Neural Tube Closure & Primitive Heartbeats
Educational content only — not medical advice.
Embryonic Age: 4 weeks post-fertilization — The neural tube completes closure; the primitive heart tube begins regular peristaltic contractions at 105-120 bpm, and limb buds emerge.
Biometric Measurements
- Approximate Length: 4 مم (CRL/CHL - INTERGROWTH-21st)
- Estimated Weight: 0.05 جم (Hadlock)
- Fundal Height: 8 cm
- Size Comparison: Lentil seed
Key Fetal Milestones
- Anterior and posterior neuropore closure (Carnegie stage 13)
- Primitive vascular loop circulation established
- Appearance of optic vesicles and pharyngeal arches
Maternal Changes
The uterus enlarges to approximately plum-size; early pregnancy symptoms such as morning sickness manifest due to hCG surge.