Obstetrics and Gynecology
Core concepts
Obstetrics rewards a timeline mindset: know what is normal at each gestational age and what deviates. Master dating (last menstrual period, ultrasound crown-rump length in the first trimester), prenatal screening windows, and the major emergencies by trimester: ectopic pregnancy (first trimester, unilateral pain, adnexal mass), miscarriage subtypes, hypertensive disorders of pregnancy (preeclampsia after 20 weeks, severe features, eclampsia), placenta previa (painless bleeding), abruption (painful bleeding, uterine tenderness), and postpartum hemorrhage (uterine atony most common). Gynecology items center on abnormal uterine bleeding by age, contraception, sexually transmitted infections, and cervical cancer screening.
Traps
"Painless versus painful bleeding" is the classic discriminator: previa is painless, abruption is painful. Questions often test whether magnesium sulfate is for seizure prophylaxis (preeclampsia with severe features) rather than blood pressure control. Another trap: an ectopic pregnancy can present with a normal-appearing uterus on exam and a positive pregnancy test; always confirm intrauterine location. For postpartum hemorrhage, the mnemonic of causes (tone, trauma, tissue, thrombin) guides the answer, and uterine massage plus oxytocin comes before invasive steps. Also watch for misinterpretation of fetal heart rate patterns: late decelerations suggest uteroplacental insufficiency, variable decelerations suggest cord compression.
Worked rule of thumb
For a bleeding-in-pregnancy stem, use gestational age and pain as a two-by-two grid. First trimester with pain and a positive test: ectopic until proven otherwise - obtain quantitative beta-hCG and transvaginal ultrasound. Second or third trimester: painless bleeding means previa (avoid digital exam until ultrasound), painful bleeding with a tender uterus means abruption (stabilize mother and fetus). Example: 32 weeks, painless bright red bleeding, soft uterus - order ultrasound, no pelvic exam, monitor mother and fetus.