Table 1.
Characteristics of records in the HES mother-baby cohort according to linkage status derived from gold standard data
| True matches (N = 71884) |
False matches (N = 636) |
St. diff. | Missed matches (N = 297) |
St. diff. | |||||
|---|---|---|---|---|---|---|---|---|---|
| N | % | N | % | N | % | ||||
| Stillbirth | 325 | 0.5 | 6 | 0.9 | 0.1 | 9 | 3.0 | 0.2 | |
| Survival to postnatal discharge | 71384 | 99.1 | 627 | 98.1 | 0.1 | 286 | 96.3 | 0.2 | |
| Delivery risk factora | 6738 | 9.4 | 105 | 16.4 | 0.2 | 49 | 16.5 | 0.2 | |
| Female infant | 34967 | 48.7 | 321 | 50.2 | 0.0 | 140 | 47.1 | 0.0 | |
| Multiple birth | 1961 | 2.7 | 126 | 19.7 | 0.6 | 31 | 10.4 | 0.3 | |
| Caesarean section | 18034 | 25.1 | 63 | 9.9 | 0.4 | 10 | 3.4 | 0.7 | |
| Pregnancy risk factorb | 7388 | 10.3 | 16 | 2.5 | 0.3 | 1 | 0.3 | 0.5 | |
| Neonatal medical conditionc | 6281 | 8.7 | 91 | 14.2 | 0.2 | 90 | 30.3 | 0.6 | |
| Neonatal ICU | 8461 | 11.8 | 32 | 5.0 | 0.2 | 33 | 11.1 | 0.0 | |
| Parity: nulliparous | 27125 | 37.7 | 335 | 52.4 | 0.3 | 192 | 64.5 | 0.6 | |
| Gestational age group | Full term (39+ wks) | 45611 | 72.3 | 102 | 44.4 | 0.7 | 27 | 44.3 | 0.7 |
| Early term (37–38 wks) | 12721 | 20.2 | 66 | 28.7 | 17 | 27.9 | |||
| Late preterm (34–36 wks) | 3280 | 5.2 | 39 | 17.0 | 6 | 9.8 | |||
| Moderate/very preterm (< 34 wks) | 1494 | 2.4 | 23 | 10.0 | 11 | 18.0 | |||
| Missing* | 8775 | 12.2 | 409 | 64.0 | 236 | 79.5 | |||
| Birthweight (g) | < 1500 | 909 | 1.4 | 14 | 6.1 | 0.7 | 7 | 10.9 | 0.7 |
| 1500–< 2500 | 1798 | 6.0 | 45 | 19.7 | 12 | 18.8 | |||
| 2500–< 4000 | 51718 | 82.0 | 160 | 69.9 | 42 | 65.6 | |||
| 4000+ | 6687 | 10.6 | 10 | 4.4 | 3 | 4.7 | |||
| Missing* | 8769 | 12.2 | 410 | 64.2 | 233 | 78.5 | |||
| Size for gestation | Small (< 10th percentile) | 5274 | 8.4 | 25 | 11.1 | 0.2 | 5 | 8.3 | 0.1 |
| Normal | 54367 | 81.6 | 187 | 93.1 | 51 | 85.0 | |||
| Large (> 10th percentile) | 6344 | 10.1 | 13 | 5.8 | 4 | 6.7 | |||
| Missing* | 8896 | 12.4 | 414 | 64.8 | 237 | 79.8 | |||
| Ethnicity | White | 48896 | 68.0 | 408 | 63.9 | 0.3 | 165 | 55.6 | 0.4 |
| Mixed | 3410 | 4.7 | 24 | 3.8 | 14 | 4.7 | |||
| Asian | 7367 | 10.3 | 49 | 7.7 | 20 | 6.7 | |||
| Black | 4866 | 6.8 | 32 | 5.0 | 25 | 8.4 | |||
| Other | 4508 | 6.3 | 77 | 12.1 | 38 | 12.8 | |||
| Unknown | 2834 | 3.9 | 49 | 7.7 | 35 | 11.8 | |||
| Newborn length of stay (days) | < 2 | 38329 | 53.3 | 315 | 49.3 | 0.2 | 131 | 44.1 | 0.7 |
| 2–6 | 28946 | 40.3 | 244 | 38.2 | 74 | 24.9 | |||
| 7+ | 4599 | 6.4 | 80 | 12.5 | 92 | 31.0 | |||
| Maternal age (years) | < 20 | 2859 | 4.0 | 21 | 3.3 | 0.1 | 13 | 4.4 | 0.2 |
| 20–24 | 11752 | 16.4 | 88 | 13.8 | 42 | 14.1 | |||
| 25–29 | 19226 | 26.8 | 155 | 24.3 | 55 | 18.5 | |||
| 30–34 | 22377 | 31.1 | 220 | 34.4 | 101 | 34.0 | |||
| 35–39 | 12433 | 17.3 | 125 | 19.6 | 64 | 21.6 | |||
| 40+ | 3234 | 4.5 | 30 | 4.7 | 22 | 7.4 | |||
| Income/deprivation quintiled | Most deprived | 27042 | 37.7 | 206 | 32.3 | 0.1 | 97 | 32.9 | 0.2 |
| 2 | 16394 | 22.9 | 170 | 26.7 | 86 | 29.2 | |||
| 3 | 13104 | 18.3 | 129 | 20.3 | 58 | 19.7 | |||
| 4 | 9040 | 12.6 | 77 | 12.1 | 37 | 12.5 | |||
| Most affluent | 6146 | 8.6 | 55 | 8.6 | 17 | 5.8 | |||
| Missing* | 155 | 0.2 | 2 | 0.3 | 2 | 0.7 | |||
0.2, 0.5, and 0.8 can be considered as small, medium and large effect sizes respectively.
St. diff, standardized differences; ICU, intensive care unit; wks, weeks.
aHypoxia, amniotic fluid embolism, placental-transfusion syndrome, umbilical cord prolapse, chorioamnionitis, fetal haemorrhage, birth trauma, complications of delivery, umbilical cord problem.
bEclampsia, gestational hypertension, diabetes, placental abruption or infarction.
cCongenital anomaly, perinatal infection, neonatal abstinence syndrome, respiratory distress syndrome.
dQuintiles of deprivation were derived from the Index of Multiple Deprivation (IMD) score based on patient postcode in HES.
*Percentage of records with missing data (excluded from other category percentages).