Background
“The evidence suggested that women planning birth in a freestanding midwifery unit had lower rates of instrumental vaginal birth and caesarean section, and therefore higher rates of spontaneous vaginal birth, than women planning birth in an alongside midwifery unit.” ([1], p133)
Methods
Participants and study data
Outcome measures
-
Perinatal outcome: ‘Birthplace primary perinatal outcome’, a composite defined as any of: stillbirth after the start of care in labour, early neonatal death, neonatal encephalopathy, meconium aspiration syndrome, brachial plexus injury, fractured humerus or clavicle.
-
Maternal interventions and outcomes: instrumental delivery (ventouse or forceps delivery); intrapartum caesarean section (CS); third or fourth degree perineal trauma; blood transfusion; admission to a higher level of care; ‘straightforward vaginal birth’, a composite measure defined as birth without intrapartum CS, instrumental delivery, third or fourth degree perineal trauma or blood transfusion. This composite measure aimed to capture birth without complications that might affect future pregnancies.
-
For completeness, we additionally considered the following interventions and outcomes: epidural or spinal analgesia, augmentation with syntocinon, immersion in water for pain relief, episiotomy, active management of the third stage and ‘initiation of breastfeeding’ (baby breastfed at least once). Detailed findings for these outcome measures are reported in the Additional file 1.
Statistical analysis
Results
Maternal characteristics of the study sample
Nulliparous | Multiparous | |||||||
---|---|---|---|---|---|---|---|---|
FMU | AMU | FMU | AMU | |||||
n = 5187 |
n = 8350 |
n = 6078 |
n = 8323 | |||||
n
| % |
n
| % |
n
| % |
n
| % | |
Maternal age
| ||||||||
Mean (SD) | 27.0 | (5.69) | 26.9 | (5.59) | 30.3 | (5.39) | 29.7 | (5.38) |
Under 20 | 578 | 11.2 | 906 | 10.9 | 98 | 1.6 | 158 | 1.9 |
20-24 | 1243 | 24.0 | 2064 | 24.8 | 886 | 14.6 | 1414 | 17.0 |
25-29 | 1538 | 29.7 | 2552 | 30.6 | 1720 | 28.3 | 2442 | 29.4 |
30-34 | 1314 | 25.4 | 2002 | 24.0 | 1930 | 31.8 | 2572 | 31.0 |
35-39 | 460 | 8.9 | 755 | 9.1 | 1230 | 20.3 | 1472 | 17.7 |
40+ | 47 | 0.9 | 56 | 0.7 | 207 | 3.4 | 242 | 2.9 |
Missing | 7 | 15 | 7 | 23 | ||||
Ethnic group
| ||||||||
White | 4779 | 92.2 | 6930 | 83.2 | 5533 | 91.1 | 6523 | 78.5 |
Indian | 46 | 0.9 | 266 | 3.2 | 41 | 0.7 | 243 | 2.9 |
Pakistani | 57 | 1.1 | 180 | 2.2 | 107 | 1.8 | 364 | 4.4 |
Bangladeshi | 42 | 0.8 | 45 | 0.5 | 105 | 1.7 | 85 | 1.0 |
Black Caribbean | 24 | 0.5 | 104 | 1.2 | 24 | 0.4 | 94 | 1.1 |
Black African | 38 | 0.7 | 191 | 2.3 | 56 | 0.9 | 328 | 3.9 |
Mixed | 61 | 1.2 | 143 | 1.7 | 63 | 1.0 | 150 | 1.8 |
Other | 138 | 2.7 | 470 | 5.6 | 146 | 2.4 | 522 | 6.3 |
Missing | 2 | 21 | 3 | 14 | ||||
Understanding of English
| ||||||||
Fluent | 5014 | 96.8 | 7633 | 91.8 | 5896 | 97.3 | 7530 | 90.8 |
Some | 142 | 2.7 | 560 | 6.7 | 131 | 2.2 | 613 | 7.4 |
None | 22 | 0.4 | 126 | 1.5 | 33 | 0.5 | 148 | 1.8 |
Missing | 9 | 31 | 18 | 32 | ||||
Marital/Partner status
| ||||||||
Married/Living together | 4608 | 89.9 | 7241 | 88.0 | 5821 | 96.7 | 7745 | 94.4 |
Single/Unsupported | 519 | 10.1 | 985 | 12.0 | 199 | 3.3 | 461 | 5.6 |
Missing | 60 | 124 | 58 | 117 | ||||
Body mass index (kg/m
2
)
| ||||||||
Mean (SD) | 23.7 | (3.54) | 23.6 | (3.66) | 24.4 | (3.82) | 24.4 | (3.85) |
Not recorded | 889 | 17.2 | 1432 | 17.2 | 972 | 16.0 | 1483 | 17.9 |
10-18.4 | 121 | 2.3 | 243 | 2.9 | 113 | 1.9 | 194 | 2.3 |
18.5-24.9 | 2738 | 52.8 | 4419 | 53.1 | 2858 | 47.1 | 3783 | 45.7 |
25.0-29.9 | 1098 | 21.2 | 1713 | 20.6 | 1550 | 25.5 | 2071 | 25.0 |
30.0-35.0 | 336 | 6.5 | 521 | 6.3 | 575 | 9.5 | 748 | 9.0 |
Missing | 5 | 22 | 10 | 44 | ||||
Index of Multiple Deprivation (IMD) quintiles
| ||||||||
1st Least deprived | 1090 | 21.1 | 1241 | 14.9 | 1405 | 23.2 | 1293 | 15.6 |
2nd | 1180 | 22.8 | 1357 | 16.3 | 1399 | 23.1 | 1281 | 15.4 |
3rd | 1094 | 21.2 | 1687 | 20.3 | 1206 | 19.9 | 1548 | 18.7 |
4th | 965 | 18.7 | 1984 | 23.8 | 1111 | 18.3 | 1860 | 22.4 |
5th Most deprived | 843 | 16.3 | 2058 | 24.7 | 941 | 15.5 | 2316 | 27.9 |
Missing | 15 | 23 | 16 | 25 | ||||
Previous pregnancies > =24 completed weeks
| ||||||||
0 Nulliparous | 5187 | 100.0 | 8350 | 100.0 | N/A | N/A | N/A | N/A |
1 previous | N/A | N/A | N/A | N/A | 3913 | 64.4 | 5621 | 67.5 |
2 previous | N/A | N/A | N/A | N/A | 1513 | 24.9 | 1933 | 23.2 |
3+ previous | N/A | N/A | N/A | N/A | 652 | 10.7 | 769 | 9.2 |
Gestation (completed weeks)
| ||||||||
Mean (SD) | 39.8 | (1.1) | 39.7 | (1.1) | 39.8 | (1.1) | 39.7 | (1.1) |
37 | 149 | 2.9 | 257 | 3.1 | 165 | 2.7 | 216 | 2.6 |
38 | 473 | 9.1 | 798 | 9.6 | 505 | 8.3 | 766 | 9.2 |
39 | 1155 | 22.3 | 1995 | 24.0 | 1512 | 24.9 | 2130 | 25.7 |
40 | 1965 | 38.0 | 3178 | 38.2 | 2392 | 39.4 | 3302 | 39.8 |
41 | 1379 | 26.7 | 1982 | 23.8 | 1439 | 23.7 | 1814 | 21.8 |
42-44 | 51 | 1.0 | 119 | 1.4 | 57 | 0.9 | 76 | 0.9 |
Missing | 15 | 21 | 8 | 19 | ||||
Birthweight (grams)
| ||||||||
Mean (SD) | 3415 | (420.0) | 3405 | (423.2) | 3549 | (439.3) | 3519 | (441.7) |
1000-2499 g | 57 | 1.1 | 109 | 1.3 | 43 | 0.7 | 50 | 0.6 |
2500-2999 g | 725 | 14.0 | 1237 | 14.9 | 597 | 9.8 | 897 | 10.8 |
3000-3499 g | 2265 | 43.7 | 3581 | 43.0 | 2163 | 35.6 | 3171 | 38.2 |
3500-3999 g | 1676 | 32.3 | 2675 | 32.1 | 2342 | 38.6 | 3001 | 36.1 |
4000-4499 g | 417 | 8.0 | 665 | 8.0 | 828 | 13.6 | 1034 | 12.5 |
4500-7500 g | 46 | 0.9 | 56 | 0.7 | 100 | 1.6 | 149 | 1.8 |
Missing | 1 | 27 | 5 | 21 |
Nulliparous | Multiparous | |||||||
---|---|---|---|---|---|---|---|---|
FMU | AMU | FMU | AMU | |||||
n = 5187 |
n = 8350 |
n = 6078 |
n = 8323 | |||||
n
| % |
n
| % |
n
| % |
n
| % | |
Prolonged rupture of membranes (>18 h) | 143 | 2.8 | 260 | 3.1 | 87 | 1.4 | 122 | 1.5 |
Meconium stained liquor | 77 | 1.5 | 134 | 1.6 | 63 | 1.0 | 99 | 1.2 |
Proteinuria (1+ or more) | 75 | 1.4 | 227 | 2.7 | 35 | 0.6 | 142 | 1.7 |
Hypertension | 46 | 0.9 | 77 | 0.9 | 31 | 0.5 | 36 | 0.4 |
Abnormal vaginal bleeding | 12 | 0.2 | 29 | 0.3 | 10 | 0.2 | 8 | 0.1 |
Non-cephalic presentation | 14 | 0.3 | 18 | 0.2 | 10 | 0.2 | 11 | 0.1 |
Abnormal fetal heart rate | 37 | 0.7 | 40 | 0.5 | 15 | 0.2 | 25 | 0.3 |
Other | 9 | 0.2 | 8 | 0.1 | 8 | 0.1 | 9 | 0.1 |
One or more complicating conditions
| 368 | 7.1 | 723 | 8.7 | 251 | 4.1 | 431 | 5.2 |
Incidence
Nulliparous | Multiparous | |||
---|---|---|---|---|
FMU | AMU | FMU | AMU | |
Adverse perinatal outcome
|
n/1000 (95% CI)
|
n/1000 (95% CI)
|
n/1000 (95% CI)
|
n/1000 (95% CI)
|
‘Birthplace primary perinatal outcome’ | 4.5 | 4.7 | 2.7 | 2.4 |
(2.8-7.1) | (3.1-7.2) | (1.6-4.6) | (1.4-4.3) | |
Maternal interventions and adverse outcomes
|
% (99% CI)
|
% (99% CI)
|
% (99% CI)
|
% (99% CI)
|
‘Straightforward vaginal birth’ | 78.8 | 71.5 | 97.0 | 94.6 |
(75.9-81.5) | (68.1-74.7) | (96.3-97.6) | (93.3-95.6) | |
Instrumental delivery (ventouse or forceps) | 10.8 | 16.3 | 1.1 | 2.5 |
(8.7-13.3) | (13.9-19.1) | (0.7-1.6) | (1.9-3.3) | |
Intrapartum caesarean section | 6.7 | 7.7 | 0.7 | 1.0 |
(5.5-8.1) | (6.3-9.3) | (0.5-1.1) | (0.7-1.5) | |
Third or fourth degree perineal trauma | 4.0 | 4.9 | 0.9 | 1.6 |
(3.1-5.1) | (4.0-6.0) | (0.6-1.4) | (1.2-2.1) | |
Blood transfusion | 0.8 | 1.3 | 0.3 | 0.6 |
(0.5-1.1) | (0.9-1.7) | (0.2-0.6) | (0.4-0.8) | |
Maternal admission for higher level care | 0.2 | 1.0 | 0.1 | 0.4 |
(0.1-0.5) | (0.4-2.8) | (0.0-0.3) | (0.2-0.7) |
Outcomes in nulliparous women
Nulliparous | Multiparous | |||||
---|---|---|---|---|---|---|
Perinatal outcome
|
Adjusted OR
|
95% CI
|
p value |
Adjusted OR
|
95% CI
|
p value |
‘Birthplace primary perinatal outcome’ | 0.96 | (0.51-1.82) | 0.907 | 1.14 | (0.52-2.50) | 0.745 |
Maternal outcomes
|
Adjusted OR
|
99% CI
|
p value |
Adjusted OR
|
99% CI
|
p value |
‘Straightforward vaginal birth’ | 1.47 | (1.17-1.85) | <0.001** | 1.86 | (1.35-2.57) | <0.001** |
Instrumental delivery (ventouse or forceps) | 0.63 | (0.46-0.86) | <0.001** | 0.41 | (0.25-0.68) | <0.001** |
Intrapartum caesarean section | 0.84 | (0.63-1.14) | 0.147 | 0.75 | (0.41-1.38) | 0.224 |
Third or fourth degree perineal trauma | 0.82 | (0.59-1.15) | 0.129 | 0.60 | (0.36-1.00) | 0.010** |
Blood transfusion | 0.71 | (0.44-1.14) | 0.063 | 0.56 | (0.26-1.21) | 0.052 |
Maternal admission for higher level care | 0.28 | (0.07-1.10) | 0.016* | 0.30 | (0.07-1.20) | 0.025* |