Anne-Marie Nybo Andersen

Physical Exercise during Pregnancy and the Risk of Preterm Birth: A Study within the Danish National Birth Cohort

According to many national recommendations, women should be physically active during pregnancy, but empirical evidence to support this recommendation is sparse. The authors aim in this study was to examine the relation between physical exercise during pregnancy and the risk of preterm birth. Self-reported data on physical exercise during pregnancy were collected prospectively for 87,232 singleton pregnancies included in the Danish National Birth Cohort between 1996 and 2002. Hazard ratios for preterm birth according to hours of exercise per week, type of exercise, and metabolic equivalent-hours per week, respectively, were calculated using Cox regression analysis. Results showed a reduced risk of preterm birth among the almost 40% of women who engaged in some kind of exercise during pregnancy in comparison with nonexercisers (hazard ratio = 0.82, 95% confidence interval: 0.76, 0.88), but no dose-response relation was seen. The association was not affected by the type of exercise, and the results were not altered when the degree of preterm birth was taken into account. These findings do not indicate any adverse effects of exercise on the risk of preterm birth and therefore do not contradict current recommendations.

Socioeconomic position and the risk of preterm birth : a study within the Danish National Birth Cohort

BACKGROUNDnLow socioeconomic position is generally associated with increased risk of preterm birth, but it remains unclear whether the inequality depends on the socioeconomic measure used, if the associations differ according to the degree of prematurity, and how individual level risk factors mediate the association.nnnMETHODSnThe hazard ratios (HR) of preterm birth associated with five different measures of socioeconomic position and three degrees of preterm birth were analysed in a dataset of 75 890 singleton pregnancies (1996-2002) from the Danish National Birth Cohort. This, and the mediating role of selected individual level risk factors (smoking, alcohol consumption, binge drinking, pre-pregnancy body mass index, gestational weight gain) were estimated, using Cox regression analyses.nnnRESULTSnMothers with <10 years of education had an elevated risk of preterm birth compared with mothers with >12 years of education and the association interacted with parity, while income and occupation affected the risk to a lesser degree. The adjusted HR for less educated nulliparous and parous women were 1.22 (95% CI 1.04-1.42) and 1.56 (95% CI 1.31-1.87), respectively, compared with women with >12 years of education. For parous women with <10 years of education inclusion of smoking in the model decreased the HR of preterm birth to 1.43 (95% CI 1.19-1.72).nnnCONCLUSIONSnMaternal educational level was the strongest predictor of preterm birth among five socioeconomic measures and the gradient did not differ significantly according to the degree of preterm birth. For parous women smoking explained some of the educational gradient but in general the selected risk factors only reduced the relative educational gradient in preterm birth marginally.

Moderate alcohol intake during pregnancy and risk of fetal death

BACKGROUNDnControversies still exist regarding the existence of a safe level of alcohol intake during pregnancy. The aim of this study was to assess the risk of fetal death (spontaneous abortion and stillbirth) according to maternal alcohol consumption in a large Danish pregnancy cohort.nnnMETHODSnA cohort study carried out within the framework of the Danish National Birth Cohort. A total of the 92u2009719 participants enrolled in the Danish National Birth Cohort who provided information about lifestyle during first trimester of pregnancy were included in the study. Information about average weekly consumption of alcohol during pregnancy, smoking, coffee drinking, occupational status and reproductive history were obtained by means of computer-assisted telephone interviews. Pregnancy outcomes (spontaneous abortion, stillbirth, live birth and other pregnancy outcome) and gestational age at end of pregnancy were obtained through register linkage with the Civil Registration System and the National Discharge Registry. Data were analysed using Cox regression models, taking the varying gestational age at recruitment and time-dependent co-variables into account.nnnRESULTSnFifty-five per cent of the participants abstained from alcohol drinking during pregnancy and only 2.2% reported four or more drinks per week. The adjusted hazard ratios for fetal death in first trimester were 1.66 [95% confidence interval (CI) 1.43-1.92] and 2.82 (95% CI 2.27-3.49) for women who reported 2-3½; drinks per week and 4 or more drinks per week, respectively, and 1.57 (95% CI 1.30-1.90) and 1.73 (95% CI 1.24-2.41) for fetal death during pregnancy weeks 13-16. No increased risk was found for fetal death after 16 weeks of pregnancy.nnnCONCLUSIONSnEven low amounts of alcohol consumption during early pregnancy increased the risk of spontaneous abortion substantially. The results indicate that the fetus is particularly susceptible to alcohol exposure early in pregnancy.

Physical exercise during pregnancy and fetal growth measures: a study within the Danish National Birth Cohort

OBJECTIVEnThe objective of the study was to examine the association between physical exercise during pregnancy and fetal growth measures.nnnSTUDY DESIGNnData on 79,692 liveborn singletons from the Danish National Birth Cohort were collected between 1996 and 2002. Mean differences in birthweight, length, ponderal index, head and abdominal circumference, and placental weight and hazard ratios of small- and large-for-gestational-age babies were calculated.nnnRESULTSnOur data indicated smaller babies in exercising women compared with nonexercisers, but the differences were small, and only a few were statistically significant. Exercising women had a slightly decreased risk of having a child small for gestational age (hazard ratio, 0.87; 95% confidence interval, 0.83-0.92) and large for gestational age (hazard ratio, 0.93; 95% confidence interval, 0.89-0.98).nnnCONCLUSIONnThe findings do not indicate sizable effects on fetal growth measures related to exercise apart from a modest decreased risk of small- and large-for-gestational-age infants. These findings do not speak against advising pregnant women to be physically active during pregnancy.

Socio-economic inequality in preterm birth: a comparative study of the Nordic countries from 1981 to 2000

During the 1980s and 1990s, there were large social and structural changes within the Nordic countries. Here we examine time changes in risks of preterm birth by maternal educational attainment in Denmark, Finland, Norway and Sweden. Information on gestational age and maternal socio-economic position was obtained from the NorCHASE database, which includes comparable population-based register data of births from Denmark, Finland, Sweden and Norway from 1981 to 2000. The risks of very preterm birth (<32 gestational weeks) and moderately preterm birth (32-36 gestational weeks) were calculated by maternal educational attainment and analysed in 5-year intervals from 1981 to 2000. Compared with mothers with >12 years of education, mothers with <10 years of education had similarly increased risks of very, and to a lesser extent moderately, preterm birth in all four countries. The educational gradient increased slightly over time in very preterm births in Denmark, while there was a slight narrowing of the gap in Sweden. In moderately preterm births, the educational inequality gap was constant over the study period in Denmark, Norway and Sweden, but narrowed in Finland. The educational gradient in preterm birth remained broadly stable from 1981 to 2000 in all four countries. Consequently, the socio-economic inequalities in preterm birth were not strongly influenced by structural changes during the period.

Characteristics of women who binge drink before and after they become aware of their pregnancy

Background Consumption of high doses of alcohol on a single occasion (binge drinking) may harm the developing foetus and pregnant women are advised to avoid binge drinking while pregnant. We present characteristics of Danish women who binge drank in the pre-and post recognised part of their pregnancy. Methods During the years 1996–2002 approximately 100,000 pregnant women were enrolled into the Danish National Birth Cohort. Women with information on binge drinking, time of recognition of pregnancy, age, reproductive history, marital status, smoking, occupational status, pre-pregnancy BMI, alcohol consumption before pregnancy, and mental disorders (nxa0=xa085,334) were included in the analyses. Results Approximately one quarter of the women reported binge drinking at least once during pregnancy; most of these in the pre-recognised part of pregnancy. Weekly alcohol consumption before pregnancy, single status and smoking were predictors for binge drinking in both the unrecognised and recognised part of pregnancy. Moreover, binge drinking in the pre-recognised part of pregnancy was more common among women aged 25–29xa0years, who were nulliparous, well educated in good jobs or skilled workers. Binge drinking after recognition of pregnancy was more common among women who were unintended pregnant, multiparous unskilled workers, had been unemployed for more than one year, or had mental/neurotic disorder. Conclusions In order to prevent binge drinking during pregnancy, health care providers should target their efforts towards pregnant women as well as pregnancy-planners. It is important to be aware that women who binge drink before versus after the pregnancy is recognised have different social characteristics.

The influence of birth weight and body mass in early adulthood on early coronary heart disease risk among Danish men born in 1953

This study examines the joint and separate influence of birth weight and body mass in young adulthood on subsequent coronary heart disease (CHD) risk. A cohort of 9,143 men born in Copenhagen, Denmark, in 1953, for whom information on birth weight and body weight and height around age 19xa0years were retrieved from birth certificates and conscript records, respectively, were followed from 1978 until 2005 (between age 25 and 52xa0years) for incident fatal and non-fatal CHD. Data on CHD were obtained through record linkage to the Cause of Death Registry and the National Patient Registry. During follow-up, a total of 475 men had a CHD diagnosis. Men with low birth weight, high body mass index (BMI) at age 19, a father from the working class, and low educational level at age 19 had an increased risk for CHD. Birth weight was inversely associated with CHD only in men with BMI of 25xa0kg/m2 or above. Adjustment for childhood social circumstances and educational status at age 19 had minor influence on the estimates. In conclusion, BMI in young adulthood seems to be strongly associated with the risk of CHD before age 52, and birth weight seem to modify the association. The risk estimates is highest for individuals with a combination of low birth weight and overweight in young adulthood.

Do childhood and adult socioeconomic circumstances influence health and physical function in middle-age?

This study examines the joint and separate contribution of social class in early and adult life to differences in health and physical function in middle-aged men. We use data from the Metropolit project which includes men born in 1953 in Copenhagen and a study of middle-aged Danish twins (MADT). In total 6292 Metropolit participants in a follow-up survey on health in 2004 were included in the study together with 2198 male twins of which 1294 were part of a male twin pair (N=647 pairs). Logistic regression was used to investigate the association between social class in early and adult life, respectively and health in midlife, measured as limitations in running 100 m, poor dental status, poor self-rated health, and fatigue. In both datasets, men with low childhood or adult social class had a higher risk of being unable to run 100 m, having poor dental status, having poor self-rated health and fatigue than men from the highest social classes. When childhood and adult social class were mutually adjusted, the estimates for both measures were attenuated. Adjustment for living without a partner, body mass index (BMI) and smoking in midlife, which were also related to the four outcomes, had marginal effects on the estimates for childhood social class, but attenuated the effect of adult social class somewhat. Among male twin pairs discordant on adult social class, the twin in the lowest class seemed to be unable to run 100 m, rate own health poorer and being fatigued more often than the high class co-twin, while there seemed to be no twin pair difference in dental status. This suggests that the associations of adult social class with functional limitations, poor self-rated health and fatigue may partly be due to causal effects related to adult social class exposures, while social class differences in dental status might be consistent with an effect of factors mainly operating early in life.

Frequency and impact of obstetric complications prior and subsequent to unexplained secondary recurrent miscarriage

BACKGROUNDnThe chance of a live birth after a diagnosis of secondary recurrent miscarriage (SRM) is reduced in patients who, prior to the miscarriages, gave birth to a boy and carry HLA class II alleles that efficiently present male-specific (H-Y) antigens to the immune system. Information about obstetric complications in births prior and subsequent to the SRM diagnosis is limited. The relations between maternal carriage of H-Y-restricting HLA, fetal sex, obstetric complications and prognosis are unknown.nnnMETHODSnWomen with unexplained SRM referred to the Danish Recurrent Miscarriage Clinic between 1986 and 2006 (n = 358) were included; 213 gave birth after the diagnosis. Controls, retrieved from the Danish National Birth Registry, were all women with singleton birth of parity 0, 1982-2005 (n = 608,068) and parity 1, 1986-2008 (n = 510,264). Cross-linkage to the National Discharge Registry identified birth complication diagnoses related to the relevant births among patients and controls.nnnRESULTSnThe sex ratio was 1.49 in births prior to SRM and 0.76 in birth after SRM (P < 0.0001). For SRM patients with only late miscarriages (>10 weeks gestation), the corresponding sex ratios were 2.31 and 0.21. Compared with the control groups, obstetric complications were more frequent both before (39% versus 24% P <or= 0.01) and after (19% versus 14%, P = 0.01) SRM diagnosis. Births were more frequently complicated when the child was a boy (44% versus 31%, P = 0.02) before and a girl (24% versus 13%, P = 0.04) after SRM diagnosis. SRM patients with H-Y-restricting HLA class II alleles and a firstborn boy gave birth to children who weighed on average 381 g less (P = 0.006) and were born 0.9 weeks earlier (P = 0.06) and their births had more obstetric complications (P = 0.05) than patients with the same HLA alleles but a firstborn girl.nnnCONCLUSIONSnObstetric complications, sex ratios in births prior and subsequent to SRM and maternal carriage of H-Y-restricting HLA class II alleles are associated parameters. Immune responses against fetal H-Y antigens initiated in the pregnancy prior to the SRM may play a causal role in SRM.

The social gradient in birthweight at term: quantification of the mediating role of maternal smoking and body mass index

BACKGROUNDnMaternal education is associated with the birthweight of offspring. We sought to quantify the role of maternal body mass index (BMI) and smoking as intermediary variables between maternal education and birthweight at term.nnnMETHODSnWe examined the association between maternal education, BMI, smoking and offsprings birthweight among women who delivered at term in the Danish National Birth Cohort (n = 75,085).nnnRESULTSnCompared with mothers with more than 12 years of education, women with 10-12 years of education had babies that were 12 (4-19) g lighter. Mothers with 9 years of education had babies that were 51 (95% CI; 39-62) g lighter. BMI and smoking affected the association between maternal education and birthweight, albeit in different directions. If all mothers had the BMI of the highest educated mothers, the deficits would be larger: -20 (-22 to -19) and -74 (-80 to -68) g, respectively. If all mothers smoked like the highest educated mothers, mothers with a shorter education would have the heaviest babies: the difference would be 9 (2-16) and 23 (11-36) g, respectively. In combination, smoking and BMI all but explained the educational gradient in birthweight at term.nnnCONCLUSIONnMaternal smoking and BMI are important intermediates of the educational gradient in birthweight at term. As the prevalence of smoking is dropping and the prevalence of obesity is increasing the educational gradient will likely reverse, but it seems unlikely that this will translate into a health advantage for the children of the least educated mothers.