Introduction: Mirtazapine is a noradrenergic and serotonergic antidepressant
mainly acting through blockade of presynaptic alpha-2
receptors. Published data on pregnancy outcome after exposure to
mirtazapine are scarce. This study addresses the risk associated with
exposure to mirtazapine during pregnancy.
Patients (or Materials) and Methods: Multicenter (n = 11), observational
prospective cohort study comparing pregnancy outcomes after
exposure to mirtazapine with 2 matched control groups: exposure
to any selective serotonin reuptake inhibitor (SSRI) as a diseasematched
control group, and general controls with no exposure to
medication known to be teratogenic or to any antidepressant. Data
were collected by members of the European Network of Teratology
Information Services (ENTIS) during individual risk counseling
between 1995 and 2011. Standardized procedures for data collection
were used in each center.
Results: A total of 357 pregnant women exposed to mirtazapine
at any time during pregnancy were included in the study and compared
with 357 pregnancies from each control group. The rate of
major birth defects between the mirtazapine and the SSRI group
did not differ significantly (4.5% vs 4.2%; unadjusted odds ratio,
1.1; 95% confidence interval, 0.5-2.3, P = 0.9). A trend toward a
higher rate of birth defects in the mirtazapine group compared with
general controls did not reach statistical significance (4.2% vs 1.9%;
OR, 2.4; 95% CI, 0.9-6.3; P = 0.08). The crude rate of spontaneous
abortions did not differ significantly between the mirtazapine,
the SSRI, and the general control groups (9.5% vs 10.4% vs 8.4%;
P = 0.67), neither did the rate of deliveries resulting in live births
(79.6% vs 84.3% in both control groups; P = 0.15). However, a
higher rate of elective pregnancy-termination was observed in the
mirtazapine group compared with SSRI and general controls (7.8%
vs 3.4% vs 5.6%; P = 0.03). Premature birth (< 37 weeks) (10.6%
vs 10.1% vs 7.5%; P = 0.38), gestational age at birth (median, 39
weeks; interquartile range (IQR), 38-40 in all groups; P = 0.29),
and birth weight (median, 3320 g; IQR, 2979-3636 vs 3230 g; IQR,
2910-3629 vs 3338 g; IQR, 2967-3650; P = 0.34) did not differ
significantly between the groups.
Conclusion: This study did not observe a statistically significant
difference in the rate of major birth defects between mirtazapine,
SSRI-exposed, and nonexposed pregnancies. A slightly higher rate
of birth defects was, however, observed in the mirtazapine and SSRI
groups compared with the low rate of birth defects in our general
controls. Overall, the pregnancy outcome after mirtazapine exposure
in this study is very similar to that of the SSRI-exposed control group.