Perinatal outcomes associated with low birth weight in a historical cohort

Coutinho, Cecatti, Surita, Costa, Morais

Description

Objective To identify perinatal outcomes associated with low birth weight (LBW). Methods A retrospective cohort study in a tertiary maternity hospital. Analysis of the database on 43,499 liveborn infants delivered between 1986 and 2004 with low (n = 6,477) and normal (n = 37,467) birth weight. Outcomes associated with LBW were identified through crude and adjusted risk ratio (RR) and 95%CI with bivariate and multivariate analysis. The main outcomes were: onset of labor, mode of delivery, indication for cesarean section; amniotic fluid, fetal heart rate pattern, Apgar score, somatic gestational age, gender and congenital malformation. Results LBW infants showed more frequently signs of perinatal compromise such as abnormal amniotic fluid volume (especially olygohydramnios), nonreassuring patterns of fetal heart rate, malformation, lower Apgar scores and lower gestational age at birth. They were associated with a greater risk of labor induction and cesarean delivery, but lower risk of forceps. Conclusion There was a clear association between LBW and unfavorable perinatal outcomes.

Sujets

• Low birth weight
• Prenatal care
• Preterm birth

Informations

• Publié par: biomed
• Publié le: 01 janvier 2011
• Nombre de lectures: 12
• Langue: English

Extrait

Coutinho et al. Reproductive Health 2011, 8:18
http://www.reproductive-health-journal.com/content/8/1/18
RESEARCH Open Access
Perinatal outcomes associated with low birth
weight in a historical cohort
*Pedro R Coutinho , José G Cecatti, Fernanda G Surita, Maria L Costa and Sirlei S Morais
Abstract
Objective: To identify perinatal outcomes associated with low birth weight (LBW).
Methods: A retrospective cohort study in a tertiary maternity hospital. Analysis of the database on 43,499 liveborn
infants delivered between 1986 and 2004 with low (n = 6,477) and normal (n = 37,467) birth weight. Outcomes
associated with LBW were identified through crude and adjusted risk ratio (RR) and 95%CI with bivariate and
multivariate analysis. The main outcomes were: onset of labor, mode of delivery, indication for cesarean section;
amniotic fluid, fetal heart rate pattern, Apgar score, somatic gestational age, gender and congenital malformation.
Results: LBW infants showed more frequently signs of perinatal compromise such as abnormal amniotic fluid
volume (especially olygohydramnios), nonreassuring patterns of fetal heart rate, malformation, lower Apgar scores
and lower gestational age at birth. They were associated with a greater risk of labor induction and cesarean
delivery, but lower risk of forceps.
Conclusion: There was a clear association between LBW and unfavorable perinatal outcomes.
Keywords: low birth weight perinatal outcomes, prenatal care, preterm
Background alone this increase is estimated to be 45.1 per 1,000
Low birth weight (LBW) is a key issue in public health, between 1995-96 and 1999-2000 [8]. This temporal
especially for developing countries. It is a result of pre- trend is also observed in developing countries. Data
term delivery or the birth of a growth restricted fetus from Latin America show a raise in PTB due to elective
[1] and represents a major determinant of adverse induction and delivery by elective cesarean section from
health outcomes throughout life, from infancy to adult- 10% in 1985-1990 to 18.5% in recent years [9]. This
hood. Along with prematurity, it is associated with trend might be responsible for an increase in preterm
poorer indicators of child morbidity [2] and mortality deliveries, which ultimately leads to higher rates of LBW
[3]. There is even evidence of its association with infants.
adverse health conditions later in life, such as coronary Many studies have accounted for the risk factors for
disease, stroke, hypertension, type 2 diabetes [4] and preterm delivery and for LBW [6,7,10,11], as well as for
recurrence of low birth weight in the offspring [5]. Esti- neonatal outcomes. The short term outcomes on ante-
mates of LBW rates vary worldwide, from 3.1% to 13.3% partum, labor and postpartum care of LBW infants have
[6]. The World Health Organization has established a not yet been properly focused. There is no a general
goal of reducing its incidence by one third in the next consensus that LBW fetuses are more susceptible to
fetal distress than normal weight, that there are differ-decade with the objective of improving child mortality
rates [7]. ences in labor, labor induction and mode of delivery
In the last decade increases in medically indicated between them, that newborns are prone to lower Apgar
labor induction and cesarean delivery have resulted in scores, and that there is a difference in gender between
rising rates of preterm birth (PTB). In the United States LBW and normal weight newborns.
Fetal heart rate monitoring is a cornerstone of ante-
partum surveillance in high-risk pregnancies [12]. LBW
* Correspondence: [e-mail]
is closely associated with preterm birth and heart rateDepartment of Obstetrics and Gynecology, School of Medical Sciences,
University of Campinas, Campinas, SP, Brazil
© 2011 Coutinho 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.Coutinho et al. Reproductive Health 2011, 8:18 Page 2 of 6
http://www.reproductive-health-journal.com/content/8/1/18
records of premature fetuses show decreased variability remaining 43,944 records of livebirths were then divided
and little fluctuation before 28 weeks [13]. Despite that, into two categories: 1) newborn infants with low birth
there is no general agreement that fetuses who turn out weight (< 2,500 grams) (6,477 cases; 14.7% of the popu-
to be LBW infants show more often non-reassuring or lation studied); and 2) newborn infants of normal weight
ominous heart rate patterns than those with normal (from 2,500 to 3,999 grams). All the 43,944 cases fulfill-
weight. In uterus passage of meconium is also a sign of ing the selection criteria were included in the cohort
fetal compromise [2] and is associated with adverse peri- with the purpose of avoiding selection bias. A previous
natal outcomes even for preterm/very LBW newborns analysis focusing on factors associated with low birth
weight was already been performed and it is published(birth weight ≤ 1,500 grams) [14]. Low Apgar scores at
the first and the fifth minute are associated with elsewhere [24].
increased risk of neurologic sequel in term infants [15]. The following delivery outcomes were considered:
LBW infants also present an increased risk of develop- onset of labor (spontaneous, elective cesarean, induc-
ing perinatal asphyxia [16]. In fact, birth weight has tion), mode of delivery (vaginal cephalic, vaginal breech,
been shown to be independently associated with birth forceps, cesarean), indication for cesarean (acute fetal
asphyxia [17]. distress, cephalopelvic disproportion, breech, other
The mode of delivery of infants weighting less than anomalous presentation, preeclampsia, previous cesar-
1,500 grams is associated with perinatal outcomes. ean, placental abruption, other). The perinatal outcomes
Cesarean is associated with increased rate of broncho- considered were: characteristics of amniotic fluid (clear,
pulmonary dysplasia and vaginal delivery with increased meconium stained, hemorrhagic, infectious), amount of
ventricular hemorrhage and higher mortality rates [18]. amniotic fluid (normal, olygohydramnios, polyhydram-
Vaginal breech delivery of premature infants is asso- nios), fetal heart rate (normal, tachycardia, early and/or
ciated with increased neonatal mortality and morbidity variable deceleration, late deceleration and/or bradycar-
(birth trauma, birth asphyxia) [19]. On the other hand, dia), first and fifth minute Apgar score (7-10, <7),
some authors suggest that cesarean is a safer route of somatic gestational age (≥37 weeks, <37 weeks), gender
delivery for extremely low birth weight infants [20]. (male, female) and congenital malformation (with, with-
It has been shown that infants with birth defects out). For each variable with missing information, the
(either chromosomal or structural abnormalities) are correspondent records were excluded when statistical
more likely to have LBW [21]. Gender also plays a role analysis was performed. Although it would be worth to
in determining perinatal outcomes. Male fetuses are have a differentiation between LBW due to preterm
more likely to be delivered prematurely than females birth or fetal growth restriction, we did not consider
and show worse morbidity and mortality rates [22]. this distinction because during the whole period there
Male sex itself is considered an independent risk factor were different capacities of determining the real gesta-
for poor pregnancy outcome [23]. tional age. In developing setting is well known the poor
In order to determine delivery and perinatal outcomes capacity of identifying the real gestational age, although
associated with LBW in the peripartum period in a it is believed that from one third to half of the cases of
cohort of 43,944 births in a tertiary public maternity in LBW were due to preterm births [25].
Campinas, Brazil, this current study was carried out. Using the Epi Info version 6.04b, a bivariate analysis
was initially carried out where the outcomes were
Materials and methods crossed with birth weight. The risk ratio (RR) and 95%
A retrospective cohort study was carried out in a ter- confidence interval (95%CI) were calculated for the
tiary referral maternity hospital located in a region of 3 occurrence of outcomes comparatively between low and
million inhabitants in the city of Campinas, state of São normal birth weight infants. These results were con-
Paulo, Brazil. Information on all obstetrical hospitaliza- trolled by some confounding factors for the adjustment
tions in the institution is systematically and prospec- of the respective RR (maternal age, schooling, body
tively collected from the women’s admission to their mass index, smoking and time of initiation of prenatal
discharge. The data are reviewed and corrected if neces- care) using the logistic regression analysis with adjust-
sary by a medical supervisor prior to recording in an ment for RR. This was performed using the SAS soft-
electronic database by a clerk. ware package, version 9.02. The study protocol was
A total of 52,136 records represent the number of approved by the Institutional Review Board prior to its
deliveries at the institution between January 1986 and initiation.
December 2004. Out of t