Жүктіліктің мерзімін анықтау шаралары

Measure of the age of a pregnancy
actual age of gestation

In obstetrics, gestational age is a measure of the age of a pregnancy taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method, if available. Such methods include adding 14 days to a known duration since fertilization (as is possible in in vitro fertilization), or by obstetric ultrasonography. The popularity of using this measure of pregnancy is largely due to convenience: menstruation is usually noticed, while there is generally no convenient way to discern when fertilization or implantation occurred. Gestational age is contrasted with fertilization age which takes the date of fertilization as the start date of gestation. There are different approaches to defining the start of a pregnancy. This definition is unusual for saying that women become "pregnant" two weeks before having sex. The definition of pregnancy and the calculation of gestational age are also relevant in the context of the abortion debate and the beginning of human personhood.

The fertilization or conceptional age (also called embryonic age and later fetal age) is the time from the fertilization. It usually occurs within a day of ovulation, which, in turn, occurs on average 14.6 days after the beginning of the preceding menstruation (LMP). There is also considerable variability in this interval, with a 95% prediction interval of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP to ovulation time of 14.6. In a reference group representing all women, the 95% prediction interval of the LMP to ovulation is 8.2 to 20.5 days. and may be mistaken as menstruation, potentially giving an estimated gestational age that is too low.

Child's gestational age at birth (pregnancy length) is associated with various likely causal maternal non genetic factors: stress during pregnancy, age, parity, smoking, infection and inflammation, BMI. Also, preexisting maternal medical conditions with genetic component, e. g., diabetes mellitus type 1, systemic lupus erythematosus, anaemia. Parental ancestral background (race) also plays a role in pregnancy duration. Gestational age at birth is on average shortened by various pregnancy aspects: twin pregnancy, prelabor rupture of (fetal) membranes, pre eclampsia, eclampsia, intrauterine growth restriction. The ratio between fetal growth rate and uterine size (reflecting uterine distension) is suspected to partially determine the pregnancy length.

Family based studies showed that gestational age at birth is partially (25–40%) determined by genetic factors.