Obstetrics and Gynaecology chapters
Drugs in pregnancy for medical disorders
Which antihypertensive, antidiabetic, antimicrobial and analgesic drugs are used in pregnancy, which are stopped, and the doses and targets for pre-eclampsia, eclampsia, diabetes, thyroid disease and thromboembolism.
- Hypertension in pregnancy: labetalol first, with nifedipine or methyldopa as alternatives, and intravenous hydralazine or labetalol for fulminating disease; stop ACE inhibitors, sartans and atenolol.
- Magnesium sulphate treats and prevents eclamptic fits: 4 g loading dose then 1 g per hour, antidote 10 ml of 10% calcium gluconate.
- Diabetes is managed with insulin, and metformin where appropriate, aiming for a capillary glucose under 5.3 mmol/l before meals and under 7.8 mmol/l one hour after.
On this page
Overview
Most pregnant women with a medical disorder need to stay on treatment: untreated hypertension, diabetes, epilepsy, asthma or thyroid disease harms both mother and baby more than a carefully chosen drug does. The exam tests which agent is preferred in each disease, which must be stopped, the few doses that are standard, and the treatment targets.
Antihypertensive drugs
Chronic (pre-existing) hypertension
- Blood pressure falls physiologically in early pregnancy, so treatment taken before pregnancy can often be stopped in the first half.
- Stop ACE inhibitors, angiotensin receptor blockers and atenolol, because of teratogenicity and poor fetal growth.
- Treat if pressure is consistently over 150/100 mmHg, to reduce severe hypertension and intracerebral bleeding. Treatment does not prevent abruption or superimposed pre-eclampsia and does not change perinatal outcome.
- Preferred agents: labetalol, nifedipine, methyldopa.
- Target: systolic below 160 mmHg and diastolic 80-100 mmHg.
- Watch for superimposed pre-eclampsia and growth restriction; delivery is usually offered around 39 weeks if treatment is needed.
- After delivery the pressure falls but tends to rise again on the third or fourth day; breastfeeding is encouraged with drugs considered acceptable in lactation.
Pre-eclampsia
In the UK, the usual fatal event in pre-eclampsia is bleeding into the brain because the systolic pressure was not controlled. The aim is to lower pressure without reducing uterine blood flow.
| Drug | Nature and use |
|---|---|
| Labetalol | Alpha and beta blocker; good safety record, oral or intravenous, first choice in most national guidelines |
| Nifedipine | Calcium channel blocker, rapid onset; may cause severe headache that mimics worsening disease |
| Methyldopa | Centrally acting; long-established safety but oral only, takes over 24 hours to work, and causes sedation and depression, which limit its use. It also gives a positive Coombs test |
| Hydralazine | Direct vasodilator; intravenous infusion for fulminating disease, titrated against the pressure, as labetalol can also be |
In mild disease (under 150/100 mmHg) there is no immediate need to treat, but monitor for rising pressure, new proteinuria and growth restriction.
Nifedipine headache can be mistaken for worsening pre-eclampsia. Check the pressure and the rest of the picture before escalating.
Prevention
Low-dose aspirin, typically 75 mg daily, started early (from about 12 weeks) and continued to delivery, modestly reduces pre-eclampsia in high-risk women: previous hypertensive pregnancy, chronic hypertension, renal disease, diabetes, antiphospholipid syndrome. Calcium supplementation may help only where dietary intake is low. There is no useful screening test, and no single biomarker is accurate enough for practice.
Eclampsia and magnesium sulphate
- Magnesium sulphate is the drug of choice to treat an eclamptic fit and to prevent fits in severe pre-eclampsia.
- Regimen: 4 g intravenously over 20 minutes, then 1 g per hour, usually continued for 24 hours after delivery.
- Blood levels need not be measured at these doses unless urine output falls below 20 ml/h, since the drug is excreted by the kidney.
- Narrow therapeutic range: overdose causes loss of reflexes, respiratory depression and cardiac arrest. Antidote: 10 ml of 10% calcium gluconate slowly intravenously.
- Alongside: senior help, airway, breathing and circulation; bloods for clotting, full blood count and biochemistry; treat the pressure (oral labetalol or nifedipine, then intravenous hydralazine or labetalol as a bolus and infusion) aiming for diastolic 90-100 mmHg, treating systolic above 160 mmHg, with pressure checked every 5 minutes; restrict fluids to 80 ml/h (1 ml/kg/h), catheterise and chart input and output; involve a haematologist if platelets fall below 50 x 10^9/l.
- Ergometrine is avoided in the third stage in these women, because it raises the blood pressure further.
Loading dose 4 g given over 20 minutes.
Maintenance 1 g/hour for 24 hours after delivery = 24 g.
Total magnesium sulphate given = 4 + 24 = 28 g
Magnesium sulphate also has a second, separate use: fetal neuroprotection in preterm birth, where it lowers the risk of cerebral palsy.
Diabetes: insulin and oral agents
| Point | Detail |
|---|---|
| Preconception | Folic acid 5 mg daily for 3 months before conception, because of the higher neural tube defect risk; optimise control first (the target HbA1c is in the region of 42 mmol/mol) |
| Monitoring | Capillary (fingerprick) glucose seven times daily: before each meal and an hour afterwards |
| Targets | Under 5.3 mmol/l before meals and under 7.8 mmol/l one hour after meals |
| Treatment | Insulin, with metformin where appropriate; good control reduces macrosomia, miscarriage, anomaly and pre-eclampsia |
| Course | Insulin resistance climbs steeply through pregnancy, so doses usually rise in the second half; with antenatal steroids extra insulin is needed, often as an inpatient |
| Labour | A sliding scale of insulin with glucose for type 1 diabetes and insulin-treated type 2; keep maternal glucose 4-7 mmol/l to reduce neonatal hypoglycaemia |
| After delivery | Requirements return at once to pre-pregnancy levels, so doses must be cut immediately; warn about hypoglycaemia, especially while breastfeeding |
| Also | Low-dose aspirin from 12 weeks, retinal and renal screening, anomaly scan at 19-20 weeks with cardiac outflow views, serial growth scans |
Gestational diabetes is managed on the same principles: the same glucose targets, and metformin and/or insulin where diet and lifestyle fail. Treatment reduces the number of large-for-gestational-age babies. Type 2 diabetes must be excluded afterwards, with a fasting glucose or HbA1c 6-13 weeks after childbirth.
Insulin needs rise through pregnancy and fall straight back after delivery. Leaving the pregnancy dose running after birth causes hypoglycaemia.
Thyroid drugs
- Hypothyroidism is treated with thyroxine; the dose usually needs to rise in pregnancy. A raised TSH with a low-normal T4 in early pregnancy means starting or increasing thyroxine, not antithyroid treatment.
- Thyrotoxicosis: carbimazole or propylthiouracil at the lowest acceptable dose, aiming to keep maternal FT3 and FT4 in the high-normal range. High doses cross the placenta and can cause fetal hypothyroidism. Both drugs can cause agranulocytosis, so check the white cell count. A beta blocker can be used while waiting for the antithyroid drug to work.
- Radioactive iodine is contraindicated: it destroys the fetal thyroid gland. Surgery is rare in pregnancy.
Antimicrobials
| Setting | Treatment |
|---|---|
| Urinary tract infection | First line amoxicillin or an oral cephalosporin; treat on strong clinical suspicion before culture returns, with paracetamol for pain |
| Pyelonephritis | Intravenous antibiotics such as a cephalosporin or gentamicin, with renal imaging as indicated; low-dose prophylaxis may follow, with urine checked at each visit |
| Chlamydia and atypical cover | Azithromycin or erythromycin; tetracyclines are avoided |
| Preterm rupture of membranes | Erythromycin improved neonatal outcomes; a 10-day course is used in many units. Antibiotics do not help with intact membranes |
| Syphilis | Penicillin, which is safe in pregnancy |
| Group B streptococcus | Intrapartum antibiotic prophylaxis |
Antibiotics to avoid: tetracyclines (teeth and bone), aminoglycosides where avoidable (streptomycin causes neonatal deafness), quinolones (cartilage damage in animals), chloramphenicol near term (gray baby syndrome), and sulfonamides near term (displaced bilirubin and kernicterus).
"Penicillins, cephalosporins, macrolides: the three safe families."
Analgesics
- Paracetamol is the analgesic of choice through pregnancy, including for symphysis pubis pain and after procedures; paracetamol with codeine is used for musculoskeletal pain.
- NSAIDs are avoided, particularly in the third trimester: they can close the ductus arteriosus and reduce fetal urine output. (Low-dose aspirin for pre-eclampsia prevention is a separate, accepted indication.)
- Opioids are used in labour but delay gastric emptying and can depress the baby's breathing; long-term use causes neonatal withdrawal.
- Local anaesthesia and regional blocks are preferred for procedures, since little drug reaches the baby.
Other common drugs
| Disease | Drug in pregnancy |
|---|---|
| Venous thromboembolism | Low molecular weight heparin is the treatment of choice: it does not cross the placenta, is as safe and effective as unfractionated heparin, and women can inject themselves. Warfarin is reserved for special cases such as mechanical heart valves. After delivery either may be continued, and both are acceptable while breastfeeding. Newer agents are not licensed in pregnancy |
| Asthma | Continue the usual treatment: inhaled salbutamol and inhaled steroid. Avoid ergometrine and prostaglandin F2 alpha, which constrict bronchi, and prefer regional to general anaesthesia |
| Epilepsy | Single drug at the lowest effective dose, preferably lamotrigine or levetiracetam, with folic acid 5 mg |
| Reflux and vomiting | Antacids; H2 receptor antagonists or proton pump inhibitors have a place |
| Cardiac disease | Anticoagulation where there is pulmonary hypertension, a prosthetic valve or atrial fibrillation; diuretics, vasodilators and digoxin for failure. Ergometrine may cause cardiovascular instability, so the third stage is managed with oxytocin alone, given carefully since it is a vasodilator |
| Inflammatory bowel disease | Methotrexate is contraindicated; most other maintenance drugs continue, with folic acid 5 mg |
| Bipolar disorder and psychosis | Neuroleptics such as chlorpromazine or haloperidol; lithium carbonate for mania, and prophylactic lithium from the first postpartum day in a woman with previous puerperal psychosis |
Pakistani practice note
Availability differs: labetalol, nifedipine, methyldopa, magnesium sulphate, insulin, metformin, amoxicillin and erythromycin are all widely used, while atosiban and some newer agents are not. National guidance on eclampsia, antibiotic choice and diabetes screening can change, so check the current national guideline (government or WHO page, checked 11 Nov 2026) before relying on a threshold or a dose.
Expect: labetalol as first choice with nifedipine and methyldopa as alternatives, and intravenous hydralazine or labetalol for fulminating disease; stopping ACE inhibitors, sartans and atenolol; treatment thresholds of 150/100 with targets below 160 systolic and 80-100 diastolic; low-dose aspirin 75 mg from early pregnancy in high-risk women; magnesium sulphate 4 g then 1 g per hour with calcium gluconate as the antidote and urine output as the monitor; glucose targets of 5.3 before and 7.8 after meals; rising insulin needs in pregnancy falling immediately after delivery; sliding scale in labour with glucose 4-7 mmol/l; folic acid 5 mg in diabetes and epilepsy; carbimazole or propylthiouracil with radioiodine contraindicated; amoxicillin or a cephalosporin for urinary infection and erythromycin after preterm rupture of membranes; the antibiotic families to avoid; paracetamol preferred over NSAIDs; and low molecular weight heparin not crossing the placenta.
Quick revision
- Labetalol first; nifedipine and methyldopa next; hydralazine or labetalol intravenously when severe.
- Stop ACE inhibitors, angiotensin receptor blockers and atenolol.
- Treat above 150/100; aim below 160 systolic, 80-100 diastolic.
- Aspirin 75 mg daily from about 12 weeks in high-risk women.
- Magnesium sulphate 4 g over 20 minutes, then 1 g per hour, 24 hours after delivery.
- Magnesium toxicity: lost reflexes then respiratory depression; give calcium gluconate.
- Avoid ergometrine in hypertension, asthma and cardiac disease.
- Diabetes: insulin with metformin where appropriate; under 5.3 before meals, under 7.8 one hour after.
- Insulin needs rise through pregnancy and fall at once after delivery.
- Thyroxine for hypothyroidism; carbimazole or propylthiouracil for thyrotoxicosis; never radioiodine.
- Safe antibiotic families: penicillins, cephalosporins, macrolides. Avoid tetracyclines, quinolones, streptomycin, sulfonamides near term.
- Paracetamol over NSAIDs; low molecular weight heparin over warfarin.
Written by The House Job from standard references (Obstetrics by Ten Teachers; Basic and Clinical Pharmacology by Katzung).
FAQ
Why is labetalol preferred to methyldopa in pre-eclampsia?
It can be given orally or intravenously, works quickly and has a good safety record, while methyldopa is oral only, slow to act and causes sedation and depression.
How is magnesium toxicity recognised at the bedside?
Tendon reflexes disappear first, then breathing is depressed; falling urine output is the warning sign that the drug is accumulating.
Why must the insulin dose be cut immediately after delivery?
Placental hormones causing insulin resistance disappear with the placenta, so requirements drop back to pre-pregnancy levels at once.
Which antihypertensive classes are unsafe and why?
ACE inhibitors and angiotensin receptor blockers damage the fetal kidneys and skull ossification, and atenolol impairs fetal growth.