Oxytocin (Pitocin)
The #1 most tested OB medication — know the monitoring and when to STOP it.
Uses
- Labor induction or augmentation — stimulates uterine contractions
- Postpartum hemorrhage — promotes uterine contraction to control bleeding (first-line)
Administration
- Given via IV infusion pump — ALWAYS on a pump (never free-flow). Piggyback into the mainline closest to the insertion site so it can be stopped quickly.
- Start low and titrate up gradually per protocol
- The mainline IV (usually LR) continues running if oxytocin is stopped
Monitoring — Continuous
- Continuous electronic fetal monitoring (EFM) is REQUIRED — monitor fetal heart rate (FHR) and contraction pattern at all times
- Normal contraction pattern: contractions every 2–3 minutes, lasting 60–90 seconds, with adequate resting tone between contractions (uterus relaxes fully)
- Monitor maternal vital signs — especially BP (oxytocin has an antidiuretic effect → risk of water intoxication and hyponatremia with prolonged use)
- Monitor I&O — watch for fluid overload
When to STOP Oxytocin — Act Immediately
- Uterine hyperstimulation (tachysystole): contractions >90 seconds, occurring <2 min apart, or no relaxation between contractions
- Non-reassuring FHR patterns: late decelerations, prolonged decelerations, fetal bradycardia (<110 bpm), absent variability
Nursing Actions if Hyperstimulation Occurs
Oxytocin has an antidiuretic effect — prolonged infusion can cause water retention → dilutional hyponatremia → headache, confusion, nausea, seizures. Monitor I&O strictly and watch for signs of fluid overload. This is a commonly tested complication.
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Magnesium Sulfate
The most tested drug in OB nursing — used for preeclampsia and preterm labor.
Uses
- Preeclampsia/Eclampsia: Prevents seizures (anticonvulsant effect) — this is the PRIMARY use. It does NOT lower blood pressure.
- Preterm labor: Neuroprotective for the fetus (reduces risk of cerebral palsy if delivered <32 weeks)
Administration
- Given IV via infusion pump — loading dose followed by continuous maintenance infusion
- Therapeutic level: 4–8 mEq/L
The Big 3 — Assess Before EVERY Dose
Toxicity Signs (In Order of Severity)
- 4–8 mEq/Ltherapeutic
- Flushing, warmth, sweating, decreased DTRs (normal therapeutic effects)
- 8–12 mEq/Ltoxicity onset
- Loss of DTRs (first sign of toxicity), drowsiness, slurred speech, nausea
- 12–15 mEq/Lserious
- Respiratory depression, severe hypotension
- 15–20 mEq/Lcritical
- Respiratory paralysis
- >20 mEq/Lfatal
- Cardiac arrest
Antidote: Calcium Gluconate
- Must be at the bedside at ALL times when a patient is on magnesium sulfate
- Given slow IV push for magnesium toxicity
- Also keep suction, oxygen, and intubation equipment available
If a question asks "which assessment is priority for a patient on magnesium sulfate?" → check DTRs and respiratory rate. If DTRs are absent OR RR <12 → STOP the infusion, give calcium gluconate, and call the provider. The most common exam distractor is "check blood pressure" — but mag sulfate is given to prevent seizures, NOT to lower BP. BP is monitored but is not the priority assessment for mag toxicity.
? A patient on magnesium sulfate has a respiratory rate of 10 and absent patellar reflex. What is the priority action?
Tocolytics (Drugs That Stop Contractions)
Used to delay preterm labor — buy time for corticosteroids to work.
Tocolytics suppress uterine contractions to delay delivery, ideally for at least 48 hours — long enough for betamethasone to promote fetal lung maturity. They do NOT prevent preterm birth long-term; they buy time.
- TerbutalineBeta-2 agonist
- Relaxes uterine smooth muscle. Side effects: maternal tachycardia, tremors, hyperglycemia, hypokalemia, pulmonary edema. Monitor maternal HR and FHR. Also used as RESCUE tocolytic for oxytocin hyperstimulation. Black box warning: not for prolonged tocolysis (>48–72 hrs).
- NifedipineCalcium channel blocker
- Given PO. Causes vasodilation → hypotension, headache, flushing. Monitor BP closely. Do NOT give with magnesium sulfate (both lower BP → severe hypotension + neuromuscular blockade).
- IndomethacinNSAID / COX inhibitor
- Inhibits prostaglandin synthesis → stops contractions. Used <32 weeks only. Can cause premature closure of fetal ductus arteriosus and oligohydramnios. Short-term use only.
Contraindications for Tocolysis
- Cervical dilation >4–6 cm (too late)
- Chorioamnionitis (infection)
- Placental abruption or previa with active bleeding
- Fetal demise or lethal anomaly
- Severe preeclampsia/eclampsia
- Fetal distress
Both drugs lower blood pressure and affect calcium channels. Together they can cause severe hypotension, respiratory depression, and neuromuscular blockade. If a question presents this combination → it's a safety concern that requires intervention.
Betamethasone (Fetal Lung Maturity)
Given to the MOTHER — but it's for the BABY's lungs.
Accelerates fetal lung maturation by stimulating surfactant production. Surfactant prevents the alveoli from collapsing — without it, preterm infants develop respiratory distress syndrome (RDS).
Key Facts
- Given to the mother IM — 2 doses, 24 hours apart
- Most effective between 24–34 weeks gestation
- Takes 24–48 hours for full effect — this is why tocolytics are given to delay delivery and buy time
- Dexamethasone is an alternative corticosteroid for the same purpose
Side Effects (Maternal)
- Hyperglycemia — monitor blood glucose, especially in gestational diabetics. May need insulin adjustment.
- Increased risk of infection (immunosuppression)
- Temporary increase in fetal activity (then may temporarily decrease — expected)
If a question says "a patient at 28 weeks is in preterm labor" → expect the orders to include: tocolytic (to stop contractions and buy 48 hours) + betamethasone IM (for fetal lung maturity) + magnesium sulfate (for fetal neuroprotection if <32 weeks). These three are almost always given together.
RhoGAM (Rh Immune Globulin)
Prevents Rh sensitization — know WHEN to give it and WHO gets it.
When an Rh-negative mother carries an Rh-positive baby, fetal blood can cross into the mother's circulation during pregnancy or delivery. The mother's immune system would then produce antibodies against Rh-positive blood. These antibodies would attack future Rh-positive babies → hemolytic disease of the newborn (erythroblastosis fetalis). RhoGAM prevents the mother from forming these antibodies.
Who Gets It
- Rh-negative mother + Rh-positive or unknown father
- The mother must be Coombs-negative (indirect Coombs test = negative means she has NOT already formed antibodies). If she's already sensitized, RhoGAM won't help.
When to Give RhoGAM
- 28 weeks gestation (routine prenatal dose)
- Within 72 hours after delivery if the baby is Rh-positive
- After ANY event that may cause fetal-maternal blood mixing:
- Miscarriage/spontaneous abortion
- Elective abortion
- Ectopic pregnancy
- Amniocentesis or chorionic villus sampling (CVS)
- Abdominal trauma
- Placental abruption
Administration
- IM injection (deltoid or gluteal)
- Must be given to the MOTHER — not the baby
- Verify correct patient, type, and Rh status with another nurse
- RhoGAM is a blood product — follow facility blood product protocols
If the question states the mother is Rh-negative and the baby is Rh-NEGATIVE → RhoGAM is NOT needed (no incompatibility). RhoGAM is only needed when the baby is Rh-positive or Rh status is unknown. Also: if the indirect Coombs is POSITIVE → the mother is already sensitized → RhoGAM is too late.
Cervical Ripening & Labor Induction Agents
Ripen the cervix first, then induce contractions.
- Dinoprostone (Cervidil, Prepidil)Prostaglandin E2
- Vaginal insert or gel. Ripens (softens and thins) the cervix before oxytocin induction. Patient lies supine 15–30 min after insertion (gel) or 2 hours (insert). Cervidil has a retrieval string — remove if hyperstimulation occurs. Monitor FHR continuously.
- Misoprostol (Cytotec)Prostaglandin E1
- PO or vaginal. Used for cervical ripening and labor induction. Also used for PPH (rectal). Contraindicated in patients with a previous cesarean scar (risk of uterine rupture). Cannot be removed once given (no retrieval method). Wait 4 hours before starting oxytocin after last dose.
- Mechanical dilationFoley bulb catheter
- Non-pharmacological option. Balloon inflated in cervix to promote dilation. Falls out when cervix reaches ~3 cm. No medication side effects. Monitor for infection.
Misoprostol (Cytotec) must NEVER be used for cervical ripening or induction in a patient with a uterine scar (prior cesarean section, prior myomectomy). The powerful uterine contractions can cause uterine rupture — a life-threatening emergency. This is heavily tested.
Postpartum Hemorrhage (PPH) Medications
When the uterus won't contract — these drugs save lives.
The #1 cause of postpartum hemorrhage is uterine atony (boggy uterus). The first intervention is always fundal massage. If the uterus remains boggy, medications are added.
- Oxytocin (Pitocin)IV infusion or IM · first-line
- First-line for PPH. Causes sustained uterine contraction. Given routinely after placental delivery. Monitor for water intoxication with prolonged use.
- Methylergonovine (Methergine)IM / PO
- Potent uterotonic — causes sustained uterine contraction. CONTRAINDICATED in hypertension (causes vasoconstriction → can worsen HTN → stroke risk). Check BP BEFORE giving. Do NOT give IV (can cause stroke/cardiac arrest).
- Carboprost (Hemabate)IM
- Prostaglandin F2-alpha — strong uterotonic. AVOID in asthma (can cause bronchoconstriction). The label contraindicates it in active pulmonary disease and says to use it cautiously with a history of asthma — either way, choose another uterotonic when one is available. Side effects: diarrhea, fever, N/V. Very effective when others fail.
- Misoprostol (Cytotec)Rectal, SL, buccal
- Prostaglandin — causes uterine contraction. Can be given rectally for PPH. Inexpensive, stable at room temperature. Side effects: diarrhea, fever.
- Tranexamic acid (TXA)IV
- Antifibrinolytic — prevents clot breakdown. Must give within 3 hours of onset of PPH. Does NOT cause uterine contraction — it prevents clot dissolution. Monitor for thrombosis.
Methergine = NO in hypertension (vasoconstriction → stroke). Hemabate = NO in asthma (bronchospasm). Misoprostol = NO in prior C-section (uterine rupture — for induction only; rectal route for PPH is acceptable). If a question asks about a hypertensive patient with PPH → Methergine is the WRONG answer.
Prenatal Vitamins & Supplements
What every pregnant patient should be taking — and why.
- Folic acidneural tube defects
- 400–800 mcg/day ideally BEFORE conception and throughout first trimester. 4 mg/day if prior NTD pregnancy. Found in leafy greens, fortified cereals, beans.
- Ironanemia prevention
- 27 mg/day during pregnancy. Take with vitamin C for absorption. Avoid dairy/antacids. Side effects: constipation, dark stools. Straw for liquid form. Blood volume ↑ 50% in pregnancy.
- Calciumfetal bone development
- 1,000 mg/day. If inadequate intake → fetal calcium comes from maternal bones. Dairy, fortified foods.
- DHA (omega-3)fetal brain & eye
- 200–300 mg/day. Found in fish (avoid high-mercury fish: shark, swordfish, king mackerel, tilefish).
- Prenatal vitamincomprehensive daily
- Contains folic acid, iron, calcium, vitamin D, DHA, and other essentials. Take daily throughout pregnancy. Best tolerated with food if nausea is an issue.
Drugs Contraindicated in Pregnancy
Know the high-risk drugs — "when in doubt, look it up before giving."
- ACE inhibitors (-pril)
- Fetal renal damage, oligohydramnios, skull defects. Use methyldopa, labetalol, or nifedipine instead.
- ARBs (-sartan)
- Same risks as ACE inhibitors. Same alternatives.
- Warfarin (Coumadin)
- Crosses placenta → fetal hemorrhage, nasal hypoplasia, bone abnormalities. Use heparin or enoxaparin (do NOT cross placenta).
- Statins (-statin)
- Teratogenic — cholesterol is needed for fetal development. Discontinue during pregnancy.
- Methotrexate
- Abortifacient and teratogenic. Must stop well before conception.
- Tetracyclines (-cycline)
- Permanent tooth discoloration, bone growth inhibition. Use amoxicillin or azithromycin.
- Isotretinoin (Accutane)
- Severe birth defects — requires iPLEDGE program with 2 forms of contraception. Discontinue before conception.
- NSAIDs (3rd trimester)
- Premature closure of ductus arteriosus, oligohydramnios. Use acetaminophen for pain.
- Finasteride (Proscar)
- Feminization of male fetus — pregnant women must NOT handle crushed tablets.
- Valproic acid
- Neural tube defects, cognitive impairment. Switch to safer anticonvulsant before pregnancy.
- Lithium
- Cardiac defect (Ebstein's anomaly) — 1st trimester. Risk vs benefit discussion; may continue with monitoring.
ACE inhibitors and ARBs are contraindicated. Safe alternatives for hypertension in pregnancy are: methyldopa (oldest, most studied), labetalol (beta-blocker, safe in pregnancy), nifedipine (CCB), and hydralazine (vasodilator, used for acute hypertensive episodes). This is commonly tested.
Frequently Asked Questions
Common student questions on this topic.
What is oxytocin (Pitocin) used for and what should I monitor?
What is magnesium sulfate used for in pregnancy?
What is terbutaline used for and what are the risks?
What is methylergonovine (Methergine) and when is it used?
Why is RhoGAM given and when?
What pain medications are safe during breastfeeding?
Quick-Reference Cheatsheet
Every key point from this guide on a single printable page.
OB/Maternity Medications Cheatsheet
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