Stressful life events, social health issues and low birthweight in an Australian population-based birth cohort: challenges and opportunities in antenatal care

The 2008 Healthy Mothers Healthy Families (HMHF) Survey questionnaire was mailed to women giving birth in two Australian states (Victoria and South Australia) in September/October 2007 at five to six months postpartum, excluding those who had a stillbirth, or whose baby was known to have died. Public and private maternity hospitals and homebirth practitioners in both states distributed questionnaires to women who gave birth under their care in the study period. All hospitals with births in the study period (n = 110) agreed to participate, however one small public hospital with approximately 90 confinements in the study period subsequently withdrew. Together South Australia and Victoria accounted for greater than 31% of the 289,496 births in Australia in 2007 [25]. The inclusion of two states provided for greater diversity in the sampled population compared with previous Victorian surveys [26‐28]. Compared with Victoria, South Australia has a higher proportion of births to women living in outer regional (11.8% versus 4.2%) and remote/very remote areas (3.9% versus 0%), a higher proportion of Aboriginal mothers (3.0% versus 1.0%) and women giving birth under 20 years (4.6% versus 2.6%), while Victoria has a higher proportion of births to women born overseas (26.6% versus 16.3%) [25].

The primary aim of the study was to assess women's views and experiences of care received during pregnancy, birth and the postnatal period in representative samples of women giving birth in South Australia and Victoria in 2007. Questionnaires, together with a covering letter inviting women to take part, an explanation of the study in six community languages (Arabic, Vietnamese, Cantonese, Mandarin, Somali and Turkish) and a reply paid envelope for returning the questionnaire free of charge, were posted to women at six months postpartum. Two reminders were sent at two-week intervals with the second including a repeat copy of the questionnaire. The timing of the survey at five to six months postpartum matches previous Victorian surveys [26‐28] and was decided taking into account the literature suggesting a 'halo' effect in relation to reporting of women's experiences of maternity care in the period immediately after childbirth [27] and the inclusion of questions on postpartum maternal health outcomes (e.g. maternal depression, urinary incontinence). A copy of the questionnaire is available on the study website: http://​www.​mcri.​edu.​au/​HMHFSurvey. The study period - four weeks in September 2007 in Victoria, and eight weeks in September/October 2007 in South Australia - was chosen to ensure sub-groups of interest (e.g. women attending six main models of care, women <25 years, single women, and women whose infant was <2,500 grams at birth) were large enough for meaningful statistical comparisons.

Information was collected on women's views and experiences of care, health service use, maternal socio-demographic characteristics, reproductive history, and maternal and infant health outcomes, including infant birthweight. The questionnaire also included questions on maternal smoking in pregnancy, maternal pre-pregnant weight and height, and stressful life events and social health issues in the 12 months before the index birth. Measures of socio-economic status included: pre-tax household income adjusted for household size and composition, possession of a current health care concession card and health insurance status (private cover/Medicare only). Women were classified as being at higher risk of complications in pregnancy if they had a previous low birthweight infant, preterm birth, or stillbirth, or if they had any substantial medical or obstetric risk factors in the current pregnancy (e.g. multiple pregnancy, gestational diabetes). Maternal pre-pregnant Body Mass Index (BMI) was calculated as the ratio of body weight in kilograms divided by the square of height in metres. Smoking status was assessed using a multiple response question enabling women to indicate if they had never smoked, quit smoking before their pregnancy, quit since the beginning of pregnancy, cut down cigarette smoking since finding out they were pregnant, continued to smoke at about the same level or increased their smoking since the beginning of pregnancy [29]. Women who said they had quit before pregnancy or never smoked were categorised as non-smokers. Women who said they quit when they found out they were pregnant were categorised as smoking in early pregnancy; women who cut down, increased or continued to smoke about the same number of cigarettes as before their pregnancy were categorised as continuing to smoke throughout their pregnancy.

Assessment of stressful life events and social health issues drew on items included in the PRAMS study [30] with additional items incorporated based on results of a pilot survey and consultations with Aboriginal community organisations and communities in the two states. Women were asked "Did any of the following things happen to you in the 12 months before your new baby was born?" and invited to tick 'yes' or 'no' to 23 items including major life events, such as separation and divorce, moving house, losing your job, death of a close family member or friend and social health issues, such as having a lot of bills you couldn't pay, not having enough money to buy food, legal troubles or being involved in a court case, serious family conflict or being homeless. A complete list is provided in an additional file (see Additional File 1). Perceived discrimination was assessed using five questions (see Additional File 1) adapted from the Measure of Indigenous Racism Experience [31] to elicit information about women's experience of being discriminated against by health professionals in the perinatal period. The questions were designed to capture the concept of being 'treated unfairly', that is being treated as inferior, with less respect or courtesy, or receiving poorer care than other people. Women were also asked if they had been insulted, stereotyped, talked down to or ignored. Although based on a measure originally designed to assess racial discrimination, the questions were framed to illicit experiences of perceived discrimination in a variety of other contexts, for example, in relation to maternal age, education and other social characteristics.

The study was approved by the Royal Children's Hospital Human Research Ethics Committee (HREC), Victorian Department of Human Services HREC, South Australian Department of Health HREC and a number of other university and hospital based HRECs.

Data on the social and obstetric characteristics of study participants were compared with routinely collected Victorian and South Australian perinatal data for all women who gave birth in the study period in order to assess the representativeness of the sample. Reporting of stressful life events and social health issues was categorised according to whether women reported no social health issues, one or two issues, or three or more issues. Data on discrimination were dichotomised to distinguish women who reported any experience of discrimination from those who reported never experiencing any of the kinds of discrimination we asked about. Data were analysed using STATA version 11.0 [32] and involved the calculation of unadjusted and adjusted odds ratios and 95% confidence intervals. Multivariable logistic regression was used to assess the relationship between number of stressful life events and social health issues as the exposure of main interest (categorised as none, one to two issues, three or more issues) and low birthweight as the primary outcome variable. Four models are reported adjusting for: maternal smoking, social characteristics, number of antenatal visits and medical risk.

Table 1 shows the social and obstetric characteristics of participants compared with all Victorian and South Australian women who gave birth in the study period according to routinely collected perinatal data for both states. The mean age of women in the sample was 31 years (range 16 to 46 years). Comparisons with routinely collected data showed that women taking part in the survey were largely representative in terms of key obstetric characteristics including parity, method of birth, and infant birthweight, but included fewer women born overseas of non-English speaking background, Aboriginal and Torres Strait Islander women, single women and women under 25 years. Eighteen percent of women reported smoking in pregnancy, including women who said that they quit or cut down smoking while pregnant. One third of participants who provided data on height and weight prior to pregnancy were overweight (25.0-29.9) or obese (≥30). Two-thirds of women reported one or more stressful life events or social health issues during pregnancy, and 17% reported three or more issues.

Table 2 summarises data on associations between maternal social characteristics and stressful life events/social health issues experienced in the 12 months before the birth. Maternal characteristics that were associated with substantially raised odds of reporting three or more stressful life events or social health issues were: being under 25 years; single, divorced or widowed; having a below average equivalised income; not completing year 12; smoking at any stage of pregnancy; being underweight (BMI <18.5); being at higher risk of obstetric complications, and being of Aboriginal and/or Torres Strait Islander origin.

Women were significantly more likely to report experiencing discrimination if they were: under 25 years, had a low income, had not completed year 12, were not married, had a very high (≥35) or a very low BMI (< 18.5), quit smoking in pregnancy or smoked throughout pregnancy and if they were at higher risk of medical complications. Women who reported three or more stressful life events/social health issues were significantly more likely to report discrimination (314/760, 41.3% versus 296/1429, 20.7%, OR = 2.69, 95% CI 2.2-3.3). Women who reported one or two stressful life events/social health issues also had significantly raised odds of experiencing discrimination (518/2123, 24.6% versus 20.7%, OR = 1.2, 95% CI 1.1-1.4) suggesting a 'dose response'.

Despite the existence of universal health cover via Medicare, uptake of antenatal care varied in relation to maternal social characteristics and the number of stressful life events or social health issues women were coping with. Younger women, those who had below average household income, women who had not completed year 12, women without a partner and women who smoked throughout pregnancy were more likely to attend a first antenatal check-up at ≥13 weeks' gestation, and to attend less than five visits (Table 3). Women who reported stressful life events or social health issues were also more likely to attend late, and to attend fewer visits.

Univariable associations between maternal characteristics and low birthweight (< 2500) are shown in Table 4. Women at higher risk of obstetric complications in pregnancy had a fourfold increase in odds of having a low birthweight infant. Other maternal factors significantly associated with low birthweight were: not completing secondary education, being born overseas, and having a low pre-pregnant BMI (< 18.5). Women reporting three or more stressful life events or social health issues had a twofold increase in odds of having a baby with a low birthweight compared with women reporting no social health issues.

In order to obtain a more precise estimate of the association between low birthweight and the number of stressful life events and social health issues, we developed the four models shown in Table 5. Maternal smoking status was fitted in all models for a priori reasons based on the known aetiological relationship between maternal smoking and infant birthweight. The first model adjusts for maternal smoking alone, and shows that the association between number of stressful life events and social health issues and low birthweight remains statistically significant after adjusting for maternal smoking in pregnancy. Model 2 adjusts for other socio-demographic factors associated with the exposure of main interest (three or more social health issues) and the outcome variable (low birthweight) in univariable analyses. Models 3 and 4 include smoking status and all of the socio-demographic variables included in model 2, and adjust separately for number of antenatal visits (model 3) and risk of complications in pregnancy (model 4). All models indicate a dose effect related to number of stressful life events and social health issues. All models that fitted maternal country of birth indicated that women born overseas in non-English speaking countries had significantly raised odds of having a low birthweight infant.