Maternal characteristics OR 95% CI Adjusted for Maternal age     Year of birth, parity, smoking 20-24 0.03 0.02-0.03   25-29 0.23 0.22-0.25   30-34 2.18 2.09-2.28   35-39 6.49 6.24-6.75   40-44 3.34 3.03-3.69   ≥45 0.47 -   Parity     Year of birth, age, smoking 1 5.09 4.88-5.31   ≥2 1.00 Reference   Smoking     Year of birth, age, parity No 1.00 Reference   <10 cigarettes/day 0.94 0.87-1.01   ≥10 cigarettes/day 0.72 0.62-0.83   Education     Year of birth <Compulsory school 0.63 0.51-0.78   Compulsory school 0.78 0.71-0.85   Gymnasiuma 1.00 Reference   <2 years post gymnasium 1.17 1.05-1.29   ≥2 years post gymnasium 1.40 1.33-1.47   Graduate studies 1.46 1.10-1.93   Body mass index     Year of birth, age, parity, smoking <19.8 0.74 0.67-0.82   19.8-25.9 1.00 Reference   ≥26 1.13 1.07-1.20   Previous miscarriage     Year of birth, age, parity, smoking None 1.00 Reference   1 1.12 1.06-1.18   2 1.16 1.03-1.29   ≥3 1.23 1.03-1.44   Work outside home     Year of birth, age, parity, smoking None 0.67 0.62-0.71   Full-time 1.00 Reference   Part-time 0.82 0.77-0.87   Non-Swedish nationality     Year of birth, age, parity, smoking In none of the parents 1.00 Reference   In any parent 0.61 0.55-0.84   aSwedish gymnasium is approximately equivalent to upper secondary school in UK and senior high school in the USA.

Table 2: Some maternal characteristics of women who give birth after IVF [15]. Odds ratios (OR) with 95% confidence intervals (95% CI) estimated with Mantel- Haenszel technique. For maternal age, each age class was compared with all other age classes.