Table 6

Risk of spontaneous preterm delivery following increasing number of induced abortions

PTD <37 weeksPTD <32 weeksPTD <28 weeks
Crude RR (99% CI)Adj.RR (99% CI)* Crude RR (99% CI)Adj RR (99% CI)Crude RR (99% CI)Adj RR (99% CI)
1 Previous abortion vs 01.50 (1.41 to 1.59) 1.47 (1.38 to 1.57) 1.70 (1.47 to 1.96) 1.59 (1.37 to 1.84) 1.44 (1.09 to 1.87)1.24 (0.94 to 1.64)
2 Previous abortions vs 01.55 (1.32 to 1.81) 1.51 (1.29 to 1.77) 1.48 (1.00 to 2.19)1.34 (0.91 to 2.00)2.27 (1.31 to 3.94) 1.89 (1.08 to 3.31)
3 Previous abortions vs 01.55 (1.04 to 2.31) 1.52 (1.01 to 2.27) 1.81 (0.74 to 4.46)1.64 (0.67 to 4.06)1.36 (0.22 to 8.37) 1.12 (0.18 to 6.96)
4 Previous abortions vs 02.13 (1.26 to 3.64) 2.10 (1.23 to 3.59) 4.62 (1.91 to 11.19) 4.27 (1.76 to 10.37) 6.94 (1.95 to 24.72) 5.96 (1.65 to 21.37)
2 Previous abortions vs 11.03 (0.87 to 1.22)1.02 (0.86 to 1.21)0.87 (0.57 to 1.31)0.84 (0.56 to 1.28)1.58 (0.86 to 2.89)1.52 (0.83 to 2.78)
3 Previous abortions vs 21.00 (0.65 to 1.54)1.01 (0.66 to 1.55)1.23 (0.46 to 3.27)1.22 (0.46 to 3.26)0.60 (0.09 to 3.99)0.60 (0.09 to 3.97)
4 Previous abortions vs 31.38 (0.71 to 2.68)1.38 (0.71 to 2.70)2.55 (0.72 to 9.01)2.60 (0.74 to 9.18)5.10 (0.56 to 46.78)5.29 (0.58 to 48.70)
  • Statistically significant relative risks are shown as bold.

  • PTD, preterm delivery.

  • * Adjusted for maternal age, year of delivery, Carstairs at first pregnancy and interpregnancy interval.