Obesity, Ethnicity, and the Risk of Late Stillbirth

Abstract and Introduction

Abstract

Background: In high income countries there has been little improvement in stillbirth rates over the past two decades. Previous studies have indicated an ethnic disparity in the rate of stillbirths. This study aimed to determine whether maternal ethnicity is independently associated with late stillbirth in New Zealand.
Methods: Cases were women with a singleton, late stillbirth (≥28 weeks' gestation) without congenital abnormality, born between July 2006 and June 2009 in Auckland, New Zealand. Two controls with ongoing pregnancies were randomly selected at the same gestation at which the stillbirth occurred. Women were interviewed in the first few weeks following stillbirth, or at the equivalent gestation for controls. Detailed demographic data were recorded. The study was powered to detect an odds ratio of 2, with a power of 80% at the 5% level of significance, given a prevalence of the risk factor of 20%. A multivariable regression model was developed which adjusted for known risk factors for stillbirth, as well as significant risk factors identified in the current study, and adjusted odds ratios and 95% confidence intervals were calculated.
Results: 155/215 (72%) cases and 310/429 (72%) controls consented. Pacific ethnicity, overweight and obesity, grandmultiparity, not being married, not being in paid work, social deprivation, exposure to tobacco smoke and use of recreational drugs were associated with an increased risk of late stillbirth in univariable analysis. Maternal overweight and obesity, nulliparity, grandmultiparity, not being married and not being in paid work were independently associated with late stillbirth in multivariable analysis, whereas Pacific ethnicity was no longer significant (adjusted Odds Ratio 0.99; 0.51–1.91).
Conclusions: Pacific ethnicity was not found to be an independent risk factor for late stillbirth in this New Zealand study. The disparity in stillbirth rates between Pacific and European women can be attributed to confounding factors such as maternal obesity and high parity.

Table 1. Characteristics of women with late stillbirth compared with gestation matched controls
	Cases	Controls	Univariable OR 95% CI
n = 155	(%)	n = 310	(%)
*Maternal age*
<20	10	(6.5)	24	(7.7)	0.80	0.38–1.71
20–34	113	(72.9)	216	(69.7)	1.00	-
≥ 35	32	(20.7)	70	(22.6)	0.86	0.53–1.42
*Maternal ethnicity*
Maori	19	(12.3)	46	(14.8)	1.08	0.57–2.04
Pacific	48	(31.0)	67	(21.6)	1.88	1.13–3.13
European	55	(35.5)	139	(44.8)	1.00	-
Other	33	(21.3)	58	(18.7)	1.46	0.85–2.51
*Country of birth*
New Zealand	83	(53.6)	168	(54.2)	1.00	-
Other	72	(46.5)	142	(45.8)	1.03	0.69–1.54
*Marital status*
Married	84	(54.2)	202	(65.2)	1.00	-
Not married	71	(45.8)	108	(34.8)	1.60	1.07–2.38
*Deprivation Index*
1–4	91	(58.7)	218	(70.3)	1.00	-
5 (most deprived)	64	(41.3)	92	(29.7)	1.74	1.14–2.67
*School leaving age*
<17 years	36	(23.2)	56	(18.1)	1.37	0.85–2.18
≥17	119	(76.8)	254	(81.9)	1.00	-
*Employment in last month*
Paid work	41	(26.5)	118	(38.1)	1.00	-
Not in paid work	114	(73.6)	192	(61.9)	1.75	1.13–2.70
*Parity*
0	77	(49.7)	144	(46.5)	1.41	0.94–2.13
1–3	62	(40.0)	156	(50.9)	1.00	-
≥4	16	(10.3)	10	(3.2)	5.13	1.99–13.21
*BMI*
< 25	55	(35.5)	156	(50.3)	1.00	-
25–29.9	39	(25.2)	67	(21.6)	1.69	1.03–2.78
≥ 30	61	(39.4)	87	(28.1)	2.08	1.30–3.33
*Ethnic specific BMI groups*
Normal/underweight	57	(36.8)	151	(48.7)	1.00	-
Overweight	44	(28.4)	81	(26.1)	1.46	0.91–2.35
Obese	54	(34.8)	78	(25.2)	1.91	1.18–3.09
*Smoking in pregnancy*
Smoke-free	80	(51.6)	201	(64.8)	1.00
Passive only	29	(18.7)	43	(13.9)	1.67	0.99–2.83
Smoker	46	(29.7)	66	(21.3)	1.78	1.11–2.85
*Recreational drugs*
No drug use	142	(91.6)	298	(96.1)	1.00	-
Any drug use	13	(8.4)	12	(3.9)	2.35	1.02–5.42
*Previous preterm birth*
Yes	11	(7.10)	15	(4.84)	1.52	0.67–3.43
No	144	(92.80)	295	(95.16)	1.00	-
*Previous small for gestational age*
Yes	12	(7.74)	15	(4.84)	1.60	0.75–3.42
No	143	(92.26)	295	(95.16)	1.00	-
*Previous stillbirth*
Yes	2	(1.29)	3	(0.97)	1.33	0.22–7.98
No	152	(98.71)	307	(99.03)	1.00	-

Table 1. Characteristics of women with late stillbirth compared with gestation matched controls

Cases

Controls

Univariable OR
95% CI

n = 155

(%)

n = 310

(%)

Maternal age

<20

(6.5)

(7.7)

0.80

0.38–1.71

20–34

113

(72.9)

216

(69.7)

1.00

≥ 35

(20.7)

(22.6)

0.86

0.53–1.42

Maternal ethnicity

Maori

(12.3)

(14.8)

1.08

0.57–2.04

Pacific

(31.0)

(21.6)

1.88

1.13–3.13

European

(35.5)

139

(44.8)

1.00

Other

(21.3)

(18.7)

1.46

0.85–2.51

Country of birth

New Zealand

(53.6)

168

(54.2)

1.00

Other

(46.5)

142

(45.8)

1.03

0.69–1.54

Marital status

Married

(54.2)

202

(65.2)

1.00

Not married

(45.8)

108

(34.8)

1.60

1.07–2.38

Deprivation Index

1–4

(58.7)

218

(70.3)

1.00

5 (most deprived)

(41.3)

(29.7)

1.74

1.14–2.67

School leaving age

<17 years

(23.2)

(18.1)

1.37

0.85–2.18

≥17

119

(76.8)

254

(81.9)

1.00

Employment in last month

Paid work

(26.5)

118

(38.1)

1.00

Not in paid work

114

(73.6)

192

(61.9)

1.75

1.13–2.70

Parity

(49.7)

144

(46.5)

1.41

0.94–2.13

1–3

(40.0)

156

(50.9)

1.00

≥4

(10.3)

(3.2)

5.13

1.99–13.21

BMI

< 25

(35.5)

156

(50.3)

1.00

25–29.9

(25.2)

(21.6)

1.69

1.03–2.78

≥ 30

(39.4)

(28.1)

2.08

1.30–3.33

Ethnic specific BMI groups

Normal/underweight

(36.8)

151

(48.7)

1.00

Overweight

(28.4)

(26.1)

1.46

0.91–2.35

Obese

(34.8)

(25.2)

1.91

1.18–3.09

Smoking in pregnancy

Smoke-free

(51.6)

201

(64.8)

1.00

Passive only

(18.7)

(13.9)

1.67

0.99–2.83

Smoker

(29.7)

(21.3)

1.78

1.11–2.85

Recreational drugs

No drug use

142

(91.6)

298

(96.1)

1.00

Any drug use

(8.4)

(3.9)

2.35

1.02–5.42

Previous preterm birth

Yes

(7.10)

(4.84)

1.52

0.67–3.43

144

(92.80)

295

(95.16)

1.00

Previous small for gestational age

Yes

(7.74)

(4.84)

1.60

0.75–3.42

143

(92.26)

295

(95.16)

1.00

Previous stillbirth

Yes

(1.29)

(0.97)

1.33

0.22–7.98

152

(98.71)

307

(99.03)

1.00

Table 2. Multivariable odds ratios for maternal characteristics associated with late stillbirth
	Adjusted OR* (95% CI)
*Maternal age*
<20	0.61	0.24–1.52
20–34	1.00	-
≥35	0.82	0.46–1.46
*Maternal ethnicity*
Maori	0.41	0.17–0.96
Pacific	0.99	0.51–1.91
European	1.00	-
Other	1.69	0.92–3.11
*Marital status*
Married	1.00	-
Not married	1.75	1.03–2.98
*Deprivation Index*
1–4	1.00	-
5	1.20	0.72–2.00
*Employment in last month*
Paid work	1.00	-
Not in paid work	1.66	1.00–2.77
*Parity*
0	1.75	1.08–2.83
1–3	1.00	-
≥4	4.22	1.44–12.40
*BMI*
< 25	1.00	-
25–29.9	1.75	1.00–3.05
≥ 30	2.11	1.14–3.91
*Smoking*
Smoke-free	1.00	-
Passive only	1.36	0.74–2.47
Smoker	1.28	0.71–2.32
*Recreational drugs*
No drug use	1.00	-
Any drug use	2.77	0.96–7.99

Table 2. Multivariable odds ratios for maternal characteristics associated with late stillbirth

Adjusted OR* (95% CI)

Maternal age

<20

0.61

0.24–1.52

20–34

1.00

≥35

0.82

0.46–1.46

Maternal ethnicity

Maori

0.41

0.17–0.96

Pacific

0.99

0.51–1.91

European

1.00

Other

1.69

0.92–3.11

Marital status

Married

1.00

Not married

1.75

1.03–2.98

Deprivation Index

1–4

1.00

1.20

0.72–2.00

Employment in last month

Paid work

1.00

Not in paid work

1.66

1.00–2.77

Parity

1.75

1.08–2.83

1–3

1.00

≥4

4.22

1.44–12.40

BMI

< 25

1.00

25–29.9

1.75

1.00–3.05

≥ 30

2.11

1.14–3.91

Smoking

Smoke-free

1.00

Passive only

1.36

0.74–2.47

Smoker

1.28

0.71–2.32

Recreational drugs

No drug use

1.00

Any drug use

2.77

0.96–7.99

Relationship between Obesity, Ethnicity and Risk of Late Stillbirth

Abstract and Introduction

Abstract

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Relationship between Obesity, Ethnicity and Risk of Late Stillbirth

Abstract and Introduction

Abstract

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Tables

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