NG-387

💉 Drugs in pregnancy, labor & the newborn

What is avoided and why, what gets given in labor, the three things every newborn is offered, and how Rh immune globulin is timed.

🚨 The one idea

The first trimester is when the organs are built, so that is when a drug does structural harm. Later exposure tends to affect growth and function rather than formation — which is why the timing of an exposure is always part of the question.

🚫 Avoided in pregnancy — and what each one does

Drug	What it does to the fetus
ACE inhibitors & ARBs “-pril”, “-sartan”	Kidney damage, too little amniotic fluid, skull defects
Warfarin	Crosses the placenta — bleeding and bone defects. Heparin does not cross and is used instead
Isotretinoin	Severe malformations — two forms of contraception are required alongside it
Tetracyclines	Stain the developing teeth and affect bone growth
NSAIDs, especially late	Close the ductus arteriosus early; reduce amniotic fluid
Valproate, carbamazepine	Neural tube defects — folic acid matters even more here
Methotrexate	Pregnancy loss and malformations
Live vaccines	MMR and varicella wait until after birth
Alcohol	No amount is established as safe — fetal alcohol spectrum disorder

🧠 Warfarin crosses. Heparin does not. If a pregnant woman needs anticoagulation, that single fact answers most of the question.

✅ Generally used in pregnancy

Acetaminophen / acetaminophen for pain and fever
Penicillins and cephalosporins for infection
Insulin — it does not cross the placenta
Labetalol, methyldopa, nifedipine for blood pressure
Levothyroxine — the dose usually needs to go up
Folic acid and iron, and the inactivated influenza and Tdap vaccines

🩸 Rh immune globulin — the timing is the question

It is given to an Rh-negative mother to stop her making antibodies against Rh-positive fetal blood. It protects the next pregnancy, not this one.

It is not given if the mother is already sensitized — that is what an indirect Coombs test checks. Once antibodies exist, the injection cannot undo them.

🏥 In labor

Drug	For	Watch
Oxytocin	Induce or augment	Tachysystole — stop it first, then reposition
Magnesium sulfate	Seizure prevention in preeclampsia; neuroprotection before 32 weeks	Reflexes go first; respiratory rate, urine output. Antidote calcium gluconate
Betamethasone	Fetal lung maturity	Maternal glucose rises
Terbutaline	Relax the uterus, short term	Maternal tachycardia
Penicillin / ampicillin	Group B strep prophylaxis	Started early enough to work
Epidural	Pain relief	Hypotension — fluid preload, keep her off her back, and vital signs frequently after it goes in
Opioids	Pain relief	Given too close to birth, the baby may be slow to breathe

👶 The newborn, and afterwards

Given to nearly every newborn

Given	Why
Vitamin K, intramuscular	Newborns cannot make clotting factors yet — prevents bleeding disease
Erythromycin eye ointment	Prevents eye infection acquired during birth
Hepatitis B vaccine	First dose of the series

Give the injection in the vastus lateralis, and give sucrose or a feed for comfort.

For the mother after birth

Rh immune globulin if she is Rh-negative and the baby is Rh-positive
Rubella vaccine if she is not immune — it is live, so it is given after birth, and she avoids pregnancy for a month
Tdap if she has not had it, to protect the baby from whooping cough
Uterotonics if she is bleeding — and remember which two are barred: methylergonovine in hypertension, carboprost in asthma

🍼 And while breastfeeding

Most medicines are compatible with breastfeeding, and stopping unnecessarily does more harm than the drug would.

Where there is a choice, take the dose right after a feed so the level is falling by the next one
A few genuinely need the feeding plan reviewed — chemotherapy, some radioactive agents, amiodarone
Check each drug rather than assuming, in either direction

WHEN IN PREGNANCY→ DOES IT CROSS→ WHAT TO WATCH

NG-387 · Maternal & Newborn unit · ADHD-friendly visual edition