WEEK 4Trimester 1•Baby: Poppy seed
Implantation and Blastocyst Differentiation
Estimated Length0.1 cm
Estimated Weight0.01 g
Fetal Morphogenesis & Anatomy Highlights
- •Blastocyst completes implantation into the secretory endometrium.
- •Trophoblast differentiates into cytotrophoblast and syncytiotrophoblast, secreting beta-hCG.
- •Embryonic disc divides into epiblast and hypoblast (bilaminar embryonic disc).
- •Early uteroplacental circulation initiates via maternal lacunae.
Same-Day Assessment / Urgent Care
Week 4 Urgent Red Flags
Immediate clinical evaluation or presentation to Winnipeg Obstetric Triage (HSC / St. Boniface) is indicated if:
- •Severe unilateral lower abdominal or pelvic pain (ectopic pregnancy risk)
- •Heavy bright red vaginal bleeding soaking > 1 pad per hour
- •Dizziness, syncope, or shoulder tip pain
Women's Hospital HSC Triage: 204-787-8600 | St. Boniface: 204-237-2263
Clinician Perspective • Physiological & Screening Protocols
Maternal Physiological Adaptations
Corpus luteum produces high progesterone under hCG stimulation to maintain decidua before the luteal-placental shift.
Expected Clinical Symptoms
Missed menstrual periodMild uterine cramping (implantation)Breast tenderness & fullnessEarly fatigue
Clinical Investigations & Screening Schedule
- ✓Home urine pregnancy test (detects beta-hCG >= 25 mIU/mL).
- ✓Confirmation quantitative serum beta-hCG if history of ectopic pregnancy or recurrent loss.
- ✓Baseline bloodwork: CBC, Blood group & Rh antibody screen, Rubella, Varicella, Hep B, HIV, Syphilis (VDRL), Urine culture.
Upcoming Visit Horizon: First prenatal visit usually booked between 8 and 10 weeks gestation unless early dating ultrasound or high risk.