Late preterm birth is a risk factor for growth faltering in early childhood: a cohort study.

Abstract

Rates of preterm birth are increasing worldwide and this increase is mostly due to infants born between 34 and 36 weeks of gestational age, the so-called "late preterm" births. The aim of this study was to assess the effect of late preterm birth over growth outcomes, assessed when children were 12 and 24 months old.
In 2004, all births taking place in Pelotas (Southern Brazil) were recruited for a cohort study. Late preterm (34/0-36/6 weeks of gestational age) and term children (37/0-42/6 weeks) were compared in terms of weight-for-age, length-for-age and weight-for-length z-scores. Weight-for-age, length-for-age and weight-for-length z-scores below -2 were considered, respectively, underweight, stunting and wasting. Singleton newborns with adequate weight for gestational age at birth, successfully followed-up either at 12 or 24 months of age were analyzed and adjusted odds ratios with 95% confidence intervals calculated through logistic regression.
3285 births were included, 371 of whom were late preterm births (11.3%). At 12 months, prevalence of underweight, stunting and wasting were, respectively, 3.4, 8.7 and 1.1% among late preterm children, against 1.0, 3.4 and 0.3% among term children. At 24 months, correspondent values were 3.0, 7.2 and 0.8% against 0.8, 2.9 and 0.4%. Comparing with the term children, adjusted odds of being underweighted among late preterm children was 2.57 times higher (1.27; 5.23) at 12 months and 3.36 times higher (1.56; 7.23) at 24; of being stunted, 2.35 (1.49; 3.70) and 2.30 (1.40; 3.77); and of being wasted, 3.98 (1.07; 14.85) and 1.87 (0.50; 7.01). Weight gain from birth to 12 and 24 months was similar in late preterm and term children, whereas length gain was higher in the former group in both periods.
Late preterm children grow faster than children born at term, but they are at increased risk of underweight and stunting in the first two years of life. Failure to thrive in the first two years may put them at increased risk of future occurrences of serious morbidity in late childhood and of chronic disease development in adult life.

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BioMed Central
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BMC Pediatrics
Open Access
Research article
Late preterm birth is a risk factor for growth faltering in early
childhood: a cohort study
Ina S Santos*1, Alicia Matijasevich1, Marlos R Domingues1,
Aluísio JD Barros1, Cesar G Victora1 and Fernando C Barros1,2
Address: 1Postgraduate Program in Epidemiology, Department of Social Medicine, Federal University of Pelotas, Pelotas, Brazil and 2Postgraduate
Program in Health and Behavior, Catholic University of Pelotas, Pelotas, Brazil
Email: Ina S Santos* - inasantos@uol.com.br; Alicia Matijasevich - amatija@yahoo.com; Marlos R Domingues - coriolis@vetorial.net;
Aluísio JD Barros - abarros.epi@gmail.com; Cesar G Victora - cvictora@terra.com.br; Fernando C Barros - fcbarros.epi@gmail.com
* Corresponding author
Abstract
Background: Rates of preterm birth are increasing worldwide and this increase is mostly due to
infants born between 34 and 36 weeks of gestational age, the so-called "late preterm" births. The
aim of this study was to assess the effect of late preterm birth over growth outcomes, assessed
when children were 12 and 24 months old.
Methods: In 2004, all births taking place in Pelotas (Southern Brazil) were recruited for a cohort
study. Late preterm (34/0-36/6 weeks of gestational age) and term children (37/0-42/6 weeks) were
compared in terms of weight-for-age, length-for-age and weight-for-length z-scores. Weight-for-
age, length-for-age and weight-for-length z-scores below -2 were considered, respectively,
underweight, stunting and wasting. Singleton newborns with adequate weight for gestational age at
birth, successfully followed-up either at 12 or 24 months of age were analyzed and adjusted odds
ratios with 95% confidence intervals calculated through logistic regression.
Results: 3285 births were included, 371 of whom were late preterm births (11.3%). At 12 months,
prevalence of underweight, stunting and wasting were, respectively, 3.4, 8.7 and 1.1% among late
preterm children, against 1.0, 3.4 and 0.3% among term children. At 24 months, correspondent
values were 3.0, 7.2 and 0.8% against 0.8, 2.9 and 0.4%. Comparing with the term children, adjusted
odds of being underweighted among late preterm children was 2.57 times higher (1.27; 5.23) at 12
months and 3.36 times higher (1.56; 7.23) at 24; of being stunted, 2.35 (1.49; 3.70) and 2.30 (1.40;
3.77); and of being wasted, 3.98 (1.07; 14.85) and 1.87 (0.50; 7.01). Weight gain from birth to 12
and 24 months was similar in late preterm and term children, whereas length gain was higher in the
former group in both periods.
Conclusion: Late preterm children grow faster than children born at term, but they are at
increased risk of underweight and stunting in the first two years of life. Failure to thrive in the first
two years may put them at increased risk of future occurrences of serious morbidity in late
childhood and of chronic disease development in adult life.
Published: 16 November 2009
BMC Pediatrics 2009, 9:71doi:10.1186/1471-2431-9-71
Received: 19 July 2009
Accepted: 16 November 2009
This article is available from: http://www.biomedcentral.com/1471-2431/9/71
© 2009 Santos et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Background
Gestational age is among the most important aspects that
dictate short and long-term health of a newborn. As the
fetus needs time to grow, and to develop tissues and
organs, premature birth can have adverse consequences
for the neonatal infant. Rates of preterm birth are increas-
ing worldwide [1] and there is evidence that this increase
is mostly due to infants born between 34 and 36 weeks of
gestational age the so-called "late preterm" births [2].
Although less than three weeks before term may appear to
be a minor difference, its implications for intrauterine
development are substantial [3].
Unfavorable outcomes associated with preterm birth are
well described [4], however most studies assess preterm
birth as a dichotomous variable based on the cutoff point
of 37 weeks, without considering the differences that may
exist between a 35-week and a 37-week infant. Few studies
have addressed the consequences of late preterm in com-
parison with term births. Although health problems are
not as evident in infants born 34-36 weeks as those born
before 32 weeks, late preterm children are still at greater
risk of health problems than those born at term [5].
The consequences of being born late preterm on later
health and development in the first two years of life are
not yet known. Hence, the aim of this paper is to evaluate
growth outcomes, assessed when children were 12 and 24
months old, by comparing late-preterm and term children
that are currently being followed-up by the 2004 Pelotas
Birth Cohort.
Methods
Pelotas is located in Southern Brazil, with a population of
323,000 people, 93% of them living in the urban area
(2000 Brazilian Demographic Census, IBGE). During the
entire year of 2004, all births taking place in the city were
recruited for a birth cohort study. More than 99% of all
deliveries took place in hospitals. Non-hospital deliveries
were also included in the cohort, since mothers normally
sought a maternity ward after delivery, and were thus
recruited to the study at this stage. Births were identified
by daily visits to the five maternity hospitals, with the
mothers interviewed soon after delivery using a pre-tested
structured questionnaire. This questionnaire included
questions on demographic, environmental, and socioeco-
nomic variables and on the characteristics of pregnancy,
labor, delivery, and healthcare service utilization. In addi-
tion to the mother interview, all babies were weighed and
measured. Length measurements were taken using
ARTHAG infantometers, and weight was determined
using the hospital scales, which were regularly calibrated
by researchers. Birth weight was measured by the nursing
professional overseeing delivery. Losses and refusals were
below 1%. The cohort methodology is best described else-
where [6].
In the first 24 hours after birth, children were examined by
trained field workers supervised by a pediatrician. Gesta-
tional age was estimated using an algorithm proposed by
the National Center for Health Statistics (NCHS) [7]
based on the last menstrual period [8]. If the birthweight,
length and head circumference were inconsistent with the
normal curves for the gestational age calculated, or if the
date of the last menstrual period was unknown, then ges-
tational age was determined using the Dubowitz method
[9] which was performed on almost all newborns. Pre-
term birth was defined as birth at <37 weeks of gestational
age. Preterm births of between 34/0 and 36/6 weeks of
gestational age were defined as late preterm births. Births
with unknown gestational age accounted for 0.3% (n =
13) of all births. Intra-uterine growth restriction (IUGR) at
birth was defined according to Williams' curves for birth
weight for gestational age and sex [10]. Newborns with
weight for age below the 10th percentile of the Williams
curve were classified as having IUGR and were excluded
from the current analyses.
Family income in the month prior to delivery was col-
lected as a continuous variable and quintiles were calcu-
lated. Women who were single, widowed, divorced, or
lived without a partner were classified as single mothers.
Maternal skin colour was classified as white or black/
mixed according to the interviewer's observation. The
mother's formal education was categorized as 0, 1-4, 5-8
and ≥ 9 completed school years. Maternal age in years at
delivery was categorized as 12-15, 16-19, 20-34 and ≥ 35
years. Smoking habits during pregnancy were based on
maternal self-report. Women who smoked at least one cig-
arette per day in any trimester of pregnancy were classified
as smokers during pregnancy. Type of delivery was classi-
fied as vaginal or caesarian section.
Children whose mothers lived in the urban area of Pelotas
were visited at home at twelve months and two years of
age. Mothers were interviewed by trained interviewers and
anthropometric measurements were performed both in
the mother and her child. Information on the child's
breastfeeding and frequency of symptoms and diseases
was collected. Losses to follow-up and refusals to partici-
pate in the study were 5.7% and 6.5% for the twelve
month and two year old follow-ups, respectively.
Maternal and child weight, as well as maternal height and
child length were measured after completing the interview.
Children were weighed undressed together with their moth-
ers after the mother had been weighed alone, and the child
weight was calculated as the difference between the two
measures. Tanita electronic scales (Tanita, Tokyo, Japan)
with a 150 kg maximum and 100 g precision were used in
the study. Scales were calibrated on a weekly basis using
standard weights. Child's length was measured in supine
position using an AHRTAG portable infantometer with 1

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mm precision, that was custom built from wood for the pur-
pose of the study. Interviewers underwent training and
standardization in anthropometric techniques and 5-10% of
interviews were repeated by supervisors. Growth indicators
(weight-for-age, length-for-age and weight-for-length z-
scores) were calculated based on the growth curves pub-
lished by the World Health Organization using Anthro 2005
software [11]. Children with z-scores below -2 for any of the
above indicators were considered to have growth failure.
Children with weight-for-age z-scores below -2 were classi-
fied as underweight; those with length-for-age z-scores below
-2, as stunted; and those with weight-for-length z-scores
below -2, as wasted. Weight and length gains between birth
and each follow-up visit were calculated by subtracting the
initial weight/length from the last weight/length values.
Information about child health problems was collected at
the twelve month and two year follow-ups. Any episode of
wheezing, medical diagnosis of pneumonia, diarrhea in
the last fifteen days before the interview was performed,
and hospital admissions (defined as a readmission after
being discharged in the post-delivery period) were
reported by the mothers.
All analyses were restricted to newborns from singleton
pregnancies, with adequate weight for age at birth, that
were successfully followed-up either at twelve months or
at two years of age. Comparison categories were late pre-
term (34/0-36/6 weeks of gestational age) and term chil-
dren (37/0-42/6). Crude associations between late
preterm birth and each growth indicator (considering
each of the growth indicators as individual outcomes)
were explored using the chi-squared test. Multivariable
analyses were carried out using logistic regression for
growth failure and linear regression for weight and length
gains. Potential confounders of the association between
late preterm birth and each outcome were entered in the
adjusted analysis. An operational definition of confound-
ing was used, that is, variables that were associated with
both the outcome and the predictor of interest, and were
not part of the causal chain. The standard significance
level of 5% was used, but variables with a p-value ≤ 0.2
were retained in the model in order to control for residual
confounding.
The study protocol was approved by the Medical Research
Ethics Committee of the Federal University of Pelotas
Medical School, affiliated with the Brazilian Federal Med-
ical Council, and by the World Health Organization. Writ-
ten informed consent was obtained from mothers prior to
any data collection.
Results
The sample included 3285 singleton live births with ade-
quate weight for gestational age at birth, 371 of whom
were late preterm births (11.3%). Table 1 shows preva-
lence and crude odds of being born late preterm for a set
of maternal characteristics in the 2004 Pelotas Birth
Cohort. Late preterm births were associated with family
income, mother's skin color and maternal schooling.
There was an almost twofold increase in the prevalence of
late preterm birth in the poorest group, compared with
the richest group (16.8% vs. 8.5%). Black/mixed skin-
color mothers were more likely to deliver late preterm
children than white skin-color mothers (14.2% vs.
10.3%). Prevalence of late preterm births was higher
among less educated mothers (15.9% in mothers with 0-
4 years of schooling vs. 9.6% in those with nine years or
more). Prevalence of late preterm births also decreased
with increasing maternal age (19.3% among adolescent
mothers aged 12-15 years and 9.5% among those aged 35
years or older). No difference was found in prevalence of
late preterm births in relation to maternal height.
Mothers of late preterm children reported shorter breast-
feeding duration at the 12 and 24 month interviews than
mothers of term children (Table 2). Prevalence of wheez-
ing and hospitalizations from birth up to 12 months of
age were higher among late preterm children than among
children born at term. From birth to 24 months pneumo-
nia and hospitalization, but not wheezing, were reported
more frequently by mothers of late preterm children.
At birth, late preterm children weighed on average
2806.83 (SD: 402.23) grams and measured 46.69 (SD:
2.13) cm in length. The corresponding values for term
newborns were 3365.05 (SD: 387.93) grams and 48.98
(SD: 1.91) cm. At 12 and 24 months late preterm children
weighted on average 9.40 (SD: 1.22) and 12.00 (SD: 1.58)
kilograms, respectively, and measured 73.47 (SD: 2.76)
and 85.70 (SD: 3.54) cm in length, respectively. The cor-
responding values for term children were 9.90 (SD: 1.27)
and 12.67 (SD: 1.71) kilograms and 74.75 (SD: 2.90) and
87.11 (SD: 3.48) cm at 12 and 24 months, respectively.
From birth to 12 months, late preterm children gained on
average 61.66 (SE: 66.72) grams more in weight and 1.04
(SE: 0.15) cm more in length than term infants. From
birth to 24 months late preterm children gained on aver-
age 121.31 (SE: 90.81) grams less than term children,
whereas their mean gain in length was 0.88 (SE: 0.18) cm
higher. Contrary to what was observed with regard to dif-
ferences in weight gain, differences in length gain were sta-
tistically significant in both follow-ups.
Prevalence of growth failure at 12 and 24 months was
greater among late preterm children than among term
children (Table 2). At 12 months the crude odds of being
underweighted, stunted and wasted were respectively,
3.39, 2.72 and 4.61 higher among late preterm than
among term children (Table 3). At 24 months, the corre-

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sponding odds were twice as high as for term children
(3.98, 2.61 and 2.34) (Table 4).
Adjusted analyses for growth failure, when comparing late
preterm with term children at 12 months, accounted for
maternal (family income, maternal skin color, maternal
schooling, maternal age and height, and smoking during
pregnancy) and child characteristics (breastfeeding dura-
tion and history of wheezing, pneumonia and hospitali-
zation). Adjusted odds of being underweight, stunted and
wasted at 12 months of age among late preterm children
were more than twice as high as for term children as indi-
cated by the OR (2.57, 2.35 and 3.98, respectively) (Table
3). Adjusted linear regression analyses confirmed what
was observed in the crude analyses, with late preterm chil-
dren gaining 1.19 cm more in length than term children
and with no difference in weight gain (Table 3).
At 24 months, adjusted odds of being underweight and
stunted remained statistically significant (OR = 3.36 and
2.30, respectively) (Table 4). Odds of being wasted at 24
months among late preterm and term children were not
statistically different in the crude and in the adjusted anal-
ysis. Regression coefficients showed that late preterm chil-
dren continued growing faster than term children during
the second year and gained 1.26 cm more in length than
children born at term.
Discussion
This study evaluated the consequences of late preterm
birth on child growth in the first two years of life as com-
pared to term deliveries in a population-based cohort
from a middle-income country. Among the strengths of
the study, besides sample size, are the low rates of refusal
and loss to follow-up, and the prospective cohort design
that allows assessment of temporal relationships.
A key limitation of the study is that most of the confound-
ers studied were self-reported by mothers. Furthermore, in
the analyses of late preterm birth and wasting at 12 and 24
months of age, the low number of children born late pre-
term that were wasted resulted in reduced precision.
Some methodological issues of this study are worthy of
being discussed. First, some of the increase in morbidity
among late preterm children may be attributable to obser-
Table 1: Maternal characteristics, prevalence and crude odds ratios (OR) with 95% confidence interval (95% CI) for being born late
preterm in the 2004 Pelotas Birth Cohort.
VariablesnLate preterm births % Crude OR (95% CI)p*
Family income (quintiles)
1 (lowest)
2
3
4
5 (highest)
Marital status
Single mother
With partner
Maternal skin color
Black/mixed
White
Maternal schooling (years)
0-4
5-8
≥ 9
Maternal age (years)
12-15
16-19
20-34
≥ 35
Maternal height (cm)
< 150
≥ 150
Smoking during pregnancy
Yes
No
Type of delivery
Caesarean section
Vaginal
609
630
656
721
669
16.8
11.1
10.4
10.3
8.5
2.16 (1.53; 3.05)
1.34 (0.93; 1.94)
1.24 (0.86; 1.80)
1.23 (0.85; 1.76)
Reference
<0.001
0.754
513
2772
11.7
11.2
1.05 (0.78; 1.41)
Reference
0.002
857
2428
14.2
10.3
1.45 (1.15; 1.83)
Reference
0.001
473
1306
1473
15.9
11.7
9.6
1.78 (1.32; 2.41)
1.25 (0.98; 1.60)
Reference
0.004
83
530
2216
454
19.3
14.7
10.5
9.5
2.03 (1.16; 3.57)
1.47 (1.11; 1.94)
0.89 (0.63; 1.25)
Reference
0.222
194
3057
13.9
11.1
1.30 (0.85; 1.98)
Reference
0.051
745
2540
13.3
10.7
1.28 (1.00; 1.63)
Reference
0.365
1507
1778
11.8
10.8
1.11 (0.89; 1.37)
Reference
* Wald test

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vation and detection bias, because mothers and medical
doctors may be more attentive to monitor symptoms and
signs of medical complications and diseases in preterm
than in term infants. However, higher hospitalization
rates indicate that late preterm children are at increased
risk of developing more severe illnesses than term chil-
dren [12]. A small number of studies have investigated
short-term rehospitalization rates (2-4 weeks of discharge
from the birth hospitalization) among late preterm chil-
dren [12-14]. These studies all reported higher rehospital-
ization rates among late preterm children than in term
infants. We were able to locate only two published studies
about rehospitalization among late preterm children after
the neonatal period [15,16]. Escobar et al found that ges-
tational age of 36 weeks was a predictor of elevated risk for
hospitalization within 15 to 182 days after discharge [15].
McLaurin et al showed that late-preterm infants, whether
discharged early (<4 days from the date of birth) or late
Table 2: Child characteristics at 12 and 24 months of age (2004 Pelotas Birth Cohort).
VariablesN Late preterm children n (%)Term children n (%) p*
Newborn's sex
Male
Female
0.241
1688
1597
180 (48.5)
191 (51.5)
1508 (51.8)
1406 (48.3)
FROM BIRTH TO 12 MONTHS:
Duration breastfeeding (BF) (months)
Never BF
<3
3-5
> = 6
0.035
112
674
591
1841
17 (4.8)
84 (23.5)
77 (21.5)
180 (50.3)
95 (3.3)
590 (20.6)
514 (18.0)
1661 (58.1)
History of wheezing2001241 (67.3) 1760 (61.5)0.032
History of pneumonia255 34 (9.5)221 (7.7)0.239
History of diarrhea in the last 15 days 438 60 (16.8) 378 (13.2)0.064
History of hospitalization 54398 (27.4) 445 (15.5) <0.001
AT 12 MONTHS:
Underweight
Stunting
Wasting
41
127
11
12 (3.4)
31 (8.7)
4 (1.1)
29 (1.0)
96 (3.4)
7 (0.3)
<0.001
<0.001
0.008
FOM BIRTH TO 24 MONTHS:
Duration breastfeeding (months)
Never BF
<3
3-5
6-11
12-23
Still BF
0.022
112
674
590
605
525
722
17 (4.7)
84 (23.4)
77 (21.5)
46 (12.8)
55 (15.3)
80 (22.3)
95 (3.3)
590 (20.5)
513 (17.9)
559 (19.5)
470 (16.4)
642 (22.4)
History of wheezing2395282 (77.5)2113 (73.1)0.072
History of pneumonia42661 (17.0) 365 (12.7)0.023
History of hospitalization 750132 (36.9)618 (21.7) <0.001
AT 24 MONTHS:
Underweight
Stunting
Wasting
33
107
13
11 (3.0)
26 (7.2)
3 (0.8)
22 (0.8)
81 (2.9)
10 (0.4)
<0.001
<0.001
0.184
Total3285371 2914-
* Wald test

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Table 3: Crude and adjusted odds ratios (OR) with 95% confidence interval (95% CI) for growth indicators at 12 months among late
preterm children, compared to term children (2004 Pelotas Birth Cohort).
Indicators Crude OR (95% CI)PAdjusted OR (95% CI)p
Underweight
Term birth
Late preterm birth
Stunting
Term birth
Late preterm birth
Wasting
Term birth
Late preterm birth
<0.0010.009
Reference
3.39 (1.71; 6.70)
Reference
2.57 (1.27; 5.23)1
<0.001<0.001
Reference
2.72 (1.78; 4.14)
Reference
2.35 (1.49; 3.70)2
0.0150.040
Reference
4.61 (1.34; 15.84)
Reference
3.98 (1.07; 14.85)3
ANTHROPOMETRIC GAINS:
Crude β(SE)P Adjusted β(SE)p
Weight gain 0-12 (g/year)4
Length gain 0-12 (cm/year)4
61.66 (66.72)
1.04 (0.15)
0.355
<0.001
103.14 (65.59)5
1.19 (0.15)6
0.116
<0.001
1 adjusted for family income, maternal skin color, schooling, smoking, maternal height, breastfeeding 0-12, pneumonia 0-12, and hospitalizations 0-12
2 adjusted for family income, maternal skin color, schooling, maternal age, maternal height, smoking, breastfeeding 0-12, wheezing 0-12, pneumonia
0-12, and hospitalizations 0-12
3 adjusted for family income, schooling, maternal age and height, breastfeeding 0-12, pneumonia 0-12, and hospitalizations 0-12
4 weight and length gains by late preterm children from birth to 12 months of age in comparison to term children
5 adjusted for family income, maternal skin color, schooling, maternal age and height, breastfeeding 0-12, and wheezing 0-12
6 adjusted for family income, maternal skin color, schooling, maternal height, smoking, breastfeeding 0-12, diarrhea 0-12, and hospitalizations 0-12
Table 4: Crude and adjusted odds ratios (OR) with 95% confidence interval (95% CI) for growth indicators at 24 months among late
preterm children, comparatively to term children (2004 Pelotas Birth Cohort).
IndicatorsCrude OR (95% CI)PAdjusted OR (95% CI)p
Underweight
Term birth
Late preterm birth
Stunting
Term birth
Late preterm birth
Wasting
Term birth
Late preterm birth
<0.0010.002
Reference
3.98 (1.91; 8.27)
Reference
3.36 (1.56; 7.23)1
<0.0010.001
Reference
2.61 (1.66; 4.12)
Reference
2.30 (1.40; 3.77)2
0.1970.351
Reference
2.34 (0.64; 8.56)
Reference
1.87 (0.50; 7.01)3
ANTHROPOMETRIC GAINS:
Crude β(SE)P Adjusted β(SE)p
Weight gain 0-24 m (g)4
Length gain 0-24 m (cm)4
-121.31 (90.81)
0.88 (0.18)
0.182
<0.001
13.23 (89.37)5
1.26 (0.18)6
0.882
<0.001
1 adjusted for family income, maternal skin color, schooling, maternal height, smoking, breastfeeding 0-24, pneumonia 0-24 and hospitalizations 0-24
2 adjusted for family income, maternal skin color, schooling, maternal age and height, smoking, breastfeeding 0-24, wheezing 0-24, pneumonia 0-24,
hospitalizations 0-24
3 adjusted for family income, maternal skin color and height, pneumonia 0-24 and hospitalizations 0-24
4 weight and length gains by late preterm children from birth to 24 months of age in comparison to term children
5 adjusted for family income, maternal skin color, schooling, maternal age and height, smoking and breastfeeding 0-24
6 adjusted for family income, maternal skin color, schooling, age and height, smoking, breastfeeding 0-24, wheezing 0-24, and pneumonia 0-24

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after birth, were almost twice as likely as term infants to
have been rehospitalized at some time during their first
year of life [16]. Severity of illness leading to hospitaliza-
tion is also reflected in the increased risk of mortality
among preterm as compared to term infants. Previous
analyses of our cohort showed that adjusted relative risks
for neonatal and infant mortality, respectively, were 5.1
(1.7- 14.9) and 2.1 (1.0, 4.6) times higher for late-preterm
children than for term children [17].
Second, in the study of McLaurin et al [16], bronchiolitis
due to respiratory syncytial virus and pneumonia were the
most common causes of rehospitalization during the first
year among both late-preterm and term infants. Although
immaturity of the respiratory system may put late preterm
children at higher risk of more severe community-
acquired pulmonary infections, part of the hospitaliza-
tions may be due to Berkson bias since late preterm births
were more prevalent among low income families.
Third, it has already been shown that preterm infants and
children born small for gestational age exhibit different
rates of growth in early childhood [18]. Prematurity and
IUGR frequently present together in the same newborn.
The exclusion of small-for-gestational age newborns from
the current study aimed to prevent this potential con-
founding effect.
The importance of analyzing the effect of late preterm
births on growth indicators is supported by the marked
increase in preterm births observed across the three popu-
lation-based perinatal studies carried out in Pelotas in
1982, 1993 and 2004. Preterm births increased from 6.3%
in 1982 to 11.4% in 1993, and 14.7% in 2004 [19].
Nearly two out of three preterm births in 2004 occurred at
late-preterm gestations. The present study showed that the
nutritional risks expressed in growth failure linked to late
prematurity during infancy are extended to early child-
hood, at least until the age of two years.
Despite growing faster, late preterm children were at
increased risk of underweight and stunting during the first
two years of life. The strength of the association between
late preterm birth and stunting was similar for the first
and the second years with an almost two-fold increase in
risk among late preterm children as compared to children
born at term. Wasting was associated with late preterm
birth only in the first year of life, although the small
number of wasted children in both follow-ups may be
responsible for the lack of association in the second year
of life. In fact, only 4 (1.1%) late preterm and 7 (0.3%)
term children showed signs of wasting at 12 months. At
24 months, there were 3 (0.8%) and 10 (0.4%) late pre-
term and term children, respectively, with signs of wast-
ing. We found no studies that have evaluated the long-
term nutritional status of late preterm children. Thus, we
know neither the prevalence rates nor risk estimates for
wasting and stunting in children from other populations.
Previous studies suggest that the gastrointestinal tract is
likely to be less developed in late preterm children [3,20],
which may lead to difficulties in sucking and swallowing,
delay in successful breastfeeding, poor weight gain, and
dehydration during early postnatal weeks [21-23].
Late preterm children and term children gained on aver-
age 9 kg in weight from birth to 24 months of age, with a
statistically non-significant advantage for late preterm
children (who gained on average 13.23 g more than term
children). Mean child length at 24 months was of 85.70
cm for late preterm children and 87.11 cm for term chil-
dren, indicating that those born at term had on average a
higher stature at the age of two years. However, linear
growth from birth to 24 months of age was higher among
late preterm children than among term children: although
still shorter than term children at 24 months, late preterm
children grew on average 1.26 cm more than term chil-
dren.
Late preterm children gained as much as weight as their
term counterparts and they grew more linearly than the
term children in both follow-ups. Their growth, however,
was not enough to prevent underweight and stunting in
the first and second year of life. Analyses from the 1982
Pelotas Birth Cohort [18] showed that despite their earlier
disadvantage, preterm children gradually caught up with
their appropriate birth weight, term counterparts. This
catch-up occurred primarily between mean ages 23 and 47
months. As a result, it is possible that the growth failure
observed in late preterm children from the 2004 cohort
will be reversed in the coming two years.
There is considerable evidence that size early in life and
growth pattern in fetal life and infancy are inversely asso-
ciated with chronic disease in late childhood and adoles-
cence. Components of growth during childhood, other
than body size at birth or later on, is being explored as a
mechanism in the development of obesity and other
chronic diseases [24]. Results from long-standing cohort
studies in Brazil, Guatemala, India, the Philippines, and
South Africa showed that lower birth weight and stunting
in the first two years of life were risk factors for high glu-
cose concentrations, blood pressure, and adverse lipid
profiles once adult body-mass index and length were
adjusted for [25].
Conclusion
Late preterm children have already shown to be at
increased risk of dying during infancy. Results of the cur-
rent study bring a new source of concern: for those who
survive, high morbidity continues and failure to thrive in

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the first two years may put them at increased risk of future
occurrences of serious morbidity in late childhood and of
chronic disease development in adult life.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
ISS, AJB, CGV and FCB are principal investigators of the
2004 Pelotas Birth Cohort, conceived of the study and
participated in its design and coordination. ISS drafted the
first version of the manuscript. AM participated in the
design of the study, performed the statistical analysis and
helped to draft the manuscript. MRD participated in the
design of the study and coordinated the literature search.
All authors read and approved the final manuscript.
Acknowledgements
This article is based on data from the 2004 Pelotas Birth Cohort study con-
ducted by
Postgraduate Program in Epidemiology at Universidade Federal de Pelotas.
The 2004 Pelotas Birth Cohort study is currently supported by the Well-
come Trust Initiative entitled Major Awards for Latin America on Health
Consequences of Population Change. Previous phases of the study were
supported by the World Health Organization, National Support Program
for Centers of Excellence (PRONEX), the Brazilian National Research
Council (CNPq), the Brazilian Ministry of Health, and the Children's Mis-
sion. The supporting agencies had no role in study design; in the collection,
analysis, and interpretation of data; in the writing of the manuscript; or in
the decision to submit the manuscript for publication.
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