Preparatory Mindset
Diagnosis of pregnancy is the first clinical skill in obstetrics — before any management, you must know *whether she is pregnant*, *how far along*, and *whether it is viable and correctly sited* (intrauterine vs ectopic). The exam mindset: a reproductive-age woman with amenorrhoea + nausea + breast tenderness → think pregnancy → urine β-hCG is the first-line test → if positive, transvaginal ultrasound confirms viability, number, and site. The key numbers to memorise: hCG appears ~10 days post-conception, doubles every ~48 hours in early viable pregnancy; transvaginal scan sees the gestational sac at ~5 weeks and fetal heartbeat at ~6 weeks. Always date the pregnancy by Naegele's rule (LMP + 7 days − 3 months) and correct with ultrasound when dates are unsure. The danger case: positive pregnancy test + pain/bleeding + empty uterus on scan = ectopic until proven otherwise.
Core Concepts
1. Signs and symptoms of pregnancy
| Symptom | Timing / mechanism |
|---|---|
| Amenorrhoea | Cardinal symptom — missed period |
| Nausea/vomiting ("morning sickness") | 6-12 weeks; hCG-driven; resolves by 2nd trimester |
| Breast changes | Tenderness, enlargement, Montgomery tubercles; estrogen/progesterone |
| Frequency of micturition | Early (bladder pressure by enlarging uterus) + late (presenting part) |
| Fatigue, appetite change | Common |
Clinical signs (probable):
- Chadwick sign — cyanotic/violet discoloration of cervix, vagina (from 6-8 weeks; vascular congestion)
- Hegar sign — softening of the uterine isthmus
- Goodell sign — softening of the cervix
- Uterine enlargement — palpable abdominally at ~12 weeks, fundus at umbilicus ~20 weeks
- Positive pregnancy test (urine β-hCG)
Positive signs (definitive, late): fetal heart auscultation (Doppler ~10-12 weeks, fetoscope ~18-20 weeks), fetal movements felt by examiner, ultrasound visualisation of fetus/heartbeat.
2. Laboratory diagnosis — β-hCG
| Test | Details |
|---|---|
| Urine β-hCG | First-line home/office screen; positive ~12-14 days post-conception (missed period) |
| Serum β-hCG | Quantitative; doubles every ~48 h in early viable intrauterine pregnancy; plateau/fall → abnormal (ectopic, threatened/missed abortion) |
| Discriminatory zone | ~1,500-2,000 IU/L (TVS) / ~6,500 (TAS): above this, an intrauterine gestational sac should be visible — if not, suspect ectopic or abnormal pregnancy |
3. Ultrasound in early pregnancy (dating)
| Gestational age | TVS finding |
|---|---|
| 4-5 weeks | Gestational sac (visible ~5 weeks) |
| 5-6 weeks | Yolk sac |
| 6 weeks | Fetal pole + cardiac activity (heartbeat ~6 weeks) |
| 6-7 weeks | Crown-rump length (CRL) measurable — most accurate dating |
| 8-10 weeks | Embryo moves; dating by CRL |
| 11-13+6 weeks | NT scan (nuchal translucency) — first-trimester combined screening (NT + β-hCG + PAPP-A) |
| 18-22 weeks | Anomaly scan (fetal anatomy survey) |
Dating: Naegele's rule = LMP + 7 days − 3 months. Ultrasound CRL dating is most accurate 8-14 weeks (correct if discrepancy > 7 days).
4. Differential diagnosis of a positive pregnancy test
- Normal intrauterine pregnancy
- Ectopic pregnancy (pain ± bleeding, hCG slow-rise, empty uterus + adnexal mass)
- Early pregnancy loss (threatened, missed, incomplete abortion — hCG falling)
- Molar pregnancy (GTD) — very high hCG, snowstorm appearance, no fetus
- Very rare: hCG-secreting tumour (germ cell, choriocarcinoma)
5. Approach to the "bleeding + positive test" patient
- Exclude ectopic pregnancy first — any pain (especially unilateral) or shoulder-tip pain with a positive test → TVS + serial hCG.
- TVS: intrauterine sac + heartbeat → viable pregnancy (manage bleeding as threatened miscarriage).
- TVS: empty uterus + abnormal hCG dynamics → ectopic until proven otherwise (laparoscopy/management per protocol).
High-Yield Points
| Topic | Must-remember |
|---|---|
| First-line test | Urine β-hCG (positive ~missed period) |
| hCG dynamics | Doubles every ~48 h in early viable IUP |
| Discriminatory zone | TVS ~1,500-2,000 IU/L — above which sac must be visible |
| Ectopic suspicion | Positive test + pain/bleeding + empty uterus → ectopic until proven otherwise |
| Gestational sac | TVS at ~5 weeks; fetal heartbeat ~6 weeks |
| Naegele's rule | LMP + 7 days − 3 months |
| NT scan | 11-13+6 weeks (combined first-trimester screen) |
| Chadwick sign | Cyanotic cervix/vagina (6-8 weeks) |
| Fundal height | Umbilicus at ~20 weeks |
Topic Summary
Pregnancy diagnosis uses amenorrhoea + symptoms + urine β-hCG as the first step; quantitative serum β-hCG (doubling every 48 h) and transvaginal ultrasound (sac ~5 wk, heartbeat ~6 wk) confirm viability, number, and site. Dating by Naegele's rule corrected with CRL at 8-14 weeks. The critical clinical rule: positive test + pain/bleeding + empty uterus = ectopic until proven otherwise. Early pregnancy is screened with NT at 11-13+6 weeks and anomaly scan at 18-22 weeks.
LMCHK OSCE Practice — Positive Pregnancy Test with Abdominal Pain
Station setup: A 26-year-old woman, 6 weeks by LMP, presents with 2 days of right iliac fossa pain and light vaginal spotting. Urine β-hCG positive. HR 100, BP 105/65. Mild right adnexal tenderness. She asks: "Is my baby OK?"
Candidate tasks (8 min):
- Take a focused history (pain character, shoulder-tip pain, syncope, PV bleeding, past ectopic/PID/surgery).
- Recognise the key danger — ectopic pregnancy must be excluded FIRST.
- State the next-step investigations: quantitative serum β-hCG (baseline, repeat in 48 h) + transvaginal ultrasound to identify gestational sac site; if empty uterus + high/plateau hCG → ectopic.
- Explain management options for confirmed ectopic (expectant, medical methotrexate if criteria met, surgical salpingectomy/salpingotomy).
- Reassure the patient about the plan and the need to return urgently for worsening pain/syncope.
Key marking cues:
- Ectopic first — never reassure "baby is fine" before siting the pregnancy.
- Orders TVS + serial hCG, aware of the discriminatory zone.
- Knows methotrexate criteria (haemodynamically stable, unruptured, sac <35 mm, no fetal heartbeat, hCG <5,000).
- Explains rupture red flags (sudden severe pain, shoulder-tip pain, dizziness/syncope, collapse).