Maternal antidepressant effects on the fetal nonstress test

Selective serotonin reuptake inhibitors (SSRIs) are commonly prescribed for mood disorders in pregnancy, though studies regarding effects on fetal behavior are conflicting. Previous studies have suggested that fetuses exposed to these medications in the third trimester may have decreased fetal heart rate variability. Since changes in variability may affect the interpretation of antenatal testing, clinicians should be aware of those medications that may impair effective testing.

A retrospective observational cohort study was performed to compare nonstress test (NST) parameters of fetuses exposed to SSRIs with unexposed fetuses at 36 weeks gestation. Subjects were excluded if they had multiple gestations, fetal anomalies including growth restriction, illicit substance use or use of other psychotropic medications. NSTs were compared for fetal baseline heart rate, variability, time to reactivity, number of accelerations over time, and number of fetal movements over time.

Of 219 participants, 12 were taking an SSRI/SNRI at the time of their 36-week NST. There were no significant differences in demographics or indications for NST between groups. NSTs were reactive in 92% of those taking an SSRI/SNRI and in 97% of those not taking an SSRI/SNRI. Time to reactivity [8.6 min vs. 12.5 min], baseline heart rate [142 bpm vs. 139 bpm], and heart rate variability [12.1 bpm vs. 11.7 bpm] were all similar between the two groups.

Though limited by sample size, lack of pharmacologic data and potential confounding by indication, the study suggests SSRI use is not associated with any significant changes in NST. Clinicians should be reassured that NST assessment remains a useful means of determining fetal wellbeing in patients using these medications.