Clinical Definition of Parity
Parity is defined as the number of pregnancies reaching viability (typically ≥24 weeks gestation) that a woman has delivered, regardless of the number of fetuses or whether the infant was born alive or stillborn, with multiple gestations (twins, triplets) counted as a single parous event.
Core Definition Components
The clinical definition of parity includes several key elements, though significant variation exists in practice:
Gestational threshold: Parity counts deliveries at or beyond viability, typically defined as ≥24 weeks of gestation 1, 2
Stillbirths inclusion: Stillbirths after 24 completed weeks should be included in parity count, though surveys reveal that 49% of midwives and 5% of doctors incorrectly exclude them 1
Multiple gestations: A twin or higher-order multiple pregnancy should be counted as a single parous event (Para 1), not as separate deliveries, though only 21% of clinicians correctly apply this definition 3. Despite this, 84% of surveyed clinicians incorrectly described a previous twin delivery as Para 2 1
Critical Clinical Context
The lack of standardization in parity definition creates significant communication problems in clinical practice. The term "parity" has been variably defined across sources as the number of conceptions, pregnancies, births, or babies, with only 8 of 23 reviewed references correctly defining multiple births as a single parous event 1.
Common Pitfalls to Avoid:
The 20-24 week gray zone: Births and abortions can be easily confused in this gestational age range, leading to inconsistent documentation 2
Multiple pregnancy miscounting: The most common error is counting twins as Para 2 rather than Para 1 1, 3
Stillbirth exclusion: Nearly half of midwives surveyed incorrectly excluded stillbirths from parity counts 1
Clinical Risk Stratification by Parity
Understanding parity definitions matters for risk assessment:
Nulliparity (Para 0): Associated with higher obstetric complications, neonatal morbidity, and perinatal mortality 4
Low multiparity (Para 1-3): Represents the lowest risk group for maternal and neonatal complications 4
Grand multiparity (Para ≥4 or ≥5): Traditionally considered high-risk, though recent evidence in twin pregnancies suggests high parity may be protective rather than harmful 4, 5
Given the documented confusion among healthcare providers, explicit documentation is essential: Rather than relying solely on "G_P_" notation, clinical notes should clearly specify the number of prior deliveries ≥24 weeks, number of living children, and outcomes of previous pregnancies to avoid miscommunication 1, 2.