Laboratory examination helps to control the duration of pregnancy in the early stages of development - is carried out to determine the level of human chorionic gonadotropin, and estriol alfafetaproteina, with an increase in the level of which it is concluded that a possible pregnancy up to a week.
In determining the relative duration of pregnancy prenatal doctor or hospital maternity hospital focuses on the information that he tells the expectant mother and the results of external obstetric examination of the patient. Most often, to determine gestational age are guided by the date of the first day of the last menstrual period and by means of graphs or special calendar is easy to navigate with a possible pregnancy. In that case, if a woman before pregnancy is determined by the doctor's advice possible date of ovulation, the basis for the calculation can take a figure.
Probable gestational age may be determined by the height of the uterine fundus above symphysis pubis - the uterus at 12 weeks up to the top edge of the womb, and then progressively increased: in 16 weeks fundus is located halfway between the symphysis pubis and the umbilicus, in the 20 weeks up to the level of the navel. At 28 weeks, is located at the level of costal arches, at 32 weeks reaches its maximum size and is located under the xiphoid process. Then the bottom of the uterus gradually drops - the presenting part of the fetus descends to the entrance of the pelvis and birth date to the bottom of the uterus again located at the level of the costal arch.
Also, when determining the duration of pregnancy can focus on the time of appearance of fetal movements and the time of detection of fetal auscultation using obstetric stethoscope, but these methods - the most unreliable and inaccurate.