INS and gestational diabetes: The ORs (95% CIs) of insulin-requiring GDM among women who reported ≤ 2, 2–≤ 4, 4–≤ 6, 6–≤ 8, 8–≤ 10, and > 10 pack-years of smoking were 1.50 (1.22–1.84), 1.71 (1.31–2.22), 1.60 (1.13–2.26), 1.97 (1.14–3.40), 2.34 (1.22–4.51), and 2.29 (1.25–4.22), respectively, compared with nonsmokers (P for trend < 0.001).