H e a l t h S t a t i s t i cs Q u a r t e r ly 2 3
Autumn 2004
Trends in live births by
mother’s country of birth
and other factors affecting
low birthweight in England
and Wales, 1983–2001
Aleks Collingwood Bakeo
Office for National Statistics
This article investigates trends
in low birthweight singleton live
births by mother’s country of
birth. 11.4 million birth records
from registration data in England
and Wales from 1983 to 2001
were used. The analysis focuses
on births to mothers born
in the UK and countries that
contribute to the main ethnic
minority groups in England and
Wales. The results show that the
prevalence of low birthweight
babies varies by mother’s country
of birth. Important differentials
also exist by mother’s age at
birth, multiplicity and registration
status.
INTRODUCTION
Health inequalities have been the focus of many research papers in recent
years. A range of socio-demographic factors affect health outcomes
including ethnicity, social class and gender. This study uses national data
from birth registration to examine factors affecting low birthweight from
1983 to 2001. Ethnicity is not routinely collected at birth registration,
but mothersʼ country of birth is collected. This study therefore focuses
on births to mothers born in the UK, Republic of Ireland, the Caribbean,
West Africa, East Africa, India, Pakistan, Bangladesh, former Yugoslavia
and the rest of Eastern Europe. The aim of this article is to investigate
variations in low birthweight live births, registration status, mean age
of mother at birth and multiplicity, among babies of mothers born in
countries that contribute to the main ethnic minority groups in England
and Wales.
Inequalities in birthweight are found between social classes, ethnic
groups, and by physical characteristics of the mother. Babies can have a
low birthweight either if they are born too early or if their fetal growth
has been restricted in some way. The extent to which this occurs can
be associated with socio-demographic factors such as the motherʼs age
and her ethnicity. Whether the baby is born inside or outside marriage
can reflect a number of social factors which can be associated with
birthweight. Babies from a multiple pregnancy are likely to be born
earlier in pregnancy than singleton babies and their birthweights are
therefore much lower on average.1 There is also evidence that low
birthweight is more prevalent in deprived areas of the UK.2,3
Babies of migrant mothers from the Caribbean, East and West
Africa and the Indian subcontinent living in the UK have different
birthweight distributions and lower birthweight on average than babies
25
NNa at itoi onna al lS St at at itsi ts itci cs s
H eal th Stati sti cs Q u a r t e rly 2 3
Autumn 2004
of predominantly White UK-born mothers. Birthweight is an important
predictor of mortality and morbidity in infancy.4,5 Low birthweight babies
have a greater risk of dying during the first months and years of life,
with the risks being particularly high among the smallest babies. There is
also increasing global evidence that birthweight relates to risk of chronic
disease in adulthood including diabetes and heart disease.6 Birthweight
analysis in this article focuses on low and very low birthweight. Trends
in mean birthweight are the subject of a separate article.
METHODS
Births that occurred in England and Wales from 1983 to 2001 were
classified by motherʼs country of birth. The country of birth groupings
used (Box 1) are based on geographical groupings used by the United
Nations Statistics Division and were designed to group births with
some common factors, including historical, social, biological or cultural
ancestry. The focus was also on numerically large migrant groupings,
so that analyses of trends were feasible. Birth records with ‘Ireland, not
statedʼ (2,306 cases) were not included in either Irish groupings. Births
to mothers born in Northern Ireland are included in the UK figures and
are also shown separately to enable comparisons to be made with the
Republic of Ireland.
Box one
Country of Birth Groupings
UK
Northern Ireland, Scotland, England, Wales, Channel islands, Isle
of Man.
Caribbean
Anguilla, Antigua & Barbuda, Aruba, Bahamas, Barbados, British
Virgin Islands, Cayman Islands, Cuba, Curacao, Dominica,
Dominican Republic, Grenada, Guadeloupe, Guyana, Haiti,
Jamaica, Martinique, Montserrat, Netherlands Antilles, Puerto
Rico, St Kitts and Nevis, St Lucia, St Vincent and the Grenadines,
Trinidad and Tobago, Turks & Caicos islands, United States
Virgin Islands.
West Africa
Benin, Ivory Coast, Liberia, Togo, Burkina Faso, The Gambia,
Ghana, Nigeria, Sierra Leone, Chad, Guinea, Guinea-Bissau, Mali,
Mauritania, Niger, Sénégal, Cape Verde.
A total of 11,831,706 live births (11,543,267 singleton births and
288,439 babies from multiple births) occurred in England and Wales
between 1983 and 2001 to women born in the UK, Caribbean, West
Africa, East Africa, India, Pakistan, Bangladesh, Former Yugoslavia, the
rest of Eastern Europe and the Republic of Ireland. Births that occurred
before 1983 were excluded because of the known poor quality of
birthweight data. Birthweights below 500 grams and above 6,000 grams
were excluded because of the possibility of incorrect recording. Births
for which birthweight or ages of mother at birth registration were missing
were also excluded. Of the live births that occurred from 1983 to 2001,
3.6 per cent (430,459) of births were excluded from the analysis for these
reasons. The proportions excluded ranged from 3.6 per cent (397,060) of
births to UK-born mothers to 5.2 per cent (3,312) of births to Caribbeanborn mothers and 7.2 per cent (6,196) of births to West Africa-born
mothers. Throughout this article, all analyses are restricted to singleton
live births except Figure 4, which includes babies from multiple births.
East Africa
Kenya, Tanzania, Uganda.
Statistical analyses include sex ratios and Chi-squared tests for trend. The
sex ratio is defined as the proportion of male to female live births. Chisquared tests for trend assess whether there is an increase or decrease in
birthweight proportions over time. The p-value stated is the significance
level. The smaller the p-value, the stronger the evidence of a linear trend
over time.
Republic of Ireland
Definitions
Low birthweight is defined as birthweights less than 2,500g and very low
birthweight as birthweights less than 1,500g.
Registration status is an indicator of the parentsʼ legal marital status. A
birth within marriage is that of a child born to parents who were lawfully
married to one another either at the date of the childʼs birth or when the
child was conceived, even if they later divorced or the father died before
the childʼs birth.
Births occurring outside marriage may be registered by both parents
jointly or by one parent. A joint registration records details of both
parents and requires them both to be present. A sole registration records
only the motherʼs details.4
The age of mother in years at the time of the babyʼs birth is derived
by the Office for National Statistics from her date of birth and the
babyʼs date of birth. Mean age of mother is the arithmetic average of
National Statistics
26
India
Pakistan
Bangladesh
Former Yugoslavia
Yugoslavia, Bosnia and Herzegovina, Croatia, Macedonia,
Montenegro, Serbia, Slovenia, Kosovo.
Rest of Eastern Europe
Czechoslovakia, Czech Republic, Hungary, Poland, Romania,
Albania, Bulgaria.
Northern Ireland
the motherʼs age at the time of birth. The mean was calculated for all
births and as a result the measure is affected by different patterns of
childbearing and the changing age distribution of women in England and
Wales born in each country.
RESULTS
Country of birth is presented in this article because ethnicity is not
routinely collected at birth registration. Table 1 shows the relationship
between these two characteristics among women in the 2001 Census
of Population. In 2001, an average of 54 per cent of females classified
into an ethnic group other than White British were born in the UK. This
proportion varied greatly between the ethnic groups. For example, 40
per cent of women classified as being of Indian ethnic origin were born
in India, 52 per cent of women classified as being of Bangladeshi ethnic
origin were born in Bangladesh and 64 per cent of women classified as
being of White Irish ethnic origin were born in the Republic of Ireland.
On the other hand, of those in the Black Other and Mixed categories, at
least 90 per cent were born in the UK.
H e a l t h S t a t i s t i cs Q u a r t e r ly 2 3
Republic of Ireland and an increase in numbers born in West Africa,
Bangladesh, former Yugoslavia and the rest of Eastern Europe. Figure
1 shows trends in sex ratios by motherʼs country of birth. There was no
difference in the sex ratio of babies born to mothers born in the UK. The
proportion of boys to girls for mothers born in India increased drastically.
A gradual increase in the sex ratio was also seen over time for babies of
mothers born in Pakistan, Caribbean and after 1987 the same pattern was
seen for babies of mothers born in Bangladesh.
Distribution of births and sex ratio
Table 2 shows the numbers of singleton live births by sex and country of
birth of mother. As the numbers of births each year in some groups were
small, they were grouped into five time periods, 1983–1986, 1987–1990,
1991–1994, 1995–1998, and 1999–2001. There was a decrease in
numbers born in the Caribbean, East Africa, India, Pakistan and the
Table 1
Autumn 2004
Census population by country of birth and ethnicity, females, 2001
England and Wales
Country of birth
United Kingdom
(including
Northern Republic of Eastern
Northern Ireland) Ireland
Ireland
Europe
Ethnicity
White: British
White: Irish
White: Other White
99.2
27.6
55.0
Asian or Asian British: Indian
Asian or Asian British: Pakistani
Asian or Asian British: Bangladeshi
Asian or Other Asian British: Other Asian
49.7
56.0
47.2
45.3
Black or Black British: Black Caribbean
Black or Black British: Black African
Black or Black British: Other Black
59.5
46.6
90.0
Mixed: White and Black Caribbean
Mixed: White and Black African
Mixed: White and Asian
Mixed: Other Mixed
95.8
88.5
89.4
93.0
0.4
7.9
0.5
0.1
64.3
0.5
Bangladesh
Pakistan
Other
South
Asia
Kenya
1.6
0.1
0.1
0.2
0.6
0.6
40.0
2.6
0.3
7.1
0.4
40.4
0.3
4.3
0.2
8.5
0.6
0.2
0.7
0.1
4.6
1.7
0.4
4.3
0.3
40.1
0.8
5.7
0.2
48.1
3.8
1.5
0.5
0.8
3.8
0.3
0.4
2.2
0.1
8.4
0.1
0.7
India
Caribbean Central and
and
Western
West Indies
Africa
0.1
40.7
0.1
0.0
0.1
0.7
0.1
0.0
0.1
0.1
0.0
0.1
0.1
0.1
0.2
0.2
0.2
0.1
0.3
0.2
0.4
0.6
1.4
1.3
0.2
0.2
52.0
1.5
0.1
0.2
5.4
0.7
0.3
0.1
0.1
1.0
0.2
0.1
34.2
1.2
0.4
Source: Census 2001
Table 2
Distribution of births and sex ratio by mother’s country of birth, 1983–2001
England and Wales
Country of birth
Key characteristics of
live singleton births
United
Kingdom
Total
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
Former
Pakistan Bangladesh Yugoslavia
Rest of
Eastern
Europe
Caribbean
West
Africa
East
Africa
India
2,211,610
2,348,296
2,265,648
2,171,527
1,491,814
18,042
14,461
10,654
9,459
7,574
11,740
14,744
17,294
20,602
14,987
24,294
22,815
19,060
15,462
9,015
43,392
35,809
28,762
25,715
19,228
52,695
48,460
48,926
49,085
40,730
16,416
19,576
22,073
27,901
22,586
482
469
1,010
2,302
5,876
2,631
2,245
2,441
4,026
5,558
24,556
23,733
20,148
18,494
11,345
13,094
12,744
11,578
10,537
7,526
Males
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
1,135,572
1,204,427
1,163,010
1,114,066
765,254
9,147
7,338
5,446
4,818
3,900
5,804
7,444
8,778
10,358
7,552
12,469
11,673
9,701
7,920
4,612
22,089
18,342
14,881
13,350
9,991
26,809
24,616
25,013
25,192
20,898
8,373
9,805
11,165
14,116
11,475
248
235
535
1,163
3,065
1,331
1,175
1,247
2,090
2,833
12,595
11,999
10,360
9,433
5,777
6,615
6,554
5,959
5,347
3,873
Females
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
1,076,038
1,143,869
1,102,638
1,057,461
726,560
8,895
7,123
5,208
4,641
3,674
5,936
7,300
8,516
10,244
7,435
11,825
11,142
9,359
7,542
4,403
21,303
17,467
13,881
12,365
9,237
25,886
23,844
23,913
23,893
19,832
8,043
9,771
10,908
13,785
11,111
234
234
475
1,139
2,811
1,300
1,070
1,194
1,936
2,725
11,961
11,734
9,788
9,061
5,568
6,479
6,190
5,619
5,190
3,653
Sex ratio
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
1.06
1.05
1.05
1.05
1.05
1.03
1.03
1.05
1.04
1.06
0.98
1.02
1.03
1.01
1.02
1.05
1.05
1.04
1.05
1.05
1.04
1.05
1.07
1.08
1.08
1.04
1.03
1.05
1.05
1.05
1.04
1.00
1.02
1.02
1.03
1.06
1.00
1.13
1.02
1.09
1.02
1.10
1.04
1.08
1.04
1.05
1.02
1.06
1.04
1.04
1.02
1.06
1.06
1.03
1.06
27
National Statistics
Republic Northern
of Ireland
Ireland
H eal th Stati sti cs Q u a r t e rly 2 3
Autumn 2004
Birthweight
From 1983 to 2001, the proportion of low birthweight babies
significantly increased over time for mothers born in India, Pakistan
and Bangladesh as shown in Table 3. In contrast, a significant decrease
in proportion over time was observed for mothers born in East Africa.
Mothers born in West Africa also showed a significant increase in the
proportion of low birthweight babies over the whole time period, whereas
Sex Ratio of live singleton births by mother’s
country of birth, 1983–2001
Figure 1
mothers born in the Caribbean showed no significant change over time.
Proportions were lower but fluctuated from 1983 to 2001 for mothers
born in former Yugoslavia, the rest of Eastern Europe, Republic of
Ireland and Northern Ireland.
Babies of mothers born in the West Africa, East Africa, India, Pakistan,
Bangladesh and the Republic of Ireland showed a significant increase in
the proportion of very low birthweight babies. The highest proportion
and most marked increase was among babies born to mothers from West
Africa. Proportions of very low birthweight babies to mothers born in the
Caribbean, former Yugoslavia, the rest of Eastern Europe and Northern
Ireland fluctuated from 1983 to 2001.
England and Wales
1.09
Throughout the time period, mothers born in East Africa, India,
Pakistan and Bangladesh consistently had the highest proportion of
low birthweight babies compared to babies of mothers born in all other
country groups. This was followed by babies of mothers born in the
Caribbean and West Africa. The pattern for very low birthweight babies
was very different. The highest proportions of very low birthweight
babies were to mothers born in West Africa, followed by mothers born
in the Caribbean. Although the proportions of low birthweight babies are
higher for mothers born in East Africa, India, Pakistan and Bangladesh
than for mothers born in the Caribbean or West Africa, Figure 2a shows
that this was only evident for babies weighing 1,500g–2,499g.
India
1.08
1.07
1.06
Sex Ratio
1.05
Caribbean
United Kingdom
East Africa
1.04
Pakistan
Bangladesh
1.03
1.02
1.01
West Africa
1.00
0.99
0.98
0.97
1983–1986
Table 3
1987–1990
1991–1994
1995–1998
1999–2001
Figure 2a also shows that the proportion of babies with birthweights
under 1,500g and 1,500–2,499g, were highest amongst babies of mothers
born in East Africa, India, Pakistan, Bangladesh, the Caribbean and West
Africa compared to babies of mothers born in the UK. The exception to
this was that the proportion of very low birthweight babies of mothers
born in Bangladesh was consistently lower than of babies of mothers
Low and very low birthweight babies by mother’s country of birth, 1983–2001
England and Wales
Country of birth
Key characteristics of
live singleton births
Caribbean
East
Africa
India
125,222
128,394
123,568
125,690
88,259
1,483
1,211
924
821
661
806
1,131
1,311
1,627
1,295
2,891
2,680
2,036
1,691
916
4,476
3,620
2,946
2,771
2,155
4,525
4,019
4,495
4,727
4,257
1,474
1,647
1,941
2,703
2,192
30
17
35
86
247
126
104
138
221
299
1,312
1,208
980
949
588
715
630
609
563
346
16,146
16,951
17,312
19,226
13,571
292
248
211
174
140
198
271
385
495
400
286
264
215
226
134
402
348
333
311
226
456
469
531
581
554
87
115
136
225
189
6
4
5
22
56
29
26
26
51
47
180
169
137
173
105
90
93
84
78
57
Proportions
Low Birthweight (<2500g)
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
Chi-squared test for trend
5.7
5.5
5.5
5.8
5.9
p=0.000
8.2
8.4
8.7
8.7
8.7
p=0.497
6.9
7.7
7.6
7.9
8.6
p=0.000
11.9
11.7
10.7
10.9
10.2
p=0.000
10.3
10.1
10.2
10.8
11.2
p=0.000
8.6
8.3
9.2
9.6
10.5
p=0.000
9.0
8.4
8.8
9.7
9.7
p=0.000
6.2
3.6
3.5
3.7
4.2
p=0.100
4.8
4.6
5.9
5.5
5.4
p=0.368
5.3
5.1
4.9
5.2
5.2
p=0.252
5.5
4.9
5.3
5.3
4.6
p=0.051
Very low birthweight (<1500g)
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
Chi-squared test for trend
0.7
0.7
0.8
0.9
0.9
p=0.000
1.6
1.7
2.0
1.8
1.8
p=0.208
1.7
1.8
2.2
2.4
2.7
p=0.000
1.2
1.2
1.1
1.5
1.5
p=0.005
0.9
1.0
1.2
1.2
1.2
p=0.000
0.9
1.0
1.1
1.2
1.4
p=0.000
0.5
0.6
0.6
0.8
0.8
p=0.000
1.2
0.9
0.5
1.0
1.0
p=0.611
1.1
1.2
1.1
1.3
0.8
p=0.363
0.7
0.7
0.7
0.9
0.9
p=0.009
0.7
0.7
0.7
0.7
0.8
p=0.982
Very low birthweight (<1500g)
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
National Statistics
28
Former
Pakistan Bangladesh Yugoslavia
Rest of
Eastern
Europe
West
Africa
Numbers
Low Birthweight (<2500g)
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
United
Kingdom
Republic Northern
of Ireland
Ireland
H e a l t h S t a t i s t i cs Q u a r t e r ly 2 3
Autumn 2004
born in the UK, over the whole time period. Figure 2a also shows the
dramatic decline in the 1,500–2,499g category for babies of mothers born
in East Africa.
A lower proportion of babies of mothers born in the Republic of Ireland
and Northern Ireland were 1,500–2,499g compared to babies of mothers
born in the UK.
In contrast, Figure 2b shows that mothers born in the UK had a higher
proportion of babies weighing 1,500–2,499g than mothers born in
Former Yugoslavia and the rest of Eastern Europe from 1987 to 2001.
The proportion in 1983–1986 among babies where mothers were born in
the former Yugoslavia was based on small numbers of births. The very
low birthweight category appears to show a different pattern for these
groups (see Figure 2b). A higher proportion of babies born to mothers in
Eastern Europe were of very low birthweight compared with those born
in the UK but these proportions were based on small numbers of births.
Registration status
Figure 2a
Tables 4 and 5 show changes in birth registration status from 1983 to
2001 by motherʼs country of birth for low birthweight babies under
2,500g and for babies with a birthweight of 2,500g or more. These need
to be interpreted in the light of overall differences between countries and
increases in the proportions of births outside marriage in the 1980s and
1990s.
Percentage of live singleton births by birthweight and mother’s country of birth, 1983–2001
England and Wales
11
Percentage of singleton births
10
9
8
United Kingdom
East Africa
Pakistan
Caribbean
India
Bangladesh
West Africa
7
6
5
4
Under 1,500g
1,500–2,499g
3
2
1
0
1983–1986
Figure 2b
1987–1990
1991–1994
1995–1998
1999–2001
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
1995–1998
1999–2001
Percentage of live singleton births by birthweight and mother’s country of birth, 1983–2001
England and Wales
11
Percentage of singleton births
10
9
United Kingdom
Republic of Ireland
Former Yugoslavia
Northern Ireland
8
Rest of Eastern Europe
7
6
5
4
3
Under 1,500g
2
1,500–2,499g
1
0
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
1983–1986
1987–1990
29
1991–1994
National Statistics
H eal th Stati sti cs Q u a r t e rly 2 3
Autumn 2004
Among babies in both birthweight categories born to Caribbean-born
mothers, at least 48 per cent of the births were registered as having
occurred outside marriage. This was a much higher proportion than
for babies born to mothers from the other countries. In particular, low
birthweight babies were more likely than those weighing 2,500g or
more to be registered by the mother alone. The proportions within each
category fluctuated between 1983–1986 and 1999–2001.
Table 4
In contrast, the proportion of babies of West African mothers registered
as having occurred outside of marriage was similar to that of babies
of UK-born mothers but these were more likely to be sole than joint
registrations. In both weight categories the proportion of babies born
inside marriage decreased significantly from 1983–1986 to 1999–2001.
The proportion of births registered outside marriage by both parents
increased to a greater extent than the proportions of sole registrations.
Proportion of births by registration status of babies weighing 2500g or more by mother’s country of birth,
1983–2001
England and Wales
Country of birth
Key characteristics of
live singleton births
United
Kingdom
Caribbean
East
Africa
80.7
72.6
66.6
60.9
56.9
p=0.000
49.5
50.6
52.3
52.4
44.5
p=0.239
81.0
71.4
61.1
60.3
63.5
p=0.000
97.1
95.4
91.3
86.7
81.7
p=0.000
98.4
98.1
97.5
97.3
97.7
p=0.000
99.4
99.0
98.6
98.3
98.4
p=0.067
99.6
99.6
99.1
99.3
99.1
p=0.260
90.3
86.7
81.7
79.4
86.3
p=0.014
87.8
84.8
81.2
81.6
77.7
p=0.001
81.3
72.0
71.5
70.3
68.5
p=0.000
83.7
75.8
72.7
71.9
70.8
p=0.000
Births outside marriage, joint registrations
1983–1986
12.4
1987–1990
19.4
1991–1994
25.6
1995–1998
31.0
1999–2001
35.1
Chi-squared test for trend
p=0.000
30.1
31.6
30.9
30.9
34.6
p=0.953
9.3
16.2
22.9
23.1
23.5
p=0.000
1.7
3.0
5.7
8.2
10.9
p=0.000
1.1
1.4
1.8
2.0
1.7
p=0.023
0.4
0.6
0.8
1.1
1.0
p=0.116
0.2
0.3
0.6
0.5
0.6
p=0.008
6.4
10.8
14.2
15.2
9.6
p=0.009
9.3
12.6
15.2
14.8
17.2
p=0.008
11.3
19.0
20.5
22.2
24.7
p=0.000
10.3
16.6
20.4
21.7
23.8
p=0.000
Births outside marriage, sole registrations
1983–1986
6.8
1987–1990
8.0
1991–1994
7.8
1995–1998
8.1
1999–2001
7.9
Chi-squared test for trend
p=0.000
20.4
17.8
16.8
16.7
20.9
p=0.058
9.6
12.3
16.0
16.5
12.9
p=0.027
1.2
1.6
3.0
5.1
7.5
p=0.000
0.5
0.5
0.7
0.8
0.6
p=0.001
0.2
0.4
0.5
0.6
0.6
p=0.741
0.2
0.2
0.3
0.3
0.3
p=0.593
3.3
2.4
4.1
5.4
4.1
p=0.508
2.9
2.6
3.6
3.6
5.1
p=0.635
7.4
9.1
8.0
7.6
6.7
p=0.675
6.0
7.6
6.9
6.4
5.3
p=0.136
Births inside marriage
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
Chi-squared test for trend
Table 5
Former
Pakistan Bangladesh Yugoslavia
Rest of
Eastern
Europe
West
Africa
India
Republic
of Ireland
Northern
Ireland
Proportion of births by registration status of babies weighing under 2500g (low birthweight) by mother’s country
of birth, 1983–2001
England and Wales
Country of birth
Key characteristics of
live singleton births
United
Kingdom
Births inside marriage
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
Chi-squared test for trend
Caribbean
West
Africa
East
Africa
India
Former
Pakistan Bangladesh Yugoslavia
Rest of
Eastern
Europe
Republic
of Ireland
Northern
Ireland
71.4
61.9
55.9
50.4
46.3
p=0.000
39.7
42.3
44.0
43.1
40.8
p=0.373
71.3
61.7
57.6
56.3
57.1
p=0.009
97.2
96.0
92.3
89.2
84.2
p=0.000
98.6
97.2
97.8
97.3
97.7
p=0.004
98.9
98.4
98.7
98.2
98.4
p=0.005
99.3
98.9
98.8
98.5
98.5
p=0.280
86.7
70.6
68.6
73.3
85.8
p=0.022
83.3
75.0
73.9
71.5
63.9
p=0.046
70.0
60.9
59.1
54.1
54.8
p=0.024
72.9
62.5
61.1
59.7
54.9
p=0.070
Births outside marriage, joint registrations
1983–1986
17.6
1987–1990
25.8
1991–1994
32.3
1995–1998
37.3
1999–2001
41.4
Chi-squared test for trend
p=0.000
34.1
33.9
34.1
35.4
34.8
p=0.913
13.8
21.0
23.5
25.0
27.4
p=0.000
1.2
2.4
5.4
6.6
9.6
p=0.000
1.0
1.7
1.3
1.7
1.8
p=0.297
0.6
1.0
0.8
1.1
1.0
p=0.021
0.3
0.2
0.6
1.0
0.9
p=0.854
10.0
23.5
28.6
17.4
9.3
p=0.002
11.9
19.2
19.6
21.3
27.4
p=0.041
17.5
26.3
27.8
31.5
31.1
p=0.022
14.0
23.8
26.4
31.1
34.1
p=0.006
Births outside marriage, sole registrations
1983–1986
11.1
1987–1990
12.3
1991–1994
11.9
1995–1998
12.3
1999–2001
12.3
Chi-squared test for trend
p=0.005
26.2
23.9
21.9
21.4
24.4
p=0.105
14.9
17.3
18.9
18.7
15.4
p=0.047
1.5
1.6
2.3
4.3
6.2
p=0.006
0.4
1.1
0.9
1.0
0.5
p=0.004
0.5
0.6
0.5
0.7
0.7
p=0.333
0.5
0.9
0.6
0.5
0.6
p=0.137
3.3
5.9
2.9
9.3
4.9
p=0.856
4.8
5.8
6.5
7.2
8.7
p=0.388
12.6
12.7
13.2
14.4
14.1
p=0.891
13.1
13.7
12.5
9.2
11.0
p=0.162
National Statistics
30
H e a l t h S t a t i s t i cs Q u a r t e r ly 2 3
Throughout the whole time period the proportion of births that occurred
inside marriage were highest for babies of mothers born in East Africa,
India, Pakistan and Bangladesh with very small proportions being
registered outside marriage. Low birthweight babies of mothers born
in East Africa were slightly more likely to have been registered inside
marriage than babies weighing 2,500g or more and the proportions of
sole registered low birthweight babies showed a significant increase
in both categories. Babies born to mothers born in Bangladesh show a
different pattern. Although the differences were small, the data indicate
that the proportion of sole registered births was marginally higher in the
low birthweight category than in the 2,500g or more category throughout
the time period.
The proportions of births that occurred inside marriage among mothers
born in the former Yugoslavia or in the rest of Eastern Europe generally
decreased significantly over time for both birthweight categories but
remained higher than that for babies of mothers born in the UK. The
proportions of births occurring outside marriage were higher for low
birthweight babies in both groups.
Autumn 2004
There was also a decrease in the proportion of births that occurred inside
marriage among babies of mothers born in the Republic of Ireland in
both birthweight categories and for Northern Ireland-born mothers with
babies weighing 2,500g or more. Low birthweight babies were up to
15 per cent less likely to be born inside marriage than babies weighing
2,500g or more. In common with the UK as a whole, the increase over
time in births outside marriage was observed mainly for jointly registered
births in Northern Ireland as in the Republic of Ireland.
Mean age of mother at birth
Table 6 compares the mean age of mothers having a birth in England and
Wales in 2001 with that in 1983. It should be noted that many mothers
born in other countries may have had one or more children before
arriving in England and Wales. In 1983, the highest mean age for births
in England and Wales was for mothers born in Former Yugoslavia (31.1
years), but in 2001, mothers born in East Africa had the highest mean age
(31.7 years). The lowest mean age in 1983 was of mothers born in the
UK (26.2 years) and the lowest mean age in 2001 was for mothers born
in Bangladesh (26.0 years).
Trends in mean age of mother at birth by mother’s country of birth, 1983–2001
Figure 3
England and Wales
a) African origin
b) South Asian origin
33
33
Caribbean
32
32
31
31
30
30
West Africa
29
29
28
28
27
27
26
East Africa
India
Pakistan
26
United Kingdom
25
25
24
24
23
United Kingdom
Bangladesh
23
1983
1985
1987
1989
1991 1993
1995
1997
1999
2001
1983
1987
1989
1991 1993
1995
1997
1999
2001
d) Former Yugoslavia and rest of Eastern Europe
c) Republic of Ireland, Northern Ireland
33
33
32
32
31
31
30
1985
Rest of Eastern Europe
30
Republic of Ireland
29
29
28
28
Former Yugoslavia
Northern Ireland
27
27
United Kingdom
26
26
25
25
24
24
23
United Kingdom
23
1983
1985
1987
1989
1991 1993
1995
1997
1999
2001
1983
1985
1987
1989
31
1991 1993
1995
National Statistics
1997
1999
2001
H eal th Stati sti cs Q u a r t e rly 2 3
Autumn 2004
Figure 3a shows that mothers born in the Caribbean and West Africa had
a higher mean age than UK-born mothers throughout the time period.
The mean age of mothers born in the UK and West Africa increased
steadily from 1983 to 2001, whereas the mean age of Caribbean-born
mothers shows a much steeper increase from 28.0 years in 1983 to 32.6
years in 1994, before decreasing rapidly to 29.3 years in 2001.
Figure 4
Percentage of multiple births by mother’s
country of birth, 1983–2001
England and Wales
4.5
West Africa
Figure 3c shows that as well as being consistently higher than for the UK
as a whole, the mean ages of mothers born in the Republic of Ireland and
Northern Ireland also increased over time. This increase was steeper for
those born in Northern Ireland compared to those born in the Republic of
Ireland. Figure 3d shows that the mean ages of mothers born in former
Yugoslavia and the rest of Eastern Europe dropped over the time period.
In 2001 the mean age was lower than for those born in the UK.
Percentage of multiple births
4.0
A steady increase was observed in the mean age of East African born
mothers as shown in Figure 3b. In contrast, a decline in mean age is
seen for Bangladesh-born women. The mean ages of mothers born in
India rose slightly from 1983 to 2001. The mean age of mothers born in
Pakistan hardly changed throughout the time period. Since 1993, mothers
born in Bangladesh and Pakistan both had lower mean ages at birth than
mothers born in the UK, and from 1999 mothers born in India and the
UK had the same mean age at birth.
Caribbean
3.5
3.0
East Africa
2.5
United Kingdom
India
2.0
Pakistan
1.5
Bangladesh
1.0
0.5
0.0
1983–1986
1987–1990
1991–1994
1995–1998
1999–2001
Multiple births
Figure 4 shows trends in the percentage of births that were multiple for
mothers born in the UK, Caribbean, West Africa, East Africa, India,
Pakistan and Bangladesh. It shows that mothers born in the Caribbean
and West Africa had the highest proportion of multiple births throughout
the time period compared to mothers from other countries. Mothers born
in India, Pakistan and Bangladesh had a lower proportion of multiple
births than mothers born in the UK. This proportion increased slightly
for mothers born in India and Pakistan and decreased for mothers born
in Bangladesh. The proportion of multiple births of mothers born in East
Africa increased the most notably over the time period although it was
still lower than for the UK in 2001.
DISCUSSION
These results are useful for understanding differences in birth outcomes.
Country of birth was used in the absence of information on ethnic origin.
Some understanding of the relationship between ethnicity and country of
birth was provided by the 2001 Census analysis. However, this analysis
related to women of all ages. It is likely that the relationship between
ethnicity and country of birth is weaker for women of childbearing age.
Females born in the UK who are not of White British ethnic origin are
likely to be second or subsequent generation migrants.
Table 6
Mean age of mother at birth by mother’s
country of birth, 1983 and 2001
England and Wales
1983
2001
United Kingdom
26.2
28.6
Caribbean
West Africa
East Africa
India
Pakistan
Bangladesh
Former Yugoslavia
Rest of Eastern Europe
Republic of Ireland
Northern Ireland
28.0
28.4
27.3
26.6
26.9
27.7
31.1
30.5
29.4
27.7
29.3
31.1
31.7
28.6
27.1
26.0
26.7
27.2
30.7
30.8
National Statistics
32
There were variations in the patterns of low birthweight and very low
birthweight by country of birth. There were even differences between
babies born to West African and Caribbean born mothers, who are
commonly believed to be of similar ancestry. These suggest that other
factors such as history, health-related behaviour and attitudes, and
socio-economic factors influence birthweight. There are also important
differences between these two groups in terms of family arrangements as
lone parenthood is much more common among Caribbeans compared to
West Africans.7,8 Studies have indicated that both of these groups have
high rates of pre-term births, which would also explain the high rates of
low birthweight and very low birthweight babies. The fact that both of
these groups had babies with higher proportions of low birthweight and
very low birthweight than the UK over time is a pattern also observed in
the US when comparing white American mothers to African American
mothers. In 2000, babies born to African-American mothers were twice
as likely to be low birthweight and nearly three times as likely to be very
low birthweight than babies born to white American mothers.9 While
low birthweight is more common among babies born outside marriage,
registration status is not a reliable estimator of low birthweight in some
ethnic groups. For example, mothers born in Bangladesh have a high
proportion of low birthweight babies but only a small proportion of
babies born outside marriage.
Babies of mothers born in East Africa, India, Pakistan and Bangladesh
had a very different birthweight distribution with lower proportions of
very low birthweight births and higher proportions in the 1,500–2,499g
group. It is unsurprising that proportions of low birthweight babies were
highest for babies born to mothers born in East Africa, Bangladesh,
India and Pakistan. South Asian countries have some of the highest
proportions of low birthweight babies in the world. Although birthweight
is unrecorded for 77 per cent of babies in these countries, estimates
published by UNICEF suggest that 30 per cent of babies born in
Bangladesh, 26 per cent of those born in India and 21 per cent of those
born in Pakistan in the late 1990s weighed under 2,500g.10 South Asian
babies born in the UK are lighter at birth but experience much ‘catch upʼ
growth in the first 10 years suggesting that environmental exposures are
important for growth trajectories postnatally.11 Studies have shown that
low birthweight can be caused by poverty, poor maternal health, and lack
of prenatal care12 and ethnic minority households are particularly at risk
of poverty, especially Pakistani and Bangladeshi households.13
H e a l t h S t a t i s t i cs Q u a r t e r ly 2 3
The age distribution of women giving birth in England and Wales varies
by country of birth of mother although this may in part reflect the age at
which the mother arrived in England and Wales. In each calendar year
the current age distribution of mothers will be affected by recent patterns
of migration. In the UK the age distribution of women giving birth has
changed over the last three decades as fewer younger mothers are having
babies and the proportion of births to women 35 years and over is rising.1
A similar pattern can be seen for mothers born in the Irish Republic.
Mean age of mothers born in former Yugoslavia and the rest of Eastern
Europe decreased over time. One possible explanation for this is that
mass migration from former Yugoslavia was confined to a short period
in the 1990s.14 Several factors may account for rises in the mean ages of
mothers born in West Africa, East Africa and India between 1983 and
2001 and having babies in England and Wales. Education, contraceptive
use and career have been reported as important factors in womenʼs
decisions to delay marriage, motherhood and subsequent births in most
developed countries. Mean age of mother has also increased steadily in
the US over the past three decades. In the United States, unlike England
and Wales, this rise has been widespread occurring for each ethnic
group.9
Key findings
●
●
●
●
●
The main limitation of these analyses by motherʼs country of birth
is that it excludes babies born to second and subsequent generation
migrants thus underestimating the number of births by ethnic group.
Birth registration data were used for the analysis and additional variables
associated with birthweight, such as gestation and parity, are either
not collected or provide only partial information. Another limitation is
the crude ‘East Africaʼ category which assumes mothers born in East
Africa to be of South Asian and mainly Indian origin. This grouping
was certainly reasonable for the early part of the period, but since the
late 1990s there have been migrants from Kenya and Tanzania of Black
African ethnicity.15 The nature of migration in the UK has changed
considerably over the years, and the 1990s have seen a large increase in
migration from Eastern European countries.14 To date, there is very little
on birth outcomes for these recent migrants. In addition, the numbers of
births and low birthweight babies of mothers born in former Yugoslavia
were very small before 1990 making it difficult to comment on trends.
This study is part of a larger project in the outcome of pregnancy.
Analyses of other differences by motherʼs country of birth and issues
relating to social class, deprivation and geographical variations are
explored in other papers which will be published separately.
ACKNOWLEDGEMENTS
This article arises from a research project entitled Monitoring inequalities
in the outcome of pregnancy which was funded by the Department
of Health on contract to Alison Macfarlane of City University. The
views expressed are those of the authors and not necessarily those
of the Department of Health. The members of the project team are
Nirupa Dattani, Joanne Maher and Aleks Collingwood Bakeo of ONS;
Christopher Dibben of the University of Oxford, Sam Pattenden of the
London School of Hygiene and Tropical Medicine, Seeromanie Harding
of the University of Glasgow and Helen Dolk of the University of Ulster.
The author(s) would like to acknowledge help and advice from Alison
Macfarlane.
Autumn 2004
●
Proportions of low birthweight babies are highest among
those born to mothers born in East Africa, India, Pakistan and
Bangladesh.
Proportions of very low birthweight babies are highest to mothers
born in the Caribbean and West Africa and the latter increased
during the 1980s and 1990s.
Low birthweight babies of mothers born in the UK, the Caribbean,
West Africa, former Yugoslavia, Eastern Europe, the Republic of
Ireland and Northern Ireland are more likely to be born outside
marriage, than larger babies.
Mothers born in the Caribbean and West Africa had a higher
mean age at birth than the UK mothers.
Caribbean and West African-born mothers had the highest
proportion of multiple births.
A greater increase in the proportion of multiple births was seen
for East Africa-born women than for the other South Asian
groups.
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National Statistics