Objective
Short height and obesity have each been associated with increased risk for preterm birth (PTB). However, the effect of short height on PTB risk, across different race/ethnicities and body mass index (BMI) categories, has not been studied. Our objective was to determine the influence of maternal height on the risk for PTB within race/ethnic groups, BMI groups, or adjusted for weight.
Study Design
All California singleton live births from 2007 through 2010 were included from birth certificate data (vital statistics) linked to hospital discharge data. Prepregnancy BMI (kg/m 2 ) was categorized as underweight (<18.5), normal (18.5-24.9), overweight (25.0-29.9), or obese (≥30.0). Maternal race/ethnicity was categorized as: non-Hispanic white, non-Hispanic black, Hispanic, and Asian. Maternal height was classified into 5 categories (shortest, short, middle, tall, tallest) based on racial/ethnic-specific height distributions, with the middle category serving as reference. Poisson regression models were used to estimate relative risks for the association between maternal height and risk of spontaneous PTB (<37 weeks and <32 weeks). Models were stratified on race/ethnicity and BMI. Generalized additive regression models were used to detect nonlinearity of the association. Covariates considered were: maternal age, weight, parity, prenatal care, education, medical payment, previous PTB, gestational and pregestational diabetes, pregestational hypertension, preeclampsia/eclampsia, and smoking.
Results
Among 1,655,385 California singleton live births, 5.2% were spontaneous PTB <37 weeks. Short stature (first height category) was associated with increased risk for PTB for non-Hispanic whites and Hispanics across all BMI categories. Among obese women, tall stature (fifth category) was associated with reduced risk for spontaneous PTB for non-Hispanic whites, Asians, and Hispanics. The same pattern of association was seen for height and risk for spontaneous PTB <32 weeks. In the generalized additive regression model plots, short stature was associated with increased risk for spontaneous PTB of <32 and <37 weeks of gestation among whites and Asians. However, this association was not observed for blacks and Hispanics.
Conclusion
Maternal shorter height is associated with a modest increased risk for spontaneous PTB regardless of BMI. Our results suggest that PTB risk assessment should consider race/ethnicity-specific height with respect to the norm in addition to BMI assessment.
In the United States, 12.3% of births occur <37 weeks of gestation, with 5.4% categorized as spontaneous preterm birth (PTB) among singleton live births. PTB is the primary cause of perinatal morbidity and mortality in the developed world and in the United States it is associated with an annual cost >$26 billion. Many maternal characteristics have been associated with PTB, including age, race/ethnicity, marital and socioeconomic status, as well as anthropometrics characteristics (weight and height). Over the past 2 decades, there has been substantial investigation into the associations among women’s prepregnancy body mass index (BMI), weight gain during pregnancy, and risk for adverse pregnancy outcomes. Both extremes of BMI categories (underweight and obese) have been associated with increased risk of PTB. Height, which is an indicator of the interplay between genetic and early-life factors, has been inversely associated with the risk of PTB in some but not all studies. Average height differs across diverse population subgroups, with non-Hispanic white or non-Hispanic black usually taller than Asian women. Previous studies that examined the association between height and risk for spontaneous PTB did not stratify according to race/ethnicity. Therefore, It remained unclear whether the inverse association of height with PTB varies across different race/ethnicities. In addition, although height is a component in BMI, its association with spontaneous PTB across BMI categories has rarely been studied.
Our aim was to investigate the association between women’s height and spontaneous PTB in a large population-based birth cohort. We examined whether the association varied across women of different races/ethnicities, across different BMI categories, or was influenced by adjustment for weight.
Materials and Methods
All singleton live births in California from 2007 through 2010 were identified from birth certificates (vital statistics) linked to prenatal screening and hospital discharge databases (ie, Office of Statewide Health Planning and Development). Inclusion criteria were linked, singleton, live births, born 20-41 weeks of gestation to non-Hispanic white, non-Hispanic black, Hispanic, and Asian mothers. Exclusion criteria were gestational week at delivery <20 or >41 (often resulting from erroneous gestational dating), missing education, maternal age <13 or >55 years, height <53 or >77 in (these height cutoffs reflect at least 3 SD for any race/ethnicity), prepregnancy weight <75 or >450 lb, and parity missing or >10. Mothers with unknown month of prenatal care initiation were grouped with those who did not initiate or initiated at ≥6 months. Additionally, unreported medical payment was grouped with uninsured and unreported smoking was grouped with nonsmokers. Prepregnancy BMI, race/ethnicity, and height were obtained from birth certificates. Maternal height was divided into 5 categories based on the approximate 20th, 40th, 60th, and 80th percentiles specific to each racial-ethnic group (shortest, short, middle, tall, tallest), with the middle category serving as reference. The numbers of women in each category are unequal because height was reported to the nearest inch, and certain values were particularly frequent. BMI was categorized according to the World Health Organization classification: underweight (<18.5); normal (18.5-24.9); overweight (25.0-29.9), or obese (≥30.0). Maternal race/ethnicity was categorized as non-Hispanic white, non-Hispanic black, Hispanic, and Asian.
Only spontaneous PTBs were included for analysis. Spontaneous PTB was defined using the following International Classification of Diseases, Ninth Revision and birth certificate codes: preterm premature rupture of membranes, premature labor with intact membranes, and those for whom tocolytic medications were administered ( International Classification of Diseases, Ninth Revision codes: 658.1, 644.0, 644.2). Spontaneous PTB was defined as <37 weeks, and subclassified for analysis as <32 completed gestational weeks.
Poisson regression models were used to estimate relative risks (RR) for the association between height and risk of spontaneous PTB (<37 or <32 weeks of gestation). Models were stratified on race/ethnicity and BMI. Covariates considered were: maternal age (continuous), parity (nulliparous, multiparous), prenatal care (initiation within first 5 months of pregnancy), education (some high school or less, high school graduate, some college, college graduate or more), payor (Medi-Cal, private insurance, uninsured, other), PTB history, gestational and pregestational diabetes and pregestational hypertension, preeclampsia/eclampsia, and smoking (yes, no/not reported). A P value of < .05 was considered statistically significant. All analyses were performed with SAS 9.3 (SAS Institute, Cary, NC). We used generalized additive regression models with polynomial spline estimation, while adjusting for weight and the covariates above to explore the relationship between PTB and height and to evaluate the nonlinearity of the association. This study was approved by the Stanford University Institutional Review Board.
Results
Included for analysis were 1,655,385 California live singleton births (20-42 weeks of gestation) in the years 2007 through 2010. Characteristics of the study population by racial/ethnic group are displayed in Table 1 . Occurrence of spontaneous PTB of <37 weeks was 4.8%, 7.7%, 5.0%, and 5.2% for non-Hispanic whites, non-Hispanic blacks, Asians, and Hispanics, respectively ( Table 1 ). Of the records, 12% were removed due to missing/outlier information. A large proportion of the missing/outlier information was attributed to missing data on maternal weight (7.85%) and height (5.25%). In addition, missing information about gestational age at birth attributed a small proportion (1.49%). The proportion of missing information for weight, height, and gestational age at birth did not differ across race groups. With regard to the outcome and covariates, there were few meaningful differences between those with and without missing height information. Compared to women with complete height information, mothers with missing height information were slightly more likely to be Medi-Cal insured and less educated, and were more likely to have missing information on other variables as well.
| Variable | Non-Hispanic white | Non-Hispanic black | Asian | Hispanic | |
|---|---|---|---|---|---|
| n (%) | |||||
| Age, y | <25 | 102,173 (21.1) | 42,069 (43.5) | 16,279 (9.7) | 362,847 (40.0) |
| 25 – 29 | 133,367 (27.6) | 24,526 (25.4) | 41,576 (24.8) | 246,675 (27.2) | |
| 30–34 | 139,551 (28.9) | 17,677 (18.3) | 64,033 (38.2) | 182,243 (20.1) | |
| ≥35 | 108,453 (22.4) | 12,378 (12.8) | 45,777 (27.3) | 115,761 (12.8) | |
| Prepregnancy BMI | Underweight | 20,365 (4.2) | 3894 (4.0) | 18,044 (10.8) | 225,660 (2.8) |
| Normal | 275,410 (57.0) | 40,731 (42.1) | 117,271 (69.9) | 390,611 (43.0) | |
| Overweight | 107,204 (22.2) | 25,461 (26.3) | 24,664 (14.7) | 270,538 (29.8) | |
| Obese I | 46,829 (9.7) | 13,949 (14.4) | 5983 (3.6) | 139,261 (15.3) | |
| Obese II | 21,077 (4.4) | 6939 (7.2) | 1336 (0.8) | 52,993 (5.8) | |
| Obese III | 12,659 (2.6) | 5676 (5.9) | 367 (0.2) | 28,463 (3.1) | |
| Prenatal care | Initiation in first 5 mo | 460,897 (95.3) | 87,991 (91.0) | 160,838 (95.9) | 841,902 (92.8) |
| Initiation ≥6 mo/no initiation/unknown | 22,647 (4.7) | 8659 (9.0) | 6827 (4.1) | 65,624 (7.2) | |
| Education | Some high school or less | 30,130 (6.2) | 16,294 (16.9) | 8782 (5.2) | 381,073 (42.0) |
| High school diploma/GED | 106,598 (22.0) | 33,539 (34.7) | 25,306 (15.1) | 279,086 (30.8) | |
| Some college | 137,358 (28.4) | 33,295 (34.4) | 30,512 (18.2) | 176,530 (19.5) | |
| College graduate or more | 209,458 (43.3) | 13,522 (14.0) | 103,065 (61.5) | 70,837 (7.8) | |
| Payor | Medi-Cal | 112,409 (23.2) | 52,074 (53.9) | 34,871 (20.8) | 594,620 (65.5) |
| Private | 351,058 (72.6) | 36,630 (37.9) | 122,972 (73.3) | 268,971 (29.6) | |
| Uninsured/unknown | 5245 (1.1) | 1700 (1.8) | 4865 (2.9) | 21,472 (2.4) | |
| Other | 14,832 (3.1) | 6246 (6.5) | 4957 (3.0) | 22,463 (2.5) | |
| Parity | 1 | 218,379 (45.2) | 40,759 (42.2) | 80,770 (48.2) | 323,233 (35.6) |
| ≥2 | 265,165 (54.8) | 55,891 (57.8) | 86,895 (51.8) | 584,293 (64.4) | |
| Previous PTB | No | 479,798 (99.2) | 95,588 (98.9) | 166,962 (99.6) | 903,436 (99.5) |
| Yes | 3746 (0.8) | 1062 (1.1) | 703 (0.4) | 4090 (0.5) | |
| Smoking | No/unreported | 456,747 (94.5) | 91,742 (94.9) | 166,627 (99.4) | 899,333 (99.1) |
| Yes | 26,797 (5.5) | 4908 (5.1) | 1038 (0.6) | 8193 (0.9) | |
| Pregestational hypertension, preeclampsia/eclampsia | No | 457,264 (94.6) | 91,291 (94.5) | 148,910 (88.8) | 834,417 (91.9) |
| Yes | 26,280 (5.4) | 5359 (5.5) | 18,755 (11.2) | 73,109 (8.1) | |
| Pregestational/gestational diabetes | No | 451,899 (93.5) | 86,251 (89.2) | 161,598 (96.4) | 852,987 (94.0) |
| Yes | 31,645 (6.5) | 10,399 (10.8) | 6067 (3.6) | 54,539 (6.0) | |
The total number of subjects for each height category based on a within race/ethnic distribution is presented in Table 2 .
| Maternal height category a | Race/ethnicity | |||||||
|---|---|---|---|---|---|---|---|---|
| Non-Hispanic white | Non-Hispanic black | Asian | Hispanic | |||||
| Height, in | n (%) | Height, in | n (%) | Height, in | n (%) | Height, in | n (%) | |
| Shortest | 53 – 62 | 80,709 (16.7) | 53–61 | 10,658 (11.0) | 53–60 | 25,827 (15.4) | 53–60 | 159,839 (17.6) |
| Short | 63 | 51,691 (10.7) | 62–63 | 21,681 (22.4) | 61 | 18,456 (11.0) | 61 | 106,563 (11.7) |
| Middle | 64–65 | 134,442 (27.8) | 64 | 13,395 (13.9) | 62 | 31,116 (18.6) | 62 | 164,341 (18.1) |
| Tall | 66 | 68,057 (14.1) | 65–66 | 25,041 (25.9) | 63–64 | 54,591 (32.6) | 63–64 | 253,286 (27.9) |
| Tallest | 67–77 | 148,645 (30.7) | 67–77 | 25,875 (26.8) | 65–77 | 37,675 (22.5) | 65–77 | 223,497 (24.6) |
a Based on cutoffs for each group at 20th, 40th, 60th, and 80th percentiles.
Among non-Hispanic whites and Hispanics the lowest height category (shortest) was associated with modest increased risk for spontaneous PTB ( Table 3 ). This was observed across all BMI categories. Adjusted RR (aRR) ranged from 1.1–1.3 (associated P values < .05). A similar trend was seen among Asians across all BMI categories. However, the lowest height category was associated with a statistically significant increased risk for spontaneous PTB with aRRs of 1.1 (95% confidence interval [CI], 1.0–1.2) and 1.2 (95% CI, 1.0–1.4) only among normal and overweight BMI categories, respectively. Among non-Hispanic blacks, the lowest height category was associated with a statistically significant increased risk for spontaneous PTB only among normal and obese BMI categories.
| Race/ethnicity | Height category | Height, in | Spontaneous PTB <37 wk | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| BMI categories | ||||||||||||||
| Underweight | Normal | Overweight | Obese | |||||||||||
| n | cRR (CI) | aRR (CI) | n | cRR (CI) | aRR (CI) | n | cRR (CI) | aRR (CI) | n | cRR (CI) | aRR (CI) | |||
| Non-Hispanic white | Shortest | 53–62 | 226 | 1.3 (1.1–1.6) a | 1.2 (1.1–1.5) a | 2454 | 1.2 (1.2–1.3) a | 1.2 (1.1–1.3) a | 1108 | 1.2 (1.1–1.3) a | 1.2 (1.1–1.3) a | 1015 | 1.2 (1.1–1.3) a | 1.2 (1.1–1.3) a |
| Short | 63 | 102 | 1.0 (0.8–1.3) | 1.0 (0.8–1.2) | 1433 | 1.0 (1.0–1.1) | 1.0 (1.0–1.1) | 550 | 1.1 (1.0–1.2) | 1.1 (1.0–1.2) | 555 | 1.1 (1.0–1.2) a | 1.1 (1.0–1.2) a | |
| Middle | 64–65 | 321 | 1.0 (ref) | 1.0 (ref) | 3631 | 1.0 (ref) | 1.0 (ref) | 1313 | 1.0 (ref) | 1.0 (ref) | 1224 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 66 | 147 | 0.9 (0.7–1.1) | 0.9 (0.8–1.1) | 1642 | 0.9 (0.9–1.0) a | 0.9 (0.9–1.0) a | 675 | 0.9 (0.9–1.0) | 1.0 (0.9–1.0) | 550 | 0.9 (0.8–1.0) | 0.9 (0.9–1.0) | |
| Tallest | 67–77 | 440 | 0.9 (0.7–1.0) a | 0.9 (0.8–1.0) | 3358 | 0.9 (0.8–0.9) a | 0.9 (0.8–0.9) a | 1296 | 0.9 (0.8–0.9) a | 0.9 (0.8–0.9) a | 1064 | 0.9 (0.8–0.9) a | 0.8 (0.8–0.9) a | |
| Non-Hispanic black | Shortest | 53–61 | 28 | 0.9 (0.6–1.5) | 0.9 (0.6–1.4) | 409 | 1.2 (1.1–1.4) a | 1.2 (1.0–1.3) a | 253 | 1.2 (1.0–1.4) | 1.2 (1.0–1.4) | 273 | 1.1 (1.0–1.3) | 1.2 (1.0–1.4) a |
| Short | 62–63 | 80 | 1.0 (0.7–1.3) | 0.9 (0.7–1.3) | 773 | 1.1 (0.9–1.2) | 1.1 (0.9–1.2) | 453 | 1.1 (0.9–1.3) | 1.1 (0.9–1.3) | 527 | 1.1 (1.0–1.3) | 1.1 (1.0–1.3) | |
| Middle | 64 | 57 | 1.0 (ref) | 1.0 (ref) | 444 | 1.0 (ref) | 1.0 (ref) | 245 | 1.0 (ref) | 1.0 (ref) | 301 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 65–66 | 98 | 0.8 (0.6–1.1) | 0.8 (0.5–1.1) | 817 | 1.0 (0.9–1.1) | 1.0 (0.9–1.1) | 418 | 0.9 (0.7–1.0) | 0.9 (0.7–1.0) | 524 | 1.0 (0.9–1.1) | 1.0 (0.9–1.1) | |
| Tallest | 67–77 | 134 | 0.8 (0.6–1.1) | 0.8 (0.6–1.1) | 673 | 0.9 (0.8–1.0) a | 0.9 (0.8–1.0) a | 438 | 0.9 (0.7–1.0) | 0.9 (0.7–1.0) a | 519 | 0.9 (0.8–1.0) | 0.9 (0.8–1.0) | |
| Asian | Shortest | 53–60 | 105 | 1.3 (1.0–1.7) a | 1.2 (1.0–1.6) | 972 | 1.1 (1.1–1.3) a | 1.1 (1.0–1.2) a | 325 | 1.2 (1.0–1.4) a | 1.2 (1.0–1.4) a | 118 | 0.9 (0.7–1.1) | 1.0 (0.7–1.3) |
| Short | 61 | 68 | 1.0 (0.8–1.4) | 1.0 (0.8–1.3) | 686 | 1.1 (1.0–1.2) | 1.1 (1.0–1.2) | 179 | 1.1 (0.9–1.3) | 1.1 (0.9–1.3) | 66 | 0.8 (0.6–1.1) | 0.9 (0.7–1.2) | |
| Middle | 62 | 161 | 1.0 (ref) | 1.0 (ref) | 1039 | 1.0 (ref) | 1.0 (ref) | 258 | 1.0 (ref) | 1.0 (ref) | 120 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 63–64 | 280 | 1.1 (0.9–1.3) | 1.1 (0.9–1.4) | 1756 | 0.9 (0.9–1.0) | 0.9 (0.9–1.0) | 409 | 1.0 (0.8–1.1) | 1.0 (0.8–1.2) | 148 | 0.8 (0.6–1.0) | 0.8 (0.6–1.0) | |
| Tallest | 65–77 | 238 | 1.0 (0.8–1.2) | 1.0 (0.8–1.2) | 1041 | 0.8 (0.8–0.9) a | 0.9 (0.8–0.9) a | 257 | 0.9 (0.8–1.1) | 0.9 (0.8–1.1) | 80 | 0.7 (0.5–0.9) a | 0.7 (0.5–0.9) a | |
| Hispanic | Shortest | 53–60 | 214 | 1.4 (1.1–1.6) a | 1.3 (1.1–1.6) a | 3547 | 1.1 (1.0–1.1) a | 1.1 (1.0–1.1) a | 2947 | 1.1 (1.0–1.2) a | 1.1 (1.0–1.2) a | 2382 | 1.1 (1.1–1.2) a | 1.1 (1.1–1.2) a |
| Short | 61 | 130 | 1.1 (0.9–1.3) | 1.0 (0.9–1.3) | 2461 | 1.0 (1.0–1.1) | 1.0 (1.0–1.1) | 1685 | 1.1 (1.0–1.1) a | 1.1 (1.0–1.1) | 1546 | 1.1 (1.0–1.2) a | 1.1 (1.0–1.2) a | |
| Middle | 62 | 297 | 1.0 (ref) | 1.0 (ref) | 3575 | 1.0 (ref) | 1.0 (ref) | 2467 | 1.0 (ref) | 1.0 (ref) | 2165 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 63–64 | 439 | 1.0 (0.9–1.2) | 1.0 (0.9–1.2) | 5434 | 0.9 (0.9–1.0) a | 0.9 (0.9–1.0) a | 3399 | 1.0 (0.9–1.0) | 1.0 (0.9–1.0) | 3422 | 1.0 (1.0–1.1) | 1.0 (0.9–1.0) | |
| Tallest | 65–77 | 579 | 1.0 (0.8–1.1) | 1.0 (0.9–1.1) | 4176 | 0.9 (0.8–0.9) a | 0.9 (0.8–0.9) a | 2824 | 0.9 (0.9–1.0) a | 0.9 (0.8–0.9) a | 3065 | 1.0 (0.9–1.1) | 0.9 (0.9–1.0) a | |
Top category of height (tallest) in contrast showed similar magnitude of reduction in risk of spontaneous PTB with aRRs approximating 0.9 for most race/ethnicities and BMI groups.
We further examined the association between height and spontaneous PTB at <32 weeks ( Table 4 ). These analyses produced similar results to the <37 weeks’ gestation comparisons. However, owing to smaller numbers many of the estimated risks had associated CI that included 1.0.
| Race/ethnicity | Height category | Height, in | Spontaneous PTB <32 wk | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| BMI categories | ||||||||||||||
| Underweight | Normal | Overweight | Obese | |||||||||||
| n | cRR (CI) | aRR (CI) | n | cRR (CI) | aRR (CI) | n | cRR (CI) | aRR (CI) | n | cRR (CI) | aRR (CI) | |||
| Non-Hispanic white | Shortest | 53 – 62 | 36 | 1.9 (1.2–3.0) a | 1.6 (1.0–2.6) a | 336 | 1.3 (1.1–1.5) a | 1.2 (1.0–1.4) a | 154 | 1.4 (1.1–1.7) a | 1.4 (1.1–1.7) a | 159 | 1.2 (1.0–1.5) | 1.2 (1.0–1.5) |
| Short | 63 | 17 | 1.5 (0.8–2.6) | 1.3 (0.8–2.4) | 169 | 0.9 (0.8–1.1) | 0.9 (0.7–1.1) | 60 | 0.9 (0.7–1.3) | 0.9 (0.7–1.3) | 88 | 1.1 (0.9–1.4) | 1.1 (0.9–1.5) | |
| Middle | 64–65 | 37 | 1.0 (ref) | 1.0 (ref) | 486 | 1.0 (ref) | 1.0 (ref) | 164 | 1.0 (ref) | 1.0 (ref) | 194 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 66 | 23 | 1.2 (0.7–2.0) | 1.2 (0.7–2.1) | 191 | 0.8 (0.7–0.9) a | 0.8 (0.7–0.9) a | 83 | 0.9 (0.7–1.2) | 0.9 (0.7–1.2) | 87 | 0.9 (0.7–1.2) | 0.9 (0.7–1.2) | |
| Tallest | 67–77 | 53 | 0.9 (0.6–1.3) | 1.0 (0.6–1.5) | 386 | 0.7 (0.6–0.8) a | 0.8 (0.7–0.9) a | 168 | 0.9 (0.7–1.1) | 0.9 (0.7–1.1) | 180 | 0.9 (0.7–1.1) | 0.9 (0.7–1.1) | |
| Non-Hispanic black | Shortest | 53–61 | 6 | 1.6 (0.5–4.7) | 1.5 (0.5–4.5) | 79 | 1.0 (0.7–1.3) | 0.9 (0.7–1.2) | 55 | 1.2 (0.8–1.8) | 1.2 (0.8–1.8) | 56 | 0.9 (0.6–1.2) | 0.9 (0.7–1.3) |
| Short | 62–63 | 15 | 1.4 (0.6–3.5) | 1.4 (0.6–3.4) | 155 | 0.9 (0.7–1.1) | 0.9 (0.7–1.1) | 102 | 1.2 (0.9–1.7) | 1.2 (0.9–1.7) | 119 | 1.0 (0.7–1.3) | 1.0 (0.7–1.3) | |
| Middle | 64 | 7 | 1.0 (ref) | 1.0 (ref) | 109 | 1.0 (ref) | 1.0 (ref) | 51 | 1.0 (ref) | 1.0 (ref) | 81 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 65–66 | 21 | 1.3 (0.5–3.0) | 1.2 (0.5–2.8) | 173 | 0.8 (0.7–1.1) | 0.8 (0.7–1.1) | 113 | 1.1 (0.8–1.6) | 1.1 (0.8–1.5) | 162 | 1.1 (0.9–1.5) | 1.1 (0.9–1.5) | |
| Tallest | 67–77 | 29 | 1.4 (0.6–3.1) | 1.3 (0.6–3.0) | 158 | 0.8 (0.6–1.0) | 0.8 (0.6–1.0) | 93 | 0.9 (0.6–1.2) | 0.9 (0.6–1.2) | 153 | 1.0 (0.8–1.3) | 1.0 (0.7–1.3) | |
| Asian | Shortest | 53–60 | 14 | 1.3 (0.7–2.6) | 1.2 (0.6–2.3) | 130 | 1.3 (1.1–1.7) a | 1.2 (1.0–1.6) | 54 | 1.2 (0.8–1.8) | 1.2 (0.8–1.8) | 24 | 1.1 (0.6–2.0) | 1.2 (0.7–2.2) |
| Short | 61 | 6 | 0.7 (0.3–1.7) | 0.6 (0.3–1.6) | 82 | 1.1 (0.9–1.5) | 1.1 (0.8–1.4) | 34 | 1.3 (0.8–2.0) | 1.3 (0.8–2.1) | 11 | 0.9 (0.4–1.8) | 0.9 (0.4–1.8) | |
| Middle | 62 | 21 | 1.0 (ref) | 1.0 (ref) | 119 | 1.0 (ref) | 1.0 (ref) | 42 | 1.0 (ref) | 1.0 (ref) | 19 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 63–64 | 36 | 1.1 (0.6–1.8) | 1.1 (0.7–1.9) | 210 | 1.0 (0.8–1.2) | 1.0 (0.8–1.3) | 60 | 0.9 (0.6–1.3) | 0.9 (0.6–1.3) | 29 | 1.0 (0.5–1.7) | 0.9 (0.5–1.6) | |
| Tallest | 65–77 | 34 | 1.1 (0.6–1.8) | 1.1 (0.6–1.9) | 111 | 0.8 (0.6–1.0) | 0.8 (0.6–1.1) | 44 | 0.9 (0.6–1.4) | 1.0 (0.6–1.5) | 16 | 0.8 (0.4–1.6) | 0.8 (0.4–1.5) | |
| Hispanic | Shortest | 53–60 | 38 | 1.6 (1.1–2.5) a | 1.6 (1.0–2.5) a | 485 | 1.0 (0.9–1.1) | 1.0 (0.9–1.1) | 477 | 1.1 (0.9–1.2) | 1.0 (0.9–1.2) | 430 | 1.1 (1.0–1.3) | 1.1 (1.0–1.3) |
| Short | 61 | 25 | 1.3 (0.8–2.2) | 1.3 (0.8–2.2) | 366 | 1.0 (0.9–1.2) | 1.0 (0.9–1.2) | 272 | 1.0 (0.9–1.2) | 1.0 (0.9–1.2) | 309 | 1.2 (1.0–1.4) a | 1.2 (1.0–1.4) a | |
| Middle | 62 | 45 | 1.0 (ref) | 1.0 (ref) | 533 | 1.0 (ref) | 1.0 (ref) | 416 | 1.0 (ref) | 1.0 (ref) | 388 | 1.0 (ref) | 1.0 (ref) | |
| Tall | 63–64 | 74 | 1.2 (0.8–1.7) | 1.2 (0.8–1.7) | 792 | 0.9 (0.8–1.0) | 0.9 (0.8–1.0) | 548 | 0.9 (0.8–1.1) | 0.9 (0.8–1.1) | 648 | 1.1 (0.9–1.2) | 1.0 (0.9–1.2) | |
| Tallest | 65–77 | 92 | 1.0 (0.7–1.4) | 1.0 (0.7–1.5) | 642 | 0.9 (0.8–1.0) a | 0.9 (0.8–1.0) | 499 | 1.0 (0.8–1.1) | 0.9 (0.8–1.0) | 557 | 1.0 (0.9–1.2) | 0.9 (0.8–1.1) | |
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