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ProjTitle.icon P.II.A.3. Terminology

​Terms for defining the foetus at the different stages of the pregnan​cy​



ZygoteThe single diploid cell formed from the fusion of the ovum and spermatozoon.
Pre-embryoThe first stage of prenatal (see below under 'Foetus') development from conception until the end of implantation in the uterus and the start of organogenesis, i.e. until the postconceptional day 15 or gestational day 29.
EmbryoThe second stage of prenatal development including the organ-forming period (i.e. organogenesis) between gestational day 29 (beginning at 4 completed weeks of gestation) and gestational day 84 (i.e. the ending at 12 completed weeks of gestation).
FoetusThis term has two meanings; the narrow definition of foetus reflects the stage of foetal development after organogenesis until the birth, while the broad definition of foetus covers the whole prenatal development from the conception until the birth.

​Terms for defining pregnancy outcomes​ ​

Pregnancy outcome
End result of pregnancy, which includes ectopic pregnancy, miscarriage, foetal death, termination of pregnancy and live birth.
Ectopic pregnancyExtrauterine pregnancy, most often in the fallopian tube.
Foetal death (intrauterine death, in utero death)Death prior to complete expulsion or extraction from the mother of a foetus, irrespective of the duration of pregnancy. Early foetal death (before 22 completed weeks of gestation) is known as miscarriage, whereas late foetal death (after 22 completed weeks of gestation) is known as stillbirth.
MiscarriageSpontaneous abortion and molar pregnancy.

Termination of pregnancy

(induced abortion, elective abortion)

Artificial interruption of pregnancy for any reason.
Live birthComplete expulsion or extraction from the mother of a foetus, irrespective of the duration of the pregnancy, that, after such separation, breathes or shows any evidence of life.
Gestational ageMeasure of the age of a pregnancy calculated from the first day of a woman's last menstrual period or as estimated by a more accurate method such as ultrasound. The method used needs to be clearly stated in any reporting. Gestational age is expressed in completed days or completed weeks (e.g. events occurring 280 to 286 days after the onset of the last menstrual period are considered to have occurred at 40 weeks of gestation).
Birth weightInitial weight of the infant at birth.
Pre-term birth (premature birth)Birth at less than 37 completed weeks (less than 259 days) of gestation.
Term birthBirth at any time from 37 to less than 42 completed weeks (259 to 293 days) of gestation.
Post-term birthBirth after 42 completed weeks of gestation or more (294 days or more).
Low birth weightBody weight of the newborn at birth of less than 2,500 grams (up to and including 2,499 g).
Very low birth weightBody weight of the newborn at birth of less than 1,500 grams (up to and
including 1,499 g).

Intrauterine growth retardation

(IUGR) ('small for gestational age')

Observed weight of a live born infant or size of a foetus lower than expected, usually below the tenth percentile, on the basis of gestational age.
Foetotoxic effectAlteration of foetal growth, functional defects or malformations caused by a medicine or other substance and which may be transient or permanent.
Withdrawal syndromeSyndrome, i.e. a set of symptoms of variable degree of severity, which occur on stopping or reducing, in dose or frequency of intake, the use of a psychoactive substance that has been taken repeatedly, usually for a prolonged period and/or in high doses. The syndrome may be accompanied by signs of physiological disturbance. A withdrawal syndrome is one of the indicators of a dependence syndrome. Withdrawal syndrome can occur in neonates whose mother used psychoactive substances just before delivery.

​Terms for defining congenital anomalies (birth defects) are:​ ​

Congenital anomaly
Morphological, functional and/or biochemical developmental disturbance in the embryo or foetus whether detected at birth or not. The term congenital anomaly is broad and includes congenital abnormalities, foetopathies, genetic diseases with early onset, developmental delay. Both onset and diagnosis of congenital anomalies can be delayed.
Congenital abnormality (structural birth defect, sometimes congenital malformation, foetal defect)A consequence of error of morphogenesis, i.e. structural-morphological defect, grossly or microscopically present at birth whether detected at birth or not.
Congenital malformationA morphological defect of an organ, part of an organ, or larger region of the body resulting from an intrinsically abnormal developmental process.
Isolated congenital abnormalityA single localized error of morphogenesis.
Multiple congenital abnormalitiesA concurrence of two or more different morphogenetical errors, i.e. component congenital abnormalities in the same person.
TeratogenA medicine or other environmental factor that can cause congenital abnormalities.
Major anomalyA life-threatening structural anomaly or one likely to cause significant impairment of health or functional capacity and which needs medical or surgical treatment. The prevalence of major abnormalities recognized at birth among live-born infants is 2%-4% in most series published.
Minor anomalyRelatively frequent structural anomaly not likely to cause any medical or cosmetic problems.
PrevalenceNumber of instances of an occurrence in a given population at a designated time. For convenience these rates are usually multiplied by 1000 or 10,000 to avoid small decimal numbers. The numerator is the number of cases of the subject of interest. The denominator is the population from which the numerator came. The calculations below are intended to include all causes of the adverse event (i.e. without prejudice regarding causality) and they should include exposures to monotherapy as well as to multiple medicines. Accordingly:
Live birth prevalence rate= Number of cases among live born infants /Total number of live born infants *1000
Birth prevalence rate= Number of cases among live and stillborn infants /Total number of (live + still) born infants *1000​
Total prevalence rate= Number of cases among live births, stillborn and terminated pregnancies /Number of live births, stillbirths and terminated pregnancies *1000

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