(253) Is low maternal BP associated with SGA in those treated for chronic hypertension in pregnancy?

Objective: In pregnant patients with mild chronic hypertension (CHTN), maintaining blood pressure (BP) < 140/90 optimizes perinatal outcome. However, treatment that leads to maternal hypotension could lead to placental hypoperfusion and subsequent poor fetal growth. Our objective was to estimate the association between maternal hypotension ('low BP') and a small for gestational age infant (SGA) infant in patients treated for mild CHTN in pregnancy.

Study Design: This is a secondary analysis of the Chronic Hypertension and Pregnancy (CHAP) Study, which randomized pregnant patients with mild CHTN to treatment to achieve BP < 140/90 versus < 160/105. For each participant we calculated mean BP between 28-34 weeks and excluded those with mean BP >140/90. We defined 'low BP' as either average BP < 110/70 or mean arterial pressure (MAP) < 80 and compared participants with low BP to those with average SBP 110-139 and/or DBP 71-89 or MAP > 80. Our primary outcome was SGA (birthweight < 5^th percentile). Logistic regression was used to estimate association between low BP and SGA.

Results: Of 2408 CHAP participants, 1205 (50%) met analysis criteria [most common exclusions: 301 for mean BP > 140/90; 125 for missing birthweight].. Of 1205, 31 (2.6%) had mean BP < 110/70, and 33 (2.7%) had MAP < 80. SGA occurred in 62 (5.1%). Low BP by either mean BP or mean MAP was not associated with an SGA infant (Table). We found a nonlinear relationship between MAP as a continuous variable and probability of SGA. As shown in the Figure, lower MAP was associated with lower probability of an SGA infant (p = 0.02). As MAP increased from 80 to 97.5 the probability of SGA increased and then plateaued.

Conclusion: Less than 3% of patients treated for mild CHTN in pregnancy achieve average BP < 110/70 or MAP < 80, and those with low BP did not have increase in odds of an SGA infant. Patients can be reassured that pharmacologic treatment of hypertension infrequently results in BP < 110/70 or MAP < 80 and low BP does not appear to increase risk for SGA.