CNM common mistakes
CNM · Understand the traps and how to avoid them.
Keeps the LMP-derived estimated due date after a first-trimester ultrasound differs by more than the redating threshold, instead of assigning the ultrasound-based date.
Candidates remember "ultrasound is more accurate" but not the gestational-age-specific discrepancy cutoffs, so they either never redate or redate on too small a difference; item writers test the exact threshold.
What to do instead
Memorize the ACOG redating table and apply it mechanically: ≤8 6/7 wk, redate if >5 days different; 9 0/7–15 6/7 wk, >7 days; 16 0/7–21 6/7 wk, >10 days; 22 0/7–27 6/7 wk, >14 days; ≥28 0/7 wk, >21 days.
Labels a new blood pressure of 142/94 at 32 weeks as chronic hypertension or white-coat effect and moves on without repeating the reading and initiating a preeclampsia evaluation.
Candidates carry a nonpregnant framework in which one elevated reading is incidental, and they under-weight that hypertension after 20 weeks is preeclampsia until proven otherwise.
What to do instead
Any elevated reading ≥20 weeks gets a repeat in 15 minutes; if confirmed ≥140/90, proceed to urine protein-to-creatinine ratio, platelet count, creatinine, AST/ALT, and fetal assessment, and treat新的 severe-range readings as an emergency requiring magnesium sulfate and delivery planning.
Classifies a fetal heart rate tracing as Category III because late decelerations are present, even though variability is moderate and there is no bradycardia or sinusoidal pattern.
Candidates conflate "reassuring vs nonreassuring" language with the three-tier NICHD system and assume any repetitive deceleration equals the worst category.
What to do instead
Recite the Category III list exactly-absent variability with recurrent late decelerations, absent variability with recurrent variable decelerations, bradycardia, or sinusoidal pattern-and practice sorting tracings into I, II, and III by that list rather than by gestalt.
Diagnoses active-phase arrest at 4 cm dilation after 2 hours of unchanged cervical examination with ruptured membranes and adequate contractions, and recommends cesarean delivery.
Candidates use the older Friedman 4-cm active-phase threshold and the old 2-hour arrest rule rather than the current 6-cm start of active phase and longer arrest durations.
What to do instead
Use the contemporary definition: active phase begins at 6 cm; arrest requires ruptured membranes plus ≥6 cm dilation with no cervical change for ≥4 hours of adequate contractions or ≥6 hours with inadequate contractions (or ≥6 hours of oxytocin augmentation).
Estimates blood loss visually after delivery and documents "moderate lochia" instead of using quantitative measurement, then delays uterotonic escalation because the estimate looks below 500 mL.
Visual estimation systematically underestimates loss by 30–50%, and candidates have learned the 500/1000 mL thresholds without learning that the thresholds only mean something when loss is measured.
What to do instead
Use calibrated under-buttock drapes and cumulative quantitative blood loss; treat ≥500 mL vaginal or ≥1000 mL cesarean as hemorrhage and move stepwise through uterine massage, oxytocin, then additional uterotonics, with tranexamic acid and blood products as indicated.
Attributes a postpartum headache at day 5 to epidural placement, sleep deprivation, or breastfeeding, and does not check a blood pressure.
Candidates associate preeclampsia with the intrapartum period and forget that new-onset hypertension can present up to 6 weeks postpartum, often with headache as the only warning sign.
What to do instead
In any postpartum patient with headache, visual changes, or epigastric pain, check blood pressure immediately; confirmed ≥140/90 plus symptoms or ≥160/110 requires magnesium sulfate, antihypertensives, and admission regardless of how recent delivery was.
Interprets a newborn total bilirubin of 14 mg/dL at 60 hours of life as reassuring without plotting it against the hour-specific nomogram and the infant's risk factors.
Candidates compare the value to adult or remembered absolute cutoffs and skip the age-in-hours axis, which is the entire point of the bilirubin nomogram.
What to do instead
Always plot total bilirubin against age in hours on the Bhutani nomogram, identify the risk zone, and combine it with gestational age, breastfeeding status, and hemolytic risk to decide on repeat testing, phototherapy, or escalation.
Applies nonpregnant reference ranges-TSH upper limit around 4.0 mIU/L, hemoglobin below 12 g/dL, or a blood pressure of 130/85-when evaluating a pregnant patient, and misses or overdiagnoses disease.
Candidates study pregnancy physiology in the antepartum domain but revert to standard adult lab values once a question is framed as primary care.
What to do instead
Keep a pregnancy-adjusted reference card: TSH trimester-specific upper limits (~2.5 first trimester, ~3.0 second/third depending on assay), physiologic hemodilution with anemia thresholds 11.0/10.5/11.0 g/dL by trimester, and know that gestational thrombocytopenia and lower bicarbonate are expected.
Sees a 58-year-old with any postmenopausal bleeding, orders a transvaginal ultrasound, and stops when endometrial thickness is 3 mm without performing endometrial sampling.
Candidates over-rely on the ultrasound-first algorithm and treat a thin stripe as fully excluding malignancy, forgetting that bleeding-not thickness-is the indication for tissue.
What to do instead
Any postmenopausal bleeding warrants endometrial biopsy (or dilation and curettage if office biopsy is nondiagnostic or insufficient), regardless of a thin endometrial stripe, and bleeding should be classified with PALM-COEIN before deciding on further imaging.
Answers an adolescent confidentiality item by selecting parental notification or "defer to state law" as the default for contraception or STI testing, instead of the minor's own consent.
Candidates let personal or general pediatric assumptions override the specific legal and ethical carve-outs that allow confidential reproductive care for minors.
What to do instead
Memorize the standard carve-outs-many jurisdictions permit minors to consent independently to STI testing/treatment, contraception, and pregnancy-related care-and on exam choose the option that protects confidentiality and the adolescent's autonomy unless the stem explicitly states a mandatory-reporting or safety exception.