Table 1.
Study population characteristics of Massachusetts birth cohort in the years of 2001 to 2015
| Overall | |
| Study population size, n | 652,167 |
| Neonatal characteristics | |
| Birth weight, g, mean (SD) | 3,367 (500) |
| Gestational age, d, mean (SD) | 275 (12) |
| Gestational age, wks, mean (SD) | 39.3 (1.8) |
| Female sex, N (%) | 323,592 (49.6) |
| Preterm, N (%) | 47,579 (7.3) |
| Parental characteristics | |
| Mother’s age, yr, mean (SD) | 29.7 (5.9) |
| Father’s age, yr, mean (SD) | 32.3 (6.6) |
| Cigarette per day before pregnancy, No., mean (SD) | 1.5 (4.8) |
| Married, N (%) | 442,726 (67.9) |
| Mother’s race, N (%) | |
| White | 468,919 (71.9) |
| African American | 58,408 (9.0) |
| Asian/Pacific Islander | 53,485 (8.2) |
| Native American | 1,619 (0.2) |
| Other nonmissing | 67,615 (10.4) |
| Missing/refused/unknown | 2,121 (0.3) |
| Father’s race, N (%) | |
| White | 436,527 (70.4) |
| African American | 56,066 (9.0) |
| Asian/Pacific Islander | 46,977 (7.6) |
| Native American | 1,445 (0.2) |
| Other nonmissing | 69,348 (11.2) |
| Missing/refused/unknown | 9,576 (1.5) |
| Mother’s education, N (%) | |
| Less than high school | 70,886 (10.9) |
| High school/general education degree | 148,094 (22.8) |
| Some college | 144,549 (22.3) |
| Bachelor’s degree | 169,104 (26.0) |
| More | 116,799 (18.0) |
| Kotelchuck index, N (%) | |
| 0 | 10,018 (1.5) |
| 1 | 53,194 (8.2) |
| 2 | 44,822 (6.9) |
| 3 | 307,597 (47.2) |
| 4 | 236,536 (36.3) |
| Prenatal care paid by government, N (%) | 221,331 (34.0) |
| Season of conception, N (%) | |
| Fall | 172,438 (26.4) |
| Spring | 150,379 (23.1) |
| Summer | 167,412 (25.7) |
| Winter | 161,938 (24.8) |
| Maternal diseases and previous birth conditions | |
| Lung, N (%) | 24,683 (3.8) |
| Cardiac, N (%) | 3,793 (0.6) |
| Diabetes, N (%) | 4,221 (0.6) |
| Chronic hypertension, N (%) | 6,932 (1.1) |
| Incompetent cervix, N (%) | 3,053 (0.5) |
| Previous infant with birth defect, N (%) | 1,851 (0.3) |
| Previous infant over 4000 g, N (%) | 3,604 (0.6) |
| Previous infant of small for gestational age, N (%) | 6,120 (0.9) |
| Renal, N (%) | 2,505 (0.4) |
| rH sensitization, N (%) | 14,663 (2.2) |
| Sickle cell. N (%) | 654 (0.1) |
| Community contextual characteristics | |
| Population density, population per square mile, median (range) | 1,508.8 (102.1–12,415.7) |
| Median household income, USD/yr, median (range) | 69,068 (49,956–88,262) |
| Black or African American percent, median (range) | 6% (1%–25%) |
Preterm birth is defined as babies born alive before 37 weeks of pregnancy are completed (https://www.who.int/news-room/fact-sheets/detail/preterm-birth). Kotelchuck index, also called Adequacy of Prenatal Care Utilization (APNCU) Index, is a more accurate and comprehensive set of measures of prenatal care utilization compared with the widely used Kessner index, here 0 = no information, 1 = inadequate, 2 = intermediate, 3 = adequate, 4 = adequate plus; Clinical factors strongly associated with preterm birth: maternal age, smoking, maternal race, maternal education, preexisting lung, cardiac, renal and sickle cell disease, rH sensitization, chronic hypertension, incompetent cervix, fetus small or large for gestational age, and previous delivery with birth defects.