FAS and viral infectious disease: We detected synergistic effects between maternal non-FAS and first-trimester fever (RERI = 2.69, 95% CI: 1.18–4.21), viral infection (RERI = 2.26, 95% CI: 1.22–3.29), and threatened abortion (RERI = 1.23, 95% CI: 0.43–2.03), as well as living in a newly renovated home during the periconceptional period (RERI = 2.51, 95% CI: 1.19–3.84).