Inequality in smoking and related risk factors for smoking in expectant mothers - a nationwide Danish register-based study.

AIMS: Foetuses exposed to smoking during pregnancy are disadvantaged due to numerous adverse obstetric outcomes. This study aimed to examine 1) inequality in maternal smoking between subgroups of pregnant women and 2) significant risk factors of maternal smoking. METHODS: Data were collected from Danish registries. Trends in maternal smoking within each study period, T1 (2000-2002) and T2 (2014-2016), were investigated by Poisson regression calculating prevalence proportion ratios, and trends between study periods were studied by adding an interaction term. The significance of risk factors for maternal smoking (low age, low education, living alone and having a moderate/severe mental health condition) were studied by interaction analysis on the additive scale. RESULTS: The prevalence of maternal smoking decreased from 21% in 2000 to 7% in 2016. Decreases were found in all subgroups of maternal age, cohabitation status, educational level and mental health condition. However, large differences in smoking prevalence between subgroups were found, and inequality in maternal smoking increased from 2000 to 2016. The probability of maternal smoking increased with the addition of risk factors, and positive additive interactions were found for almost all combinations of multiple risk factors. CONCLUSIONS: Our results provide knowledge on risk factors and increasing levels of inequality in maternal smoking which points to a need for targeted interventions in relation to maternal smoking for subgroups of pregnant women in future smoking cessation programmes and in antenatal care.

Implementation of universal umbilical cord pH analysis in Denmark. A national register-based study.

INTRODUCTION: Umbilical cord blood gas analysis provides information about intrapartum hypoxia and is considered an important measure of quality in maternity care. Universal measurement of umbilical cord pH (UC-pH), as part of umbilical cord blood gas analysis, has been recommended in Denmark since 2009. The recommendation is that UC-pH is measured from the umbilical cord artery (pHUA ) and vein (pHUV ). The aim of this study was to evaluate the national implementation of universal measurement of UC-pH. MATERIAL AND METHODS: The study consisted of two parts. First, an evaluation of the implementation, that is, the proportion of births with measured UC-pH since the recommendation was introduced. Second, an evaluation of the cases in which UC-pH was missing. This analysis only involved births with gestational age ≥35 + 0 weeks. RESULTS: In the period 2009 to 2018 there were 560 889 singleton, live births with registered gestational age in Denmark. The proportion of births with measured pHUA and pHUV increased from 12.4% in 2009 to 82.8% in 2015 and then declined to 76.9% in 2018 (p < 0.001). When comparing the group with missing pH from one or both vessels to the group with both pHUA and pHUV we found lower occurrence of pregnancy and births complications in the first group, body mass index ≥35 (unadjusted RR: 0.89, 95% CI: 0.85-0.93), pregnancy induced medical conditions (RR: 0.86, 95% CI: 0.84-0.89), fetal distress during birth (RR: 0.77, 95% CI: 0.76-0.79), emergency cesarean section (RR: 0.80, 95% CI: 0.78-0.83) and serious births events (RR: 0.80, 95% CI: 0.74-0.86). In contrast, the occurrence of placental insufficiency (RR: 1.07, 95% CI: 1.03-1.11), small for gestational age (RR: 1.36, 95% CI: 1.30-1.43, for <2.3th percentile), hypothermia treatment (RR: 1.60, 95% CI: 1.21-2.14) and neonatal death (RR: 1.96, 95% CI: 1.40-2.74) were higher in the group without measured pHUA and pHUV . CONCLUSIONS: The use of UC-pH measurement has increased markedly in Denmark since universal measurement was recommended in 2009. Missing UC-pH from one or both vessels was associated with less complicated pregnancies and with small for gestational age, hypothermia treatment and neonatal death.

Association of birth by cesarean section with academic performance and intelligence in youth: A cohort study.

INTRODUCTION: It is suggested that birth by elective cesarean section (CS) reduces the risk of birth-related infant mortality and injury. Other studies suggest an increased risk of somatic immune-related diseases among children born by CS such as asthma, type 1 diabetes, and inflammatory bowel disease. The WHO Statement on Cesarean Section Rates 2015 described an increase in CS globally. The statement concluded that the effects of CS on social and psychological outcomes remain unclear and that more research is needed to fully understand the effects of CS, including effects on cognition and intelligence in the child. Therefore, we aimed to investigate the association between delivery by CS (elective and acute) and school performance and intelligence in youth. MATERIAL AND METHODS: This cohort study included all Danish live-born children in 1978-2000. We retrieved data regarding pregnancies, births, parents, school grades, and intelligence of the children from Danish registers and performed multiple imputations to avoid discarding data. The final cohort after exclusion comprised 1 408 230 children. Associations between CS and school graduation, grades, conscription attendance, and conscription intelligence scores were analyzed using univariate and multivariate logistic and linear regressions. RESULTS: Adjusted odds ratio with 95% CI of graduating from lower (LSE) and upper (USE) secondary education and of attending conscription were significantly lower in the CS group: LSE graduation: 0.87 (0.84-0.89), USE graduation: 0.93 (0.92-0.94), attending conscription: 0.95 (0.93-0.98). The CS group had significantly lower grade point averages (GPA) in LSE with adjusted differences in mean total GPA of -0.090 (-0.10 to -0.007), and mean core subject GPA of -0.098 (-0.11 to -0.08), in USE with total GPA difference of -0.091 (-0.11 to -0.075) and lower mean intelligence scores of -0.36 (-0.46 to -0.27) in adjusted linear models. A sub-analysis revealed lower chances of graduating LSE and USE when born by acute rather than elective CS. CONCLUSIONS: Chances of LSE and USE graduation and of attending conscription were significantly lower for children born by CS. However, even significant differences in mean GPAs and intelligence scores were very small, so performances when graduating school and attending conscription were comparable regardless of delivery mode.

GnRH agonist supplementation in hormone replacement therapy-frozen embryo transfer cycles: a randomized controlled trial.

RESEARCH QUESTION: Will two boluses of gonadotrophin-releasing hormone agonist (GnRHa) during hormone replacement therapy-frozen embryo transfer (HRT-FET) cycles reduce the total pregnancy loss rate? DESIGN: Randomized controlled trial including a total of 287 HRT-FET cycles performed between 2013 and 2019. After randomization participants allocated to the GnRHa group (n = 144) underwent a standard HRT protocol, supplemented with a total of two boluses of triptorelin 0.1 mg; one bolus 2 days before starting vaginal progesterone and one bolus on the 7th day of progesterone. The control group (n = 143) underwent a standard HRT-FET protocol only. RESULTS: The intention-to-treat analysis showed no significant difference in total pregnancy loss between the GnRHa group and the control group (21% versus 33%; relative risk [RR] 0.63, 95% confidence interval [CI] 0.35-1.11), nor was the biochemical pregnancy loss per positive human chorionic gonadotrophin (HCG) significantly lower in the GnRHa group (12%, 8/67) compared with the control group (25%, 18/72) (RR 0.48, 95% CI 0.22-1.02). Participants with a live birth had a significantly higher mean progesterone concentration compared with participants without a live birth (25.0 ± 12.2 versus 23.8 ± 8.9 nmol/l; P = 0.001). Furthermore, a trend for a higher live birth rate (LBR) correlated with the highest oestradiol quartile concentration (oestradiol >0.957 nmol/l). CONCLUSIONS: Although a difference of 14% in biochemical loss and 12% in total pregnancy loss in favour of GnRHa supplementation was seen this did not reach statistical difference. Luteal progesterone and oestradiol concentrations correlate with LBR in the HRT-FET cycle, emphasizing the importance of luteal serum progesterone and oestradiol monitoring.

Patients' choices and opinions on chorionic villous sampling and non-invasive alternatives for prenatal testing following preimplantation genetic testing for hereditary disorders: A cross-sectional questionnaire study.

OBJECTIVE: The aim of this study was to investigate choices of and reasoning behind chorionic villous sampling and opinions on non-invasive prenatal testing among women and men achieving pregnancy following preimplantation genetic testing (PGT) for hereditary disorders. METHODS: A questionnaire was electronically submitted to patients who had achieved a clinical pregnancy following PGT at the Center for Preimplantation Genetic Testing, Aalborg University Hospital, Denmark, between 2017 and 2020. RESULTS: Chorionic villous sampling was declined by approximately half of the patients. The primary reason for declining was the perceived risk of miscarriage due to the procedure. Nine out of 10 patients responded that they would have opted for a non-invasive prenatal test if it had been offered. Some patients were not aware that the nuchal translucency scan offered to all pregnant women in the early second trimester only rarely provides information on the hereditary disorder for which PGT was performed. CONCLUSION: Improved counseling on the array of prenatal tests and screenings available might be required to assist patients in making better informed decisions regarding prenatal testing. Non-invasive prenatal testing is welcomed by the patients and will likely increase the number of patients opting for confirmatory prenatal testing following PGT for hereditary disorders.

Female cigarette smoking and successful fertility treatment: A Danish cohort study.

INTRODUCTION: Despite smoking being a well-established risk factor for adverse pregnancy and neonatal outcomes, a substantial proportion of women of reproductive age smoke. Previously, meta-analyses have indicated a significantly negative impact of female smoking on outcomes of assisted reproduction, yet most of the included studies have several, essential methodological limitations. We aimed to investigate whether female cigarette smoking may affect the chance of achieving a clinical pregnancy and live birth among women and couples receiving medically assisted reproduction treatment. MATERIAL AND METHODS: A cohort study with longitudinally and repeatedly collected exposure information from 1 January 2010 to 31 August 2015, including data on 1708 women and potential partners initiating either intrauterine insemination, in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) or frozen embryo transfer treatment cycles at the public Fertility Clinic, Aarhus University Hospital, Denmark. Smoking was assessed from self-reported questionnaires completed before treatment. Outcomes were a clinical pregnancy and a live birth. Information on these was obtained from the Danish national health registries, allowing complete follow-up. To evaluate associations between female occasional/daily cigarette smoking and successful medically assisted reproduction treatments, a modified Poisson regression with robust standard errors was used. RESULTS: Female occasional/daily cigarette smoking was not associated with the chance of achieving a clinical pregnancy or a live birth in all intrauterine insemination or IVF/ICSI treatment cycles. When compared with nonsmokers, the adjusted relative risk for obtaining a live birth for those reporting smoking was 1.22 (0.70-2.12) among women initiating 1456 intrauterine insemination treatment cycles. Among women initiating 2788 IVF/ICSI treatment cycles, those reporting occasional/daily smoking had a relative risk for obtaining a live birth of 1.15 (0.82-1.60) when compared with nonsmokers. CONCLUSIONS: Occasionally/daily cigarette smoking women had similar chance of achieving a clinical pregnancy or a live birth as the nonsmokers when receiving medically assisted reproduction treatments. However, tobacco use before and during pregnancy remains a major cause of reduced fertility as well as maternal, fetal, and infant morbidity and mortality, and should strongly be discouraged.

Length of hospital stay after cesarean section in Denmark from 2004 to 2016: A national register-based study.

INTRODUCTION: Length of hospital stay after birth has decreased during the last decades, but nationwide data on length of hospital stay after cesarean section are lacking. Elements of Enhanced Recovery Programs were reported to reduce the length of hospital stay. The aim of this nationwide study was to describe the length of hospital stay after cesarean section in Denmark from 2004 to 2016 taking into account birth- and health-related factors as well as demographic changes and, further, to assess potential differences between the five Danish regions. MATERIAL AND METHODS: Length of hospital stay was assessed in 164 209 deliveries by cesarean section in Denmark from 2004 to 2016. Data were obtained from the Danish National Patient Register. All deliveries by cesarean section at gestational age <22 weeks were excluded. Median length of hospital stay was reported based on crude and adjusted analyses. RESULTS: The median length of hospital stay was significantly reduced by 39 hours (95% confidence interval [CI] 37.9-40.1), from 97 hours (4.0 days) in 2004 to 58 hours (2.4 days) in 2016. Reductions were observed among both planned and emergency cesarean sections. When birth- and health-related factors as well as demographic changes were accounted for, median length of hospital stay was reduced by 30 hours (95% CI 29.3-30.8) in the period. The decrease in length of hospital stay from 2004 to 2016 varied between the five Danish regions, with adjusted reductions between 19 and 46 hours. CONCLUSIONS: A nationwide decrease in length of hospital stay after cesarean section was observed from 2004 to 2016 across all five regions but with significant regional variations. Further studies on the optimal length of hospital stay are needed, especially with regard to implementation of enhanced recovery programs.

Effect of early discharge after planned cesarean section on recovery and parental sense of security. A randomized clinical trial.

INTRODUCTION: In some European countries, discharge the day after planned cesarean section has become an accepted procedure. However, little is known about the patients' perception of early discharge. The aim of this study was to compare early discharge with standard care in relation to parental sense of security. Further, we evaluated postoperative pain, mobilization, and readmission. MATERIAL AND METHODS: We performed a randomized clinical trial including parous, singleton pregnant women with a planned cesarean section at term. The women were allocated to either discharge within 28 hours (intervention group) or after 48 hours (standard care group) following the cesarean section. Women discharged within 28 hours after cesarean section were offered a home visit by a midwife the following day. The primary outcome was the postnatal sense of security, which was reported by the woman and her partner in the "Parents' Postnatal Sense of Security" questionnaire 1 week postpartum. Secondary outcomes were pain score, use of analgesics, mobilization, readmission, and contacts with the healthcare system in the postoperative period. RESULTS: We included 143 women, of whom 72 were allocated to the intervention group and 71 were allocated to the standard care group. There were no differences in baseline characteristics. The two groups did not differ concerning the postnatal sense of security for the women (P = .98) or the postnatal sense of security for the partners (P = .38). We found no difference in pain scores, step count, use of analgesics, or number of contacts with the health-care system between the groups. CONCLUSIONS: Parental postnatal sense of security is not compromised by discharge within 28 hours followed by a home visit compared with discharge after 48 hours after planned cesarean section among parous women.

Idiopathic early ovarian aging: is there a relation with premenopausal accelerated biological aging in young women with diminished response to ART?

PURPOSE: To evaluate whether young women with idiopathic early ovarian aging, as defined by producing fewer oocytes than expected for a given age over multiple in vitro fertilization (IVF) cycles, have changes in telomere length and epigenetic age indicating accelerated biological aging (i.e., increased risk of morbidity and mortality). METHODS: A prospective cohort study was conducted at two Danish public fertility clinics. A total of 55 young women (≤ 37 years) with at least two IVF cycles with ≤ 5 harvested oocytes despite sufficient stimulation with follicle-stimulating hormone (FSH) were included in the early ovarian aging group. As controls, 52 young women (≤ 37 years) with normal ovarian function, defined by at least eight harvested oocytes, were included. Relative telomere length (rTL) and epigenetic age acceleration (AgeAccel) were measured in white blood cells as markers of premenopausal accelerated biological aging. RESULTS: rTL was comparable with a mean of 0.46 (± SD 0.12) in the early ovarian aging group and 0.47 (0.14) in the normal ovarian aging group. The AgeAccel of the early ovarian aging group was, insignificantly, 0.5 years older, but this difference disappeared when adjusting for chronological age. Sub-analysis using Anti-Müllerian hormone (AMH) as selection criterion for the two groups did not change the results. CONCLUSION: We did not find any indications of accelerated aging in whole blood from young women with idiopathic early ovarian aging. Further investigations in a similar cohort of premenopausal women or other tissues are needed to fully elucidate the potential relationship between premenopausal accelerated biological aging and early ovarian aging.

Uterine fibroids increase time to pregnancy: a cohort study.

Objectives: The primary purpose of the study was to investigate a possible association between uterine fibroids and time to pregnancy (TTP), and, secondly, to explore the effect of myomectomy on TTP.Methods: This historical cohort study used data from the Danish National Birth Cohort and the Danish National Patient Registry. The study population consisted of 86,323 women with 92,696 pregnancies. The main outcome was TTP; groups were compared using a binary outcome: TTP >12 months or TTP ≤12 months.Results: Women who had a fibroid diagnosis code before attempting to conceive (n = 92) had an increased risk of TTP >12 months compared with women without a fibroid diagnosis code (n = 87,358) (adjusted odds ratio [OR] 1.67; 95% confidence interval [CI] 1.05, 6.68). Women who had a fibroid diagnosis code after pregnancy (n = 963) also had an increased risk of TTP >12 months compared with women without a fibroid diagnosis code (adjusted OR 1.24; 95% CI 1.04, 1.47).Conclusion: We found an association between having a uterine fibroid diagnosis code and TTP >12 months. We were not able to make a valid assessment of the effect of myomectomy on TTP.

Exploring motivations, attitudes and experiences of oocyte donors: A qualitative study.

INTRODUCTION: The demand for fertility treatment with donated oocytes is increasing in many European countries. In order to offer oocyte donors an attractive treatment, it is necessary to understand the views of the donors. Therefore, the aim of this study was to explore how women who donate oocytes describe their motives and attitudes towards oocyte donation, as well as their experiences with oocyte donation. MATERIAL AND METHODS: A qualitative study based on individual face-to-face interviews with 12 oocyte donors with a donor identity as either anonymous or open. Oocyte donors who had donated oocytes at least once were recruited from the fertility clinic at Herlev University Hospital, Denmark. Data were collected using a piloted, semi-structured interview guide and were analyzed using qualitative content analysis. The analysis was handled in NVIVO 11 PRO. RESULTS: The analysis resulted in three themes: (1) helping others, (2) the treatment, and (3) being an oocyte donor. The financial compensation had varying degrees of importance for the oocyte donors but was always secondary to the desire to help others. All participants were interested in knowing whether their donation had resulted in pregnancy or birth of a child. Many donors had not gained a full understanding of the realistic outcomes of their donation. CONCLUSIONS: Our results suggest that oocyte donors are mainly motivated by altruism, and financial compensation was found to be a secondary motive. Further, political awareness could be directed toward particularly open donors and the need to provide information about the outcome of their donation. Finally, it seems that future oocyte donors, in a treatment with a high need for information, can benefit from clinicians giving more exact information in relation to the probability of the birth of a donor child.

Conservative treatment of rectosigmoid endometriosis: A prospective study.

INTRODUCTION: Deep infiltrating endometriosis is a common cause of pelvic pain. However, some patients have limited problems that may be controlled by medical treatment, so avoiding the potentially severe complications of major surgery. This approach requires detailed knowledge on quality of life and clinical symptoms over time. The aim of the study was to monitor these parameters in patients with rectosigmoid endometriosis treated with oral contraceptives, oral gestagens, and/or the levonorgestrel-releasing intrauterine device. Moreover, nodule size measurements performed with transvaginal sonography were correlated to severity of symptoms. MATERIAL AND METHODS: Conservatively treated patients on oral contraceptives, oral gestagens, or the levonorgestrel-releasing intrauterine device underwent transvaginal sonography and answered a self-administered questionnaire regarding clinical symptoms and quality of life (Short Form 36 and Endometriosis Health Profile 30) at baseline, and 6 and 12 months later. RESULTS: Eighty women completed the follow up. Scores of quality of life were comparable to normative data for Danish women of similar age and did not change with time. No association between change in size of the rectosigmoid nodule and change in symptoms was seen. CONCLUSIONS: This study supports that simple treatment with oral contraceptives, oral gestagens, or the levonorgestrel-releasing intrauterine device represents a viable therapeutic approach to rectosigmoid Deep infiltrating endometriosis, provided that proper selection of patients in need of surgery exists.

Similar evolution of pain symptoms and quality of life in women with and without endometriosis undergoing assisted reproductive technology (ART).

INTRODUCTION: Altogether 10% of all women of fertile age suffer from endometriosis, and up to 25% of these women require assisted reproductive technology (ART) to conceive. During ART the process of controlled ovarian stimulation causes high levels of estrogen, which in theory increases the risk of the progression of symptoms related to this estrogen-dependent disorder. Because several case reports have described the worsening of endometriosis during ART we carried out this study to investigate whether controlled ovarian stimulation during ART aggravates symptoms in women with endometriosis in terms of pain and quality of life. MATERIAL AND METHODS: This prospective cohort study was based on questionnaires containing the Endometriosis Health Profile (EHP-30) and pain evaluated on the numerical rating scale (NRS). Women aged below 40 years were recruited and divided into three groups according to their endometriosis and ART status. Questionnaires were administered before and after controlled ovarian stimulation in one ART cycle. Change in EHP-30 and NRS scores from the 1st to 2nd questionnaire was analyzed. RESULTS: In total 52 women with endometriosis undergoing ART, 50 not undergoing ART, and 52 without endometriosis undergoing ART completed two questionnaires each. Both groups with endometriosis experienced a small increase in their quality of life, while women without endometriosis experienced a decrease. Pelvic pain worsened among women undergoing ART, but no greater worsening was detected among women with endometriosis compared with women without. CONCLUSIONS: This study showed no worsening in quality of life and a slight worsening in pelvic pain during ART regardless of endometriosis status.

Outpatient vs inpatient total laparoscopic hysterectomy: A randomized controlled trial.

INTRODUCTION: The objective of the study was to investigate whether outpatient total laparoscopic hysterectomy (TLH) could be performed as a routine without compromising patient satisfaction. The main outcomes were patient satisfaction with length of hospital stay, quality of life, complications and readmissions, and time to return to work. MATERIAL AND METHODS: A non-blinded prospective randomized controlled trial (Canadian Task Force classification I) performed in a single-center teaching hospital in Denmark. A total of 204 women scheduled for TLH on benign indication were randomized to same-day discharge or overnight stay after TLH. Visual analogue scales (VAS), a validated questionnaire EQ-5D, and a diary were filled in pre- and postoperatively. VAS scores on satisfaction with length of hospital stay and pain were administered taken with the EQ-5D and the diary during a follow up over 4 weeks. Student's t test, Chi-square and non-parametric statistics were used for analysis. The study was registered with ClinicalTrials.gov #NCT02933047. RESULTS: A total of 204 women gave informed consent and 203 underwent surgery (101 outpatient and 102 inpatient women). Complete data were available for 76 women in the outpatient group and 86 women in the inpatient group. There were no differences in baseline characteristics. No group differences were found in satisfaction with length of hospital stay (P = 0.35). The EQ-5D revealed no difference in patient satisfaction. However, one-third in the outpatient group chose overnight stay without medical indication. The groups were comparable in clinical outcomes. Sick leave was longer in the outpatient group regardless of the actual treatment (P = 0.015). CONCLUSIONS: Routine outpatient TLH implies that one-third of the patients stay overnight if this option is available without medical indication. Within this context the procedure can be performed with high patient satisfaction, but may lengthen the time to return to work.

Pelvic Pain and Quality of Life Before and After Laparoscopic Bowel Resection for Rectosigmoid Endometriosis: A Prospective, Observational Study.

BACKGROUND: Surgery for rectosigmoid endometriosis carries a substantial risk of short- and long-term complications, which has to be counterbalanced against the potential effect of the procedure. Prospective data are scarce in the field of deep infiltrating endometriosis surgery. OBJECTIVE: The study aimed to assess pelvic pain and quality of life before and after laparoscopic bowel resection for rectosigmoid endometriosis. DESIGN: The study involved prospectively collected data regarding pelvic pain and quality of life before and after surgery. SETTINGS: It was conducted at a tertiary endometriosis referral unit at Aarhus University Hospital. PATIENTS: A total of 175 women were included. INTERVENTION: Patients underwent laparoscopic bowel resection for endometriosis. MAIN OUTCOME MEASURES: Questionnaires for pain (Numerical Rating Scale) and quality of life (RAND Short Form-36) were answered before and 1 year after surgery. Data on analgesic and hormone treatment were collected. Preoperative and postoperative pelvic pain and quality-of-life scores were compared, and risk factors for improvement/worsening were identified. RESULTS: A total of 97.1% of the women completed the 1-year follow up. A significant decrease (p = 0.0001) was observed on all pelvic pain parameters. Most profound was the decrease in dyschezia. A significant improvement on all quality-of-life scores was observed (p = 0.0001). A surgical complication did not have a negative impact on outcome 1 year after surgery. The postoperative outcome was not related to the type of surgery. LIMITATIONS: This is an observational study without a control group. Risk factor data should be interpreted with caution, because the study was relatively underpowered for some of the rare outcomes. CONCLUSIONS: A significant and clinically relevant improvement in pelvic pain and quality of life 1 year after laparoscopic bowel resection for endometriosis was found. We strongly recommend surgery for rectosigmoid endometriosis that is unresponsive to conservative treatment. See Video Abstract at http://links.lww.com/DCR/A472.

Information bias in epidemiological studies with a special focus on obstetrics and gynecology.

Information bias occurs when any information used in a study is either measured or recorded inaccurately. This paper describes some of the most common types of information bias, using examples from obstetrics and gynecology, and describes how information bias may affect results of observational studies. Non-differential misclassification occurs when the degree of misclassification of exposure status among those with and those without the disease is the same; in cohort studies, this type of bias is most likely and will bias estimates toward no association when exposure is dichotomized. Non-differential underreporting of an exposure with more than two categories may mask a true threshold effect as a dose-response relation and, if a true threshold effect exists, the threshold will be set at too low a level, if the exposure is underreported. Differential misclassification may cause bias in either direction and is particularly likely, when exposure status is reported after the outcome occurred. Misclassification of confounders is an issue that needs special attention by researchers, as failure to measure accurately one or more (strong) confounders may seriously bias the observed results. Misclassification of disease status may also cause bias of estimates of association in either direction. Information bias is probably best prevented during planning of data collection, as there are few and insufficient methods available for correcting inaccurate information.

Cross-sectional studies - what are they good for?

Cross-sectional studies serve many purposes, and the cross-sectional design is the most relevant design when assessing the prevalence of disease, attitudes and knowledge among patients and health personnel, in validation studies comparing, for example, different measurement instruments, and in reliability studies. This paper describes the use of cross-sectional studies and provides examples within obstetrics and gynecology. Caveats are also described; for example, when cross-sectional data is used for analytical purposes of associations between an exposure and an outcome, authors and readers should be careful not to make causal inferences, unless the exposure may safely be assumed to be stable over time and not influenced by experiencing the outcome. In such cases, analyses are also subject to selection and information bias as well as confounding.

Alcohol binge drinking in early pregnancy and the effect on fetal growth: a cohort study.

INTRODUCTION: Alcohol binge drinking is common in early pregnancy and is a well-established risk factor for subsequent child health. Yet, very few studies have investigated the effect on fetal growth. Furthermore, it has been speculated that the timing of binge drinking may be a determining factor for neonatal growth. The objective of this study was to assess the potential effect of binge drinking and different drinking patterns (timing and number of binge drinking episodes) in early pregnancy on fetal growth estimated by birthweight and birth length. MATERIAL AND METHODS: From 1 March to 31 August 2000, 1836 pregnant Danish women from Aarhus University Hospital and Fredericia Hospital were included in the study and interviewed around the early second trimester about their drinking habits during their pregnancy. Information on anthropometric measures at birth was obtained from the Danish Medical Birth Registry. The potential effect of binge drinking and different drinking patterns was estimated using a multivariate general linear regression model adjusted for potential confounders that were selected a priori based on the currently available scientific literature. RESULTS: The women who reported any binge drinking gave birth to children with a reduction in birth length of -0.02 cm (95% CI -0.23 to 0.18) and an increase in birthweight of 0.2 g (95% CI -42.8 to 43.2). The number of binge episodes and the timing of these episodes were also not associated with fetal growth. CONCLUSIONS: The study suggests that binge drinking and different drinking patterns in early pregnancy do not affect fetal growth.

Is TWEAK a valid screening questionnaire to identify alcohol risk drinkers among pregnant women in Denmark?

INTRODUCTION: Identification of pregnant alcohol risk drinkers is crucial to prevent adverse birth outcomes. The TWEAK screening instrument has shown promising results for identifying risk drinkers. However, as the effectiveness of the screening questionnaire has only been investigated among American women with mainly low socioeconomic status, we aimed to investigate the ability of TWEAK to identify alcohol risk drinkers among pregnant Danish women. MATERIAL AND METHODS: During 2000, Danish-speaking women referred to the Midwife Center at Aarhus University Hospital (n = 1554) and Fredericia Hospital (n = 499) for routine antenatal care were invited to participate in the study at their first visit. The women were interviewed about their periconceptional and current drinking habits including average weekly alcohol consumption and binge drinking. Additionally, the women were also asked the questions related to the TWEAK questionnaire. RESULTS: We found that the sensitivity of TWEAK to identify periconceptional risk drinking was quite low, but its ability to identify risk drinkers during pregnancy was marginally higher. Our results suggested that older age (odds ratio 1.46, 95% confidence interval 0.95-2.23), current smoking (odds ratio 2.33, 95% confidence interval 1.63-3.33), being single (odds ratio 2.38, 95% confidence interval 1.38-4.11) and a TWEAK score with a cut-off score of ≥1 (odds ratio 2.75, 95% confidence interval 2.02-3.76) increased the risk of high-risk drinking during pregnancy. CONCLUSIONS: In a Danish setting, TWEAK does not seem as an optimal screening tool to identify periconceptional risk drinkers but it may be useful in identifying high-risk drinking during pregnancy.

Associations between parity and maternal BMI in a population-based cohort study.

INTRODUCTION: We aimed to investigate the change in prevalence of overweight and obesity in pregnant Danish women from 2004 to 2012, and investigate whether increasing parity was associated with a change in body mass index (BMI) prevalence. MATERIAL AND METHODS: We obtained a population-based cohort from the Danish Medical Birth Registry consisting of all Danish women giving birth in 2004-2012 (n = 572 321). This registry contains information on 99.8% of all births in Denmark. We calculated the overall change in prepregnancy BMI status among pregnant women in Denmark, and a multiple linear regression model with adjustment for several potential confounders was used to examine the change in prepregnancy BMI with increasing parity. RESULTS: In 2004, the prevalence of prepregnancy overweight and obesity (BMI ≥ 25) and obesity alone (BMI ≥ 30) was 31.9 and 11%, respectively. In 2012, the prevalence had reached 34.2 and 12.8%. The mean BMI increased for every additional parity from 23.80 (95% CI 23.77-23.82) in parity group 1 to 26.70 (26.52-26.90) in parity group 5+. A multiple linear regression adjusted for potential confounders showed that women on average gained 0.62 (0.58-0.65) BMI units after every additional birth. CONCLUSIONS: This study showed a 7.2% increase in overweight and obesity (BMI ≥ 25) and a 16.4% increase in obesity alone (BMI ≥ 30) for pregnant women in Denmark from 2004 to 2012. In addition, an increase in interpregnancy BMI was seen at every additional delivery, suggesting that obesity is an increasing challenge in obstetrics.