Table 1.
Descriptive statistics of the study population (2008–2018).
| Characteristics | Total pregnancies (n = 427,870) | Non-SPROMs (n = 390,013) | SPROMs (n = 37,857) |
|---|---|---|---|
|
| |||
| Maternal age (n, %) | |||
| < 25 | 83,170 (19.44) | 75,880 (19.46) | 7,290 (19.26) |
| 25–34 | 253,755 (59.31) | 231,148 (59.27) | 22,607 (59.72) |
| ≥ 35 | 90,945 (21.26) | 82,985 (21.28) | 7,960 (21.03) |
| Race/Ethnicity (n, %) | |||
| African American | 32,275 (7.54) | 29,580 (7.58) | 2,695 (7.12) |
| Asian | 53,829 (12.58) | 48,578 (12.46) | 5,251 (13.87) |
| Hispanic | 218,804 (51.14) | 199,269 (51.09) | 19,535 (51.60) |
| Non-Hispanic White | 111,717 (26.11) | 102,338 (26.24) | 9,379 (24.77) |
| Multiple/Others | 11,199 (2.62) | 10,203 (2.62) | 996 (2.63) |
| Missing | 46 (0.01) | 45 (0.01) | 1 (0.00) |
| Education level (n, %) | |||
| Less than college | 133,596 (31.22) | 123,063 (32.55) | 10,533 (27.82) |
| College | 229,984 (53.75) | 208,955 (53.58) | 21,029 (55.55) |
| Higher than college | 55,879 (13.06) | 50,352 (12.91) | 5,527 (14.60) |
| Missing | |||
| BMI, kg/m2 (n, %) | 8,411 (1.97) | 7,643 (1.96) | 768 (2.03) |
| Underweight (<18.5) | 10,453 (2.44) | 9,538 (2.45) | 915 (2.42) |
| Normal weight (18.5–24.9) | 181,905 (42.51) | 165,909 (42.54) | 15,996 (42.25) |
| Overweight (25.0–29.9) | 119,181 (27.85) | 108,336 (27.78) | 10,845 (28.65) |
| Obese (≥30.0) | 112,859 (26.38) | 103,009 (26.41) | 9,850 (26.02) |
| Missing | 3,472 (0.81) | 3,221 (0.83) | 251 (0.66) |
| Smoking status (n, %) | |||
| Never smoker | 357,244 (83.49) | 325,650 (83.50) | 31,594 (83.46) |
| Past smoker | 48,813 (11.41) | 44,488 (11.41) | 4,325 (11.42) |
| Smoker during pregnancy | 21,769 (5.09) | 19,833 (5.09) | 1,936 (5.11) |
| Missing | 44 (0.01) | 42 (0.01) | 2 (0.01) |
| Parity (n, %) | |||
| Primiparous | 176,862 (41.34) | 156,316 (40.08) | 20,546 (54.27) |
| Multiparous | 250,444 (58.53) | 233,172 (59.79) | 17,272 (45.62) |
| Missing | 564 (0.13) | 525 (0.13) | 39 (0.10) |
| Season of conception Cool (November-April) | 216,761 (50.66) | 197,169 (50.55) | 19,592 (51.75) |
| Warm (May-October) | 211,109 (49.34) | 192,844 (49.45) | 18,265 (48.25) |
| History of PROM | |||
| Never having PROM | 418,384 (97.78) | 381,693 (97.87) | 36,691 (96.92) |
| Having PROM before | 9,486 (2.22) | 8,320 (2.13) | 1,166 (3.08) |
| Income level, US Dollars (mean ± SD) | 59,664 (21,801) | 59,652 (21,804) | 59,784 (21,766) |
Note: There were 1,359 (0.32%), 1,279 (0.33%), and 80 (0.21%) pregnancies with missing data on the income level among total pregnancies, non-SPROM cases, and SPROM cases, respectively. Abbreviation: BMI, body mass index; SD, standard deviation; SPROM, spontaneous premature rupture of membranes.