Maternal socioeconomic and lifestyle factors during pregnancy and the risk of congenital heart defects

The objective of study was to estimate the importance of maternal socioeconomic and lifestyle factors during pregnancy in the risk of congenital heart defects in Kaunas infant population in 1999–2005. Material and methods. An epidemiological case-control study was conducted. The study comprised 187 newborns with congenital heart defects (cases) and 643 randomly selected newborns without any defects (controls), born in Kaunas city during 1999–2005. Modern epidemiological methods were used for data analysis. A multivariate logistic regression was used to determine adjusted risk factors of congenital heart defects. Results. The logistic multivariate regression analysis showed that low and moderate maternal education significantly increased the risk of congenital heart defects (primary or basic [OR=3.43; 95% CI, 1.54–7.64] and secondary [OR=1.56; 95% CI, 1.00–2.45] vs advanced vocational or higher education). The housewives and workers had a higher risk of delivering a newborn with congenital heart defects than the office workers (OR=2.34; 95% CI, 1.34–4.10 and OR=1.28; 95% CI, 0.79–2.07, respectively). Maternal smoking during pregnancy tended to increase the risk of congenital heart defects by 48% (OR=1.48; 95% CI, 0.82–2.67). Conclusions. According to our study results, unfavorable maternal socioeconomic factors and smoking during pregnancy increased the risk of congenital heart defects. Medicina (Kaunas) 2009; 45(11)


Introduction
Congenital heart defects (CHDs) are among the most frequent major congenital malformations throughout the world, with a prevalence of 8 to 11 per 1000 live births (1)(2)(3). They remain a major cause of death in infancy and childhood (4). More than 85% of CHD causes are multifactorial including environmental teratogens with genetic and chromosomal conditions (1).
It is important in research area, whether intensive socioeconomic transformations in Lithuania and the associated lifestyle changes of the society and also women, especially before and during pregnancy, may impact newborn's health. The families, in which defective newborns were born, experience a psychosocial trauma and their quality of life changes. Malformations are the biggest social and economic problem not only in families but in the state as well (3).
The objective of this study was to estimate the importance of maternal socioeconomic and lifestyle factors during pregnancy in the risk of CHDs in Kaunas infant population in 1999-2005.

Materials and methods
A population-based case-control study included all newborns born in Kaunas city during 1999-2005. We used the database containing information on newborn's birth date, gender, health status, and mother's residence. This database served as an initial source for the registration of CHDs. To record all newborn cases of CHD, we used all available information from Kaunas city hospitals, clinics, and consultant centers.
This study involved 187 cases with CHDs and randomly selected 643 controls without any defects. CHDs were registered based on clinical diagnosis after its verification using the data from consulting centers and pediatric outpatient departments. Information on potential newborns' health risk factors was collected by using standardized questionnaires. Case and control mothers were interviewed personally at their home or by phone. The questionnaire consisted of 55 questions and recorded information on risk factors, referred to such as in the scientific literature: maternal age at delivery, education, marital status, occupation, maternal health, previous pregnancies, psychological stress, health risk behaviors, and hazardous occupational factors.
The importance of maternal socioeconomic (age at delivery, education, marital status, occupation) and lifestyle factors (smoking, alcohol consumption) for CHDs was evaluated. In this study, we did not examine a factor such as household income. Maternal age was categorized as follows: less and 19 years, 20-29 years, 30-34 years, and 35 years and more. Maternal education was grouped into the following categories: primary or basic, secondary, and advanced vocational or higher. According to marital status, mothers were categorized as single and married. Maternal occupations were grouped in the following categories: housewives, workers, office workers, professional workers, farmers, and students. Information about lifestyle factors was estimated by respondents' answers.
Modern epidemiological methods were used for data analysis. We calculated crude and adjusted odds ratios of risk factors along with 95% confidence intervals. A P value of <0.05 was considered statistically significant.

Results
The distribution of case infants with CHD and healthy control infants and the risk of CHD according to maternal socioeconomic and lifestyle factors are presented in Table. The majority of mothers having newborns with CHDs were aged 20-29 years. The mean age at delivery was 27.8 years (range, 15 to 43 years) for cases and 28.6 years (range, 17 to 47 years) for controls. The group of mothers aged 20-29 years was selected as the reference group, and the odds ratios to deliver a newborn with CHD for other age groups were calculated (Table). The risk was increased by 43% among young mothers (≤19 years), but did not reach statistical significance.
The majority of mothers both in case and control groups were married, although 8.7% of all study mothers were single (Table). Single mothers were more likely to have a 32% increased risk of having a newborn with CHD as compared with married mothers (reference group) (NS).
Half of case mothers had advanced vocational or higher education. Low and moderate maternal education was associated with a significantly higher risk of CHD. Mothers with primary or basic education had a 5.06-fold higher risk of delivering a newborn with CHD (95% CI, 2.44-10.48) (P<0.001), while secondary education was associated with a 2.28-fold increased CHD risk as well (95% CI, 1.58-3.27) (P<0.001), if compared with women who had advanced vocational or higher education (Table).
The prevalence of CHD was highest among the newborns of workers, office workers, and housewives. The information about maternal occupation was missing for 9 women (1.1%). Office workers were used as the reference group when the risk to deliver a newborn with CHD was compared. Housewives had a 3.67-fold higher risk of having a newborn with CHD (95% CI, 2.27-5.93) (P<0.001), while the odds ratios of CHD among the newborns of professional workers and workers were 2.69 (95% CI, 1.05-6.89) (P<0.05) and 1.81 (95% CI, 1.20-2.71) (P<0.01), respectively (Table). The occupation as professional worker was not included in the multivariate logistic regression model due to the small number of mothers with this occupation.
Housewives and workers accounted for 50% and 31.3% in the group of case mothers with primary or basic education, and in the group of case mothers with secondary education, there were 55.9% of workers and 30.9% of housewives. Accordingly, in the group of control mothers with low and moderate education, housewives and workers made up the greatest proportions. More than half (52.1%) of case and 65.5% of control mothers working as office workers had advanced vocational or higher education.
The analysis of lifestyle factors revealed that 12.8% of case mothers smoked cigarettes during pregnancy: 9.6% of them smoked less than 10 cigarettes per day and 3.2%, 10 and more cigarettes per day. More than one-quarter (25.1%) of case mothers smoked three or more years before pregnancy and 3.7% about two years. Among smoking mothers in both the groups, 32.7% continued this habit during pregnancy. The risk to deliver a newborn with CHD was more than twice higher among smoking women (OR=2.45; 95% CI, 1.43-4.20) (P<0.001) (Table). The odds ratio of having a newborn with CHD for mothers who smoked before pregnancy three or more years was 2.16 (95% CI, 1.44-3.22) (P<0.001) if compared with nonsmoking women. The odds ratio for mothers who smoked less than 10 cigarettes per day during pregnancy was 2.04 (95% CI, 1.13-3.70), while the highest odds ratio was for women who smoked 10 and more cigarettes per day (OR=6.14; 95% CI, 1.71-21.04), but there was a small number of exposed cases.
Medicina (Kaunas) 2009; 45 (11) Almost 14% of case and 11.4% of control mothers consumed alcohol during pregnancy (Table). The risk of delivering a newborn with CHD for mothers who used alcohol several times within a month was increased by 34% and for those who consumed several times within a week by 73%, but it did not reach statistical significance. This factor was not included in the multivariate logistic regression model, because the amount of consumed alcohol was not precisely estimated.
The factors increasing the risk of CHD statistically significantly were selected and included in the multivariate logistic regression model, and adjusted odds ratios were calculated (Fig).
The results of our multivariate analysis showed that the risk of CHD was 2.34 times higher among

Discussion
An epidemiological case-control study was conducted in order to assess the relations between maternal socioeconomic and lifestyle factors during pregnancy and CHD risk. The effect of abovementioned risk factors for CHD was evaluated, and their crude and adjusted odds ratios were calculated.
Housewives differ from women working during pregnancy; they may represent mothers whose newborns have the lowest risk of adverse pregnancy outcomes (14). According to the results of our study, a higher risk of CHD among the newborns of housewives and workers compared with infants of office workers could be partly explained by the facts that the majority of women had primary or basic and secondary education, they smoked more both before and during pregnancy. Workers are employed in occupations with exposures to strenuous physical exertion, chemicals, ionizing radiation, heat, noise, vibration, infectious agents, and stress. These factors can, in some cases, pose risks to pregnant workers and their developing fetuses (15).
Educational level, occupational status, and income are dimensions of socioeconomic status (16). Education most strongly and consistently predicts health (17); it may directly influence knowledge about health protective behaviors, accessing health services and psychosocial mechanisms such as engagement in social network and ability to cope with life stressors (18). Kramer et al. reported that a low level of education limits a person's access to jobs and other social resources. Poor socioeconomic conditions lead to unhealthy behaviors (17), which can affect the mother's and newborn's health. High socioeconomic status, whatever the measure, is associated with better health status (19).
There are very few articles presenting the results about the association between unfavorable maternal socioeconomic factors (education, occupation, and income) and the risk of CHD. In 2007, Yang et al. published the results of study that lower maternal education was associated with an increased risk of dextrotransposition of great arteries (7). Researchers reported that low socioeconomic status increased the risk of conotruncal heart defects (20,21) and dextrotransposition of great arteries (22). However, some studies showed no association between maternal education, income, occupation and risk of CHD (23,24).
The findings of our population-based study indicated that maternal smoking during pregnancy tended to increase the risk of CHD. Few studies have investigated the association between maternal cigarette

Risk factor
Occupation ( (11) smoking and CHD. The results from recent study by Malik et al. showed the association between the risk of septal defects in infants and exposure to moderate and heavy smoking as compared with exposure to light smoking, and maternal smoking of ≥25 cigarettes per day was associated with right-sided obstructive defects (12). According to the case-control study performed in Lithuania, maternal smoking increased the risk of having an infant with CHD two times (6). Kallen found a statistically significant association between some groups of CHD (either truncus abnormalities or atrial septal defects) and maternal smoking (10). In a retrospective cohort study, Woods and Raju found that abnormalities of the cardiovascular system are significantly associated with maternal smoking (11). The Baltimore-Washington Infant Study reported an adjusted 12-fold increased risk to have an infant with pulmonic stenosis for women who were >34 years and who smoked more than one pack cigarettes per day (9). Maternal cigarette smoking during pregnancy leads to perinatal mortality, preterm delivery, growth retardation, and congenital anomalies (11,(24)(25)(26)(27)(28). This study investigated an infant population in only one town of Lithuania. No studies have been performed about the associations between maternal socioeconomic and lifestyle factors during pregnancy and CHD in all Lithuania. It is important to carry out research in other towns of the country because it could reflect real infants' state of health and risk factors of CHD as well.

Conclusions
1. Univariate analysis revealed that maternal education (primary or basic and secondary); occupation including housewives, workers, and professional workers; and maternal smoking during pregnancy were associated with a significantly increased risk of congenital heart defects.
2. Logistic multivariate regression analysis showed that low and moderate maternal education (primary or basic and secondary) significantly increased the risk of congenital heart defects, if compared with women with advanced vocational or higher education.
3. The housewives had a 2.34-fold increased risk of delivering a newborn with congenital heart defects, and this risk was 28% higher among workers, if compared with the office workers.
4. Maternal smoking during pregnancy tended to increase the risk of congenital heart defects by 48%.