A human’s gestational period, or pregnancy, is the time (measured in weeks) from conception till birth. A full term, single pregnancy will generally last between 37-42 weeks.
Gestation is measured from the first day of the woman’s last menstrual period; conception however actually occurs around two weeks later. Unless women have been charting their menstrual cycle using the Fertility Awareness Method, the day of conception can be hard to pinpoint. Healthcare providers therefore use the system of dating from the first day of a woman’s last period as it is generally considered a more memorable and accurate method. However this does mean that a pregnancy is dated for two weeks longer than it actually is.
One of the most important aspects of pregnancy care is determining an estimated due date. From this, healthcare professionals can monitor growth and development of the unborn child. Doctors will arrange an initial ultrasound, often referred to as the dating scan, within the first 8-14 weeks of the gestational period. This scan often gives a more accurate estimated due date, especially if you are unsure of menstrual dates. The sonographer will measure the head circumference and length of the unborn baby’s limbs, to produce a reasonably accurate estimation of the child’s gestational age.
The length of full-term gestation can vary by up to 5 weeks and whilst the average length is considered to be 40 weeks, the actual due date can only ever be given as an estimate – babies tend to arrive in this world when they’re ready!