Introduction
While the majority of Aboriginal and Torres Strait Islander (hereafter respectfully called Aboriginal) mothers and babies have positive pregnancy and birth outcomes, national data continue to show disproportionate adverse outcomes for Aboriginal compared to non-Aboriginal Australians [
1]. Aboriginal infants have almost twice the rate of low birth weight, preterm birth and perinatal mortality as non-Aboriginal infants [
1]. Poor perinatal health is associated with subsequent development and health [
2‐
4]. To drive improvements, the Coalition of Aboriginal and Torres Strait Islander Peak Organisations and Australian state and federal governments recently set a new Closing the Gap outcome – “Children are born healthy and strong” – with a target of 91% of Aboriginal liveborn singletons having a healthy birth weight by 2031 [
5].
Notably, this new Closing the Gap target excludes multiple births. However, Aboriginal twins and higher multiples may be a particularly high-risk group. Studies in non-Aboriginal populations report that serious complications are more common in multifetal pregnancies than singletons, including anaemia, pre-eclampsia and possibly gestational diabetes, and complications such as twin-to-twin transfusion syndrome are unique to multiple pregnancies with monochorionicity [
6,
7]. Multiples are also much more likely than singletons to have adverse birth outcomes such as preterm birth, low birth weight, perinatal mortality and postnatal morbidity [
8‐
10]. Specifically, perinatal mortality rates are approximately 3-times higher in twins and 12-times higher in higher-order multiples than singletons [
1]. Given these differences, guidelines recommend heightened monitoring of multifetal pregnancies and access to specialist medical care during birth [
11,
12].
Multiples account for approximately 3% of babies born each year in Australia [
1] yet there is little epidemiological information available on Aboriginal multifetal pregnancies and births. Australia’s annual report on pregnancies and births does not separately report on Aboriginal multiples and researchers frequently exclude multiples from analyses [
1,
13]. Knowledge of these pregnancies and births is needed to inform the health service response to a population group at high risk of experiencing adverse outcomes. Many Aboriginal mothers live in remote and low socioeconomic status areas, far from the hospitals that provide specialist obstetric and infant care, including neonatal intensive care units (NICUs). For example, all NICUs in the state of Western Australia (WA) are located in Perth, more than 1500 km from the state’s northern-most region, the Kimberley, where 22% of Aboriginal mothers live (and 1% of non-Aboriginal mothers) [
14]. Furthermore, delayed and less frequent antenatal care is more common among women who experience socioeconomic deprivation or live in remote areas [
8].
This paper aims to fill the gap in knowledge of Aboriginal twins by describing the pregnancies, births and perinatal outcomes for all Aboriginal twins born in WA from 2000 to 2013 and New South Wales (NSW) from 2002 to 2008 using linked administrative data, alongside data on Aboriginal singletons in both states and non-Aboriginal births in NSW.
Results
The WA cohort consisted of 33,229 Aboriginal singletons, 880 twins and 18 triplets. In NSW, there were 31,524 Aboriginal singletons, 794 twins, 30 triplets and 4 quadruplets and 582,355 non-Aboriginal singletons, 18,338 twins, 516 triplets and 24 quadruplets. Multiples made up 2.6% of the Aboriginal babies in WA and NSW and 3.1% of the non-Aboriginal babies in NSW.
Demographic characteristics
Mothers of twins were at least 1 year older, on average, than mothers of singletons for each of the three groups: Aboriginal WA births, Aboriginal NSW births and non-Aboriginal NSW births (Table
1). For Aboriginal births, nulliparity was less common among mothers of twins than mothers of singletons (WA twins: 27% nulliparous, WA singletons: 32%, NSW twins: 28%, NSW singletons: 35%), but for non-Aboriginal NSW infants, nulliparity was similar among mothers of twins and singletons (twins: 44%, singletons: 42%). Compared to mothers of singletons, the proportions of mothers of twins living in the most advantaged areas and major cities were 1 to 3 percentage points higher for both Aboriginal and non-Aboriginal births.
Table 1
Demographics of Western Australian (2000–2013) and New South Wales’ (2002–2008) births by plurality and Aboriginality
Groups compared and statistical significance reported1 | A | A | B | B | C | C |
| | D | | D | |
Maternal characteristics |
Age (mean (SD)) | 26.6 (5.9) | 24.9 (6.0) | 27.5 (6.2) | 25.7 (6.2) | 31.5 (5.2) | 30.1 (5.5) |
Age group ABCD |
< 20 | 112 (13) | 6909 (21) | 75 (9) | 5616 (18) | 268 (1) | 17,969 (3) |
20–24 | 232 (26) | 10,561 (32) | 217 (27) | 9537 (30) | 1610 (9) | 79,062 (14) |
25–29 | 282 (32) | 8165 (25) | 208 (26) | 7662 (24) | 4256 (23) | 160,857 (28) |
30–34 | 156 (18) | 5026 (15) | 164 (21) | 5609 (18) | 6893 (38)2 | 198,560 (34) |
35+ | 98 (11) | 2560 (8) | 130 (16) | 3082 (10) | 5307 (29)2 | 125,749 (22) |
Parity (mean (SD)) | 1.9 (1.9) | 1.7 (1.8) | 1.8 (1.8) | 1.5 (1.7) | 0.9 (1.2) | 1.0 (1.1) |
Parity group ABCD |
0 | 234 (27) | 10,773 (32) | 224 (28) | 11,058 (35) | 8120 (44) | 244,868 (42) |
1 | 220 (25) | 8352 (25) | 206 (26) | 8370 (27) | 6003 (33)2 | 197,772 (34) |
2+ | 426 (48) | 14,104 (42) | 364 (46) | 12,024 (38) | 4181 (23)2 | 138,629 (24) |
Previous multiple birthA | 26 (3) | 465 (1) | – | – | – | – |
Insurance at time of birtha | 64 (7) | 1621 (5) | – | – | – | – |
Socioeconomic disadvantageBCD |
Quintile 1 (most advantaged) | 64 (7) | 1946 (6) | 56 (7) | 1246 (4) | 4489 (25) | 125,066 (22) |
Quintile 2 | 82 (9) | 3083 (9) | 74 (9) | 2877 (9) | 3059 (17) | 93,835 (16) |
Quintile 3 | 156 (18) | 5249 (16) | 166 (21) | 5906 (19) | 3639 (20)2 | 115,981 (20) |
Quintile 4 | 182 (21) | 7612 (23) | 278 (35) | 12,240 (39) | 4115 (23)2 | 138,903 (24) |
Quintile 5 (most disadvantaged) | 390 (45) | 14,778 (45) | 214 (27) | 8982 (29) | 2884 (16) | 103,054 (18) |
Remoteness of residenceabCD |
Major cities | 394 (45) | 14,004 (42) | 386 (49) | 14,410 (46) | 14,702 (81) | 456,767 (79) |
Inner regional | 66 (8) | 2131 (6) | 256 (32) | 10,052 (32) | 2671 (15)2 | 91,304 (16) |
Outer regional | 128 (15) | 5272 (16) | 120 (15) | 5436 (17) | 761 (4)2 | 26,874 (5) |
Remote | 168 (19) | 6187 (19) | 20 (3) | 1217 (4) | 52 (< 1) | 1806 (< 1) |
Very remote | 124 (14) | 5585 (17) | 6 (1) | 136 (< 1) | 0 (0) | 88 (< 1) |
Infant characteristics |
SexC |
Male | 450 (51) | 16,823 (51) | 404 (51) | 16,169 (51) | 9190 (50) | 299,820 (51) |
Female | 430 (49) | 16,404 (49) | 390 (49) | 15,350 (49) | 9146 (50) | 282,499 (49) |
Same sex twin3 | 648 (74) | – | 546 (69) | – | 12,252 (67) | – |
Comparing mothers of Aboriginal twins and non-Aboriginal twins, mothers of Aboriginal twins from both states were at least 4 years younger than mothers of non-Aboriginal twins from NSW and they resided in more remote and disadvantaged areas.
Maternal health and pregnancy complications
Antenatal care in the first trimester was more common for twin pregnancies than singleton pregnancies for both Aboriginal and non-Aboriginal pregnancies (Table
2). The prevalence of pre-existing conditions was similar for mothers of twins and singletons. Gestational diabetes was also similar at 5% for mothers of WA Aboriginal singletons and twins, 4% for NSW Aboriginal singletons and twins, and 5% for NSW non-Aboriginal singletons and 6% for non-Aboriginal twins. When both hospital and birth records were used to ascertain gestational diabetes among the NSW 2009/2012 school starters, the proportion of women diagnosed with gestational diabetes was two percentage points higher for twin pregnancies compared to singleton pregnancies (Aboriginal twins: 6%, Aboriginal singletons: 4%, non-Aboriginal twins: 8%, non-Aboriginal singletons: 6%) (Additional file
2, Table S1). Other pregnancy complications were more common among mothers of twins compared to singletons; for example, in WA, pre-eclampsia/eclampsia/gestational hypertension were twice as common in mothers of Aboriginal twins (17%) compared to mothers of Aboriginal singletons (8%). These hypertensive disorders were less common in the mothers of NSW babies when only the Perinatal Data Collection diagnoses were considered (Table
1), but similar to the WA cohort when hospital diagnoses were also included for the subset of children who started school in 2009/2012 (Additional file
2, Table S1).
Table 2
Pregnancies in Western Australia (2000–2013) and New South Wales (2002–2008) by plurality and Aboriginality
Groups compared and statistical significance reported1 | A | A | B | B | C | C |
| | | D | | D | |
Gestation at first antenatal visitbCD, 2 |
13 weeks or less | 120 (49) | 3797 (45) | 508 (64) | 18,955 (60) | 13,894 (76) | 410,156 (70) |
14 weeks or more | n.p. | 4551 (54) | 270 (34) | 11,545 (37) | 4244 (23) | 166,711 (29) |
No visit (WA) / No visit or missing (NSW) | n.p. | 125 (1) | 16 (2) | 1024 (3) | 200 (1) | 5488 (1) |
Maternal health and pregnancy complications |
Gestational diabetesCd | 48 (5) | 1724 (5) | 28 (4) | 1105 e(4) | 1095 (6)3 | 26,541 (5) |
Pre-existing diabetesbCd | 8 (1) | 557 (2) | 12 (2) | 230 (1) | 142 (1) | 3315 (1) |
Pre-eclampsia/eclampsia/gestational hypertensionABCd | 148 (17) | 2650 (8) | 69 (9) | 1618 (5) | 2087 (11)3 | 31,855 (5) |
Pre-existing hypertensionC | 18 (2) | 415 (1) | 8 (1) | 286 (1) | 237 (1)3 | 5547 (1) |
Threatened abortionA | 56 (6) | 1002 (3) | – | – | – | – |
Antepartum haemorrhageA | 84 (10) | 1787 (5) | – | – | – | – |
Threatened preterm labourA | 256 (29) | 3099 (9) | – | – | – | – |
Preterm prelabour rupture of membranesA | 174 (20) | 1695 (5) | – | – | – | – |
Comparing NSW Aboriginal and non-Aboriginal twin pregnancies, the likelihood of pregnancy complications was similar, with the exception of antepartum haemorrhage among the NSW 2009/2012 school starters (13 and 6% for Aboriginal and non-Aboriginal twin pregnancies, respectively, and 4 and 3% for Aboriginal and non-Aboriginal singleton pregnancies).
Birth
The majority of WA Aboriginal twins were born in public principal referral/women’s hospitals (65%) compared to only 26% of singletons (Table
3). In NSW, the most common hospital category for the birth of Aboriginal twins was large hospital (50%), followed by public principal referral/women’s hospital (41%). For non-Aboriginal twins, the most common hospital category was public principal referral/women’s hospital (47%), followed by private hospital (25%).
Table 3
Birth characteristics in Western Australia (2000–2013) and New South Wales (2002–2008) by plurality and Aboriginality
Groups compared and statistical significance reported1 | A | A | B | B | C | C | |
| | D | | D | | |
Hospital category for birthABCD |
Public principal referral/women’s | 573 (65) | 8608 (26) | 324 (41) | 8204 (26) | 8689 (47) | 189,260 (32) | |
Large public | 141 (16) | 9397 (28) | 394 (50) | 17,171 (54) | 4595 (25) | 209,070 (36) | |
Medium/small public | 105 (12) | 12,032 (36) | 42 (5) | 4759 (15) | 318 (2) | 35,198 (6) | |
Private | 54 (6) | 2730 (8) | 28 (4) | 1201 (4) | 4658 (25) | 146,078 (25) | |
Born outside hospital | 7 (1) | 345 (1) | 6 (1) | 189 (1) | 78 (< 1) | 2749 (< 1) | |
Mother transferred prior to birth2,ABCd | 116 (13) | 1358 (4) | 40 (17) | 559 (6) | 616 (11) | 3456 (2) | |
Time from home to hospital (median (IQR))ABCD | 38 (20, 401) | 19 (9, 51) | 21 (11, 49) | 19 (10, 39) | 20 (11, 35) | 17 (11, 28) | |
0–29 min | 324 (37) | 19,695 (60) | 440 (56) | 20,668 (66) | 12,631 (69) | 437,239 (76) | |
30–59 min | 146 (17) | 3110 (9) | 174 (22) | 5833 (19) | 3604 (20) | 103,700 (18) | |
1 h-2 h | 80 (9) | 2889 (9) | 108 (14) | 3522 (11) | 1558 (9) | 31,413 (5) | |
3 h or greater | 269 (31) | 4342 (13) | 66 (8) | 1227 (4) | 392 (2) | 4529 (1) | |
Location of WA private hospital unknown | 54 (6) | 2730 (8) | – | – | – | – | |
PresentationABC |
Vertex | 558 (63) | 31,693 (95) | 196 (67) | 11,957 (96) | 4532 (73) | 200,288 (96) | |
Breech | 291 (33) | 1165 (4) | 84 (29) | 389 (3) | 1482 (24) | 7561 (4) | |
Other | 31 (4) | 371 (1) | 11 (4) | 97 (1) | 215 (3) | 1581 (1) | |
DeliveryABCD |
Vaginal birth | 427 (49) | 25,564 (77) | 317 (40) | 24,469 (78) | 6765 (37) | 421,801 (72) | |
Spontaneous labour | 258 (29) | 19,269 (58) | 212 (27) | 18,411 (58) | 3706 (20) | 302,880 (52) | |
Induced labour | 169 (19) | 6295 (19) | 105 (13) | 6058 (19) | 3059 (17) | 118,921 (20) | |
Caesarean | 453 (51) | 7665 (23) | 477 (60) | 7022 (22) | 11,567 (63) | 160,129 (28) | |
Labour |
Spontaneous labour | 134 (15) | 2279 (7) | 187 (24) | 2112 (7) | 3032 (17) | 40,546 (7) | |
Induced labour | 39 (4) | 1440 (4) | 16 (2) | 1225 (4) | 849 (5) | 27,946 (5) | |
No labour | 280 (32) | 3946 (12) | 274 (35) | 3685 (12) | 7686 (42) | 91,637 (16) | |
Planned/emergency | | | – | – | – | – | |
Planned caesarean | 166 (19) | 2999 (9) | – | – | – | – | |
Emergency caesarean | 287 (33) | 4666 (14) | – | – | – | – | |
Instruments usedCd |
No | 803 (91) | 30,084 (91) | 755 (95) | 29,526 (94) | 16,912 (92) | 519,869 (89) | |
Yes | 77 (9) | 3145 (9) | 39 (5) | 1973 (6) | 1420 (8) | 62,182 (11) | |
Accoucheur (WA)3 | | | | | | | Model of care (NSW)3 |
ObstetricianA | 319 (36) | 5683 (17) | 42 (14) | 1298 (10) | 2818 (45) | 75,804 (36) | Private obstetricianbCD |
Other medical practitionerA | 553 (63) | 8842 (27) | 223 (76) | 5274 (42) | 3274 (52) | 77,227 (37) | Hospital-based medicalbCD |
MidwifeA | 195 (22) | 19,998 (60) | 30 (10) | 2260 (18) | 150 (2) | 15,807 (8) | General practitionerBCD |
StudentA | 82 (9) | 4569 (14) | 192 (65) | 8948 (72) | 3570 (57) | 132,379 (63) | Hospital-based midwifebCd |
Self/other/unknown | 28 (3) | 855 (3) | 0 (0) | 20 (< 1) | 9 (< 1) | 519 (< 1) | Independent midwife |
Mothers of twins were more likely to be transferred to another hospital prior to the birth (WA Aboriginal twins and singletons: 13 and 4%, NSW Aboriginal twins and singletons: 17 and 6%, and NSW non-Aboriginal twins and singletons: 11 and 2%). Mothers of Aboriginal twins often gave birth far from home. In WA, almost a third (31%) of the Aboriginal twin births in hospital were at least 3 h by road from the mother’s home; in NSW, the percentage was 8%.
Caesarean section was the most common method of birth for twins in all three groups and this was more than twice as common for twins than singletons. NSW non-Aboriginal twins were the most likely to be born by caesarean section (63%), followed by NSW Aboriginal twins (60%) and WA Aboriginal twins (51%). 63% (287/453) of WA Aboriginal twin caesarean sections were categorised as emergency caesarean sections.
In WA, twin births were twice as likely to be attended by obstetricians (36%) as singleton births (17%). In NSW, Aboriginal twins were much more likely to have a hospital-based medical model of care (76%) than Aboriginal singletons (42%). Private obstetricians were involved in a large proportion of non-Aboriginal NSW twin births (45%), compared to only 14% for Aboriginal twin births.
Perinatal outcomes
Twins were only slightly more likely than singletons to be stillborn, but in both states 3% of liveborn Aboriginal twins died within 28 days, compared with less than half a percent of Aboriginal singletons (Table
4). Twins were roughly one-kilogram lighter at birth than singletons for both Aboriginal and non-Aboriginal liveborn infants. Aboriginal twins from WA had the lowest mean weight at 2225 g. Among liveborn infants, 35% of WA Aboriginal twins were born at 37 or more weeks’ gestational age compared to 42% of NSW Aboriginal twins and 51% of NSW non-Aboriginal twins. Twins were more than twice as likely to be admitted to a NICU/SCN and twin infants and their mothers both averaged at least twice as long in hospital as singleton infants and their mothers. The median length of stay in hospital was 7 days for WA Aboriginal twins and NSW Aboriginal 2009/2012 school starters twins (interquartile range [IQR]: 4–14 days for WA Aboriginal twins and 4–16 days for NSW Aboriginal twin 2009/2012 school starters) and 6 days [IQR: 4–8 days] for their mothers (Table
4 and Additional file
2, Table S1). Selected perinatal outcomes for triplets are reported in Additional file
1.
Table 4
Perinatal outcomes in Western Australia (2000–2013) and New South Wales (2002–2008) by plurality and Aboriginality
Groups compared and statistical significance reported1 | A | A | B | B | C | C |
| | D | | D | |
All births | N = 880 | N = 33,229 | N = 794 | N = 31,524 | N = 18,338 | N = 582,355 |
StillbirthaC | 20 (2) | 398 (1) | 10 (1) | 262 (1) | 332 (2) | 3295 (1) |
Live births only | N = 860 | N = 32,831 | N = 784 | N = 31,262 | N = 18,006 | N = 579,060 |
Neonatal deathABC | 29 (3) | 147 (< 1) | 20 (3) | 105 (< 1) | 294 (2) | 1182 (< 1) |
Birth weight (grams) (mean (SD)) | 2225 (682) | 3207 (636) | 2311 (661) | 3283 (622) | 2436 (605) | 3419 (545) |
Birth weight bands ABCD |
< 1000 | 59 (7) | 252 (1) | 35 (4) | 174 (1) | 535 (3) | 1673 (< 1) |
1000–1499 | 67 (8) | 315 (1) | 67 (9) | 224 (1) | 840 (5) | 2070 (< 1) |
1500–1999 | 153 (18) | 709 (2) | 101 (13) | 549 (2) | 2213 (12) | 4458 (1) |
2000–2499 | 240 (28) | 2292 (7) | 239 (31) | 1895 (6) | 5101 (28) | 16,228 (3) |
2500–2999 | 248 (29) | 7097 (22) | 251 (32) | 5970 (19) | 6477 (36) | 81,429 (14) |
3000–3499 | 88 (10) | 11,544 (35) | 72 (9) | 10,742 (34) | 2498 (14) | 212,821 (37) |
3500+ | 5 (1) | 10,622 (32) | 18 (2) | 11,695 (37) | 320 (2) | 260,131 (45) |
Gestational age (median (IQR)) | 36 (33, 37) | 39 (38, 40) | 36 (34, 37) | 39 (38, 40) | 37 (35, 38) | 39 (38, 40) |
Gestational age categories ABCD |
20–23 | 22 (3) | 62 (< 1) | 9 (1) | 52 (< 1) | 152 (1) | 479 (< 1) |
24–27 | 30 (3) | 183 (1) | 24 (3) | 139 (< 1) | 345 (2) | 1200 (< 1) |
28–31 | 68 (8) | 414 (1) | 75 (10) | 261 (1) | 1001 (6) | 2712 (< 1) |
32–34 | 198 (23) | 922 (3) | 126 (16) | 743 (2) | 2658 (15) | 7137 (1) |
35–36 | 240 (28) | 2329 (7) | 211 (27) | 1638 (5) | 4475 (25) | 18,783 (3) |
37–38 | 279 (32) | 10,030 (31) | 292 (38) | 7119 (23) | 8216 (46) | 124,134 (21) |
39+ | 23 (3) | 18,846 (57) | 31 (4) | 21,298 (68) | 861 (5) | 424,508 (73) |
ResuscitationABC | 449 (52) | 11,170 (34) | 455 (58) | 13,190 (42) | 10,463 (58) | 235,578 (41) |
Length of stay (median (IQR) in days)A | 7 (4–14) | 3 (2–4) | – | – | – | – |
Admitted to NICU or SCN2,ABCd | 452 (64) | 4343 (29) | 500 (64) | 5984 (19) | 10,521 (57) | 82,257 (14) |
Cerebral palsy. | 5 (1) | 114 (< 1) | – | – | – | – |
Respiratory distress syndrome of newbornsA | 146 (17) | 883 (3) | – | – | – | – |
Maternal outcomes |
PPH requiring blood transfusionAC | 36 (4) | 607 (2) | 10 (3) | 403 (3) | 175 (3) | 3389 (2) |
Mother’s length of stay (median (IQR) in days)A | 6 (4–8) | 3 (2–5) | – | – | – | – |
Discussion
This large population-based study in two Australian states showed that the journey from pregnancy to discharge from hospital presented major challenges for many Aboriginal mothers and their twins. Pregnancy complications, birth interventions, travel far from home and adverse perinatal outcomes were more common for Aboriginal twins than Aboriginal singletons, consistent with data for non-Aboriginal singletons and twins, and more common for Aboriginal twins than non-Aboriginal twins.
As expected, mothers of twins in the Aboriginal and non-Aboriginal cohorts had higher proportions of pregnancy complications than singletons, except for gestational diabetes among non-Aboriginal births. The time period covered by this study largely preceded changes in the diagnostic criteria and testing for gestational diabetes which were progressively implemented in Australian jurisdictions following the publication of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study in 2008 [
28]. These changes greatly increased diagnoses of gestational diabetes [
28] so the proportion of women diagnosed with gestational diabetes in this study (approximately 5%) is low compared to the national percent of 13.5% reported recently [
1]. Our finding of similar prevalence of gestational diabetes among twin and singleton births in both WA and NSW Aboriginal births and only a slight difference for NSW non-Aboriginal births is consistent with some other studies [
29,
30], though not all [
7,
31,
32]. The slight increase in gestational diabetes for NSW non-Aboriginal mothers of twins may be due to maternal age as gestational diabetes is more common among older women [
33] and Egeland and Irgens found that the higher risk for multiple pregnancies was largely attenuated after adjustment for maternal age [
32]. It is also possible that some diagnoses are missed for Aboriginal women; a study in remote WA of births in 2013 found that Aboriginal women were less likely to be screened for gestational diabetes with the recommended oral glucose tolerance test [
34]. Hypertensive disorders, including pre-eclampsia, eclampsia and gestational hypertension combined, were over twice as common in twin pregnancies, compared to singletons, as found in other populations [
35‐
37]. Prior twin cohort studies have found that hypertensive disorders often onset earlier and have greater severity in twin pregnancies compared to singletons [
37,
38].
While pregnancy complications were more common among twin pregnancies compared with singleton pregnancies, percentages were generally similar for NSW Aboriginal and non-Aboriginal twin pregnancies. However, there was some evidence that gestational diabetes and hypertensive disorders were more common in mothers of non-Aboriginal twins and antepartum haemorrhage was roughly twice as common for mothers of Aboriginal twins (13%) than non-Aboriginal twins (6%) in NSW 2009/2012 school starters. This was noteworthy as rates were similar for Aboriginal and non-Aboriginal singleton pregnancies (4 and 3%, respectively, Table
S1) and those singleton rates were in line with findings from other Australian jurisdictions [
39]. Additionally, another Australian study on (predominantly non-Aboriginal) twin pregnancies found antepartum haemorrhage affected only 5% of pregnancies [
40]. Possible explanations include that this was a chance result in this subsample of NSW Aboriginal twins or that antepartum haemorrhage risk factors which are more common among Aboriginal mothers (for example, increased parity and tobacco use [
21]) pose a particularly high risk for twin pregnancies, and further investigation is warranted.
We found that Aboriginal twins had more adverse perinatal outcomes than Aboriginal singletons and non-Aboriginal NSW twins. Perinatal death (stillbirth or neonatal death) was higher for twins (compared to singletons) in both states, particularly WA Aboriginal twins. The persistent gap between Aboriginal and non-Aboriginal singleton birth weight and gestational age was also apparent among twins [
1]. There was marked a difference between the proportion of Aboriginal and non-Aboriginal twins born at 37 weeks’ gestation or more (35% of WA Aboriginal, 42% of NSW Aboriginal and 51% of NSW non-Aboriginal twins), despite similar prevalence of pregnancy complications and a greater proportion of mothers of Aboriginal twins aged 20 to 34 years, an age range with lower risk of preterm birth at the population level [
41,
42]. The increased risk of preterm birth for Aboriginal twins may result from factors associated with spontaneous preterm birth which were not explored in this study, such as infection and smoking [
43,
44]. Another explanation may be that although Aboriginal twins were more likely to be born in facilities with greater medical oversight than Aboriginal singletons (a higher percentage of twin births were at principal referral or specialist women’s hospitals and obstetricians were more likely to be present), their health care still differed from non-Aboriginal twins.
This study is the first to describe in detail the pregnancies and births of Aboriginal twins, providing baseline data to inform the response of health services to this important population. Many studies exclude multiples from analyses or provide limited information about Aboriginal twins. Our study covered almost half of the Aboriginal Australian population [
20] ensuring sufficient twins for meaningful estimates in each state and allowing assessment of whether patterns were consistent in both states. While these communities share some common recent history, including colonisation and its effects, major differences exist within, and between, these states, including cultural and linguistic differences, remoteness and availability of healthcare. Both have large urban populations (40% of Aboriginal people in WA and 46% in NSW), but in WA, 24% of Aboriginal people live in very remote areas, compared to only 1% in NSW [
20].
By using population-based linked data, selection bias – common in cohort studies or surveys using primary data collection – was minimised. Limitations of our study include that the data were collected for administrative, not research, purposes and lacked some relevant information such as reasons for giving birth in a distant hospital and the use of assisted reproductive technologies. However, Aboriginal women are much less likely to access assisted reproductive technologies than non-Aboriginal women – a study of 5 Australian states found that only 3% (9/304) of Aboriginal twin pregnancies were the result of assisted reproductive technology, compared to 24% (2280/9519) of non-Aboriginal mothers [
40]. There were also differences in information recorded in WA and NSW, though most data were comparable. Additionally, different methods of identifying Aboriginal infants were used in the two states and some data could only be reported for a subset of NSW births because linked hospital data were not available for all NSW births. While approximate travel times were an indicator of distance from home and community at the time of birth, the mother’s actual method of transport to hospital was not recorded. Finally, mothers from border regions may have travelled interstate, as is common practice in the Far West Local Health District of NSW. As such, some information on birth outcomes may be missing from our data and may disproportionately include high-risk multiple births among Aboriginal women.
Our findings highlight that it is more common for the mothers of Aboriginal twins to face a number of practical challenges that may impact on their antenatal care, pregnancy and birth outcomes than mothers of Aboriginal singletons and non-Aboriginal twins; challenges that have major implications for birth planning and the birth experience for mothers of Aboriginal twins. Specialised medical care and NICUs are concentrated in large urban areas and many mothers needed to travel to access that care. We did not have data about the location of antenatal scans and appointments, but travel may also have been necessary during high-risk twin pregnancies. Mothers may have missed valuable support from their family and community for extended periods of time. This travel may also have led to substantial costs for additional antenatal scans, transport, accommodation and, potentially, childcare for older children and reduced work-related income for herself and any accompanying support people. At present, some government support is available for women to travel. For example, NSW women who must travel over 100 km can access the Isolated Patients Travel and Accommodation Assistance Scheme, although the full costs of travel and accommodation are not covered and food is not subsidised [
45].
While all mothers of twins face challenges, the circumstances of many Aboriginal women mean that these challenges may be more difficult to overcome. Aboriginal women report loneliness and distress with relocation for birth [
46]. Additionally, costs associated with antenatal care and birth may impact on Aboriginal women who are disproportionately socio-economically disadvantaged following over 200 years of colonisation. Aboriginal women are also more likely to have older children (only 27 and 28% of mothers of Aboriginal twins in WA and NSW were nulliparous compared to 44% of mothers of non-Aboriginal twins) and these children may need to travel with their mothers or be cared for by others. Some women may be distressed that their babies are not born on country [
46]. Finally, Aboriginal women often access antenatal and postnatal care through primary health care organisations operated by local Aboriginal communities. Births in a distant hospital may require a transfer of care from midwives at these local Aboriginal services to a large, mainstream hospital which may be perceived as less culturally safe and disrupt continuity of care [
47].
Given the range of challenges that mothers of twins may face during pregnancy and birth, this group needs more support than mothers of singletons. While Australian State and Federal Governments currently fund services and develop guidelines for specific groups of mothers (for example, teenage mothers, nulliparous mothers, Aboriginal mothers), as far as we are aware, there are no targeted supports for parents of twins, let alone mothers of Aboriginal twins who are more likely to live in remote and socioeconomically deprived areas, be younger, and have other children than mothers of non-Aboriginal twins. Aboriginal mothers of twins are a small group, but they are an important high-risk group, and these mothers should be considered for targeted support. Research with parents and Aboriginal community controlled health organisations (particularly in remote areas) and the major hospitals where many Aboriginal twins are born is needed to identify upfront costs during pregnancy for the birth and the impact of these costs, any medical or psychosocial consequences of relocation for birth, whether additional financial or other practical support is needed and, if so, the optimal timing of the support.
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