Cohort Studies | |||||||
---|---|---|---|---|---|---|---|
First author, publication year | Age at first birth | No. in cohort | No. study outcomes N (%) | Point estimate (+CI) a Base model | Point estimate (+CI) a Final model | Adjusted for or matched on. If underlined, also adjusted in base model. | Notes on study considerations and limitations. |
Colditz 1987 [26] | <19 | 6671 b | 3 (0.004) |  | 1.3 (0.4–4.3) | c D: age; SE: - BM: - HB: - R: - | Very few events in the exposure category of <19. Short follow-up in a relatively young age group. |
20–22 | 145,708 | 42 (0.029) | 0.9 (0.6–1.2) | ||||
23–25 | 257,170 | 108 (0.042) | 1 (ref) | ||||
26–29 | 151,206 | 82 (0.54) | 1.1 (0.8–1.5) | ||||
≥ 30 | 77,091 | 35 (0.045) | 0.8 (0.5–1.2) | ||||
Cooper 1999 [27] | 15–24 | 7996 b | 8 (0.100) |  | 1.29 (0.5–3.0) | D: age; SE: - BM: - HB: - R: - | Number of outcomes very low in all exposure categories |
25–29 | 17,698 | 14 (0.079) | 1 (ref) | ||||
30–32 | 5341 | 3 (0.056) | 0.71 (0.2–2.5) | ||||
33–43 | 3715 | 8 (0.215) | 2.9 (1.2–6.9) | ||||
Otterblad- Olausson 2004 (CVD) [9] | <20 | 60,686 | 41 (0.07) | 2.2 (1.5–3.1) | 1.8 (1.2–2.6) | D: age; SE: background SES in 1960 (parents), socio-economic position (‘90), family situation (‘90), welfare dependency (‘90) BM: - HB: - R: Parity | Conducted amongst women aged 30–45, follow-up time of 5 years, resulting in low number of events. Some women still having children. |
20–29 | 399,748 | 110 (0.03) | 1 (ref) | 1 (ref) d | |||
Otterblad- Olausson 2004 (CHD) [9] | <20 | 60,686 | Data not | 2.8 (1.5–5.4) | 2.2 (1.2–4.3) | ||
20–29 | 399,748 | provided | 1 (ref) | 1 (ref) d | |||
Otterblad- Olausson 2004 (CeVD) [9] | <20 | 60,686 | Data not | 1.5 (0.8–2.9) | 1.4 (0.7–2.7) | ||
20–29 | 399,748 | provided | 1 (ref) | 1 (ref) d | |||
Yang CY 2006 | <26 | 859,942 | 102 (0.012) | 1 (ref) | Â | D: - SE: - BM: - HB: - R: Parity | No adjustment for participant age is reported (while due to study set-up women with older age at first birth were older at follow-up). Cut-off for youngest group <26 |
26–30 | 372,895 | 70 (0.019) | 1.78 (1.3–2.4) | ||||
≥ 31 | 59,625 | 17 (0.029) | 2.96 (1.8–5.0) | ||||
Continuous |  |  | 1.10 (1.06–1.1) | 1.08 (1.04–1.1) | |||
Henretta 2007 Heart disease [30] | <20 | 991 | Data not provided |  | 0.36 (P:<.01) | D: age, race, US-born, unmarried at first birth, marital status; SE: Father’s education, education, log net worth, log income; BM: - HB: - R: Birth >39, birth interval, parity | No information on the number of outcomes per exposure group; no confidence intervals |
≥ 20 | 2956 | ||||||
Henretta 2007 Stroke [30] | <20 | 991 | Data not provided |  | −.03 P-value or CI not provided | ||
≥ 20 | 2956 | ||||||
Sakauchi 2007 CHD [36] | <23 | Data not provided | 121 |  | 1.09 (0.8–1.5) | D: age, study area; SE: - BM: - HB: - R: - | No denominator information provided |
23–25 | 116 | 1 (ref) | |||||
≥ 26 | 131 | 1.17 (0.9–1.5) | |||||
Sakauchi 2007 (CeVD) [36] | <23 | Data not provided | 291 |  | 1.19 (0.99–1.4) | ||
23–25 | 294 | 1 (ref) | |||||
≥ 26 | 326 | 1.07 (0.9–1.3) | |||||
Yang L 2009, Ischemic stroke [39] | <23 | 11,942 | 68 (0.57) | 1.1 (0.7–1.5) | 1.0 (0.6–1.5) | D: age; SE: education; BM: BMI, high blood pressure, DM; HB: alcohol, smoking, physical activity; R: - | Young age at first birth category not compared to lowest risk category. Few cases for hemorrhagic stroke. |
21–25 | 9905 | 49 (0.49) | 1 (ref) | 1 (ref) | |||
≥ 26 | 17,444 | 48 (0.28) | 0.6 (0.4–0.9) | 0.7 (0.4–1.1) | |||
Yang L | <21 | 11,942 | 28 (0.23) | 2.0 (1–4) | 1.8 (0.8–4.1) | ||
2009 hemorrhagic stroke | 21–25 | 9905 | 11 (0.11) | 1 (ref) | 1 (ref) |  |  |
≥ 26 | 17,444 | 19 (0.11) | 1.1 (0.5–2.3) | 1.2 (0.5–2.6) | |||
Grundy 2010 [29] Women | <20 | 862,007 b | 572 (0.07) | 1.47 (1.3–1.6) | 1.22 (1.1–1.3) | D: age, year, region residence, log population size, marital status; SE: level of education; BM: - HB: - R: parity |  |
20–24 | 3,200,462 | 1567 (0.05) | 1 (ref) | 1 (ref) | |||
25–29 | 1,670,417 | 574 (0.03) | 0.67 (0.6–0.7) | 0.81 (0.7–0.9) | |||
≥ 30 | 646,983 | 224 (0.03) | 0.60 (0.5–0.7) | 0.78 (0.7–0.9) | |||
Grundy 2010 Men [29] | <23 | 1,164,183 b | 2190 (0.19) | 1.39 (1.3–1.5) | 1.23 (1.2–1.3) | ||
23–28 | 3,238,174 | 4804 (0.15) | 1 (ref) | 1 (ref) | |||
29–34 | 1,313,342 | 1772 (0.13) | 0.88 (0.8–0.9) | 0.93 (0.9–0.99) | |||
≥ 35 | 473,472 | 571 (0.12) | 0.87 (0.8–0.95) | 0.93 (0.9–1.01) | |||
Chang 2011 CVD [25] | 15–19 | 844 | 144 (17.1) | 1.00 (ref) | 1.00 (ref) d | D: age at entry; SE: education, occupation; BM: BMI, HT HB: drinking, smoking R: - For CVD there was a mention of a fourth model in which the authors additionally corrected for reproductive variables and marital status, which did not change the findings. | Extensive adjustment in final model. Few CHD events. |
20–22 | 1646 | 230 (14.0) | 0.74 (0.6–0.9) | 0.74 (0.6–0.9) | |||
≥ 23 | 787 | 104 (13.2) | 0.75 (0.6–0.96) | 0.76 (0.6–0.98) | |||
Chang 2011 CHD [25] | 15–19 | 844 | 12 (1.42) | 1.00 (ref) | 1.00 (ref) d | ||
20–22 | 1646 | 24 (1.46) | 0.88 (0.4–1.8) | 0.89 (0.4–1.8) | |||
≥ 23 | 787 | 11 (1.40) | 0.93 (0.4–2.1) | 0.90 (0.4–2.1) | |||
Chang 2011 Stroke [25] | 15–19 | 844 | 87 (10.3) | 1.00 (ref) | 1.00 (ref) d | ||
20–22 | 1646 | 142 (8.6) | 0.76 (0.6–0.99) | 0.78 (0.6–1.02) | |||
≥ 23 | 787 | 68 (8.6) | 0.80 (0.6–1.1) | 0.84 (0.6–1.2) | |||
Gallagher 2011 CHD [28] | <20 | 12,460 | 43 (0.35) |  | 0.93 (0.7–1.3) | D: age; SE: - BM: - HB: - R: - | Young age at first birth category not compared to lowest risk category. |
20–24 | 72,570 | 239 (0.33) | 1 (ref) | ||||
25–29 | 124,044 | 101 (0.08) | 0.75 (0.6–0.95) | ||||
≥ 30 | 45,041 | 37 (0.08) | 0.85 (0.6–1.2) | ||||
Gallagher 2011 Ischemic stroke [28] | <20 | 12,460 | 75 (0.60) |  | 1.23 (0.96–1.6) | ||
20–24 | 72,570 | 309 (0.43) | 1 (ref) | ||||
25–29 | 124,044 | 141 (0.11) | 0.88 (0.7–1.1) | ||||
≥ 30 | 45,041 | 50 (0.11) | 0.95 (0.7–1.3) | ||||
Gallagher 2011 Hemorrhagic Stroke [28] | <20 | 12,460 | 178 (1.43) |  | 1.09 (0.9–1.3) | ||
20–24 | 72,570 | 850 (1.17) | 1 (ref) | ||||
25–29 | 124,044 | 423 (0.34) | 0.84 (0.7–0.9) | ||||
≥ 30 | 45,041 | 132 (0.29) | 0.81 (0.7–0.97) | ||||
Webb 2011 [10] | N/A | 1,021,417 b | 46 (0.0045) | Â | 1 (ref) | D: age, decade; SE: - BM: - HB: - R: - | Few events in <20 category. Nulliparous group includes young women who did not have children yet. |
<20 | 159,716 | 16 (0.0100) | 1.25 (0.7–2.2) | ||||
≥ 20 | 732,462 | 71 (0.0097) | 0.93 (0.6–1.4) | ||||
<20 | 159,716 | 16 (0.0100) | 1.35 (0.8–2.3) | ||||
≥ 20 | 732,462 | 71 (0.0097) | 1 (ref) | ||||
Merritt 2015 (FTP) (CVD) [32] | <21 | 39,201 | 304 (0.78) |  | 1.15 (0.99–1.3) | D: age, site; SE: education; BM: BMI; HB: physical activity, smoking (duration and intensity); R: menopausal status. | Extensive adjustment in final model and no unadjusted model for comparison. |
21–23 | 71,322 | 497 (0.70) | 1.11 (0.98–1.3) | ||||
24–25 | 52,056 | 359 (0.69) | 1.05 (0.9–1.2) | ||||
26–30 | 75,927 | 557 (0.73) | 1 (ref) | ||||
≥ 31 | 27,027 | 237 (0.88) | 1.06 (0.9–1.2) | ||||
Merritt 2015 (FTP) (CeVD) [32] | <21 | 39,201 | 97 (0.25) |  | 1.14 (0.9–1.5) | ||
21–23 | 71,322 | 150 (0.21) | 0.96 (0.8–1.2) | ||||
24–25 | 52,056 | 122 (0.23) | 1 (ref) | ||||
26–30 | 75,927 | 199 (0.26) | 0.97 (0.8–1.2) | ||||
≥ 31 | 27,027 | 79 (0.29) | 0.90 (0.7–1.2) | ||||
Merritt 2015 (FTP) (CHD) [32] | <21 | 39,201 | 105 (0.27) |  | 1.14 (0.9–1.5) | ||
21–23 | 71,322 | 140 (0.20) | 0.96 (0.7–1.2) | ||||
24–25 | 52,056 | 106 (0.20) | 1 (ref) | ||||
26–30 | 75,927 | 166 (0.22) | 0.99 (0.8–1.3) | ||||
≥ 31 | 27,027 | 74 (0.27) | 1.10 (0.8–1.5) | ||||
Barclay 2016 Women [22] | 15–19 | 2998 | 1148 (38.3) | 1.18 (1.1–1.3) | 1.25 (1.1–1.4) | D: birth cohort [2]; SE: (sibling fixed effect model) age of person’s mother at time of their own birth, attained socioeconomic status, educational attainment, marital status; BM: - HB: - R: Completed parity |  |
20–24 | 5232 | 1894 (36.2) | 1.11 (1.02–1.2) | 1.23 (1.1–1.4) | |||
25–29 | 3052 | 1022 (33.5) | 1 (ref) | 1 (ref) | |||
30–34 | 1010 | 322 (31.9) | 0.94 (0.8–1.1) | 0.89 (0.7–1.1) | |||
35+ | 343 | 120 (35.0) | 1.14 (0.9–1.4) | 1.09 (0.8–1.5) | |||
Barclay 2016 Men [22] | 15–19 | 1469 | 661 (45.0) | 1.45 (1.3–1.6) | 1.37 (1.2–1.6) | ||
20–24 | 9380 | 3595 (38.3) | 1.11 (1.1–1.2) | 1.10 (1.03–1.2) | |||
25–29 | 9533 | 3395 (35.6) | 1 (ref) | 1 (ref) | |||
30–34 | 4590 | 1623 (35.4) | 0.98 (0.9–1.04) | 1.03 (0.9–1.1) | |||
35+ | 2211 | 793 (35.9) | 0.98 (0.9–1.1) | 0.97 (0.9–1.1) | |||
Parikh 2016 [35] | Nullipara | 10,462 | Data not provided. Total cases: 4607 |  | 1.00 (0.9–1.1) | D: age at enrollment; SE: income, education, neighborhood SES variables; BM: history of high cholesterol requiring pills, hypertension, diabetes; HB: smoking; nr of still births, nr of miscarriages, breastfed for >1 month | Extensive adjustment in final model |
<20 | 8780 | 1.65 (1.5–1.8) | 1.27 (1.1–1.4) | ||||
20–24 | 29,803 | 1.25 (1.2–1.4) | 1.14 (1.1–1.2) | ||||
≥ 25 | 23,937 | 1 (ref) | 1 (ref) |