Table 6. Birth weight percentiles in relation to different GA estimates among singleton stillbirths.
| Birth Weight Norms and Percentiles | Stillbirths | Live Births | Using Percentiles Based on GA at Delivery | |||
| GA at Death | GA at Delivery Minus 2 d | GA at Delivery | Crude OR for SB (95% CI)a | Adjusted OR for SB (95% CI)b | ||
| Weighted sample size, number c | 528 | 561 | 570 | 1,382 | ||
| Individualized norms, percent d | ||||||
| <5th percentile | 33 | 44 | 48 | 9 | 11.25 (8.62–14.67) | 11.27 (8.40–15.12) |
| 5th–<10th | 8 | 6 | 6 | 6 | 2.04 (1.33–3.14) | 2.22 (1.36–3.62) |
| 10th–90th | 42 | 37 | 35 | 72 | Reference | Reference |
| >90th–95th | 4 | 3 | 2 | 5 | 0.87 (0.48–1.55) | 1.02 (0.55–1.87) |
| >95th | 13 | 11 | 8 | 7 | 2.48 (1.69–3.64) | 2.15 (1.40–3.29) |
| <10th | 41 | 50 | 54 | 15 | 7.34 (5.77–9.33) | 7.70 (5.91–10.04) |
| >90th | 17 | 14 | 11 | 12 | 1.79 (1.28–2.49) | 1.68 (1.16–2.42) |
| Ultrasound norms, percent e | ||||||
| <5th percentile | 36 | 45 | 51 | 10 | 11.34 (8.79–14.63) | 10.79 (8.11–14.35) |
| 5th–<10th | 9 | 8 | 7 | 7 | 2.17 (1.43–3.31) | 2.24 (1.41–3.57) |
| 10th–90th | 43 | 38 | 34 | 77 | Reference | Reference |
| >90th–95th | 4 | 2 | 2 | 3 | 1.62 (0.83–3.18) | 1.56 (0.76–3.19) |
| >95th | 8 | 7 | 5 | 3 | 3.87 (2.37–6.34) | 2.98 (1.73–5.12) |
| <10th | 45 | 53 | 58 | 17 | 7.58 (6.01–9.57) | 7.53 (5.80–9.78) |
| >90th | 12 | 9 | 8 | 6 | 2.79 (1.86–4.19) | 2.31 (1.48–3.61) |
| Population norms, percent f | ||||||
| <5th percentile | 12 | 23 | 25 | 4 | 8.98 (6.36–12.68) | 9.20 (6.33–13.39) |
| 5th–<10th | 9 | 9 | 9 | 4 | 3.10 (2.06–4.66) | 2.90 (1.78–4.72) |
| 10th–90th | 75 | 65 | 63 | 84 | Reference | Reference |
| >90th–95th | 2 | 1 | <1 | 4 | 0.34 (0.13–0.89) | 0.53 (0.19–1.45) |
| >95th | 3 | 2 | 2 | 4 | 0.67 (0.36–1.25) | 0.62 (0.34–1.15) |
| <10th | 20 | 31 | 34 | 8 | 6.01 (4.59–7.88) | 6.02 (4.44–8.16) |
| >90th | 4 | 4 | 3 | 8 | 0.53 (0.31–0.89) | 0.58 (0.34–1.01) |
Birth weight percentiles for stillbirths ≥20 wk gestation using three GA estimates: GA at delivery, GA at delivery minus 2 d, and GA at death estimated using the SCRN algorithm [17]. Percentages may add to slightly more or less than 100% because of rounding.
Unadjusted OR for stillbirth for infants with birth weight in the percentile group shown compared to infants in the reference group from a logistic regression model that included effects for percentile group only.
Adjusted OR for stillbirth for infants with birth weight in the percentile group shown compared to infants in the reference group from a logistic regression model that in addition to the percentile group indicators included study site number; paternal age (<20, 20–34, 35–39, ≥40 y); the following maternal variables (categorized as shown in Table 1 or as noted): maternal age (<20, 20–34, 35–39, ≥40 y), race/ethnicity, education, marital status, insurance, family income, smoking during the 3 mo prior to pregnancy, alcohol use during the 3 mo prior to pregnancy, drug use, BMI, blood type, Rh factor, pregestational hypertension, pregestational diabetes, seizure disorder, and pregnancy history; and infant sex.
Analysis weights that accounted for the basic study design plus other aspects of the sampling were used.
Unweighted sample sizes were 527, 561, and 570 stillbirths for GA at death, GA at delivery minus 2 d, and GA at delivery, respectively, and 1,821 live births. Unweighted (weighted) sample sizes included in computation of adjusted ORs were 491 (489) stillbirths and 1,665 (1,261) live births.
Individualized norm percentiles were derived using the fetal weight for GA equation from Bukowski et al. [15].
Ultrasound norm percentiles were derived using the fetal weight for GA equation and standard error from Hadlock et al. [19].
Alexander et al. population norm percentiles of birth weight for GA were used [18].
Simple linear interpolation was used with the Alexander et al. birth weight percentiles reported for completed weeks of GA in whole weeks to derive birth weight percentiles for GA in weeks and days.