Difference of Socioeconomic Factors among Mothers of Preterm and Full-Term Infant

Objective: To analyze the difference of socioeconomic factors among mothers of preterm and full-term infants. Material and Methods: A cross-sectional retrospective study was developed with 250 mothers of children aged three to five years. The sample was divided into two groups: 125 mothers of preterm infants from the referral center of a public hospital in the city of Belo Horizonte, Brazil and 125 mothers of children born full-term at a daycare center within the same city. A pre-tested questionnaire was used to collect socioeconomic data and type of breastfeeding. To verify if there was association between the dependent variable gestational age at birth and the independent variables, the chi-square test was used. A final model with multiple Poisson regression estimated prevalence ratio values for each independent variable was developed. Results: The final multiple regression model showed that mothers that have a low monthly income of up to USD 450.28 (PR = 1.979, 95% CI = 1.082–3.620), used drugs, cigarettes, or alcohol during their pregnancy (PR = 4.095, 95% CI = 2.422–6.921), and did not breastfeed (PR = 2.294, 95% CI = 1.205– 4.369) were more likely to give birth to preterm infants. Conclusion: Low monthly family income, use of drugs, alcohol, or smoking during pregnancy and absence of breastfeeding were more frequent on mothers of preterm infants.


Introduction
Approximately 15 million children are born prematurely annually around the world, accounting for 11.1% of all births [1]. Newborns with a gestational age of less than 37 weeks are considered premature [1].
Preterm birth is the leading cause of death in the neonatal period and the second leading cause of death in children under five years of age [2,3]. More than one million babies die each year from complications of preterm birth, and survivors may face several life-long sequelae, including motor deficits, learning disabilities, visual and hearing problems, and increased risk of chronic diseases in adulthood. The fragility of the general health of the preterm infant implies public policy expenditures [2].
In Brazil, from the 1980's, advances in maternal and child health care were observed, although there was an increase in preterm births [4]. Approximately 12% of births in Brazil are premature [5], and this number is higher than observed in developed countries. For instance, in European countries, the prevalence of preterm birth is 5% [1,2]. Notably, Brazil is among the 10 countries with the highest number of preterm births [1,2].
Several factors are associated with preterm birth, including mother's age, pregnancy in adolescence or above 35 years, gestation of twins, chronic diseases and infections, socioeconomic and nutritional factors, race, short interval between pregnancies, and maternal anemia in the first semester of pregnancy. Other factors associated with the fetus, such as genetic diseases, are also associated with premature birth [1,6,7]. Indeed, most of the factors related to the etiology of prematurity are potentially preventable [8][9][10].
The understanding of the profile of mothers of preterm children can support management decisions, prevention, clinical decisions, and public policies aimed at reducing preterm birth rates. Thus, the objective of the study was to analyze the difference of sociodemographic factors among mothers of preterm and full-term infants.

Study Design and Sample
A comparative epidemiological cross-sectional study with a convenience sample was developed with 250 mothers of children from three to five years of age. The sample was divided in two groups: G1 consisted of 125 mothers of preterm infants from the preterm infants care referral center at a public hospital in the city of Belo Horizonte, Brazil; G2 consisted of 125 mothers of full-term infants from a public daycare center within the same city. The daycare center was selected for convenience and according to the city's Department of Education.

Data Collection
The preterm mothers were contacted through the medical records of a university hospital referral center. Full-term mothers were contacted at a public day care center. The mothers were interviewed by the researcher with the use of questionnaires developed by the team of researchers. The same questionnaire was used for both groups to obtain information on gestational age, sociodemographic aspects (mother's age, mother's profession, family income, child's sex, and child's age), and infant development (diseases, medication use, hospitalizations, and weight). This questionnaire was previously tested during a pilot study with 20 mothers to evaluate the methodology proposed for this study. No change in methodology was required.
Participants in the pilot study were not included in the main study.
Monthly family income was defined according to the Brazilian minimum wage, which corresponded to 450.00 USD at the time of the study, and was established as the average monthly income of all economically active members of the family. For statistical analysis, household income was categorized as follows: parents/caregivers of children whose families have a monthly income ≤ 2 BMW or > 2 BMW.

Statistical Analysis
Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS Inc, version 23.0, New Armonc, USA). A descriptive analysis of the data was performed. Bivariate analyzes using the chi-square test were performed to evaluate the association between the independent variables and the dependent variable "gestational age". The dependent variable "gestational age" was dichotomized as mothers of preterm infants and mothers of full-term infants. Independent variables with a p value of <0.20 were incorporated into the Poisson regression model [11].

Ethical Aspects
This study was approved by the Human Research Ethics Committee (Protocol # 49803115.4.0000.5149). Inclusion criteria consisted of mothers with children aged three to five years with good general health status. Illiterate mothers were excluded from the study.

Results
A total of 250 mothers participated in this study, with children of both sexes, of whom 113 boys (45.2%) and 137 girls (54.8%). The mean age of the mothers was 35.33 years (± 7.45). Of the total sample, 120 mothers gave birth to infants less than 34 weeks of gestation and 5 gave birth to infants between 35 and 37 weeks gestation. The majority of mothers belonged to families with incomes up to 450.28 USD (n = 129; 51.6%). A large percentage of mothers reported they did not use drugs during pregnancy (n = 226; 94.16%), and more than half had a planned pregnancy (n = 136; 54.4%). A large proportion of the mothers gave birth by cesarean section (n = 164; 65.6%) and breastfed after hospital discharge (n = 202; 80.2%). Most of the mothers offered bottle-feeding (n = 198; 79.2%) and breastfed (n = 201; 80.4%) ( Table 1).
Sample power was calculated using the prevalence of families with incomes up to 450.28 USD in the present study (35.1% for both mothers of preterm infants and full-term infants) and the number of participants of 250. The calculation was performed through the PS (Power and Sample Size calculation, version 3.0, Nashville, TN, USA) program. A 95% confidence interval and a 5% error were considered acceptable. A sample power of approximately 95% was obtained.
The multivariate Poisson regression model showed that family income, drug use during in pregnancy, and breastfeeding remained associated with the gestational age variable. The likelihood of remaining in the mothers of preterm infant group was higher for families that have a monthly income up to 450.28 USD (PR = 1.979, 95% CI = 1.082-3.620), mothers who used drugs, alcohol, or cigarettes during their pregnancy (PR = 4.095, 95% CI = 2.422-6.921), and mothers who did not breastfeed (PR = 2.294, 95% CI = 1.205-4.369) ( Table 2).

Discussion
This study aimed to evaluate the socioeconomic aspects that influence the mothers who gave birth to preterm infants and full-term infants. The low income was more prevalent in mothers of preterm infants.
Preterm birth rates are highest on average for low-income countries (11.8%), followed by low-middle income countries (11.3%), and the lowest for middle-high and high income (9.4% and 9.3%) [1]. A study developed in the U.S. conducted a multilevel logistic regression analysis to estimate the effect of poverty on the risk of preterm birth in 634,994 nested births in 115 counties in the state of Missouri. Results indicated that women residing in socioeconomically deprived areas are at increased risk of preterm birth, above other underlying risk factors [12]. Access to educational and employment opportunities and medical care in low-income individuals is limited [13]. Factors related to socioeconomic deprivation, such as medical comorbidities, lack of prenatal care, and behavioral factors (smoking and alcohol consumption), are risk factors for premature birth [14]. The difficulty of access to health and behavioral factors related to the low family income of the mothers of the present study may have influenced the premature birth.
Studies have shown that the use of drugs, cigarettes, or alcohol during pregnancy is also associated with teenage pregnancy [15,16]. The use of illegal drugs in adolescent pregnancy is associated with an increased incidence of concurrent use of cigarettes and alcohol, social morbidity, and low income [6,15,17]. In the present study, the majority of mothers who were less than 20 years of age were mothers of premature children and had low family incomes. The age and low income of these mothers may have influenced the use of drugs, tobacco, or alcohol during pregnancy. In addition, several studies support that drug, cigarette, or alcohol use during pregnancy are risk factors for preterm delivery [18][19][20]. The use of these drugs is associated with spontaneous preterm delivery, premature rupture of membranes, and prepartum bleeding [18][19][20].
The absence of breastfeeding was higher among mothers of preterm infants. Preterm infants may present difficulties in initiating breastfeeding due to the immaturity of coordinating sucking, swallowing, and breathing functions [21,22]. Breastfeeding a premature infant can be challenging for the mother, as she needs to pump milk regularly until her child has acquired the ability to suck the breast during neonatal hospitalization [23]. Accordingly, breastfeeding rates for very premature infants are lower than for full term infants [24][25][26]. Moreover, the use of cigarettes by mothers of preterm infants may have influenced breastfeeding initiation, as maternal smoking and exposure to smoke have been shown to affect the initiation and duration of breastfeeding [27][28][29].
Prematurity is not restricted only to biological factors, as behavioral and social factors also influence premature birth. This study highlights the importance of the pregnant woman's vision in its entirety by health professionals. Social support and educational campaigns on risk orientation of preterm birth should be encouraged.
There are some limitations that deserve comment. The study population was limited to a convenience sample, which does not guarantee its reproduction in other socioeconomic and cultural realities. There is the possibility of memory bias, although the information collected has happened during or shortly after exposure.
It is important that future studies in this area be conducted with a variety of designs, both quantitative and qualitative.

Conclusion
In this study, low monthly family income, use of drugs, alcohol, or tobacco during pregnancy, and the absence of breastfeeding were more frequent on mothers of preterm infants. Educational campaigns that guide mothers of all social classes should be encouraged to promote the health of children. Public policies should be encouraged to promote health in low-income communities.