Prenatal Development
The journey from a single fertilized cell to a newborn, lasting about 38 weeks from conception. It is the fastest and most dramatic period of change in the entire human lifespan.
The three periods
Section titled “The three periods”- Germinal period — weeks 1–2; the fertilized egg divides and implants in the uterus.
- Embryonic period — weeks 3–8; the body plan is laid down and all major organs begin to form.
- Fetal period — week 9 to birth; organs mature and the fetus grows dramatically.
What is happening
Section titled “What is happening”A single cell carrying one set of instructions becomes trillions of specialized cells, organized into every tissue and organ — guided by genes switching on and off in a precise sequence, and by chemical signals passing between neighboring cells.
Why it matters
Section titled “Why it matters”Events here set the starting conditions for an entire life. Nutrition, infection, and exposures during pregnancy can leave lasting marks, a link studied as the developmental origins of later health.