[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Obstetric pharmacotherapy: pre-eclampsia and preterm labour # Obstetric pharmacotherapy: pre-eclampsia and preterm labour How medicines are used to control blood pressure and prevent seizures in pre-eclampsia, and to delay preterm labour long enough to help the baby's lungs. Updated Nov 12, 2026 Pre-eclampsia and preterm labour are leading causes of maternal and newborn harm. Drug treatment does not cure either: it buys time and safety until delivery can happen at the right moment and place. This page groups the antihypertensives, magnesium sulfate, tocolytics and antenatal corticosteroids into one approach. ## Key points - Pre-eclampsia has no cure except delivery; antihypertensives lower stroke risk and magnesium sulfate prevents and treats eclamptic seizures. - Pregnancy-compatible antihypertensives include labetalol, nifedipine, methyldopa and hydralazine; ACE inhibitors and ARBs are avoided. - Magnesium sulfate requires monitoring of reflexes, breathing, urine output and magnesium levels, with intravenous calcium at hand as antidote. - Low-dose aspirin from around week 12 is used to lower pre-eclampsia risk in higher-risk pregnancies, with calcium when dietary intake is low. - Tocolytics such as nifedipine or atosiban delay delivery to allow a course of antenatal corticosteroids or transfer to a higher-level facility. - Antenatal corticosteroids (betamethasone or dexamethasone) cross the placenta and speed fetal lung maturation. ## Pre-eclampsia: the approach Pre-eclampsia is new hypertension in the second half of pregnancy with organ involvement such as proteinuria. Severity is assessed by a specialist; mild cases can be followed as outpatients with more frequent visits and growth scans, severe cases are admitted. Delivery is the only definitive treatment, and is often brought forward, sometimes before term, when the risks to mother or baby outweigh those of prematurity. Blood pressure can stay raised for weeks after birth and still needs treatment and checks. ## Antihypertensives in pregnancy Treating severe hypertension protects the mother from stroke. Drugs with long experience in pregnancy are used: oral labetalol, nifedipine and methyldopa for ongoing control, and intravenous labetalol or hydralazine, or oral nifedipine, for acute severe rises. ACE inhibitors, ARBs and direct renin inhibitors harm the fetal kidney and are avoided. Lowering pressure too fast can reduce placental blood flow, so targets are moderate. ## Magnesium sulfate Magnesium sulfate is the drug of choice to prevent and control seizures in pre-eclampsia and eclampsia. Because magnesium is cleared only by the kidney and toxicity depresses reflexes and breathing, the knee-jerk reflex, respiratory rate and urine output are checked regularly, serum magnesium is measured, and intravenous calcium is kept ready as antidote. Kidney impairment calls for lower doses. Continuous use beyond 5 to 7 days can cause fetal hypocalcaemia and bone abnormalities, which is one reason it is not used as a long-term tocolytic. ## Preterm labour: tocolysis Tocolytics relax the uterus. Their value is not in carrying the pregnancy to term but in buying a short delay so that antenatal corticosteroids can act or the woman can be moved to a centre with neonatal intensive care. WHO recommends nifedipine for acute and maintenance tocolysis in women likely to deliver preterm, but only when specific conditions set out in its guideline are met. - Nifedipine: calcium channel blocker; may cause flushing, headache and low blood pressure. - Atosiban: oxytocin receptor antagonist; authorised in the EU for imminent preterm birth. - Older options such as prostaglandin synthesis inhibitors (indometacin) and beta2 agonists (terbutaline) are limited by fetal or maternal side effects. ## Antenatal corticosteroids and other measures Betamethasone or dexamethasone given to the mother before an expected preterm birth cross the placenta and accelerate fetal lung maturation, reducing respiratory complications in the newborn. WHO attaches conditions to this recommendation so that benefit outweighs harm, and it also covers a single repeat course in selected cases. In women with a short cervix or previous preterm birth, progesterone and cervical cerclage are preventive options; bed rest does not prevent preterm birth. ## Memory aid Pre-eclampsia trio: Pressure down, Magnesium on, Plan delivery (the 3 P-M-P steps). ## Test yourself Think of the answer, then tap the question to see it. ## Why is intravenous calcium kept ready during magnesium sulfate therapy? Calcium counteracts magnesium toxicity, which depresses reflexes and breathing; it is the antidote. ## What is the main purpose of tocolysis in preterm labour? To delay delivery briefly so antenatal corticosteroids can act or the mother can be moved to a centre with neonatal intensive care. ## Why are ACE inhibitors avoided for hypertension in pregnancy? They harm the fetal kidney and can cause fetal injury; labetalol, nifedipine or methyldopa are used instead. ## How do antenatal corticosteroids help a baby born preterm? They cross the placenta and speed lung maturation, reducing breathing problems after birth. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/topics/obstetric-pharmacotherapy-pre-eclampsia-and-preterm-labour/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) ## Example drugs - [Magnesium sulfate](https://durgical.com/en/pharmacology/magnesium-sulfate/) - [Labetalol](https://durgical.com/en/pharmacology/labetalol/) - [Nifedipine](https://durgical.com/en/pharmacology/nifedipine/) - [Methyldopa](https://durgical.com/en/pharmacology/methyldopa/) - [Hydralazine](https://durgical.com/en/pharmacology/hydralazine/) - [Betamethasone](https://durgical.com/en/pharmacology/betamethasone/) - [Dexamethasone](https://durgical.com/en/pharmacology/dexamethasone/) - [Indometacin](https://durgical.com/en/pharmacology/indometacin/) - [Terbutaline](https://durgical.com/en/pharmacology/terbutaline/) - [Acetylsalicylic acid](https://durgical.com/en/pharmacology/acetylsalicylic-acid/) - [Calcium gluconate](https://durgical.com/en/pharmacology/calcium-gluconate/) ## Connections ## Related classes 5 - [Calcium channel blockers](https://durgical.com/en/pharmacology/classes/calcium-channel-blockers/) - [Beta blockers](https://durgical.com/en/pharmacology/classes/beta-blockers/) - [Corticosteroids (glucocorticoids)](https://durgical.com/en/pharmacology/classes/corticosteroids/) - [Uterotonics (oxytocin and analogues)](https://durgical.com/en/pharmacology/classes/uterotonics/) - [Antiplatelet drugs](https://durgical.com/en/pharmacology/classes/antiplatelet-drugs/) [← All of pharmacology](https://durgical.com/en/pharmacology/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Pre-eclampsia - Treatment](https://www.nhs.uk/conditions/pre-eclampsia/treatment/) (NHS, 2026); [DailyMed - MAGNESIUM SULFATE IN WATER- magnesium sulfate heptahydrate injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f5f6b4c9-4a68-4342-b1e4-f4b61b7fb9cb) (DailyMed (U.S. National Library of Medicine), 2026); [New recommendations from WHO to help improve the health of preterm infants](https://www.who.int/news/item/30-09-2022-new-recommendations-from-WHO-to-help-improve-the-health-of-preterm-birth) (World Health Organization, 2022); [What treatments are used to prevent preterm labor and birth?](https://www.nichd.nih.gov/health/topics/preterm/conditioninfo/treatments) (Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/topics/obstetric-pharmacotherapy-pre-eclampsia-and-preterm-labour/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/topics/obstetric-pharmacotherapy-pre-eclampsia-and-preterm-labour/