Magnesium Sulfate

THE SAFETY OF MAGNESIUM SULFATE DURING PREGNANCY OR BREASTFEEDING

The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

THIS MEDICATION CAN CAUSE HARM TO YOUR BABY:
The short-term (< 48 hours) use of magnesium sulfate in clinically indicated conditions is expected to pose a low risk of harm to an infant. Long-term use of magnesium sulfate for 5-7 days can increase the risk of bone abnormalities in the developing baby. The administration of magnesium sulfate close to the time of delivery can increase the risk of temporary neurological/respiratory depression or loss of muscle tone in the baby. Magnesium sulfate is considered compatible with breastfeeding. Caution is advised when using this medication while nursing an infant. 

What is magnesium sulfate?

Magnesium sulfate is a medication that is taken to treat multiple conditions. It is currently available as a generic or brand name medication depending on the formulation. Magnesium sulfate is available as oral capsules, granules, or injectable solution (intravenous or intramuscular) – times per day administered depends on the indication and severity of an individual's clinical condition. It is available by prescription from your doctor. 

What is magnesium sulfate used to treat?

Magnesium sulfate is used to treat constipation, severe preeclampsia or eclampsia, and hypomagnesemia (low magnesium levels) as well as multiple off-label indications such as prevention of preterm labor, and it is used as a soaking aid to relieve stiff muscles (called Epsom Salt). Magnesium sulfate can be used in infants (depends on the indication), children, adolescents, and adults. Several types of high blood pressure can affect pregnant women including preeclampsia/eclampsia. Preeclampsia is characterized by high blood pressure during pregnancy and the presence of proteins in the urine. 

How does magnesium sulfate work?

Magnesium sulfate works by moving fluid into the colon and causing a bowel movement when used to treat constipation. It replenishes magnesium levels, which are essential for normal cell function in the body, in cases of hypomagnesemia. In women with severe preeclampsia, magnesium sulfate relaxes smooth muscle and causes vasodilation to maintain blood supply to vital organs in the body. Magnesium sulfate plays a role in propagating nerve impulses in the brain and spinal cord and has been used to prevent and treat eclampsia and preeclampsia-associated seizures. 

If I am using magnesium sulfate, can it harm my baby?

Short-term use of magnesium sulfate is not expected to pose a risk of harm to a baby. Administration of magnesium sulfate close to the time of delivery may increase the risk of adverse effects in the baby such as temporary neurologic and respiratory depression or poor muscle tone.

Evidence from animal studies with magnesium sulfate:

When given to pregnant rats late in pregnancy at doses 1.25 times the maximum recommended human dose, magnesium sulfate was associated with maternal toxicity, low birth weight, and skeletal abnormalities in the babies. Pregnant sheep given injectable magnesium sulfate had offspring with short-term changes in heart rate. Rats experienced liver toxicity and increases in fetal liver enzymes with magnesium exposure. Mouse offspring exposed to magnesium sulfate in utero showed better learning abilities over time.

Evidence for the risks of magnesium sulfate in human babies:

Short-term use

Magnesium sulfate crosses the human placenta and reaches the developing baby. The Collaborative Perinatal Project found no increase in the risk of birth defects in women exposed to injectable magnesium sulfate during pregnancy versus women not exposed during pregnancy. The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine support short-term, less than 48 hours use of magnesium sulfate for any of the following indications: prevention and treatment of preeclampsia or eclampsia-related seizures; fetal neuroprotection in expected preterm deliveries (less than 32 weeks gestation); and prolongation of pregnancy more than 48 hours in women at risk of preterm delivery who require steroid treatment. 

Magnesium sulfate has several short-term uses including treatment and prevention of seizures in eclampsia and preeclampsia before delivery, neuroprotection and prevention of poor neurological development for the baby in preterm delivery (not proven to be effective), and treatment of cardiac and respiratory arrest. The use of magnesium sulfate to treat eclampsia/preeclampsia during pregnancy has not been shown to have negative long-term effects on neurological development in babies. 

Long-term use

Long-term, continuous use of magnesium sulfate for greater than 5 to 7 days can cause hypocalcemia (low calcium levels) in infants as well as abnormal bone formation and fractures. The U.S Food and Drug Administration warns against the use of magnesium sulfate to prevent preterm labor in pregnant women for more than 5 to 7 day due to risks to the baby. Studies have shown a mixed effect of magnesium sulfate to prevent preterm delivery and newborn admission to special intensive care units in the hospital. There have also been reports of intestinal perforation in newborns with a very low birth weight who are exposed to prenatal magnesium sulfate. 

Beneficial effects

Controversial studies have reported beneficial effects for the baby of magnesium sulfate use during pregnancy. Positive effects reported include a decreased risk of bleeding in the brain and cerebral palsy in preterm infants. Some studies show there is a decreased risk of cerebral palsy with magnesium sulfate given before 32 weeks gestation. One study suggests magnesium sulfate given less than 12 hours before delivery of a preterm infant decreases the risk of cerebral palsy; however, a similar study found no effect of magnesium sulfate delivered less than 12 hours versus more than 18 hours before delivery on outcomes. Magnesium sulfate is reported to decrease the baby's heart rate fluctuations, has no negative effect on cerebral blood flow, and is associated with fewer miscarriages and preterm births. Increased levels of magnesium sulfate in the umbilical cord have not been shown to correlate to the condition of a newborn on delivery. 

Potential side effects

Studies have reported the following potential side effects on babies when magnesium sulfate was used during pregnancy: 

  • Bone abnormalities (magnesium sulfate used for more than 5-7 days before delivery)
  • Changes in heart rate
  • Short-term neurological depression
  • Respiratory depression
  • Muscle weakness
  • Loss of reflexes
  • Drug interactions with antibiotics and heart medications

Monitoring for 24-48 hours is recommended in newborns whose mothers are exposed to magnesium sulfate close to the time of delivery. Elevated levels of magnesium sulfate in newborns can remain high for up to 7 days after delivery. Maternal toxicity is also possible with prolonged use of magnesium sulfate during pregnancy.

Bottom line: The short-term (less than 48 hours) use of magnesium sulfate in clinically indicated conditions is expected to pose a low risk of harm to an infant. Long-term use of magnesium sulfate for 5-7 days can increase the risk of bone abnormalities. The administration of magnesium sulfate close to the time of delivery can increase the risk of temporary neurologic/respiratory depression or loss of muscle tone in the baby.

If I am taking magnesium sulfate and become pregnant, what should I do?

If you are taking magnesium sulfate and become pregnant, you should contact your doctor immediately. Your doctor will determine if your medication is medically necessary, or if it should be discontinued until after the birth of your baby.

If I am taking magnesium sulfate, can I safely breastfeed my baby?

Adverse events have not been reported in nursing infants exposed to magnesium in breast milk. Magnesium sulfate is excreted into the breast milk. Injectable magnesium sulfate only elevates levels of magnesium slightly in breast milk. Use of injectable magnesium for greater than 6 hours postpartum can make it take longer for your milk to come in. Oral magnesium sulfate is
minimally absorbed by a baby who is nursing. Magnesium is normally found in breast milk. Caution is advised when taking magnesium sulfate while breastfeeding a baby. However, the use of magnesium sulfate to treat or prevent seizures in breastfeeding women is considered compatible by the World Health Organization. The American Academy of Pediatrics considers magnesium sulfate compatible with breastfeeding. 

Bottom line: Magnesium sulfate is  considered compatible with breastfeeding. Caution is recommended in women using this medication while breastfeeding babies.

If I am taking magnesium sulfate, will it be more difficult to get pregnant?

There is no available information on the effect of magnesium sulfate on male or female fertility.

If I am taking magnesium sulfate, what should I know?

The short-term use of magnesium sulfate is expected to pose a low risk of harm to an infant. Long-term use of magnesium sulfate can increase the risk of bone abnormalities in the baby. The administration of magnesium sulfate close to the time of delivery can increase the risk of temporary neurologic/respiratory depression or loss of muscle tone. Magnesium sulfate is considered compatible with breastfeeding. Caution is recommended in women using this medication while breastfeeding babies.

If I am taking any medication, what should I know?

This report provides a summary of available information about the use of magnesium sulfate during pregnancy and breastfeeding. Content is from the product label unless otherwise indicated.

You may find Pregistry's expert report about preeclampsia here, our report about constipation here, and reports about various other health conditions as well as the individual medications used to treat them here.   Additional information can also be found in the resources below. 

For more information about magnesium sulfate during and after pregnancy, contact http://www.womenshealth.gov/ (800-994-9662 [TDD: 888-220-5446]) or check the following links:

ACOG: Preeclampsia and Hypertension in Pregnancy: Resource Overview.

U.S. Food and Drug Administration: FDA Recommends Against Prolonged Use of Magnesium Sulfate to Stop Preterm Labor Due to Bone Changes in Exposed Babies.

ACOG: Magnesium sulfate use in obstetrics.

Read the whole report
Last Updated: 27-04-2019
General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.