Table 4 Unadjusted and adjusted odds of preterm birth for most invasive treatment in the cycle of conception

Most invasive treatment used during cycle of conception

 None

Reference

Reference

Reference

 Drugs

2.17 (1.08, 4.36)

2.17 (0.99, 4.75)

1.34 (0.52, 3.45)

 IUI

2.75 (1.35, 5.61)

3.17 (1.4, 7.19)

2.16 (0.82, 5.69)

 IVF

3.09 (1.74, 5.48)

4.24 (2.05, 8.77)

1.46 (0.59, 3.58)

Etiology

 No female factor

Reference

Reference

 Any female factor

2.99 (1.5, 5.97)

3.00 (1.32, 6.79)

 No male factor

Reference

Reference

 Any male factor

1.01 (0.58, 1.76)

0.99 (0.51, 1.95)

Multiple gestation

 Singleton

Reference

 Multiple

27.91 (13.25, 58.79)

Maternal age at delivery

 ≤ 30

Reference

Reference

 31+

1.03 (0.5, 2.09)

0.91 (0.38, 2.19)

Paternal age at delivery

 ≤ 30

Reference

Reference

 31+

1.54 (0.8, 2.97)

1.42 (0.64, 3.13)

BMI category (at delivery)

 Underweight/Normal

Reference

Reference

 Overweight/Obese

0.9 (0.52, 1.55)

1.19 (0.61, 2.33)

Income

 Less than $50,000

Reference

Reference

 50,000–$99,999

1.13 (0.6, 2.14)

0.81 (0.38, 1.72)

 Over $100,000

0.71 (0.28, 1.84)

0.85 (0.27, 2.73)

Education level

 Less than college grad

Reference

Reference

 College grad or more

0.7 (0.4, 1.23)

0.84 (0.42, 1.67)

Religion

 Non-LDS

Reference

Reference

 Latter-day Saint

0.87 (0.45, 1.67)

0.73 (0.32, 1.66)

Attempt duration ending in conception

 < 24

Reference

Reference

 ≥ 24

0.59 (0.33, 1.06)

0.66 (0.33, 1.34)