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How do pregnancy outcomes differ in teenage mothers? A Western Australian study

Lucy N Lewis, Martha Hickey, Dorota A Doherty and S Rachel Skinner
Med J Aust 2009; 190 (10): 537-541.
Abstract

Objectives: To determine whether teenage pregnancy and Indigenous status are associated with increased risk of adverse pregnancy outcomes.

Design, setting and participants: A cross-sectional descriptive analysis of nulliparous women with singleton pregnancies who delivered at the sole tertiary obstetric hospital in Western Australia between June 2004 and September 2006, using data obtained from computerised midwifery records.

Main outcome measures: Maternal risk factors, pregnancy characteristics, and obstetric and perinatal outcomes for teenage and adult pregnancies.

Results: Of the 4896 births reviewed, 560 (11%) were to teenage mothers. Teenagers were more likely to be Indigenous and to experience maternal risk factors such as anaemia and smoking. Indigenous women were more likely than non-Indigenous women to be smokers, with young Indigenous teenagers (aged 12–16 years) being most likely to smoke (odds ratio [OR], 6.29; 95% CI, 3.99–9.92). Perinatal outcomes for teenage and adult births were similar, while adjustment for smoking and Indigenous status changed the observed association for the Indigenous population of preterm delivery < 37 weeks’ gestation (OR, 1.31; 95% CI, 1.01–1.71), admission to special care nursery (OR, 1.41; 95% CI, 1.10–1.81) and low birthweight (OR, 1.43; 95% CI, 1.10–1.87). However, older teenagers (aged 17–18 years) were the group at highest risk of stillbirth (OR, 1.99; 95% CI, 1.03–3.76).

Conclusions: These results improve our understanding of the obstetric and medical issues associated with teenage pregnancy and birth in WA and how we might tailor our approach to care. Indigenous teenagers need special attention, and there is significant scope for public health interventions around anaemia and smoking in this population.

Although the birth rate among Australian teenagers aged 15–19 years has fallen in recent decades to a low of 15.4 per 1000 in 2006,1 Australia continues to have a teenage birth rate several times higher than rates in comparable countries.2,3 Improved access to contraception and abortion may underlie the falling teenage birth rate.4 However, there is increasing evidence that some groups of Australian teenagers are not experiencing this decline, especially those living in rural5 and socially disadvantaged6 areas, and Indigenous teenagers,7,8 who in 2006 had a fertility rate of 69 per 10001 — more than five times that of non-Indigenous women.

Although others have assessed the effects of teenage pregnancy on obstetric risk factors and pregnancy outcomes for whole populations within the public health care system in Australia,5,7,8 no such exploration has occurred in Western Australia. Published data relating to Indigenous teenage pregnancy are also now quite old,7,8 with limited research on maternal risk factors and birth outcomes in this cohort in an urban setting. Stillbirth rates in WA have been investigated,9 with the conclusion that higher rates in teenagers may be fully explained by sociodemographic factors.

Being a teenage mother is a precursor to poor medical, educational and psychosocial outcomes.3,10 Although most studies report that teenagers’ babies are at greater risk of preterm birth, low birthweight11 and neonatal death,12 some studies find no such association, especially if high-quality antenatal care is provided.13 It has also been suggested that adverse perinatal outcomes are associated with ethnicity7,8 and are independently associated with younger,11 socially disadvantaged6 mothers who smoke.14,15

We aimed to assess the effect of teenage pregnancy on obstetric risk factors and adverse birth outcomes in an urban tertiary maternity hospital in WA. We hypothesised that poor pregnancy outcomes in teenagers could largely be explained by smoking and Indigenous status.

Methods

We conducted a retrospective hospital-based study using computerised perinatal data collected by the Obstetrics and Gynaecology Clinical Care Unit at King Edward Memorial Hospital (KEMH) in Perth. Maternal age was defined as the age of the mother in completed years at the time of conception. Only nulliparous women were included, to remove confounding caused by parity. The total population of 4896 nulliparous women with singleton pregnancies who delivered from 22 weeks’ gestation between June 2004 and September 2006 were evaluated. As the sole tertiary maternity hospital in WA, KEMH has a high rate of preterm delivery. The study was approved by the KEMH Ethics Committee.

Antenatal risk factors included socioeconomic status (calculated using the Index of Relative Socio-Economic Disadvantage from the Australian Bureau of Statistics Socio-Economic Indexes For Areas [SEIFA], with the lowest quartile representing the most disadvantaged group),16 ethnicity, anaemia (haemoglobin level < 110 g/L), urinary tract infection, pregnancy-induced hypertension (daily repeated blood pressure readings over several hours exceeding 140/90 mmHg), and smoking during pregnancy (ever having smoked while pregnant). Delivery data included analgesia use and caesarean section. Perinatal outcomes included preterm birth (before 37 weeks’ gestation), Apgar score, resuscitation, admission to special care, birthweight, low birthweight (< 2500 g), and stillbirth.

Statistical analysis

Medians and interquartile ranges were used to summarise continuous data. Frequency distributions were used to summarise categorical data. Univariate comparisons between adult and teenage women were performed using Mann–Whitney tests and χ2 tests, as appropriate. Multivariable comparisons of binary outcomes were performed using logistic regression, with odds ratios (ORs) and 95% confidence intervals used to summarise the effect sizes. P values < 0.05 were considered statistically significant. SPSS statistical software (version 15; SPSS Inc, Chicago, Ill, USA) was used for data analysis.

Results

Of the total study population of 4896 pregnant women, 560 (11%) were teenagers. Teenagers’ ages ranged from 12 to 18 years, with a median age of 17 years. Of these, 183 were young teenagers (aged 12–16 years) and 377 were older teenagers (aged 17–18 years).

Compared with adults, teenagers were more likely to be Indigenous and less likely to be white (P < 0.001), were more likely to smoke (P < 0.001) and came from more socioeconomically disadvantaged backgrounds (P < 0.001) (Box 1). Antenatally, teenagers experienced anaemia (P < 0.001), urinary tract infection (P < 0.001) and pregnancy-induced hypertension (P = 0.004) more often than adults. Teenagers were less likely to deliver by caesarean section (P < 0.001), and their babies were at increased risk of having low Apgar scores (P = 0.042), low birthweight (P = 0.016), lower median birthweight at term (3120 g v 3205 g; P = 0.028), and stillbirth (P = 0.014). Compared with older teenagers, young teenagers were more likely to be Indigenous and less likely to be white (P = 0.008) (Box 1).

Compared with non-Indigenous adults, all Indigenous women were more likely to smoke (Box 2). Young Indigenous teenagers were the most likely to smoke (OR, 6.29; 95% CI, 3.99–9.92), followed by Indigenous adults (OR, 5.19; 95% CI, 3.78–7.11) and older Indigenous teenagers (OR, 4.00; 95% CI, 2.68–5.93).

Compared with non-Indigenous teenagers, Indigenous teenagers were more likely to smoke (P = 0.001), have anaemia (P < 0.001) and experience pregnancy-induced hypertension (P = 0.034) (Box 3). Their babies experienced similar birth outcomes to those of non-Indigenous teenagers, with the exception of lower median birthweight (2965 g v 3220 g; P < 0.001).

Compared with adult women, young teenage (OR, 1.61; 95% CI, 1.02–2.54) and Indigenous women (OR, 4.46; 95% CI, 3.23–6.15) were at increased risk of anaemia, while Indigenous women (OR, 1.70; 95% CI, 1.16–2.48) and older teenagers (OR, 1.48; 95% CI, 1.03–2.11) experienced pregnancy-induced hypertension more often (Box 4). Only older teenagers were more likely than adults to experience urinary tract infection (OR, 2.61; 95% CI, 1.71–3.98). Babies of Indigenous mothers were more likely to require admission to special care (OR, 1.30; 95% CI, 1.00–1.67) and experience low birthweight (OR, 1.32; 95% CI, 0.99–1.75), and were slightly more likely to be born preterm (OR, 1.31; 95% CI, 1.01–1.71). However, older teenagers were the group at highest risk of stillbirth (OR, 1.99; 95% CI, 1.03–3.76).

Discussion

Overall, we found that maternal risk factors were more common in teenagers than adults. This was particularly true for low socioeconomic status, smoking during pregnancy, anaemia, urinary tract infection and pregnancy-induced hypertension. Simultaneous evaluation of the effects of maternal age, Indigenous status and smoking showed that preterm delivery, low birthweight and special care admission were related to mothers being Indigenous, without the effect of age. Compared with adults, teenagers had an increased risk of stillbirth. After adjusting for low socioeconomic status, ethnicity and smoking, this association was specific to older teenage mothers.

Our finding that maternal risk factors were more common in teenagers than adults is consistent with other studies.7,8 Two of these risk factors, anaemia and smoking, are modifiable antenatally. A high proportion (32%) of pregnant teenagers, especially Indigenous teenagers, smoked. Smoking during pregnancy is associated with low birthweight14,15 and preterm delivery.17 Although antenatal smoking cessation programs do reduce smoking,17 it has also been found that the pregnant women least likely to quit smoking are teenagers and Indigenous women, especially if they are socioeconomically disadvantaged.18 Smoking in these populations remains a significant public health issue; tobacco use has been found to be a leading cause of premature morbidity and mortality in Indigenous women.19

Other studies have also reported a higher incidence of anaemia in pregnant teenagers,13,20 suggesting poor nutrition could be a contributing cause.7,13 Anaemia in pregnancy is common and associated with low birthweight, preterm delivery21 and a decrease in maternal tolerance to haemorrhage. Daily oral iron–folic acid supplementation is the initial treatment recommended to pregnant teenagers attending KEMH as it improves haematological response.22 However, the direct link between iron–folic acid supplementation and an improvement in health outcomes for women and their babies has not been proven, as there are a paucity of well designed trials22,23 addressing this question.

Stillbirth in older teenagers was the only increased adverse pregnancy outcome found in teenagers after controlling for confounding factors. Stillbirth has previously been linked to maternal age, with the youngest mothers having the highest risk,11 a higher incidence of preterm delivery24 compared with adults, and low socioeconomic status.9 After controlling for the effects of young maternal age, preterm delivery and socioeconomic status, we found no evidence that stillbirth in our population of teenagers was linked to these risk factors (Box 4). However, the limitation of using SEIFA codes alone to assess social deprivation should not be overlooked,9 because lack of additional data (such as marriage status and educational attainment) prevented exhaustive investigation of the effects of social deprivation on stillbirth.

Although the health of Indigenous women and their infants is improving,25 our study clearly illustrates that pregnant Indigenous women are disadvantaged compared with non-Indigenous women. Consistent with other studies,1,8 Indigenous status was more common in teenagers giving birth than in adults giving birth, perhaps reflecting an overall younger age of first birth among Indigenous women. Although Indigenous teenagers smoked, had anaemia and experienced pregnancy-induced hypertension more often than their non-Indigenous counterparts, we found little evidence of adverse perinatal outcomes in this group. Previous research has suggested that adverse perinatal outcomes for Indigenous teenagers may be related to rural residence,8 with teenagers from urban areas having better perinatal outcomes than their rural counterparts.5 As most teenagers in our study were from an urban setting, we hypothesise that better access to maternity care was a contributing factor.

This is the first analysis of its kind of teenage births in WA. As smoking and nutritional status remain among the few modifiable factors in pregnancy, teenagers and Indigenous women need special attention in terms of innovative, culturally appropriate system-wide services targeted at addressing these important health issues in pregnancy.

1 Distribution of maternal risk factors, pregnancy characteristics and outcomes in adult and teenage women, and in young teenagers (aged 12–16 years) and older teenagers (aged 17–18 years)

Risk factor

All teenagers
(n = 560)

Adults
(n = 4336)

P

Teenagers 12–16
years (n = 183)

Teenagers 17–18
years (n = 377)

P


Ethnicity

< 0.001

0.008

White

307 (55%)

3187 (74%)

83 (45%)

224 (59%)

Indigenous

185 (33%)

171 (4%)

77 (42%)

108 (29%)

Other*

46 (8%)

690 (16%)

14 (8%)

32 (8%)

Low socioeconomic status

127 (23%)

598 (14%)

< 0.001

42 (23%)

85 (22%)

0.915

Smoking during pregnancy

177 (32%)

608 (14%)

< 0.001

67 (37%)

110 (29%)

0.076

Anaemia

77 (14%)

270 (6%)

< 0.001

31 (17%)

46 (12%)

0.127

Urinary tract infection

41 (7%)

136 (3%)

< 0.001

8 (4%)

33 (9%)

0.062

Pregnancy-induced hypertension

59 (10%)

308 (7%)

0.004

17 (9%)

42 (11%)

0.503

Analgesia

Narcotic

224 (40%)

1188 (27%)

< 0.001

77 (42%)

147 (39%)

0.485

Nitrous oxide

256 (46%)

1606 (37%)

< 0.001

85 (46%)

171 (45%)

0.808

Epidural/spinal

326 (58%)

2926 (68%)

< 0.001

92 (50%)

234 (62%)

0.008

Caesarean section

94 (17%)

1417 (33%)

< 0.001

18 (10%)

76 (20%)

0.002

Gestation < 37 weeks

144 (26%)

997 (23%)

0.152

43 (23%)

101 (27%)

0.403

Apgar score < 7 at 5 min

22 (4%)

144 (3%)

0.042

6 (3%)

16 (4%)

0.618

Resuscitation

287 (51%)

2101 (48%)

0.213

83 (45%)

204 (54%)

0.052

Special care admission

169 (30%)

1192 (27%)

0.182

50 (27%)

119 (32%)

0.305

Birthweight < 2500 g

133 (24%)

842 (19%)

0.016

41 (22%)

92 (24%)

0.602

Birthweight, median (IQR)

3120 (2550–3550)

3205 (2675–3590)

0.028

3117 (2571–3502)

3125 (2535–3607)

0.679

Stillbirth

18 (3%)

76 (2%)

0.014

6 (3%)

12 (3%)

0.910


IQR = interquartile range. Figures expressed as number (%) unless otherwise specified. Percentages may not add up to 100% due to missing values for some variables.
* African, Asian, Maori, Polynesian and Indian. More than one type of analgesia could be used.

2 Frequencies and odds ratios for the likelihood of smoking during pregnancy in Indigenous adults and Indigenous and non-Indigenous teenagers

Maternal age group

No. (%) of smokers

Odds ratio (95% CI)

P


Non-Indigenous adults*

534 (13%)

1.00

< 0.001

Indigenous adults

74 (43%)

5.19 (3.78–7.11)

Non-Indigenous 12–16 years

30 (28%)

2.68 (1.74–4.13)

Indigenous 12–16 years

37 (48%)

6.29 (3.99–9.92)

Non-Indigenous 17–18 years

70 (26%)

2.39 (1.79–3.19)

Indigenous 17–18 years

40 (37%)

4.00 (2.68–5.93)


* Referent group.

3 Differences between Indigenous and non-Indigenous teenagers*

Indigenous (n = 185)

Non-Indigenous (n = 353)

P


Low socioeconomic status

42 (23%)

78 (22%)

0.872

Smoking during pregnancy

77 (42%)

100 (28%)

0.001

Anaemia

43 (23%)

30 (8%)

< 0.001

Urinary tract infection

13 (7%)

26 (7%)

0.886

Pregnancy-induced hypertension

26 (14%)

29 (8%)

0.034

Caesarean section

36 (19%)

56 (16%)

0.293

Gestation < 37 weeks

55 (30%)

84 (24%)

0.135

Apgar score < 7 at 5 min

9 (5%)

11 (3%)

0.322

Resuscitation

88 (48%)

188 (53%)

0.210

Special care admission

65 (35%)

99 (28%)

0.090

Birthweight < 2500 g

53 (29%)

76 (21%)

0.066

Birthweight, median (IQR)

2965 (2430–3440)

3220 (2722–3642)

< 0.001

Stillbirth

6 (3%)

12 (3%)

0.924


IQR = interquartile range. Figures expressed as number (%) unless otherwise specified. Percentages may not add up to 100% due to missing values for some variables. * Ethnicity of 22 teenagers not known.

4 Pregnancy outcomes for young and older teenage mothers compared with adults, adjusting for simultaneous effects of Indigenous status

Adjusted*


Multivariable


Outcome

Odds ratio (95% CI)

P

Odds ratio (95% CI)

P


Anaemia

Teenagers 12–16 years

1.61 (1.02–2.54)

0.039

Teenagers 17–18 years

1.31 (0.91–1.89)

0.148

Indigenous

4.46 (3.23–6.15)

< 0.001

Pregnancy-induced hypertension

Teenagers 12–16 years

1.14 (0.66–1.97)

0.632

Teenagers 17–18 years

1.48 (1.03–2.11)

0.036

Indigenous

1.70 (1.16–2.48)

0.006

Urinary tract infection

Teenagers 12–16 years

1.15 (0.54–2.49)

0.705

Teenagers 17–18 years

2.61 (1.71–3.98)

< 0.001

Indigenous

1.30 (0.78–2.15)

0.311

Caesarean section

Teenagers 12–16 years

0.22 (0.13–0.37)

< 0.001

0.21 (0.12–0.35)

< 0.001

Teenagers 17–18 years

0.52 (0.40–0.68)

< 0.001

0.48 (0.36–0.63)

< 0.001

Indigenous

1.12 (0.85–1.47)

0.413

1.05 (0.80–1.39)

0.726

Gestation < 37 weeks

Teenagers 12–16 years

0.89 (0.62–1.29)

0.555

0.85 (0.58–1.23)

0.406

Teenagers 17–18 years

1.12 (0.87–1.44)

0.374

1.02 (0.78–1.33)

0.884

Indigenous

1.31 (1.01–1.71)

0.042

1.17 (0.89–1.55)

0.268

Special care admission

Teenagers 12–16 years

0.82 (0.58–1.17)

0.281

0.79 (0.55–1.13)

0.199

Teenagers 17–18 years

1.08 (0.85–1.37)

0.525

1.00 (0.78–1.28)

0.980

Indigenous

1.41 (1.10–1.81)

0.007

1.30 (1.00–1.67)

0.051

Birthweight < 2500 g

Teenagers 12–16 years

0.96 (0.66–1.40)

0.853

0.94 (0.63–1.39)

0.749

Teenagers 17–18 years

1.16 (0.90–1.51)

0.253

1.08 (0.82–1.42)

0.574

Indigenous

1.43 (1.10–1.87)

0.008

1.32 (0.99–1.75)

0.056

Stillbirth

Teenagers 12–16 years

2.06 (0.84–5.03)

0.113

2.06 (0.84–5.03)

0.113

Teenagers 17–18 years

1.99 (1.03–3.76)

0.040

1.99 (1.03–3.76)

0.040

Indigenous

0.06 (0.28–1.53)

0.326

0.06 (0.28–1.53)

0.326


* Adjusted for maternal age (12–16 years, 17–18 years and adults > 19 years), smoking during pregnancy and Indigenous status. Adjusted for maternal age (12–16 years, 17–18 years and adults > 19 years), smoking during pregnancy, Indigenous status, low socioeconomic status and statistically significant () factors. Outcomes not affected by maternal age, Indigenous status and smoking during pregnancy (Apgar score < 7 at 5 min postpartum and resuscitation at birth) are not shown.

Received 
8 Sep 2008
accepted 
16 Mar 2009
Lucy N Lewis, RM, BSc(Health Sciences), MN, Research Midwife1,2
Martha Hickey, MB ChB, MD, FRANZCOG, Professor of Gynaecology2
Dorota A Doherty, BSc(Hons), PhD, Biostatistician2
S Rachel Skinner, MB BS, PhD, FRACP, Senior Lecturer and Adolescent Physician3
1 School of Paediatrics and Child Health, University of Western Australia, Perth, WA.
2 School of Women’s and Infants’ Health, University of Western Australia, Perth, WA.
3 Discipline of Paediatrics and Child Health, University of Sydney, Sydney, NSW.
Correspondence: 
Acknowledgements: 

This study was supported by a Princess Margaret Hospital for Children Clinical Research Scholarship and the Women and Infants Research Foundation, Western Australia. We would like to thank Maureen Hutchinson and the midwives and other health care workers at KEMH for the perinatal data supplied by the Obstetric and Gynaecology Clinical Care Unit. We are grateful for the biostatistical support provided by James Humphreys and Angela Jacques.

Competing Interests: 

None identified.

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