Birthweight of babies born to migrant mothers - What role do integration policies play?

Birthweights of babies born to migrant women are generally lower than those of babies born to native-born women. Favourable integration policies may improve migrants' living conditions and contribute to higher birthweights. We aimed to explore associations between integration policies, captured by the Migrant Integration Policy Index (MIPEX), with offspring birthweight among migrants from various world regions. In this cross-country study we pooled 31 million term birth records between 1998 and 2014 from ten high-income countries: Australia, Belgium, Canada, Denmark, Finland, Japan, Norway, Spain, Sweden and United Kingdom (Scotland). Birthweight differences in grams (g) were analysed with regression analysis for aggregate data and random effects models. Proportion of births to migrant women varied from 2% in Japan to 28% in Australia. The MIPEX score was not associated with birthweight in most migrant groups, but was positively associated among native-born (mean birthweight difference associated with a 10-unit increase in MIPEX: 105 g; 95% CI: 24, 186). Birthweight among migrants was highest in the Nordic countries and lowest in Japan and Belgium. Migrants from a given origin had heavier newborns in countries where the mean birthweight of native-born was higher and vice versa. Mean birthweight differences between migrants from the same origin and the native-born varied substantially across destinations (70 g-285 g). Birthweight among migrants does not correlate with MIPEX scores. However, birthweight of migrant groups aligned better with that of the native-born in destination counties. Further studies may clarify which broader social policies support migrant women and have impacts on perinatal outcomes.

Are the educational differences in incidence of cardiovascular disease explained by underlying familial factors? A twin study.

To isolate the effect of education from the influence of potential underlying factors, we investigated the association of education with the risk of cardiovascular disease (CVD) and ischemic heart disease (IHD) using twin data to adjust for familial factors shared within twins, including genetic make-up and childhood environment. The study was based on data from the Danish Twin Registry linked to administrative and heath registers in Statistics Denmark. A total of 11,968 monozygotic and 20,464 dizygotic same sexed twins were followed from 1980 to 2009, including more than 8000 events of CVD. Unpaired and intra-pair analyses were compared. In the unpaired analyses, an inverse educational gradient in CVD- and IHD risk was observed. This association was not replicated in the intra-pair analyses that control for shared familial factors exploiting that twins share their intrauterine- and childhood environment and are matched partly or fully on genetic setup. The attenuation of association of education with CVD and IHD in the intra-pair analyses suggests that shared familial factors account for a substantial part of the observed association of education with CVD and IHD in Denmark.

Preterm birth and birthweight-for-gestational age among immigrant women in Denmark 1978-2007: a nationwide registry study.

BACKGROUND: We sought to examine whether age at immigration and length of residence were associated with preterm and small-for-gestational age (SGA) delivery among immigrant women in Denmark. METHODS: We included all live singleton deliveries from Danish-born women (1626880) and women from the five largest immigrant groups (68936) from 1978 to 2007. Data from the Danish Medical Birth Registry were linked to: parental country of origin, length of residence and age at immigration. Linear and logistic regression models were used to estimate absolute and relative differences with Danish-born women as the reference group. RESULTS: All immigrant groups had an increased risk of SGA delivery with the highest risk among Lebanese-, Somali- and Pakistani-born women: risk differences (RDs) and 95% confidence intervals [CI] per 1000 deliveries of 50.2 [95% CI 43.7, 56.7], 70.1 [95% CI 62.2, 77.9] and 85.7 [95% CI 78.5, 92.9]. Turkish- and Pakistani-born women had increased RDs of 1.8 [95% CI 0.5, 3.1] and 2.2 [95% CI 0.1, 4.2] for very preterm and RDs of 3.5 [95% CI 0.9, 6.1] and 10.2 [95% CI 5.9, 14.5] for moderate preterm delivery. Lebanese-born women had a decreased risk of very preterm delivery, RD of -1.9 [95% CI -3.5, -0.3] and Somali-born women a lower risk of moderate preterm delivery, RD of -7.8 [-12.0, -3.6]. No differences were seen for the remaining groups. The association with length of residence for most immigrant groups was U-shaped, with highest risks among recent and long-term residents. CONCLUSION: Immigration was more strongly related to SGA than to preterm delivery. Observed differences in birth outcomes varied by age at immigration and length of residency in Denmark.

Opposite effects of microchimerism on breast and colon cancer.

BACKGROUND: Detection of Y chromosome, thought to originate from previous pregnancies with a male fetus, is common in women. Lower concentrations have been reported in women with breast cancer than cancer-free women. Data in women with other types of cancer are sparse. The purpose of the study was to determine whether the lower concentrations predate cancer diagnosis, and whether a possible beneficial effect was specific to breast cancer. METHODS: We conducted a prospective case-cohort study of 50-64-year-old Danish women enrolled in the diet, cancer and health cohort. Blood samples and questionnaire data were obtained during 1993-1997 when all women were cancer-free. In 2006 all women were followed up for incident breast and colon cancer in national registers. In blinded analyses, we analysed buffy coat DNA for Y chromosome (DYS14) as a marker of male microchimerism. RESULTS: We detected male microchimerism in 70% of 272 cancer-free women, 40% of 89 women who later developed breast cancer, and 90% of 67 women who later developed colon cancer. The corresponding odds ratios were 0.30 (95% confidence interval (CI) 0.17-0.52) for breast, and 3.9 (95%CI 1.6-9.5) for colon cancer. CONCLUSION: Detection of male microchimerism was strongly associated with reduced risk of developing breast cancer and also the increased risk of developing colon cancer. Confirmatory findings based on an improved study design, failure to identify important confounders and the strength of the associations lead us to believe that microchimerism may be highly relevant to later cancer development. However, the present study does not allow us to identify the underlying biological mechanisms.

Gestational age and basic school achievements: a national follow-up study in Denmark.

OBJECTIVE: Children born at <32 weeks' gestation are at increased risk of intellectual impairment. Few studies have focused on the majority of preterm children born at 32 to 36 weeks' gestation. We aimed to investigate the association between the full range of gestational ages at birth and the risk of not completing basic school. METHODS: This longitudinal, register-based study included all live-born infants in Denmark from 1988 to 1989. Data were obtained from national registers. School achievements were evaluated by using the examination marks. The association between gestational age and not completing basic school was estimated, taking into account the effect of their parents' educational level, being small for gestational age, plurality, and cerebral palsy. RESULTS: The cohort constituted 120,585 infants, of whom 118,281 (98.6%) were alive in 2007. Of these infants, 5.01% (n = 5.928) were born before 37 weeks' gestation. Of the subjects born before 37 weeks' gestation, 11.5% (95% confidence interval: 10.7-12.4) did not complete basic school compared with 7.5% (95% confidence interval: 7.3-7.6) of those born at term. The percentage of subjects who did not complete basic school increased with decreasing gestational age. The increase was steeper at <31 weeks (4.2% per week) than at 31 to 36 weeks' gestation (0.5% per week). CONCLUSIONS: The risk of not completing basic school increased with decreasing gestational age. The risk was moderate at ≥31 weeks' gestation and increased steeply at <31 weeks' gestation. The increase at <31 weeks' gestation was only partly explained by cerebral palsy.

Maternal use of nicotine replacement therapy during pregnancy and offspring birthweight: a study within the Danish National Birth Cohort.

Smoking is a well-established risk factor for fetal growth restriction and other adverse pregnancy outcomes, and nicotine may be one of the chemical compounds that drive these associations. Nicotine replacement therapy (NRT) is a smoking cessation aid, which can facilitate smoking cessation. It is, however, unknown whether NRT used during pregnancy impairs fetal growth. The aim of this study was to estimate the association between the use of NRT during pregnancy and offspring birthweight. The study population consisted of 72 761 women enrolled in the Danish National Birth Cohort between 1996 and 2002. Information on NRT and potential confounders was obtained from two computer-assisted telephone interviews conducted in the second and third trimesters, respectively. Multiple linear regression in a multilevel model was used to estimate the association between NRT use and birthweight adjusted for gestational age and potential confounders. The adjusted analyses showed no significant association between the duration of NRT use and birthweight (b = 0.25 g per week of NRT use [95% CI -2.31, 2.81]) and neither was the type of NRT product (patch, gum, inhaler) associated with reduced birthweight. However, simultaneous use of more than one NRT product was associated with reduced birthweight (b = -10.73 g per week of NRT use [95% CI -26.51, 5.05]), although the association was not statistically significant. The results of this study suggest that maternal use of NRT in pregnancy does not seriously affect birthweight, but there could be a negative effect on birthweight associated with simultaneous use of more than one type of NRT product.

Non-occupational exposure to paint fumes during pregnancy and fetal growth in a general population.

Occupational exposure to organic solvents during pregnancy has been associated with reduced fetal growth. Though organic solvents in the form of paint fumes are also found in the home environment, no studies have investigated the effect of such exposure in a general population. We studied associations between residential exposure to paint fumes during pregnancy and fetal growth within the Danish National Birth Cohort which consecutively recruited pregnant women from 1996 to 2002 from all over Denmark. Around the 30th pregnancy week, 19,000 mothers were interviewed about use of paint in their residence during pregnancy. The mothers were also asked about smoking habits and alcohol consumption during pregnancy, pre-pregnancy weight, height, parity and occupation. Information on birth weight and gestational age was obtained from national registers. We found that 45% of the mothers had been exposed to paint fumes in their residence during pregnancy. We found a statistically significant inverse relationship between exposure to paint fumes and the risk of being small for gestational age. There were no statistically significant associations between exposure to paint fumes and birth weight and risk of preterm birth after adjustment for potential confounders. Our results suggest that there are no causal relationship between non-occupational exposure to paint fumes in the residence during pregnancy and fetal growth.

Sex of prior children and risk of stillbirth in subsequent pregnancies.

BACKGROUND: Delivery of a boy has been reported to increase a woman's risk of recurrent miscarriage in subsequent pregnancies. We explored whether delivery of boys similarly increases the risk of a subsequent stillbirth. METHODS: We identified all Danish women delivering their first child (singleton) between 1980 and 1998 (n = 499,731) using the Danish Birth Registry. These women had subsequent singleton births through 2004 (n = 558,314). We assessed the risk of stillbirth conditional on sex of prior children. RESULTS: The risk of stillbirth was increased by 12% after deliver of boys compared with girls (relative risk = 1.12 [95% confidence interval = 1.02-1.23]). This association did not appear to be explained by maternal confounders. CONCLUSION: Stillbirth risk appears to be slightly higher among the pregnancies of women who have previously delivered a boy. One possible mechanism is maternal immune response to male-specific minor histocompatibility antigens initiated during pregnancies with boys.

Income-related and educational inequality in small-for-gestational age and preterm birth in Denmark and Finland 1987-2003.

AIMS: In this paper, we examine income- and education-related inequality in small-for-gestational age (SGA) and preterm birth in Denmark and Finland from 1987 to 2003 using concentration indexes (CIXs). METHODS: From the national medical birth registries we gathered information on all births from 1987 to 2003. Information on highest completed maternal education and household income in the year preceding birth of the offspring was obtained for 1,012,400 births in Denmark and 499,390 in Finland. We then calculated CIXs for income- and education-related inequality in SGA and preterm birth. RESULTS: The mean household income-related inequality in SGA was -0.04 (95% confidence interval: -0.05, -0.04) in Denmark and -0.03 (-0.04, -0.02) in Finland. The maternal education-related inequality in SGA was -0.08 (-0.10, -0.06) in Denmark and -0.07 (-0.08, -0.06) in Finland. The income-related inequality in preterm birth was -0.03 (-0.03, -0.02) in Denmark and -0.03 (-0.04, -0.02) in Finland. The education-related inequality in preterm birth was -0.05 (-0.07, -0.04) in Denmark and -0.04 (-0.05, -0.03) in Finland. In Denmark, the income-related and education-related inequity in SGA increased over time. In Finland, the income-related inequality in SGA birth increased slightly, while education-related inequalities remained stable. Inequalities in preterm birth decreased over time in both countries. CONCLUSIONS: Denmark and Finland are examples of nations with free prenatal care and publicly financed obstetric care of high quality. During the period of study there were macroeconomic shocks affecting both countries. However, only small income- and education-related inequalities in SGA and preterm births during the period were observed.

Maternal use of oral contraceptives and risk of fetal death.

Intrauterine exposure to artificial sex hormones such as oral contraceptives may be associated with an increased risk of fetal death. Between 1996 and 2002, a total of 92 719 women were recruited to The Danish National Birth Cohort and interviewed about exposures during pregnancy. Outcome of pregnancy was identified through linkage to the Civil Registration System and the National Discharge Registry. The authors analysed the risk of fetal death after recruitment to the cohort by using proportional hazards regression models with gestational age as the underlying time scale. In total, 1102 (1.2%) women took oral contraceptives during pregnancy. Use of combined oestrogen and progesterone oral contraceptives (COC) or progesterone-only oral contraceptives (POC) during pregnancy was not associated with increased hazard ratios of fetal death compared with non-users, HR 1.01 [95% CI 0.71, 1.45] and HR 1.37 [95% CI 0.65, 2.89] respectively. Neither use of COC nor POC prior to pregnancy was associated with fetal death. Stratification by maternal age and smoking showed elevated risks of fetal death for women <30 years and smokers using oral contraception during pregnancy, but the interactions were not significant. In conclusion, there was no evidence that oral contraceptive use before or during pregnancy is associated with an increased risk of fetal death.