Association between small-for-gestational-age at birth and placental abruption in normotensive pregnancies: a retrospective cohort study

BACKGROUND: Hypertensive disorders in pregnancy (HDP) are well-established risk factors for placental abruption (PA). Impaired fetal growth is another candidate, yet its association with abruption in the absence of hypertension remains unverified. We used small-for-gestational-age (SGA) at birth as a pragmatic proxy to investigate whether it is independently associated with PA in normotensive pregnancies. METHODS: A retrospective cohort study was conducted at a tertiary hospital in South China. The study population consisted of women with singleton deliveries between January 1, 2019, and December 31, 2024. Fetal growth was categorized using sex-specific percentiles of birthweight for gestational age. Birthweight < 10th percentile reflects SGA at birth. Severe SGA refers to < the 3rd percentile (P3), and those > P10 was the reference group. RESULTS: A review of 36,544 singleton deliveries identified 654 cases of PA, of which 521 (80%) occurred in normotensive pregnancies (n = 32,269). SGA at birth was significantly associated with a higher odds of PA (2.2% vs. 1.5%, adjusted OR 1.6, 95% CI 1.21–2.16). Other associated factors for abruption included age ≥ 35 years, nulliparity, anemia, and preterm gestation. Subgroup analyses based on these factors showed that the < P3 cohort had significantly greater risk of abruption than the> P10 cohort. The corresponding relative risks (RRs) were 2.3, 1.7, 1.7, and 2.3 in the ≥ 35 years, nulliparity, anemia, and term gestation, respectively. In the comparison of the P3-P10 and the > P10 cohorts, the RRs were both 1.8 in the ≥ 35 years and term gestation. The risk between < P3 and P3–P10 was not significant in any subgroup. CONCLUSIONS: These findings suggest that SGA at birth is independently associated with an elevated risk of PA in normotensive pregnancies, potentially explained by a shared pathophysiology of ischemic placental disease. Increased vigilance is warranted, particularly in SGA pregnancies complicated by advanced maternal age and term gestation.