The stalked barnacle Pollicipes pollicipes (Gmelin, 1789), is a strictly littoral and essentially intertidal pedunculate cirripede that lives by forming dense aggregates or clumps on exposed rocky shores and cliffs associated with a high degree of hydrodynamism (Barnes 1996).
Since some women are unsure of the date of their last menstruation (perhaps due to period irregularities), a baby is considered full term if its birth falls between 37 to 42 weeks of its estimated due date. 1  The unborn baby spends around 37 weeks in the uterus (womb), but the average length of pregnancy, or gestation, is calculated as 40 weeks.
A perfect normal full term pregnancy is 40 weeks. However, it is normal to go into labor at 37-38 weeks. A full term pregnancy is 40 weeks, but it is safe to delivery a baby between 38-42 without it having any health issue. 40. 40 weeks from the first day of your last period.  as said by brain child is correct. that is how the due date is calculated.