By the end of which week of development is the conceptus termed a fetus, with all major structures present, and approximately how long is human gestation?

Answer: C. End of the 8th week; gestation approximately 38-40 weeks

Embryonic to fetal period and gestation length

The embryonic period spans the first 8 weeks, when organogenesis occurs. By the end of the 8th week, all major structures are present and the conceptus is termed a fetus.

Gestation

• Human gestation (fertilization to birth) is approximately 38-40 weeks.
• By convention, pregnancy is dated from the first day of the last menstrual period (about 2 weeks before fertilization), giving the familiar 40-week figure; term is 37+0 to 41+6 weeks.

Clinical relevance

The embryonic period (organogenesis) is when the conceptus is most vulnerable to teratogens, so this window is critical for avoiding harmful exposures.

Why the others are wrong

The fetal stage begins at 8 weeks (not 4, 6, 12 or 20), and gestation is ~38-40 weeks (not 30, 34, 44 or 50).