20 April 2022 : Clinical Research
Effects of Interaction Between Gestational Hypertension and History of Preterm Birth on the Risk of Preterm Birth: An Analysis Based on the National Vital Statistics System Database
Xiaoqin Cao1AE, Daoming Zu2BCD, Yang Liu1AE*DOI: 10.12659/MSM.935094
Med Sci Monit 2022; 28:e935094
Table 1 Characteristics of the study participants.
| Variables | Total (n=2,822,624) | Groups | Statistics | P | |
|---|---|---|---|---|---|
| Control (n=2,516,862) | Case| (n=305,762) | ||||
| Age, years, n (%) | Z=29.735 | <0.001 | |||
| <20 | 78,085 (2.77) | 68,571 (2.72) | 9,514 (3.11) | ||
| 20–29 | 1,311,517 (46.46) | 1,175,169 (46.69) | 136,348 (44.59) | ||
| 30–34 | 882,726 (31.27) | 792,704 (31.50) | 90,022 (29.44) | ||
| ≥35 | 550,296 (19.50) | 480,418 (19.09) | 69,878 (22.85) | ||
| Race, n (%) | χ=9678.997 | <0.001 | |||
| White (only) | 2,138,878 (75.78) | 1,923,060 (76.41) | 215,818 (70.58) | ||
| Black (only) | 361,077 (12.79) | 305,194 (12.13) | 55,883 (18.28) | ||
| ALAN (only) | 22,029 (0.78) | 19,311 (0.77) | 2,718 (0.89) | ||
| Asian (only) | 218,888 (7.75) | 197,191 (7.83) | 21,697 (7.10) | ||
| NHOPI (only) | 7,869 (0.28) | 6,716 (0.27) | 1,153 (0.38) | ||
| More than one race | 73,883 (2.62) | 65,390 (2.60) | 8,493 (2.78) | ||
| Educational attainment, n (%) | Z=−62.839 | <0.001 | |||
| 8 grade or less | 63,380 (2.25) | 55,559 (2.21) | 7,821 (2.56) | ||
| 9 through 12 grade | 836,393 (29.63) | 732,056 (29.09) | 104,337 (34.12) | ||
| Bachelor’s degree | 1,498,962 (53.11) | 1,344,370 (53.41) | 154,592 (50.56) | ||
| Master’s degree or above | 423,889 (15.02) | 384,877 (15.29) | 39,012 (12.76) | ||
| Pre-pregnancy BMI, kg/m, n (%) | Z=51.183 | <0.001 | |||
| Underweight <18.5 | 83,655 (2.96) | 73,573 (2.92) | 10,082 (3.30) | ||
| Normal 18.5–24.9 | 1,208,600 (42.82) | 1,089,737 (43.30) | 118,863 (38.87) | ||
| Overweight 25.0–29.9 | 761,259 (26.97) | 679,927 (27.01) | 81,332 (26.60) | ||
| Obesity I 30.0–34.9 | 425,406 (15.07) | 375,000 (14.90) | 50,406 (16.49) | ||
| Obesity II 35.0–39.9 | 205,967 (7.30) | 180,015 (7.15) | 25,952 (8.49) | ||
| Obesity III >40.0 | 137,737 (4.88) | 118,610 (4.71) | 19,127 (6.26) | ||
| Weight gain during pregnancy, pounds, n (%) | Z=−97.035 | <0.001 | |||
| <11 | 252,594 (8.95) | 213,789 (8.49) | 38,805 (12.69) | ||
| 11–20 | 484,997 (17.18) | 419,376 (16.66) | 65,621 (21.46) | ||
| 21–30 | 816,059 (28.91) | 731,464 (29.06) | 84,595 (27.67) | ||
| 31–40 | 700,912 (24.83) | 638,969 (25.39) | 61,943 (20.26) | ||
| 41–98 | 568,062 (20.13) | 513,264 (20.39) | 54,798 (17.92) | ||
| Cigarette smoking before pregnancy, n (%) | χ=1519.916 | <0.001 | |||
| No | 2,641,622 (93.59) | 2,360,454 (93.79) | 281,168 (91.96) | ||
| Yes | 181,002 (6.41) | 156,408 (6.21) | 24,594 (8.04) | ||
| Cigarette smoking during pregnancy, n (%) | χ=14762.66 | <0.001 | |||
| No | 2,678,657 (94.90) | 2,402,448 (95.45) | 276,209 (90.33) | ||
| Yes | 143,967 (5.10) | 114,414 (4.55) | 29,553 (9.67) | ||
| Pre-pregnancy diabetes, n (%) | χ=4083.661 | <0.001 | |||
| No | 2,800,127 (99.20) | 2,499,769 (99.32) | 300,358 (98.23) | ||
| Yes | 2,2497 (0.80) | 17,093 (0.68) | 5,404 (1.77) | ||
| Gestational diabetes, n (%) | χ=2381.176 | <0.001 | |||
| No | 2,627,430 (93.08) | 2,349,277 (93.34) | 278,153 (90.97) | ||
| Yes | 195,194 (6.92) | 167,585 (6.66) | 27,609 (9.03) | ||
| GH, n (%) | χ=35482.04 | <0.001 | |||
| No | 2,598,570 (92.06) | 2,343,667 (93.12) | 254,903 (83.37) | ||
| Yes | 224,054 (7.94) | 173,195 (6.88) | 50,859 (16.63) | ||
| Previous cesarean, n (%) | χ=2323.624 | <0.001 | |||
| No | 2,387,472 (84.58) | 2,137,937 (84.94) | 249,535 (81.61) | ||
| Yes | 435,152 (15.42) | 378,925 (15.06) | 56,227 (18.39) | ||
| HPB, n (%) | χ=29512.78 | <0.001 | |||
| No | 2,730,558 (96.74) | 2,450,703 (97.37) | 279,855 (91.53) | ||
| Yes | 92,066 (3.26) | 66,159 (2.63) | 25,907 (8.47) | ||
| Payment source for delivery, n (%) | χ=5663.578 | <0.001 | |||
| Medicaid | 995,105 (35.25) | 868,767 (34.52) | 126,338 (41.32) | ||
| Private insurance | 1,612,435 (57.13) | 1,453,712 (57.76) | 158,723 (51.91) | ||
| Self-pay | 112,534 (3.99) | 102,521 (4.07) | 10,013 (3.27) | ||
| Other | 102,550 (3.63) | 91,862 (3.65) | 10,688 (3.50) | ||
| Method of delivery, n (%) | χ=42464.18 | <0.001 | |||
| Cesarean | 888,811 (31.49) | 742,763 (29.51) | 146,048 (47.77) | ||
| Forceps | 14,777 (0.52) | 13,611 (0.54) | 1,166 (0.38) | ||
| Spontaneous | 1,845,156 (65.37) | 1,691,156 (67.19) | 154,000 (50.37) | ||
| Vacuum | 73,880 (2.62) | 69,332 (2.75) | 4,548 (1.49) | ||
| Number of fetus, n (%) | χ=212579.9 | <0.001 | |||
| Single | 2,730,417 (96.73) | 2,477,439 (98.43) | 252,978 (82.74) | ||
| Multi | 92,207 (3.27) | 39,423 (1.57) | 52,784 (17.26) | ||
| Infection, n (%) | χ=568.855 | <0.001 | |||
| No | 2,767,788 (98.06) | 2,469,685 (98.13) | 298,103 (97.50) | ||
| Yes | 54,836 (1.94) | 47,177 (1.87) | 7,659 (2.50) | ||
| Eclampsia, n (%) | χ=4985.065 | <0.001 | |||
| No | 2,815,422 (99.74) | 2,512,300 (99.82) | 303,122 (99.14) | ||
| Yes | 7,202 (0.26) | 4,562 (0.18) | 2,640 (0.86) | ||
| Age, years, n (%) | Z=17.017 | <0.001 | |||
| <20 | 37,392 (1.32) | 32,781 (1.30) | 4,611 (1.51) | ||
| 20–29 | 1,009,237 (35.76) | 901,235 (35.81) | 108,002 (35.32) | ||
| 30–34 | 857,856 (30.39) | 771,392 (30.65) | 86,464 (28.28) | ||
| ≥35 | 918,139 (32.53) | 811,454 (32.24) | 106,685 (34.89) | ||
| Race, n (%) | χ=8641.218 | <0.001 | |||
| White (only) | 2,101,009 (74.43) | 1,888,450 (75.03) | 212,559 (69.52) | ||
| Black (only) | 422,565 (14.97) | 359,840 (14.30) | 62,725 (20.51) | ||
| ALAN(only) | 21,355 (0.76) | 18,670 (0.74) | 2,685 (0.88) | ||
| Asian (only) | 196,853 (6.97) | 178,077 (7.08) | 18,776 (6.14) | ||
| NHOPI (only) | 8,812 (0.31) | 7,597 (0.30) | 1,215 (0.40) | ||
| More than one race | 72,030 (2.55) | 64,228 (2.55) | 7,802 (2.55) | ||
| Educational attainment, n (%) | Z=−70.653 | <0.001 | |||
| 8 grade or less | 77,081 (2.73) | 67,646 (2.69) | 9,435 (3.09) | ||
| 9 through 12 grade | 1,057,070 (37.45) | 926,248 (36.80) | 130,822 (42.79) | ||
| Bachelor’s degree | 1,345,735 (47.68) | 1,210,266 (48.09) | 135,469 (44.31) | ||
| Master’s degree or above | 342,738 (12.14) | 312,702 (12.42) | 30,036 (9.82) | ||
| Sex of infant, n (%) | χ=565.388 | <0.001 | |||
| Female | 1,376,712 (48.77) | 1,233,785 (49.02) | 142,927 (46.74) | ||
| Male | 1,445,912 (51.23) | 1,283,077 (50.98) | 162,835 (53.26) | ||
| ALAN – American Indian or Alaska Native; NHOPI – Native Hawaiian or Pacific Islander; GH – gestational hypertension; HPB – history of preterm birth. | |||||