* Embryo - <9 weeks gestation
* Foetus - 9 weeks gestation until delivery
* Neonate - Infant below 28 days old
* Small for gestational age (SGA) - Birth weight < 10th centile
* Large for gestational age (LGA) - Birth weight > 90th centile
* Appropriate for gestational age (AGA) - Birth weight between 10th - 90th centile
* Low birth weight (LBW) - Infants = Birth weight < 2500 g at birth
* Very low birth weight (VLBW) - Infants = Birth weight < 1500 g at birth
* Extremely low birth weight (ELBW) - Infants = Birth weight < 1000 g at birth
* Stillbirth - Foetal death and expulsion from the uterus after 24 weeks gestation
* Abortion - Foetal death and expulsion from the uterus before 24 weeks gestation
* Stillbirth rate - Number of stillbirths per 1000 of all births (live and still)
* Neonatal mortality rate - Number of deaths of live born infants within 28 days of birth per 1000 live births
* Perinatal mortality rate - Number of stillbirths plus deaths within the first seven days per 1000 births (live and still)
* Postneonatal mortality rate - Number of deaths between 28 days and one year per 1000 live births
* Infant mortality rate - Number of deaths between birth and one year per 1000 live births
* Prematurity is defined as gestation of less than 37 weeks.
* Post term > 42 weeks gestation.
* Head circumference less than 3 standard deviations below the mean for gestation is defined as microcephaly.