Final answer:
A post-term pregnancy is defined as when a pregnancy exceeds 42 completed weeks of gestation. The average full-term pregnancy lasts about 38.5 to 40.5 weeks from conception or the first day of the last menstrual period respectively.
Step-by-step explanation:
To determine what gestational age would define a postpartum pregnancy, it's essential to consider the typical benchmarks for pregnancy durations. A full-term pregnancy typically lasts from conception to birth for about 270 days, which is roughly 38.5 weeks. When counted from the first day of the last menstrual period (LMP), the due date is generally set at 284 days, approximately 40.5 weeks, assuming conception occurred around day 14 of the menstrual cycle.
The pregnancy period is divided into three trimesters, and a fetus is considered full-term between 36 to 40 weeks. By the 38th week, nearly all of the fetus's organ systems are developed enough for it to survive outside of the uterus. Birth is expected to occur around this period; however, when the gestation goes beyond this, it's classified according to specific terms. A pregnancy is considered post-term once it exceeds 42 completed weeks of gestation, which corresponds to option 4. Thus, the correct answer to the question is option 4) 42 completed weeks.