(843) Chronic Hypertension: Timing of Delivery and Associated Morbidity

The American College of Obstetricians and Gynecologists (ACOG) recommends delivery for uncomplicated chronic hypertension (cHTN) at 37w0d-39w6d. We assessed delivery timing for cHTN and its association with cesarean birth, severe maternal morbidity (SMM), and severe neonatal morbidity (SNM) in a quality collaborative.

Study Design:

Retrospective cohort study of nulliparous term singleton vertex births across 71 hospitals using clinically abstracted values from the Obstetrics Initiative, a quality collaborative supported by Blue Cross Blue Shield of Michigan and Blue Care Network. We included births complicated by cHTN from 01/2020 to 12/2023. The exposure was week of delivery and outcomes were cesarean rate, SMM (Centers for Disease Control definition), and SNM (unexpected complications in term newborns, PC-06). Adjusted odds ratios (aOR) were calculated with generalized linear mixed models with hospital random effects (to control for clustering) and adjustment for age, body mass index, diabetes, substance use, and social vulnerability index. A sensitivity analysis excluding 37-week deliveries was performed to assess delivery timing with assumption of better controlled cHTN at later gestational age.

Results:

Among 3963 (3.6%) births with cHTN, delivery occurred at 37 (31.1%), 38 (33.8%), 39 (25.4%), and 40+ weeks (9.7%). Compared to 37 weeks, cesarean was lower at 38 (aOR 0.79, 95% CI 0.75-0.84) and higher at 40+ (aOR 1.15, 95% CI 1.10-1.21). SMM and SNM were lower at all gestational weeks compared to 37 weeks (Table 1). In the sensitivity analysis SMM was lower (aOR 0.92, 95% CI 0.92-0.93) and SNM was higher (aOR 1.02, 95% CI 1.02-1.02) in births at 39+ weeks versus those at 38 weeks with no difference in cesarean (aOR 0.92, 95% CI 0.82-1.15).  

Conclusion:

Almost 10% of patients with cHTN delivered at 40+ weeks, outside ACOG recommendations for cHTN. Delivery at 37 weeks is associated with morbidity that is likely related to severity of cHTN or superimposed preeclampsia. If delivery is not indicated at 37 weeks, there was no clear benefit of delivery at 38 vs. 39 weeks.