you might wonder if magnesium can help you reach a healthy full-term pregnancy.

Magnesium is an essential nutrient. It supports the health of every system in your body and the health of your growing fetus. As a supplement, magnesium is typically beneficial and very safe for pregnant people.

There are some people who cannot take magnesium. For example, magnesium is contraindicated for certain muscle disorders, such as myasthenia gravis or muscular dystrophy, and kidney complications.

If you choose to boost your magnesium levels, first, be sure to include magnesium-rich foods in your diet. These foods are often recommended during pregnancy because magnesium foods are also high in other nutrients.

If you aren’t getting enough magnesium from your diet, or if you’re depleting magnesium rapidly, you might notice leg cramps, tension, difficulty sleeping, constipation, and other symptoms of low magnesium.

Consider a supplement like Natural Calm to boost your magnesium intake during pregnancy. Natural Calm magnesium dissolves in water, so it’s rapidly absorbed. And it tastes great, with no sugar or artificial sweeteners (just organic stevia)!

calm rl 16

Remember to use Natural Calm in moderation (following recommended dosing guidelines) to maintain normal levels of magnesium. If you take too much, you may experience diarrhea. Simply reduce your dose, or take smaller doses throughout the day.

Consult your healthcare provider if you have concerns about taking magnesium during pregnancy.

More research on magnesium for preterm contractions

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