Doctors ask the expectant mother how her week of pregnancy went. Everyone else is interested in what month she is in. Why such confusion?
In fact, the weekly countdown allows medical professionals to monitor the dynamics of fetal development and describe it correctly. Using the same terminology, doctors know exactly what is at stake and can assess the condition of a patient who has previously been seen elsewhere.
Knowing the first day of the last menstrual cycle, you can set the gestational (intrauterine) age of the child. Doctors agreed among themselves that they would calculate the term this way and not otherwise. However, given that conception occurred about 2 weeks later, your baby's actual gestational age is less.