Table 2. Multivariate logistic regression analyses results on PTB.
| Factor | OR | 95% CI | P value |
|---|---|---|---|
| Sex (female vs. male) | 0.910 | 0.907–0.913 | <0.001 |
| Maternal age (year) | |||
| <20 vs. 20–30 | 1.155 | 1.144–1.166 | <0.001 |
| 31–40 vs. 20–30 | 1.108 | 1.104–1.113 | <0.001 |
| >40 vs. 20–30 | 1.389 | 1.377–1.402 | <0.001 |
| Maternal BMI | |||
| Underweight vs. normal | 1.224 | 1.212–1.236 | <0.001 |
| Overweight vs. normal | 0.984 | 0.980–0.988 | <0.001 |
| Obesity vs. normal | 0.998 | 0.993–1.002 | <0.001 |
| Marital status (unmarried vs. married) | 1.142 | 1.137–1.146 | <0.001 |
| Race of mother | |||
| Black vs. White | 1.425 | 1.418–1.432 | <0.001 |
| AIAN vs. White | 1.074 | 1.056–1.093 | <0.001 |
| Asian vs. White | 1.113 | 1.104–1.122 | <0.001 |
| NHOPI vs. White | 1.310 | 1.272–1.348 | <0.001 |
| >1 race vs. White | 1.067 | 1.055–1.079 | <0.001 |
| Mother’s education | |||
| < High school vs. ≥ bachelor’s degree | 1.167 | 1.158–1.176 | <0.001 |
| High school vs. ≥ bachelor’s degree | 1.115 | 1.108–1.122 | <0.001 |
| Associate degree vs. ≥ bachelor’s degree | 1.080 | 1.075–1.086 | <0.001 |
| Father’s education | |||
| <High school vs. ≥ bachelor’s degree | 1.180 | 1.172–1.189 | 0.047 |
| High school vs. ≥ bachelor’s degree | 1.173 | 1.166–1.180 | <0.001 |
| Associate degree vs. ≥ bachelor’s degree | 1.099 | 1.093–1.105 | <0.001 |
| Prenatal care starting time | |||
| 4th to 6th month vs. 1st to 3rd month | 1.249 | 1.243–1.255 | <0.001 |
| 7th to final month vs. 1st to 3rd month | 0.994 | 0.985–1.003 | 0.217 |
| No vs. 1st to 3rd month | 2.284 | 2.256–2.312 | <0.001 |
| Smoking | |||
| Smoking cessation vs. no smoking | 0.943 | 0.932–0.955 | <0.001 |
| Smoking vs. no smoking | 1.208 | 1.199–1.217 | <0.001 |
| History of preterm (yes vs. no) | 2.771 | 2.752–2.790 | <0.001 |
| Hypertensive eclampsia (yes vs. no) | 4.075 | 3.987–4.164 | <0.001 |
| Infertility treatment | |||
| Other treatments vs. no | 2.550 | 2.462–2.642 | <0.001 |
| FEDT vs. no | 2.728 | 2.690–2.766 | <0.001 |
| ART vs. no | 2.977 | 2.940–3.014 | <0.001 |
| Diabetes | |||
| Pre-pregnancy diabetes vs. no | 2.015 | 1.988–2.042 | <0.001 |
| Gestational diabetes vs. no | 1.234 | 1.226–1.241 | <0.001 |
| Hypertension | |||
| Pre-pregnancy hypertension vs. no | 2.243 | 2.222–2.264 | <0.001 |
| Gestational hypertension vs. no | 2.547 | 2.534–2.561 | <0.001 |
| History of cesareans (yes vs. no) | 1.089 | 1.084–1.094 | <0.001 |
| Live birth order | |||
| 2 vs. 1 | 1.029 | 1.024–1.034 | <0.001 |
| 3 vs. 1 | 1.092 | 1.086–1.098 | <0.001 |
| 4 vs. 1 | 1.206 | 1.198–1.215 | <0.001 |
| 5 vs. 1 | 1.284 | 1.271–1.297 | <0.001 |
| 6 vs. 1 | 1.271 | 1.253–1.290 | <0.001 |
| 7 vs. 1 | 1.219 | 1.193–1.245 | <0.001 |
| ≥8 vs. 1 | 1.081 | 1.059–1.104 | <0.001 |
| Nativity | |||
| Not in the US vs. in the US | 0.978 | 0.973–0.982 | <0.001 |
| Unknown vs. in the US | 0.987 | 0.943–1.034 | 0.585 |
| Gonorrhea (yes vs. no) | 1.140 | 1.100–1.181 | <0.001 |
| Syphilis (yes vs. no) | 1.095 | 1.040–1.153 | <0.001 |
| Chlamydia (yes vs. no) | 1.028 | 1.014–1.042 | <0.001 |
PTB, preterm birth; OR, odds ratio; CI, confidence interval; BMI, body mass index; AIAN, American Indian/Alaskan Native; NHOPI, Native Hawaiian or Other Pacific Islander; FEDT, fertility-enhancing drugs therapy; ART, assisted reproductive technology; US, United States.