Gestation is the continuous developmental interval from a defined temporal origin to birth, and because "conception" lacks a rigorous definition, the field anchors the timeline at the last menstrual period (LMP), designated week zero, and measures elapsed time in completed weeks rather than months or trimesters. This weeks-from-LMP convention imposes a shared, reproducible coordinate system on which the staged events of prenatal development — fertilization, embryogenesis with organogenesis, and fetal development — and the viability and term thresholds are located. The concept belongs to human developmental biology and obstetrics, serving as the dating framework that lets developmental stages and clinical outcome boundaries be stated as positions on a single standardized axis.
Gestation is the continuous developmental interval from a defined temporal origin to birth, and because "conception" lacks a rigorous definition, the field anchors the timeline at the last menstrual …