We evaluated the impact of assisted reproductive technology (ART) on the association between first-trimester pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (β-hCG) and adverse pregnancy outcomes. PAPP-A and β-hCG levels were obtained between 11 and 13 (6)/ (7) weeks' gestation and converted to multiples of the median (MoM). MoM < 5th percentile was defined as low PAPP-A or β-hCG and those > 90th percentile as high. Adverse outcomes included small-for-gestational-age (SGA) infants, preeclampsia, pregnancy loss, and preterm delivery (PTD). Univariate and multivariate analyses were used to estimate the association. Of 4000 women meeting the inclusion criteria, 265 (7.6%) pregnancies were conceived by ART. ART pregnancies with low PAPP-A had a higher risk of having an SGA infant (odds ratio [OR] = 4.1, 95% confidence interval [CI] 1.2, 14.0) or PTD < 32 weeks (OR = 5.3, 95% CI 1.5, 18.6) compared with non-ART pregnancies with low PAPP-A (OR = 2.8, 95% CI 1.7, 4.7; OR = 3.9, 95% CI 2.1, 7.0, respectively). High PAPP-A was associated with pregnancy loss (OR = 6.1, 95% CI 1.1, 33.7) in ART pregnancies. Low β-hCG was associated with increased risk for PTD only in ART pregnancies (OR = 8.3, 95% CI 1.9, 35.9) for PTD < 37 weeks (OR 6.1, 95% CI 1.6, 23.0) for PTD < 35 weeks and (OR = 10.8, 95% CI 2.7, 43.7) for PTD < 32 weeks. High β-hCG was associated with increased risk for SGA (OR = 1.6, 95% CI 1.0, 2.5) and PTD < 37 weeks (OR = 1.4, 95% CI 1.0, 1.9) in non-ART pregnancies. The association between PAPP-A and β-hCG with adverse pregnancy outcomes is influenced by the mode of conception.