Table 1. Descriptive Statistics of the Study Population Based on SMM Status, 2008 to 2018.
| Characteristic | Pregnancies, No. (%) | ||||
|---|---|---|---|---|---|
| Total pregnancies (N = 403 602) | Non-SMM (n = 396 504) | SMM21 (n = 7098) | SMM20 (n = 3446) | SMMcardio (n = 684) | |
| Maternal age, y | |||||
| <25 | 76 290 (18.90) | 74 981 (18.91) | 1309 (18.44) | 575 (16.69) | 130 (19.01) |
| 25-34 | 239 707 (59.39) | 235 838 (59.48) | 3869 (54.51) | 1857 (53.89) | 344 (50.29) |
| ≥35 | 87 605 (21.71) | 85 685 (21.61) | 1920 (27.05) | 1014 (29.43) | 210 (30.70) |
| Race and ethnicitya | |||||
| African American | 31 432 (7.79) | 30 660 (7.73) | 772 (10.88) | 413 (11.98) | 81 (11.84) |
| Asian | 50 852 (12.60) | 49 867 (12.58) | 985 (13.88) | 482 (13.99) | 92 (13.45) |
| Hispanic | 204 817 (50.75) | 201 347 (50.78) | 3470 (48.89) | 1598 (46.37) | 310 (45.32) |
| Non-Hispanic White | 105 886 (26.24) | 104 223 (26.29) | 1663 (23.43) | 855 (24.81) | 180 (26.32) |
| Otherb | 10 583 (2.62) | 10 376 (2.62) | 207 (2.92) | 97 (2.81) | 21 (3.07) |
| Missing | 32 (0.01) | 31 (0.01) | 1 (0.01) | 1 (0.03) | 0 |
| Education level | |||||
| <College | 123 416 (30.58) | 121 331 (30.60) | 2085 (29.37) | 1024 (29.72) | 204 (29.82) |
| ≥College | 272 168 (67.43) | 267 351 (67.43) | 4817 (67.86) | 2322 (67.38) | 458 (66.96) |
| Missing | 8018 (1.99) | 7822 (1.97) | 196 (2.76) | 100 (2.90) | 22 (3.22) |
| Income level, $ | |||||
| Mean (SD) | 59 871 (21 835) | 59 889 (21 834) | 58 853 (21 881) | 59 434 (22 363) | 58 721 (21 148) |
| Missing | 1237 (0.31) | 1217 (0.31) | 20 (0.28) | 10 (0.29) | 2 (0.29) |
| Insurance type | |||||
| Medicaid | 38 500 (9.54) | 37 724 (9.51) | 776 (10.93) | 383 (11.11) | 73 (10.67) |
| Other | 359 983 (89.19) | 353 753 (89.22) | 6230 (87.77) | 3023 (87.72) | 606 (88.60) |
| Missing | 5119 (1.27) | 5027 (1.27) | 92 (1.30) | 40 (1.16) | 5 (0.73) |
| Season of conception | |||||
| Cool (November-April) | 205 781 (50.99) | 202 122 (50.98) | 3659 (51.55) | 1723 (50.00) | 344 (50.29) |
| Warm (May-October) | 197 821 (49.01) | 194 382 (49.02) | 3439 (48.45) | 1723 (50.00) | 340 (49.71) |
| BMI | |||||
| Underweight (<18.5) | 9587 (2.38) | 9403 (2.37) | 184 (2.59) | 74 (2.15) | 14 (2.05) |
| Normal weight (18.5-24.9) | 171 348 (42.45) | 168 375 (42.46) | 2973 (41.89) | 1409 (40.89) | 272 (39.77) |
| Overweight (25.0-29.9) | 112 861 (27.96) | 110 900 (27.97) | 1961 (27.63) | 959 (27.83) | 170 (24.85) |
| Obese (≥30.0) | 107 751 (26.70) | 105 818 (26.69) | 1933 (27.23) | 978 (28.38) | 221 (32.31) |
| Missing | 2055 (0.51) | 2008 (0.51) | 47 (0.66) | 26 (0.75) | 7 (1.02) |
| Parity | |||||
| Primiparous | 164 837 (40.84) | 161 499 (40.73) | 3338 (47.03) | 1563 (45.36) | 348 (50.88) |
| Multiparous | 236 771 (58.66) | 233 112 (58.79) | 3659 (51.55) | 1833 (53.19) | 327 (47.81) |
| Missing | 1994 (0.49) | 1893 (0.48) | 101 (1.42) | 50 (1.45) | 9 (1.32) |
| Smoking status | |||||
| Never smoked | 335 882 (83.22) | 329 944 (83.21) | 5938 (83.66) | 2877 (83.49) | 563 (82.31) |
| Past smoking | 46 949 (11.63) | 46 185 (11.65) | 764 (10.76) | 375 (10.88) | 77 (11.26) |
| Smoked during pregnancy | 20 746 (5.14) | 20 350 (5.13) | 396 (5.58) | 194 (5.63) | 44 (6.43) |
| Missing | 25 (0.01) | 25 (0.01) | 0 | 0 | 0 |
| Medical conditions | |||||
| Preterm birth | 31 319 (7.76) | 29 866 (7.53) | 1453 (20.47) | 866 (25.13) | 233 (34.06) |
| Gestational diabetesc | 41 137 (10.19) | 40 374 (10.18) | 763 (10.75) | 379 (11.00) | 78 (11.40) |
| Gestational hypertension | 19 057 (4.72) | 18 528 (4.67) | 529 (7.45) | 272 (7.89) | 89 (13.01) |
| Preexisting diabetes | 5382 (1.33) | 5162 (1.30) | 220 (3.10) | 131 (3.80) | 35 (5.12) |
| Chronic hypertension | 13 886 (3.44) | 13 439 (3.39) | 447 (6.30) | 264 (7.66) | 86 (12.57) |
Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); SMM, severe maternal morbidity; SMM20, SMM measured without the blood product transfusion; SMM21, SMM measured with all 21 indicators; SMMcardio, the cardiovascular-related subcategory in SMM.
Race and ethnicity data were self-reported and recorded in the social history of electronic health records. The data were reported to account for differences in risk of SMM and to assess potential differences in susceptibility to heat exposure.
Other included Native American Alaskan, Pacific Islander, other unspecified races or ethnicities, and multiple races or ethnicities, consolidated due to the relatively small sample size of each group in the present study.
The missing numbers of gestational diabetes among total pregnancies, non-SMM cases, SMM21 cases, SMM20 cases, and SMMcardio cases are 26 440 (6.55%), 25 680 (6.48%), 760 (10.71%), 398 (11.55%), and 95 (13.89%), respectively.