Anne Kjersti Daltveit

Self-selection and bias in a large prospective pregnancy cohort in Norway.

Self-selection in epidemiological studies may introduce selection bias and influence the validity of study results. To evaluate potential bias due to self-selection in a large prospective pregnancy cohort in Norway, the authors studied differences in prevalence estimates and association measures between study participants and all women giving birth in Norway. Women who agreed to participate in the Norwegian Mother and Child Cohort Study (43.5% of invited; n = 73 579) were compared with all women giving birth in Norway (n = 398 849) using data from the population-based Medical Birth Registry of Norway in 2000-2006. Bias in the prevalence of 23 exposure and outcome variables was measured as the ratio of relative frequencies, whereas bias in exposure-outcome associations of eight relationships was measured as the ratio of odds ratios. Statistically significant relative differences in prevalence estimates between the cohort participants and the total population were found for all variables, except for maternal epilepsy, chronic hypertension and pre-eclampsia. There was a strong under-representation of the youngest women (<25 years), those living alone, mothers with more than two previous births and with previous stillbirths (relative deviation 30-45%). In addition, smokers, women with stillbirths and neonatal death were markedly under-represented in the cohort (relative deviation 22-43%), while multivitamin and folic acid supplement users were over-represented (relative deviation 31-43%). Despite this, no statistically relative differences in association measures were found between participants and the total population regarding the eight exposure-outcome associations. Using data from the Medical Birth Registry of Norway, this study suggests that prevalence estimates of exposures and outcomes, but not estimates of exposure-outcome associations are biased due to self-selection in the Norwegian Mother and Child Cohort Study.

Are smoking and other lifestyle factors associated with female urinary incontinence? The Norwegian EPINCONT Study

Objective To examine whether modifiable lifestyle factors such as smoking, obesity, physical activity and intake of alcohol or caffeinated drinks were associated with urinary incontinence in women.

Age- and Type-Dependent Effects of Parity on Urinary Incontinence: The Norwegian EPINCONT Study

OBJECTIVE To investigate the association between parity and urinary incontinence, including subtypes and severity of incontinence, in an unselected sample, with special emphasis on age as a confounder or effect modifier. METHODS This was a cross‐sectional study (response rate 80%) with 27,900 participating women. Data on parity and urinary leakage, type, frequency, amount, and impact of incontinence were recorded by means of a questionnaire. A validated severity index was used. Relative risks (RR) with nulliparous women as reference were used as an effect measure. RESULTS Incontinence was reported by 25% of participants. Prevalences among nulliparous women ranged from 8% to 32%, increasing with age. Parity was associated with incontinence, and the first delivery was the most significant. The association was strongest in the age group 20–34 years with RR 2.2 (95% confidence interval [CI] 1.8, 2.6) for primiparous women and 3.3 (2.4, 4.4) for grand multiparous women. A weaker association was found in the age group 35–64 years (RRs between 1.4 and 2.0), whereas no association was found among women over 65 years. For stress incontinence in the age group 20–34 years, the RR was 2.7 (2.0, 3.5) for primiparous women and 4.0 (2.5, 6.4) for grand multiparous women. There was an association with parity also for mixed incontinence, but not for urge incontinence. Severity was not clinically significantly associated with parity. CONCLUSION Parity is an important risk factor for female urinary incontinence in fertile and peri‐ and early postmenopausal ages. Only stress and mixed types of incontinence are associated with parity. All effects of parity seem to disappear in older age.

Prescription drug use among fathers and mothers before and during pregnancy. A population‐based cohort study of 106 000 pregnancies in Norway 2004–2006

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Mothers are using medicines during pregnancies; the extent varies across the world and is generally difficult to compare. In this registry-based study, we examined more than 100,000 Norwegian pregnancies and described the drug prescription pattern of both fathers and mothers around conception and during pregnancy (mothers). WHAT THIS STUDY ADDS In every trimester of pregnancy, about 30% of the mothers was dispensed a drug. The total drug exposure did not seem to diminish throughout pregnancy. One-quarter of the fathers was dispensed drugs during the last 3 months prior to conception. AIMS The primary aim of this study was to describe the use of prescribed drugs in both mothers and fathers before and during pregnancy in Norway. METHODS This population-based cohort study was based on data retrieved from the Medical Birth Registry of Norway and the Norwegian Prescription Database. These registries cover the entire population of Norway. Information on >100,000 births during 2004-2006 in the birth registry was linked to prescription data. Prescriptions issued to mothers just prior to, during and after the pregnancies as well as prescriptions to fathers just prior to conception were identified. RESULTS Among mothers, 83% were prescribed drugs during the period 3 months prior to estimated conception until 3 months after giving birth. The mothers who received drugs were prescribed on average 3.3 different Anatomical Therapeutic Chemical (ATC) codes (range 1-38). During pregnancy, 57% were prescribed drugs. In the first trimester, 33% of mothers were dispensed drugs, while the figure was 29% for mothers in the last trimester. Among fathers, 25% used prescribed drugs during the 3 months prior to conception, with on average 1.9 different ATC codes (range 1-22). CONCLUSION Large proportions of both fathers and mothers were dispensed drugs prior to conception or during pregnancy. While there is a high awareness of the issues involved in maternal drug use in pregnancy, possible teratogenic effects of drug use in fathers shortly before conception should be further explored.

Neonatal outcomes in offspring of women with anxiety and depression during pregnancy

SummaryBackground: The presence of mental disorder during pregnancy could affect the offspring.Aims: To examine the effects of anxiety disorder and depression in pregnant women on neonatal outcomes, and to compare neonatal outcomes between offspring of attendees and non-attendees in a general population-based health survey.Method: Pregnant women (n = 680) were identified from the population-based health study of Nord-TrØndelag County (HUNT-2) by linkage with the Medical Birth Registry of Norway. The women rated themselves on the Hospital Anxiety and Depression Rating Scale (HADS). Outcome variables were gestational length, birth weight, and Apgar scores.Results: HADS-defined anxiety disorder during pregnancy was associated with lower Apgar score at one minute (score < 8; odds ratio = 2.27; p = .03) and five minutes (score < 8; odds ratio = 4.49; p = .016). No confounders were identified. Anxiety disorder and depression during pregnancy was not associated with low birth weight or preterm delivery. Offspring of non-attendees had a lower birth weight (77 g; t = 3.27; p = 0.001) and a shorter gestational length (1.8 days; t = 2.76; p = 0.006) than that of offspring of attendees, a difference that may be explained by a higher load of psychosocial risk factors among the non-attendees.Conclusion: In our study that may be biased towards the healthier among pregnant women, anxiety disorder or depression during pregnancy were not strong risk factors for adverse neonatal outcomes although low Apgar score in offspring of women with anxiety disorder may indicate poor neonatal adaptation.

Cesarean Section and Risk of Severe Childhood Asthma: A Population-Based Cohort Study

OBJECTIVE To explore the possible association between delivery by cesarean section (CS) and later development of asthma. STUDY DESIGN A population-based cohort study of 1,756,700 singletons reported to the Medical Birth Registry of Norway between 1967 and 1998, followed up to age 18 years or the year 2002. Exposure was the mode of delivery (spontaneous vaginal, instrumental vaginal, or CS, with planned and emergency CS separately from 1988 onward). Outcome was asthma registered in the National Insurance Scheme, which provides cash benefits to families of children with severe chronic illnesses. We used multivariate Cox proportional hazard models to examine associations between exposure and outcome. RESULTS The cumulative incidence of asthma was 4.0/1000. Children delivered by CS had a 52% increased risk of asthma compared with spontaneously vaginally delivered children (adjusted hazard ratio [HR] = 1.52; 95% confidence interval [CI] = 1.42 to 1.62). Between 1988 and 1998, planned and emergency CS was associated with a 42% (HR = 1.42; 95% CI = 1.25 to 1.61) and 59% (HR = 1.59; 95% CI = 1.44 to 1.75) increased risk of asthma, respectively. CONCLUSION We found a moderately increased risk of asthma in the children delivered by CS. The possibly stronger association with emergency CS compared with planned CS could be worth pursuing to investigate possible causal mechanisms.

Cohort Profile Update: The Norwegian Mother and Child Cohort Study (MoBa)

This is an update of the Norwegian Mother and Child Cohort Study (MoBa) cohort profile which was published in 2006. Pregnant women attending a routine ultrasound examination were initially invited. The first child was born in October 1999 and the last in July 2009. The participation rate was 41%. The cohort includes more than 114 000 children, 95 000 mothers and 75 000 fathers. About 1900 pairs of twins have been born. There are approximately 16 400 women who participate with more than one pregnancy. Blood samples were obtained from both parents during pregnancy and from mothers and children (umbilical cord) after birth. Samples of DNA, RNA, whole blood, plasma and urine are stored in a biobank. During pregnancy, the mother responded to three questionnaires and the father to one. After birth, questionnaires were sent out when the child was 6 months, 18 months and 3 years old. Several sub-projects have selected participants for in-depth clinical assessment and exposure measures. The purpose of this update is to explain and describe new additions to the data collection, including questionnaires at 5, 7, 8 and 13 years as well as linkages to health registries, and to point to some findings and new areas of research. Further information can be found at [www.fhi.no/moba-en]. Researchers interested in collaboration and access to the data can complete an electronic application available on the MoBa website above.

Pregnancy, delivery, and birth outcome in women with multiple sclerosis

Using data from the compulsory Medical Birth Registry of Norway, the authors investigated the effect of maternal multiple sclerosis (MS) on pregnancy, delivery, and birth outcome in 649 births by MS mothers and 2.1 million control births. The mothers with MS had a higher proportion of neonates small for gestational age and also more frequent induction and operative interventions during delivery.

Vaginal delivery parameters and urinary incontinence: The Norwegian EPINCONT study

OBJECTIVE The study was undertaken to investigate the effect of nine delivery parameters on urinary incontinence in later life. STUDY DESIGN Incontinence data from the EPINCONT study were linked to the Medical Birth Registry of Norway. Effects of birth weight, gestational age, head circumference, breech delivery, injuries in the delivery channel, functional delivery disorders, forceps delivery, vacuum delivery, and epidural anesthesia were investigated. The study covered women younger than 65 years, who had had vaginal deliveries only (n=11,397). RESULTS Statistically significant associations were observed between any incontinence and birth weight 4000 g or greater (odds ratio [OR] 1.1, 95% CI 1.0-1.2); moderate or severe incontinence and functional delivery disorders (OR 1.3, 95% CI 1.1-1.6); stress incontinence and high birth weight (OR 1.2, 95% CI 1.1-1.3) and epidural anesthesia (OR 1.2, 95% CI 1.0-1.5); and urge incontinence and head circumference 38 cm or larger (OR 1.8, 95% CI 1.0-3.3). CONCLUSION The effects were too weak to explain a substantial part of the association between vaginal delivery and urinary incontinence, and statistically significant results may have incurred by chance.

A case-control study of smoking and sudden infant death syndrome in the Scandinavian countries, 1992 to 1995

AIM To establish whether smoking is an independent risk factor for sudden infant death syndrome (SIDS), if the effect is mainly due to prenatal or postnatal smoking, and the effect of smoking cessation. METHODS The analyses were based on data from the Nordic epidemiological SIDS study, a case-control study with 244 cases and 869 controls. Odds ratios were computed by conditional logistic regression analysis. RESULTS Smoking emerged as an independent risk factor for SIDS, and the effect was mainly mediated through maternal smoking in pregnancy (crude odds ratio 4.0 (95% confidence interval 2.9 to 5.6)). Maternal smoking showed a marked dose–response relation. There was no effect of paternal smoking if the mother did not smoke. Stopping or even reducing smoking was beneficial. SIDS cases exposed to tobacco smoke were breast fed for a shorter time than non-exposed cases, and feeding difficulties were also more common. CONCLUSIONS Smoking is an independent risk factor for SIDS and is mainly mediated through maternal smoking during pregnancy. Stopping smoking or smoking less may be beneficial in reducing the risk of SIDS.