From the Guidelines
Parity is defined as the number of times a woman has given birth to a viable fetus, with a woman being considered nulliparous (parity of 0) before her first delivery and becoming primiparous (parity of 1) after delivering her first child, as stated in the 2024 U.S. Selected Practice Recommendations for Contraceptive Use 1.
Definition of Parity
Parity comes after a woman has given birth to a viable fetus, typically after 20 weeks of gestation. A woman's parity count increases with each subsequent delivery. It is essential to note that parity specifically counts births, not pregnancies. Multiple births during the same pregnancy (such as twins) count as one parity. Miscarriages and abortions before 20 weeks do not affect parity, though they are tracked separately as gravidity.
Clinical Importance of Parity
Understanding parity is crucial because higher parity can be associated with certain obstetric risks, including postpartum hemorrhage, abnormal placentation, and uterine rupture, as implied by the classifications for hormonal contraceptive methods and intrauterine devices in the 2024 recommendations 1. Healthcare providers use this information to assess risk factors during pregnancy and delivery and to tailor appropriate care plans for women based on their obstetric history.
Parity Classification
According to the 2024 U.S. Selected Practice Recommendations for Contraceptive Use, parity is classified as follows:
- Nulliparous: a woman who has never given birth
- Parous: a woman who has given birth one or more times This classification is used to determine the suitability of various contraceptive methods, such as Cu-IUD, LNG-IUD, implant, DMPA, POP, and CHC, as shown in TABLE A1 of the recommendations 1.
Key Points
- Parity counts births, not pregnancies
- Multiple births during the same pregnancy count as one parity
- Miscarriages and abortions before 20 weeks do not affect parity
- Higher parity can be associated with certain obstetric risks
- Healthcare providers use parity to assess risk factors and tailor care plans for women based on their obstetric history, as guided by the 2024 recommendations 1.
From the Research
Definition of Parity
- The definition of parity is variable and can be defined as the number of conceptions, pregnancies, births, and babies 2.
- A study found that 5% of doctors and 49% of midwives did not include stillbirths after 24 completed weeks in their definition of parity 2.
- Another study classified parity into three groups: nulliparity, low multiparity (parity 1,2, and 3), and grand multipara (parity 4 to 8) 3.
Parity and Pregnancy Outcomes
- There is a significant association between different parity levels and pregnancy outcomes, including obstetric complications, neonatal morbidity, and perinatal mortality 3.
- Mothers and babies of nulliparity and grand multiparity are at higher risk of complications compared to those of low multiparity 3.
- Grand multiparity is defined as parity 4 or more, or the 5th baby 3.
Aspirin Use and Parity
- Aspirin use during pregnancy has been studied in relation to preventing placenta-mediated complications, but the evidence does not directly relate to the definition of parity 4, 5, 6.
- Aspirin has been found to be effective in preventing preeclampsia in high-risk populations, but the optimal timing and dose are still being studied 6.
- The role of aspirin in preventing fetal growth restriction is still questioned, and further studies are needed to improve the identification of patients who may benefit from prophylactic aspirin 6.