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Epidemiology

Poster Session 4

(1057) Redefining birth weight centiles: Parity is more significant than gender

Wednesday, February 14, 2024
1:00 PM – 2:30 PM  
Location: Prince George's Exhibit Hall CDE, Lower Atrium Level
Objective: To determine the impact of parity on birth weight patterns at term

Study Design: A retrospective cohort study was conducted between 2012-2023 at a single university-affiliated medical center characterized by a highly parous population with over 12,000 deliveries per year.  The study group was comprised of patients who delivered liveborn singletons at term. The cohort was divided into 4 groups: Group 1–nulliparous patients, Group 2-parity of 1-3, Group 3-parity of 4-6 and Group 4-parity of ≥7. We calculated the 10th, 50th and 90th centile of birth weights for each of the study groups delivering at 37, 38, 39, 40, 41 and 42 weeks. Data was analyzed using ANOVA and Tukey-Kramer test for post-hoc analysis.

Results:

129,752 patients were included in the study group. Group 1-23,331 patients, Group 2-56,240 patients, Group 3–31,779 patients, Group 4-14,740 patients.
Increasing parity was significantly associated with increasing neonatal birthweight across the 10th, 50th and 90th centiles (p< 0.0001). The results of the post-hoc analysis revealed statistically significant differences for all pairwise comparisons between the four groups (p< 0.0001) and these differences persisted when stratifying for each week of gestation (Graph). The mean birthweight for Nulliparas (Group 1) was 155g lower than Multiparas (3209g vs. 3364g) (95% CI 149-161 p< 0.0001). Similarly, the mean birthweight of male neonates was 128g greater than female neonates (3397g vs. 3269g) (95% CI 123-133 p< 0.0001).

Conclusion:

There is a positive correlation between increasing parity and neonatal birthweight for each week of gestation at term across the 10th, 50th and 90th centiles This relationship is consistent across all parity groups. Moreover, birthweights for nulliparous women were significantly lower than their multiparous counterparts. The effect of nulliparity on birthweight is greater than that of fetal gender for which growth curves are commonly adjusted. Parity should be taken into consideration in the clinical decision-making process when a diagnosis of either growth restriction or Large for Gestational Age is established at term.