OMSB Obstetrics and Gynecology (OEOG) cheat sheet

Gestational age by Naegele rule: first day of last menstrual period + 280 days; ultrasound dating overrides LMP when the discrepancy exceeds 7 days in the first trimester.

Estimated blood loss thresholds: postpartum hemorrhage is ≥1000 mL or any loss with hemodynamic instability; early PPH is within 24 hours, late PPH from 24 hours to 6 weeks.

Uterine atony causes about 70-80% of PPH; the four T's are Tone, Trauma, Tissue, Thrombin, evaluated in that order.

Magnesium sulfate for eclampsia prophylaxis: 4-6 g IV loading over 15-20 minutes, then 1-2 g/hour; monitor deep tendon reflexes, respiratory rate, and urine output.

Group B streptococcus prophylaxis: intrapartum penicillin G is first line; clindamycin only after confirmed susceptibility, since resistance rates approach 15-20%.

Shoulder dystocia sequence: call for help, McRoberts maneuver, suprapubic pressure, then internal rotational maneuvers; the HELPERR mnemonic structures the response.

Preterm labor before 34 weeks: antenatal corticosteroids (betamethasone 12 mg IM twice, 24 hours apart) plus magnesium sulfate for neuroprotection if delivery is anticipated before 32 weeks.

Preeclampsia with severe features includes systolic ≥160 or diastolic ≥110 mmHg, platelets <100,000, transaminases twice normal, creatinine >1.1 mg/dL, pulmonary edema, or visual/cerebral symptoms.

Active third-stage management (uterotonic, controlled cord traction, uterine massage) reduces PPH and need for transfusion compared with expectant management.

Abnormal uterine bleeding is classified by PALM-COEIN: structural causes are Polyp, Adenomyosis, Leiomyoma, Malignancy; nonstructural are Coagulopathy, Ovulatory dysfunction, Endometrial, Iatrogenic, Not yet classified.

Postmenopausal bleeding carries roughly a 10% risk of endometrial cancer; transvaginal ultrasound endometrial thickness ≤4 mm has a high negative predictive value, but tissue sampling remains the definitive test.

Bacterial vaginosis: Amsel criteria require three of four - homogeneous discharge, pH >4.5, positive whiff test, clue cells; vaginal pH >4.5 with clue cells is the most specific combination.

Vulvovaginal candidiasis: pseudohyphae on KOH microscopy; treatment with fluconazole 150 mg single dose for uncomplicated cases.

Trichomoniasis: motile flagellated organisms on wet mount; treat with metronidazole 500 mg twice daily for 7 days and treat partners.

Emergency contraception: copper IUD is the most effective option; levonorgestrel 1.5 mg is effective up to 72 hours, ulipristal acetate up to 120 hours.

Cervical cancer screening: start at age 21 with cytology every 3 years, or age 25 with primary HPV testing every 5 years; cotesting every 5 years from age 30.

Endometriosis: laparoscopy remains the diagnostic gold standard; GnRH agonists induce hypoestrogenism and are used for symptom control, not cure.

Ectopic pregnancy: discriminatory zone for transvaginal ultrasound is a beta-hCG of about 1500-3500 mIU/mL; a rise of less than 50% in 48 hours suggests a nonviable pregnancy.

Endometrial cancer is the most common gynecologic malignancy; type I is endometrioid, estrogen-driven, and associated with obesity, diabetes, and unopposed estrogen.

Ovarian cancer: CA-125 lacks screening utility in the general population; risk-reducing salpingo-oophorectomy is recommended for BRCA1 carriers by age 35-40 and BRCA2 by age 40-45.

Cervical cancer staging is clinical (FIGO) rather than surgical; stage IB1 is ≤2 cm, and stage IIA involves the upper two-thirds of the vagina without parametrial involvement.

Cervical cancer screening: HPV 16 and 18 genotyping triages abnormal cytology; colposcopy is indicated for ASC-US with positive HPV or any HSIL cytology.

Gestational trophoblastic neoplasia: choriocarcinoma secretes beta-hCG; methotrexate or actinomycin D is used for low-risk disease, and EMA-CO for high-risk disease.

Epithelial ovarian cancer: high-grade serous carcinoma most often arises from fallopian tube epithelium; primary treatment is cytoreductive surgery plus platinum-taxane chemotherapy.

Vulvar cancer: squamous cell carcinoma predominates; sentinel lymph node biopsy is appropriate for tumors ≤4 cm with clinically negative groin nodes.

Uterine leiomyosarcoma: presents with rapid growth or postmenopausal bleeding; diagnosis is histologic, and morcellation of an undiagnosed sarcoma worsens prognosis.

First-trimester aneuploidy screening: combined nuchal translucency plus free beta-hCG and PAPP-A at 11-13+6 weeks; cell-free DNA has the highest detection rate for trisomy 21.

RhD alloimmunization prophylaxis: anti-D immune globulin at 28 weeks and within 72 hours of delivery of an RhD-positive infant; also after amniocentesis, ectopic pregnancy, or miscarriage.

Fetal heart rate interpretation: category I is baseline 110-160 with moderate variability, no late or variable decelerations; category III includes absent variability with recurrent decelerations or sinusoidal pattern.

Intrauterine growth restriction: estimated fetal weight <10th percentile; Doppler of the umbilical artery shows increased resistance before absent or reversed end-diastolic flow.

Amniotic fluid index: oligohydramnios is AFI ≤5 cm, polyhydramnios is AFI ≥24 cm (or deepest vertical pocket >8 cm).

Preterm birth prevention: cervical length <25 mm at 16-24 weeks supports cerclage or vaginal progesterone; history-indicated cerclage at 12-14 weeks for prior preterm birth.

Twin-twin transfusion syndrome: monochorionic twins with oligohydramnios/polyhydramnios sequence; fetoscopic laser ablation is definitive treatment before 26 weeks.

Gestational diabetes screening: 50 g glucose challenge at 24-28 weeks; diagnosis by 75 g OGTT with fasting ≥92, 1-hour ≥180, 2-hour ≥153 mg/dL (any one value).

Infertility is failure to conceive after 12 months of regular unprotected intercourse; evaluate earlier at 6 months if age ≥35, or immediately with oligomenorrhea or known pathology.

Polycystic ovary syndrome uses the Rotterdam criteria: two of three - oligo/anovulation, clinical or biochemical hyperandrogenism, polycystic ovaries on ultrasound (≥12 follicles 2-9 mm or ovarian volume >10 mL).

Ovulation induction: clomiphene citrate is first line for anovulatory infertility; letrozole has higher live birth rates than clomiphene in PCOS.

Semen analysis reference: volume ≥1.5 mL, concentration ≥15 million/mL, total motility ≥40%, normal morphology ≥4% (WHO 2010).

Ovarian reserve: antral follicle count and anti-Mullerian hormone are the best markers; AMH does not predict spontaneous fertility in the general population.

Controlled ovarian hyperstimulation risk: ovarian hyperstimulation syndrome peaks 5-9 days after hCG trigger; symptoms include ascites, hemoconcentration, and oliguria.

Hypothalamic amenorrhea: low FSH, low LH, low estradiol; treatment is caloric restoration and pulsatile GnRH or gonadotropins for fertility.

Primary ovarian insufficiency: before age 40, with FSH >40 mIU/mL on two occasions 4 weeks apart; requires estrogen replacement for bone and cardiovascular protection.

Stress urinary incontinence: leakage with increased intra-abdominal pressure; the cough stress test and urodynamics confirm the diagnosis when surgery is planned.

Pelvic organ prolapse quantification (POP-Q) uses six points (Aa, Ba, C, D, Bp, Ap) relative to the hymen; stage II is 1 cm above to 1 cm below the hymen.

Midurethral sling is the standard surgical treatment for stress urinary incontinence; synthetic mesh carries risks of erosion and dyspareunia.

Overactive bladder: first-line therapy is behavioral (bladder training, pelvic floor muscle training); antimuscarinics or beta-3 agonists are second line.

Urodynamic stress incontinence is diagnosed when involuntary leakage occurs during filling cystometry with increased abdominal pressure in the absence of detrusor contraction.

Anterior colporrhaphy repairs cystocele; posterior colporrhaphy repairs rectocele; sacrocolpopexy is used for apical prolapse.

Urinary tract injury during pelvic surgery: the ureter is most commonly injured at the level of the uterine artery pedicle; intraoperative cystoscopy with IV indigo carmine aids detection.

Vesicovaginal fistula: continuous urinary leakage after pelvic surgery; diagnosis by speculum examination, dye test, or cystoscopy; repair after tissue healing.