Objective: We examined the possible impact of selective serotonin reuptake inhibitor (SSRI)-trajectories describing the timing of different SSRI dosages on adverse neonatal outcomes. Design: Longitudinal register study Setting: Population based study from Kuopio University Hospital Birth Register. Population or Sample: Altogether 508 mothers who reported using SSRIs in pregnancy, where matched to a five-fold comparison group (n=2540), based on maternal depression, psychiatric diagnoses and age. Methods: We applied unsupervised k-Means longitudinal clustering method to identify four distinct patterns of SSRI use, and propensity score adjusted generalized estimating equations to examine the associations between the exposure groups and the neonatal outcomes, using the unexposed group as reference. Main Outcome Measures: Birth weight, placenta weight, placenta-to-birth-weight ratio (PBWR), umbilical cord length, gestational length, premature birth, low 5-min Apgar score, neonatal intensive care unit (NICU) admission. Results: Compared to the no SSRI group, we found no associations between the use of SSRI up to standard doses and the neonatal outcomes. However, the sustained high dose group (~twice the standard dose) displayed significantly higher mean PBWR (B=1.65, 95% CI=0.83, 2.47). In addition, the odds of low Apgar score for the high dose group were about 3.2-fold (OR=3.2; 95%CI=1.04, 9.79), and the odds of NICU admission 2.6-fold (OR=2.6; 95%CI=1.10,6.03), compared with no SSRI group. Conclusions: Sustained, increasing, or decreasing use of SSRI up to standard doses were not associated with adverse neonatal outcomes. However, caution is advised as sustained higher doses may be linked to reduced placental efficacy and higher risk of adverse neonatal health.