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Table 2 Changes in birth characteristics during China’s two-child policy

From: Association of China’s two-child policy with changes in number of births and birth defects rate, 2008–2017

   Monthly percentage % (mean (standard deviation)) The partial two-child policy period The universal two-child policy period
one-child policy period partial two-child policy period universal two-child policy period Level change β2 (95% CI, P-value) Trend change β3 (95% CI, P-value) Level change β4 (95% CI, P-value) Trend change β5 (95% CI, P-value)
Maternal characteristics mother age ≥ 35 7.39 (0.72) 10.59 (0.72) 13.65 (1.42) 3.42 (3.04 to 3.81, < 0.001) −0.01 (− 0.04 to 0.03, 0.861) 0.97 (0.49 to 1.46, 0.045) 0.24 (0.19 to 0.28, < 0.001)
Nulliparous births 2.51 (0.72) 5.29 (0.51) 6.46 (1.06) 1.64 (1.38 to 1.9, < 0.001) −0.01 (− 0.03 to 0.01, 0.513) −0.25 (− 0.58 to 0.07, 0.438) 0.13 (0.1 to 0.16, < 0.001)
Multiparous births 18.27 (2.13) 19.89 (1.29) 24.03 (1.95) 4.5 (3.75 to 5.24, < 0.001) 0.04 (−0.02 to 0.1, 0.513) 1.61 (0.68 to 2.55, 0.087) 0.31 (0.23 to 0.4, < 0.001)
Birth outcomes Caesarean delivery 54.02 (3.58) 47.86 (1.62) 47.73 (1.45) −3.84 (−5.44 to −2.25, 0.018) −0.03 (− 0.16 to 0.09, 0.786) −0.81 (− 2.81 to 1.2, 0.688) 0.21 (0.03 to 0.4, 0.254)
Nulliparous births 57.19 (5.19) 44.51 (2.12) 43.73 (1.58) −5.77 (−7.64 to −3.9, 0.003) −0.01 (− 0.16 to 0.14, 0.97) −0.97 (− 3.32 to 1.39, 0.683) 0.29 (0.07 to 0.51, 0.186)
Multiparous births 46.88 (4.68) 53.82 (1.8) 53.52 (1.7) −0.55 (−1.71 to 0.61, 0.634) − 0.11 (− 0.2 to − 0.01, 0.253) −1.65 (− 3.11 to − 0.19, 0.26) 0.02 (− 0.11 to 0.16, 0.861)
Sex ratio 114.32 (4.33) 110.44 (3.22) 109.86 (3.81) −0.86 (− 1.31 to − 0.4, 0.062) 0.06 (0.02 to 0.1, 0.11) −0.06 (− 0.64 to 0.51, 0.911) −0.1 (− 0.15 to − 0.05, 0.065)
Nulliparous births 107.61 (4.51) 106.54 (3.75) 106.71 (4.45) −3.45 (− 5.75 to − 1.15, 0.136) 0.27 (0.08 to 0.45, 0.149) 0.29 (− 2.61 to 3.18, 0.922) − 0.52 (− 0.79 to − 0.25, 0.056)
Multiparous births 131.51 (10.48) 117.78 (6.47) 114.61 (5.79) −7.63 (− 12.26 to − 3.01, 0.102) 0.28 (− 0.09 to 0.65, 0.453) −2.26 (− 8.08 to 3.56, 0.699) − 0.3 (− 0.85 to 0.24, 0.582)
Gestation < 37 weeks 5.22 (0.97) 7.77 (0.66) 7.84 (0.73) 0.69 (0.35 to 1.02, 0.041) 0.03 (0 to 0.06, 0.241) −1.15 (− 1.56 to − 0.73, 0.007) 0.01 (− 0.03 to 0.05, 0.845)
Nulliparous births 4.55 (0.85) 6.67 (0.73) 6.85 (0.71) 0.41 (0.08 to 0.74, 0.216) 0.05 (0.02 to 0.08, 0.058) −1.17 (− 1.58 to − 0.75, 0.006) 0 (− 0.04 to 0.04, 0.918)
Multiparous births 6.72 (1.49) 9.71 (0.93) 9.27 (0.97) 0.72 (0.19 to 1.25, 0.174) 0 (− 0.04 to 0.04, 0.962) −1.38 (−2.05 to − 0.72, 0.04) 0.02 (− 0.05 to 0.08, 0.804)
Birth weight < 2500 g 3.67 (0.56) 5.3 (0.54) 5.36 (0.43) 0.53 (0.3 to 0.77, 0.024) 0.04 (0.02 to 0.06, 0.036) −0.83 (−1.12 to − 0.53, 0.006) −0.01 (− 0.04 to 0.02, 0.706)
Nulliparous births 3.22 (0.52) 4.72 (0.68) 4.86 (0.35) 0.41 (0.17 to 0.65, 0.092) 0.05 (0.03 to 0.07, 0.008) −0.67 (− 0.97 to − 0.36, 0.031) −0.04 (− 0.07 to − 0.01, 0.182)
Multiparous births 4.68 (0.96) 6.34 (0.62) 6.09 (0.73) 0.48 (0.07 to 0.9, 0.249) 0.02 (−0.01 to 0.05, 0.572) −1.2 (− 1.72 to − 0.68, 0.023) 0.03 (− 0.02 to 0.07, 0.605)
Birth defect 0.98 (0.19) 1.17 (0.3) 0.82 (0.15) 0.28 (0.18 to 0.39, 0.009) −0.01 (− 0.02 to 0, 0.386) −0.17 (− 0.3 to − 0.03, 0.216) 0 (−0.02 to 0.01, 0.755)
Nulliparous births 0.96 (0.23) 1.12 (0.31) 0.76 (0.18) 0.34 (0.22 to 0.47, 0.007) −0.01 (− 0.02 to 0, 0.312) −0.17 (− 0.33 to − 0.02, 0.271) 0 (−0.01 to 0.02, 0.874)
Multiparous births 1.02 (0.34) 1.24 (0.41) 0.9 (0.22) 0.14 (−0.03 to 0.32, 0.42) 0 (−0.02 to 0.01, 0.893) − 0.18 (− 0.4 to 0.04, 0.426) −0.02 (− 0.04 to 0, 0.407)