Gravidity and parity
- For other uses of the term in other fields, see Parity (disambiguation).
In biology and human medicine, gravidity and parity are two terms that refer to the number of times a female has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These terms are usually coupled, sometimes with additional terms, to indicate more details of the woman's obstetric history. When using these terms:
- Gravida indicates the number of times the woman has been pregnant, regardless of whether these pregnancies were carried to term. A current pregnancy, if any, is included in this count.
- Parity, or "para" indicates the number of >20-week births (including viable and non-viable; i.e., stillbirths). Pregnancies consisting of multiples, such as twins or triplets, count as one birth for the purpose of this notation.
- Abortus is the number of pregnancies that were lost for any reason, including induced abortions or miscarriages. The abortus term is sometimes dropped when no pregnancies have been lost. Stillbirths are not included.
- The term "gravida" can be used to refer to a pregnant woman.
- A "nulligravida" is a woman who has never been pregnant.
- A "primigravida" is a woman who is pregnant for the first time or has been pregnant one time.
- A "multigravida" or "secundogravida" is a woman who has been pregnant more than one time.
Terms such as "gravida 0", referring to a nulligravida, "gravida 1" for a primigravida, and so on, can also be used. The term "elderly primigravida" has also been used to refer to a woman in her first pregnancy, who is at least 35 years old. 
In biology, the term "gravid" (Latin: gravidus "burdened, heavy") is used to describe the condition of an animal (most commonly fish or reptiles) when carrying eggs internally. For example, Astatotilapia burtoni females can transform between reproductive states, one of which is gravid, and the other non-gravid. In entomology it describes a mated female insect.
A woman who has never carried a pregnancy beyond 20 weeks is nulliparous, and is called a nullipara or para 0. A woman who has given birth once before is primiparous, and is referred to as a primipara or primip; moreover, a woman who has given birth two or more times is multiparous and is called a multip. Finally, grand multipara describes the condition of having given birth three or more times.
Like gravidity, parity may also be counted. A woman who has given birth one or more times can also be referred to as para 1, para 2, para 3 and so on.
Viable gestational age varies from region to region, for example in the UK it is considered to be 24 weeks whilst in the USA 23 weeks is considered viable.
In agriculture, parity is a factor in productivity in domestic animals kept for milk production. Animals that have given birth once are described as "primiparous"; those that have given birth more than once are described as "pluriparous". Those that have given birth twice may also be described as "secondiparous", in which case "pluriparous" is applied to those that have given birth three times or more.
A number of systems are incorporated into a woman's obstetric history to record the number of past pregnancies and pregnancies carried to viable age. These include:
- The Gravida/para/abortus (GPA) system, or sometimes just gravida/para (GP), is one such shorthand. For example, when recording the history of a woman who has had two pregnancies (both of which resulted in live births) would be noted as G2P2. The obstetrical history of a woman who has had four pregnancies, one of which was a miscarriage before 20 weeks, would be noted as G4P3A1 (in the UK this is written as G4P3+1). That of a woman who has had one pregnancy of twins with successful outcomes would be noted as G1P2.
- TPAL is one of the methods to provide a quick overview of a female's obstetric history. In TPAL, the T refers to term births (after 37 weeks gestation), the P refers to premature births, the A refers to abortions, and the L refers to living children. When reported, the "abortions" number refers to the total number of induced abortions and miscarriages except ectopic pregnancies prior to 20 wks. If a fetus is aborted after 20 wks, spontaneously or electively, then it is counted as a premature birth and P will increase but L will not. The TPAL is described by numbers separated by hyphens. Multiple births (twins, triplets and higher multiples) count as one birth, but each living child is counted separately. For example, a pregnant woman who carried one pregnancy to term with a surviving infant; carried one pregnancy to 35 weeks with surviving twins; carried one pregnancy to 9 weeks as an ectopic (tubal) pregnancy; and has 3 living children would have a TPAL annotation of T1, P1, A1, L3. This could also be written as 1-1-1-3.
- The term GTPAL is used when the TPAL is prefixed with gravidity, and "GTPALM" when GTPAL is followed by number of multiple pregnancies. For example, gravidity and parity of a woman who has given birth at term once and has had one miscarriage at 12 weeks would be recorded as G2 T1 P0 A1 L1. This notation is not standardized and can lead to misinterpretations.
Though similar, GPA should not be confused with the TPAL system, which may be used to provide information about the number of miscarriages, preterm births, and live births by dropping the "A" and including four separate numbers after the "P", as in G5P3114. This indicates 5 pregnancies, with 3 term births, 1 preterm birth, 1 induced abortion or miscarriage, and 4 living children.
A nulliparous woman (a nullipara or para 0) has never given birth.
Prolonged nulliparity is a risk factor for breast cancer. For instance, a meta-analysis of 8 population-based studies in the Nordic countries found that nulliparity was associated with a 30% increase in risk of breast cancer compared with parous women, and for every 2 births, the risk was reduced by about 16%. Women having their first birth after the age of 35 years had a 40% increased risk compared to those with a first birth before the age of 20 years.
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