The bidirectional association between premenstrual disorders and perinatal depression: A nationwide register-based study from Sweden.

BACKGROUND: Premenstrual disorders (PMDs) and perinatal depression (PND) share symptomology and the timing of symptoms of both conditions coincide with natural hormonal fluctuations, which may indicate a shared etiology. Yet, there is a notable absence of prospective data on the potential bidirectional association between these conditions, which is crucial for guiding clinical management. Using the Swedish nationwide registers with prospectively collected data, we aimed to investigate the bidirectional association between PMDs and PND. METHODS AND FINDINGS: With 1,803,309 singleton pregnancies of 1,041,419 women recorded in the Swedish Medical Birth Register during 2001 to 2018, we conducted a nested case-control study to examine the risk of PND following PMDs, which is equivalent to a cohort study, and transitioned that design into a matched cohort study with onward follow-up to simulate a prospective study design and examine the risk of PMDs after PND (within the same study population). Incident PND and PMDs were identified through clinical diagnoses or prescribed medications. We randomly selected 10 pregnant women without PND, individually matched to each PND case on maternal age and calendar year using incidence density sampling (N: 84,949: 849,482). We (1) calculated odds ratio (OR) and 95% confidence intervals (CIs) of PMDs using conditional logistic regression in the nested case-control study. Demographic factors (country of birth, educational level, region of residency, and cohabitation status) were adjusted for. We (2) calculated the hazard ratio (HR) and 95% CIs of PMDs subsequent to PND using stratified Cox regression in the matched cohort study. Smoking, BMI, parity, and history of psychiatric disorders were further controlled for, in addition to demographic factors. Pregnancies from full sisters of PND cases were identified for sibling comparison, which contrasts the risk within each set of full sisters discordant on PND. In the nested case-control study, we identified 2,488 PMDs (2.9%) before pregnancy among women with PND and 5,199 (0.6%) among controls. PMDs were associated with a higher risk of subsequent PND (OR 4.76, 95% CI [4.52,5.01]; p < 0.001). In the matched cohort with a mean follow-up of 7.40 years, we identified 4,227 newly diagnosed PMDs among women with PND (incidence rate (IR) 7.6/1,000 person-years) and 21,326 among controls (IR 3.8). Compared to their matched controls, women with PND were at higher risk of subsequent PMDs (HR 1.81, 95% CI [1.74,1.88]; p < 0.001). The bidirectional association was noted for both prenatal and postnatal depression and was stronger among women without history of psychiatric disorders (p for interaction < 0.001). Sibling comparison showed somewhat attenuated, yet statistically significant, bidirectional associations. The main limitation of this study was that our findings, based on clinical diagnoses recorded in registers, may not generalize well to women with mild PMDs or PND. CONCLUSIONS: In this study, we observed a bidirectional association between PMDs and PND. These findings suggest that a history of PMDs can inform PND susceptibility and vice versa and lend support to the shared etiology between both disorders.

Gonadotropin Releasing Hormone agonist (GnRHa) during chemotherapy and post-cancer childbirths - a Nationwide population-based cohort study of 24,922 women diagnosed with cancer in Sweden.

Background: Worldwide, an increasing number of women with cancer are receiving Gonadotropin Releasing Hormone agonist (GnRHa) co-treatment during chemotherapy aiming at ovarian protection. There is divergence among guidelines, and some have recommended GnRHa co-treatment for women with breast cancer, however, the effect of GnRHa on future fertility is uncertain. Methods: In this population-based cohort study we included all women diagnosed with cancer at ages 15-45 between July 2005 and March 2017 in Sweden, identified in the Swedish Cancer Register. Exposure to GnRHa co-treatment was captured using the Prescribed Drug Register. Post-cancer childbirth, extracted from the Medical Birth Register, was the main outcome. Secondary outcomes included childbirths achieved through natural conception (NC), infertility diagnosis and cancer mortality. For each outcome, adjusted hazard ratios (aHR) and 95% confidence intervals (CI) were estimated using delayed-entry Cox models, stratified by age and cancer site. Findings: Among 24,922 women diagnosed with cancer, 1.5% had GnRHa co-treatment. Breast cancer diagnoses were found in 80.2% of GnRHa exposed women and the GnRHa exposure was not associated with higher rates of childbirth (aHR 1.23, 95% CI 0.80-1.89), or NC childbirth (aHR 1.02, 95% CI 0.62-1.67), whereas the rate of infertility was significantly higher (aHR 2.42, 95% CI 1.44-4.08). In women with lymphoma and other cancers, GnRHa exposure was not associated with higher rates of childbirth, NC childbirth or infertility. GnRHa exposure was not associated with higher cancer mortality for any cancer type. Interpretation: We did not find evidence of improved or maintained fertility, estimated as childbirth rates post-cancer, in women who received GnRHa during cancer treatment. Funding: This study was financed by research grants from The Swedish Cancer Society (CAN 2017/704; 190249Pj, 200170F), The Swedish Research Council (Dnr 2019-00446), the Nordic Cancer Union NCU (Grant 2017), The Swedish Childhood Cancer Fund (KP2016-0031), Radiumhemmets Forskningsfonder (Dnr: 201313), Stockholm County Council (FoUI-953912) and Karolinska Institutet (Dnr 2020-01963).

Fetal growth after fresh and frozen embryo transfer and natural conception: A population-based register study.

OBJECTIVE: To investigate fetal growth trajectories and risks of small and large for gestational age (SGA and LGA), and macrosomia in pregnancies after fresh and frozen embryo transfer (ET), and natural conception (NC). DESIGN: Longitudinal population-based cohort study. SETTING: Swedish national registers. POPULATION: A total of 196 008 singleton pregnancies between 2013 and 2017. METHODS: Of all singleton pregnancies resulting in live births in the Swedish Pregnancy Register, 10 970 fresh ET, 6520 frozen ET, and 178 518 NC pregnancies with ultrasound data were included. A general least squares model was used to examine the effect of fresh or frozen ET on fetal growth while adjusting for confounders. MAIN OUTCOME MEASURES: Fetal growth velocity. SGA, LGA and macrosomia. RESULTS: At 120 days, fetal weights were lower in fresh ET pregnancies compared with NC pregnancies. Thereafter fresh ET as well as FET fetuses had higher fetal weights than NC fetuses, with no differences between themselves until the second trimester. From 210 days, FET fetuses were heavier than fresh ET fetuses, whereas fresh ET fetuses had lower fetal weights than NC fetuses from 245 days. After fresh ET, SGA was more frequent, whereas LGA and macrosomia were less frequent, than after FET. CONCLUSIONS: This study gives new insights into the differences in fetal growth dynamics between fresh and frozen ET and NC pregnancies. Clinically relevant differences in proportions of SGA, LGA and macrosomia were observed.

Perinatal Depression and Risk of Suicidal Behavior.

Importance: Suicidal ideation is common among women with perinatal depression (PND). However, prospective data are limited on the risk, particularly long-term risk, of suicidal behavior (suicide attempt and completed suicide) among women with perinatal depression. Objective: To examine the association between PND and risk of short- and long-term suicidal behavior. Design, Setting, and Participants: A nationwide population-matched cohort study was conducted in Sweden including 86 551 women with PND from 2001 to 2017 and 865 510 unaffected women individually matched on age and calendar year at delivery. Sibling comparison was used to account for familial confounding. Data were analyzed from January 2022 to November 2023. Exposure: PND was identified through depression diagnosis or filled prescriptions of antidepressants from pregnancy to 1 year post partum in registers. Main Outcomes and Measures: All women were followed up for the first event of suicidal behavior recorded in registers. Hazard ratios (HR) of suicidal behavior were estimated using time-to-event analysis. Results: Women with PND (86 551 participants) received a diagnosis at a mean (SD) age of 30.67 (5.23) years. During a median (IQR) follow-up of 6.91 (3.62-10.88) years, 3604 events of suicidal behavior (incidence rate [IR], 5.62 per 1000 person-years) were identified among women with PND and 6445 (IR, 1.01 per 1000 person-years) among population-unaffected women. Women with PND had an elevated risk of suicidal behavior when compared with matched unaffected women (HR, 3.15; 95% CI, 2.97-3.35). Comparable, albeit somewhat attenuated, associations were yielded when comparing PND women with their PND-free sisters (HR, 2.75; 95% CI, 2.10-3.61). In the population-matched cohort, the association was greater for postnatal depression and among women without a history of psychiatric disorders. The excess risk was pronounced during the first year after diagnosis (HR, 7.20; 95% CI, 6.07-8.54), yet remained statistically significant during 5 to 18 years of follow-up (HR, 2.34; 95% CI, 2.12-2.57). Conclusions and Relevance: In this nationwide cohort study, women with PND were at an increased risk of suicidal behavior, particularly within the first year after diagnosis with persistent risk elevations throughout the 18 years of follow-up, highlighting the need for vigilant clinical monitoring of this vulnerable group.

Perinatal depression and risk of mortality: nationwide, register based study in Sweden.

OBJECTIVE: To determine whether women with perinatal depression are at an increased risk of death compared with women who did not develop the disorder, and compared with full sisters. DESIGN: Nationwide, register based study. SETTING: Swedish national registers, 1 January 2001 to 31 December 2018. PARTICIPANTS: 86 551 women with a first ever diagnosis of perinatal depression ascertained through specialised care and use of antidepressants, and 865 510 women who did not have perinatal depression were identified and matched based on age and calendar year at delivery. To address familial confounding factors, comparisons were made between 270 586 full sisters (women with perinatal depression (n=24 473) and full sisters who did not have this disorder (n=246 113)), who gave at least one singleton birth during the study period. MAIN OUTCOME MEASURES: Primary outcome was death due to any cause. Secondary outcome was cause specific deaths (ie, unnatural and natural causes). Multivariable Cox regression was used to estimate hazard ratios of mortality comparing women with perinatal depression to unaffected women and sisters, taking into account several confounders. The temporal patterns of perinatal depression and differences between antepartum and postpartum onset of perinatal depression were also studied. RESULTS: 522 deaths (0.82 per 1000 person years) were reported among women with perinatal depression diagnosed at a median age of 31.0 years (interquartile range 27.0 to 35.0) over up to 18 years of follow-up. Compared with women who did not have perinatal depression, women with perinatal depression were associated with an increased risk of death (adjusted hazard ratio 2.11 (95% confidence interval 1.86 to 2.40)); similar associations were reported among women who had and did not have pre-existing psychiatric disorder. Risk of death seemed to be increased for postpartum than for antepartum depression (hazard ratio 2.71 (95% confidence interval 2.26 to 3.26) v 1.62 (1.34 to 1.94)). A similar association was noted for perinatal depression in the sibling comparison (2.12 (1.16 to 3.88)). The association was most pronounced within the first year after perinatal depression but remained up to 18 years after start of follow up. An increased risk was associated with both unnatural and natural causes of death among women with perinatal depression (4.28 (3.44 to 5.32) v (1.38 (1.16 to 1.64)), with the strongest association noted for suicide (6.34 (4.62 to 8.71)), although suicide was rare (0.23 per 1000 person years). CONCLUSIONS: Even when accounting for familial factors, women with clinically diagnosed perinatal depression were associated with an increased risk of death, particularly during the first year after diagnosis and because of suicide. Women who are affected, their families, and health professionals should be aware of these severe health hazards after perinatal depression.

Overweight or obesity in children born after assisted reproductive technologies in Denmark: A population-based cohort study.

BACKGROUND: The association between assisted reproductive technologies (ARTs) and the body mass index (BMI) of children remains controversial. Confounding by morbidity and other factors associated with parental infertility may have biased studies comparing children born after ART with children born after no treatment. We investigated the associations between different fertility treatments and BMI in children at age 5 to 8 years, adjusting for and stratifying by causes of parental infertility. METHODS AND FINDINGS: This Danish cohort study included 327,301 children born between 2007 and 2012 (51% males, median age at follow-up 7 years). Of these, 13,675 were born after ART, 7,728 were born after ovulation induction with or without intrauterine insemination [OI/IUI], and 305,898 were born after no fertility treatments. Using the International Obesity Task Force (IOTF) standards, we defined overweight (BMI ≥ IOTF-25) and obesity (BMI ≥ IOTF-30). We compared children born after ART versus OI/IUI; intracytoplasmic sperm injection (ICSI) versus conventional in vitro fertilization (IVF); and frozen-thawed versus fresh embryo transfer and estimated crude and adjusted prevalences of children with overweight or obesity at age 5 to 8 years, prevalence odds ratios (PORs), and differences in mean BMI z-scores. Adjustment was performed using stabilized inverse probability of treatment weights, including parity, year of conception, parental causes of infertility, age, educational level, comorbidities, maternal country of origin, BMI, and smoking as covariates. The crude prevalence of obesity was 1.9% in children born after ART, 2.0% in those born after OI/IUI, and 2.7% in those born after no fertility treatment. After adjustment, children born after ART and OI/IUI had the same prevalence of being overweight (11%; POR 1.00, 95% confidence interval [CI] 0.91 to 1.11; p = 0.95) or obese (1.9%; POR 1.01, 95% CI 0.79 to 1.29; p = 0.94). Comparison of ICSI with conventional IVF yielded similar pattern (POR 0.95, 95% CI 0.83 to 1.07; p = 0.39 for overweight and POR 1.16, 95% CI 0.84 to 1.61; p = 0.36 for obesity). Obesity was more prevalent after frozen-thawed (2.7%) than fresh embryo transfer (1.8%) (POR 1.54, 95% CI 1.09 to 2.17; p = 0.01). The associations between fertility treatments and BMI were only modestly different in subgroups defined by the cause of infertility. Study limitations include potential residual confounding, restriction to live births, and lack of detailed technical information about the IVF procedures. CONCLUSIONS: We found no association with BMI at age 5 to 8 years when comparing ART versus OI/IUI or when comparing ICSI versus conventional IVF. However, use of frozen-thawed embryo transfer was associated with a 1.5-fold increased risk of obesity compared to fresh embryo transfer. Despite an elevated relative risk, the absolute risk difference was low.

Birth Weight, Gestational Age, and Risk of Cardiovascular Disease in Early Adulthood: Influence of Familial Factors.

The association between intrauterine growth restriction and cardiovascular disease (CVD) later in life might be confounded by familial factors. We conducted a binational register-based cohort study to assess associations of birth weight for gestational age (GA), a proxy for intrauterine growth restriction, and GA with CVD risk in early adulthood, before and after addressing familial factors via sibling comparison. We included 3,410,334 live nonmalformed singleton births from Sweden (1973-1996) and Denmark (1978-1998). During a median follow-up period of 10 years from age 18 years onwards, 29,742 individuals developed incident CVD (hypertension, ischemic heart disease, or cerebrovascular disease). Compared with individuals born with appropriate birth weight for GA (AGA; 10th-90th percentiles) or full term (39-40 gestational weeks), individuals born severely small for GA (SGA; ≤3rd percentile) or preterm (22-36 weeks) were at increased risk of CVD (hazard ratio (HR) = 1.38 (95% confidence interval (CI): 1.32, 1.45) and HR = 1.31 (95% CI: 1.25, 1.38), respectively). The association was attenuated when comparing individuals born SGA with their AGA siblings (HR = 1.11, 95% CI: 0.99, 1.25) but remained robust when comparing individuals born preterm with their term siblings (HR = 1.21, 95% CI: 1.07, 1.37). Our findings suggest that both SGA and preterm birth are associated with CVD risk in early adulthood, with greater familial confounding noted for SGA birth.

Obstetric and Perinatal Outcomes of Singleton Births Following Single- vs Double-Embryo Transfer in Sweden.

Importance: Pregnancies resulting from assisted reproductive technology are associated with an increased risk of adverse perinatal outcomes compared with those following natural conception. Previous studies have shown an association of pregnancies resulting from transfer of multiple embryos with these negative findings. Objective: To determine the risk for adverse outcomes in singletons conceived through assisted reproduction using double-embryo transfer (DET) vs single-embryo transfer (SET). Design, Setting, and Participants: This cohort study used data from women who achieved singleton deliveries after SET or DET in Sweden between 2007 and 2017 as recorded in the National Quality Registry for Assisted Reproduction. All embryo transfers, at cleavage or blastocyst stage, replaced in fresh or frozen treatment cycles were included. Data on obstetric and neonatal outcomes were retrieved by linkage to the National Medical Birth Register. Naturally conceived singletons were included as a reference group. Data were analyzed between September 2021 and August 2022. Exposures: Double-embryo transfer leading to singleton birth. Main Outcomes and Measures: Relative risk ratios or odds ratios (ORs) and absolute risk differences (ARDs) in percentage points with 95% CIs were calculated for obstetric and perinatal outcomes in singleton births conceived using DET vs SET. Results: Among 1 115 863 singleton births, 30 713 singletons were born after SET and 5123 after DET. A higher risk of neonatal death was found in singletons after DET vs SET (OR, 2.67 [95% CI, 1.28-5.55]; ARD, 0.2 percentage points [95% CI, 0.0-0.4 percentage points]). In frozen embryo transfers, DET was associated with a higher risk of low birth weight (OR, 1.64 [95% CI, 1.19-2.25]; ARD, 2.0 percentage points [95% CI, 0.5-3.5 percentage points]). Among blastocyst transfers, DET was associated with very preterm birth (relative risk ratio, 2.64 [95% CI, 1.50-4.63]; ARD, 1.8 percentage points [95% CI, 0.3-3.4 percentage points]) and low birth weight (OR, 1.83 [95% CI, 1.29-2.60]; ARD, 3.2 percentage points [95% CI, 0.9-5.5 percentage points]). Conclusions and Relevance: These results indicate a higher risk of adverse outcomes following DET, even when the result is a singleton birth, vs singletons born after SET. Adverse outcomes were mainly observed in singletons following DET using frozen embryos and blastocysts.

A population-based study of concurrent prescriptions of opioid analgesic and selective serotonin reuptake inhibitor medications during pregnancy and risk for adverse birth outcomes.

BACKGROUND: Pregnant women with painful conditions often have mental health problems, including depression and anxiety. Co-morbid conditions may cause pregnant women to use multiple medications, although safety of such practice is poorly understood. OBJECTIVES: We investigated the influence of combined prescriptions of opioid analgesics and selective serotonin reuptake inhibitors (SSRIs) during pregnancy on two adverse birth outcomes. METHODS: We analysed Swedish population-based births (n = 688 914) between 2007 and 2013. Using national registers, we obtained data on filled medication prescriptions, birth outcomes, and a wide range of parental characteristics. We estimated preterm birth and small-for-gestational-age risk following independent or combined prescriptions of the two medications compared with no filled prescriptions for either medication. We adjusted for confounders using inverse probability of treatment weights. RESULTS: After adjusting for confounders, preterm birth risk was higher among women with opioid analgesic prescriptions only (5.9%; risk ratio [RR] 1.27, 95% confidence interval [CI] 1.22, 1.33), SSRIs only (6.2%; RR 1.34, 95% CI 1.27, 1.42), and both medications (7.8%; RR 1.70, 95% CI 1.47, 1.96) compared with unexposed women (4.6%). The interaction between the medications on preterm birth was small (risk difference [RD] 0.4%, 95% CI -0.8%, 1.6%); relative excess risk due to interaction [RERI] 0.09, 95% CI -0.17, 0.34; RR 1.00, 95% CI 0.85, 1.17). For small for gestational age, risk was approximately 2% across all groups, and there was no interaction between the medications (RD 0.3%, 95% CI -0.4%, 1.1%); RERI 0.15, 95% CI -0.16, 0.47; RR 1.15, 95% CI 0.87, 1.52). CONCLUSIONS: Compared with unexposed pregnancies, those with either medication alone had a small increased risk for preterm birth but no increased risk for small for gestational age. The magnitude of associations with combined exposure to both medications were not greater than the sum of the associations with each medication considered individually.

The Uppsala-Stockholm Assisted Reproductive Techniques (UppStART) study.

PURPOSE: The Uppsala-Stockholm Assisted Reproductive Techniques (UppStART) study is a prospectively recruited sample of couples undergoing assisted reproduction in Stockholm and Uppsala county in Sweden. The study was initiated to (1) investigate possible changes in the epigenetic profile of infants inferred through the ART procedures and their consequence and (2) to assess the impact of lifestyle and health exposures on treatment outcome. PARTICIPANTS: Recruitment took place between September 2011 and December 2013, and in vitro fertilisation (IVF) cycles initiated and pregnancies conceived during this time were followed until December 2014. The cohort includes 971 participants (n= 514 women; n= 457 men), and 129 pregnancies were achieved from the first IVF cycle included in the study. FINDINGS TO DATE: Self-reported demographic, health and lifestyle data were collected from a baseline questionnaire, and to assess changes to lifestyle, a follow-up questionnaire was issued at the time of oocyte retrieval, and at subsequent IVF cycles. Questionnaire data were linked to data extracted from medical records. Biological samples were collected at baseline: blood for extraction of serum, plasma and DNA, morning and evening saliva samples for cortisol measurement and at delivery including samples of maternal blood, placenta and amniotic fluid, and cord blood for epigenetic analysis. FUTURE PLANS: Through the unique identification number assigned to each Swedish citizen at birth or immigration, UppStART study participants will be linked to the Swedish population-based national and quality registers to provide data from prenatal, obstetrical, neonatal and infant care, and subsequent updates will provide data on childhood health and educational outcomes. Collaboration and use of UppStART data is encouraged, and more information about access can be found at www.ki.se/meb/uppstart.

Relation of in-utero exposure to antiepileptic drugs to pregnancy duration and size at birth.

BACKGROUND: The associations of individual antiepileptic drugs (AEDs) with pregnancy duration and size at birth, and potential dose relations, are not well characterized. METHODS: This cohort study used nationwide Swedish register data (1996-2013). Adjusting for smoking, epilepsy and other AED indications, we used linear and quantile regression to explore associations with pregnancy duration, and birth weight, length, and head circumference (the last three operationalized as z-scores). We used logistic regression for preterm delivery, small for gestational age, and microcephaly. Lamotrigine was the reference drug. RESULTS: 6,720 infants were exposed to AEDs in utero; AED exposure increased over the study period. Relative to lamotrigine-exposed infants, carbamazepine-exposed infants were born, on average, 1.3 days earlier (mean [95% confidence interval]: -1.3 [-2.3 to -0.3]); were 0.1 standard deviations (SDs) lighter (-0.1 [-0.2 to 0.0]); and had a head circumference that was 0.2 SDs smaller (-0.2 [-0.3 to -0.1]). Pregabalin-exposed infants were born, on average, 1.1 days earlier (-1.1 [-3.0 to 0.8]); were 0.1 SDs lighter (-0.1 [-0.3 to 0.0]); and had the same head circumference as lamotrigine-exposed infants. Levetiracetam-exposed infants were born, on average, 0.5 days earlier (-0.5 [-2.6 to 1.6]); were 0.1 SDs lighter (-0.1 [-0.3 to 0.0]); and had a head circumference 0.1 SDs smaller (-0.1 [-0.3 to 0.1]). Valproic acid-exposed infants had, on average, the same duration of gestation and birth weight z-score as lamotrigine-exposed infants, but had a head circumference 0.2 SDs smaller (-0.2 [-0.2 to -0.1]). Associations between carbamazepine exposure and pregnancy duration and between valproic acid exposure and pregnancy duration and birth weight z-score were more negative at the left than at the right tails of the outcome distributions. Effect-measure modification and dose-response relations were noted for some of the associations. CONCLUSIONS: Relative to lamotrigine, valproic acid and carbamazepine were associated with smaller head circumference.

Pregnancy complications following fertility treatment-disentangling the role of multiple gestation.

Background: To assess the extent to which multiple gestations mediate risk of pregnancy complications from fertility treatment and to address possible confounding by the underlying infertility. Methods: From the nearly 1.8 million pregnancies recorded in the Swedish Medical Birth Register between 1996 and 2013, we selected the 9.9% (N = 174 067) that occurred to couples with known trouble conceiving (clinical infertility). Fertility treatment was identified from self-reports, medical records and procedural information from fertility clinics. We used logistic regression to estimate odds ratios (ORs) and their 95% confidence intervals (CIs), and decomposed the total effect into direct and mediated effects to estimate the proportion mediated by multiple gestations. Results: Compared with pregnancies achieved without any assistance, those having received some treatment had higher odds of all studied complications except gestational diabetes. Associations with placenta previa (OR 2.17, 95% CI 1.95-2.40) and placental abruption (OR 1.77, 95% CI 1.54-2.03) were almost entirely independent of multiple gestations. In contrast, the majority of the associations with preterm birth (OR 1.69, 95% CI 1.62-1.77), caesarean delivery (RR 1.15, 95% CI 1.13-1.17) and pre-eclampsia (OR 1.17, 95% CI 1.11-1.22) were mediated by multiple gestations (87%, 62% and 91% of the effect mediated, respectively). Both direct and mediated pathways contributed to the remaining positive associations with chorioamnionitis, labour induction and postpartum haemorrhage. Results were similar when considering primi- and multi-parous women separately, and after restriction to assisted reproductive technologies only. Conclusion: Multiple gestations are responsible for a large proportion of pregnancy complications associated with fertility treatment, suggesting that interventions to restrict the occurrence of multiples could reduce excess risk of pre-eclampsia, preterm birth and caesarean delivery after fertility treatment. However, the elevated risk of serious placental complications after fertility treatment appears to be largely independent of multiple gestations.

Outcome-dependent associations between short interpregnancy interval and offspring psychological and educational problems: a population-based quasi-experimental study.

Background: Causal interpretation of associations between short interpregnancy interval (the duration from the preceeding birth to the conception of the next-born index child) and the offspring's psychological and educational problems may be influenced by a failure to account for unmeasured confounding. Methods: Using population-based Swedish data from 1973-2009, we estimated the association between interpregnancy interval and outcomes [autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), severe mental illness, suicide attempt, criminality, substance-use problem and failing grades] while controlling for measured covariates. We then used cousin comparisons, post-birth intervals (the interval between the second- and third-born siblings to predict second-born outcomes) and sibling comparisons to assess the influence of unmeasured confounding. We included an exploratory analysis of long interpregnancy interval. Results: Interpregnancy intervals of 0-5 and 6-11 months were associated with higher odds of outcomes in cohort analyses. Magnitudes of association were attenuated following adjustment for measured covariates. Associations were eliminated for ADHD, severe mental illness and failing grades, but maintained magnitude for ASD, suicide attempt, criminality and substance-use problem in cousin comparisons. Post-birth interpregnancy interval and sibling comparisons suggested some familial confounding. Associations did not persist across models of long interpregnancy interval. Conclusions: Attenuation of the association in cousin comparisons and comparable post-birth interval associations suggests that familial genetic or environmental confounding accounts for a majority of the association for ADHD, severe mental illness and failing grades. Modest associations appear independently of covariates for ASD, suicide attempt, criminality and substance-use problem. Post-birth analyses and sibling comparisons, however, show some confounding in these associations.

A Family-Based Study of the Association Between Labor Induction and Offspring Attention-Deficit Hyperactivity Disorder and Low Academic Achievement.

The current study examined associations between labor induction and both (1) offspring attention-deficit hyperactivity disorder (ADHD) diagnosis in a Swedish birth cohort born 1992-2005 (n = 1,085,008) and (2) indices of offspring low academic achievement in a sub-cohort born 1992-1997 (n = 489,196). Associations were examined in the entire sample (i.e., related and unrelated individuals) with adjustment for measured covariates and, in order to account for unmeasured confounders shared within families, within differentially exposed cousins and siblings. We observed an association between labor induction and offspring ADHD diagnosis and low academic achievement in the population. However, these associations were fully attenuated after adjusting for measured covariates and unmeasured factors that cousins and siblings share. The results suggest that observed associations between labor induction and ADHD and low academic achievement may be due to genetic and/or shared environmental factors that influence both mothers' risk of labor induction and offspring neurodevelopment.

Association of Labor Induction With Offspring Risk of Autism Spectrum Disorders.

IMPORTANCE: Induction of labor is a frequently performed obstetrical intervention. It would thus be of great concern if reported associations between labor induction and offspring risk of autism spectrum disorders (ASD) reflected causal influence. OBJECTIVE: To assess the associations of labor induction with ASD, comparing differentially exposed relatives (siblings and cousins discordant for induction). DESIGN, SETTING, AND PARTICIPANTS: Follow-up of all live births in Sweden between 1992 and 2005, defined in the Medical Birth Register. The register was linked to population registers of familial relations, inpatient and outpatient visits, and education records. Diagnoses of ASD were from 2001 through 2013, and data were analyzed in the 2015-2016 year. EXPOSURES: Induction of labor. MAIN OUTCOMES AND MEASURES: Autism spectrum disorders identified by diagnoses from inpatient and outpatient records between 2001 and 2013. Hazard ratios (HRs) quantified the association between labor induction and offspring ASD. In addition to considering a wide range of measured confounders, comparison of exposure-discordant births to the same woman allowed additional control for all unmeasured factors shared by siblings. RESULTS: The full cohort included 1 362 950 births, of which 22 077 offspring (1.6%) were diagnosed with ASD by ages 8 years through 21 years. In conventional models of the full cohort, associations between labor induction and offspring ASD were attenuated but remained statistically significant after adjustment for measured potential confounders (HR, 1.19; 95% CI, 1.13-1.24). When comparison was made within siblings whose births were discordant with respect to induction, thus accounting for all environmental and genetic factors shared by siblings, labor induction was no longer associated with offspring ASD (HR, 0.99; 95% CI, 0.88-1.10). CONCLUSIONS AND RELEVANCE: In this nationwide sample of live births we observed no association between induction of labor and offspring ASD within sibling comparison. Our findings suggest that concern for ASD should not factor into the clinical decision about whether to induce labor.

Cancer risks in twins and singletons from twin and non-twin families.

The unique intrauterine environment has been proposed to put twins at increased risk of certain cancers compared to singletons, still large population comparisons have generally indicated lower risks in twins. To improve the understanding of potential twin influence on cancer we compared twins to their singletons siblings, to target a unique twinning influence. Singletons from twin families were contrasted to singletons from non-twin families to further capture potential twin family influence on risk of cancer. Family relations were identified using the Swedish Multi-Generation Register. Among individuals born between 1932 and 1958, 49,156 twins and N = 35,227 singletons were identified from 18,098 unique twin families. All incident cases of specific cancer types were identified in the National Cancer Register up to the end of 2007. Standardized survival functions were estimated using weighted Cox proportional hazard regression and the corresponding cumulative risks plotted against age. Overall, primary cancers were identified in 9% and 18% of all male and female twins, compared to 11% and 19% of their male and female singleton siblings. When specific cancer sites were compared using standardized cumulative risk plots, no consistent statistically significant differences were noted either between twins and singletons of twin families or between singletons of twin and non-twin families. Despite a different intrauterine experience, twinning does not seem to have any greater negative influence on life-time risks of cancer. The findings also indicate that twin family membership has no substantial influence on cancer risks.

Are epidemiological approaches suitable to study risk/preventive factors for human birth defects?

Birth defects are a major cause of infant morbidity and mortality and contribute substantially to long-term disability. One out of every 33 babies is born with some type of birth defect. Despite decades of research on environmental, behavioral and genetic risk factors, the vast majority of birth defects still occur without known cause. It is possible that birth defects are largely stochastic (and unavoidable) events, at which efforts to investigate their causes would be futile and unjustified. In this commentary we argue for the continued research into risk/preventive factors of human birth defects, and outline why epidemiological studies are suitable for such endeavors. First we discuss what factors to target (genetic or environmental) and how to define the pertinent research questions. Then we present a short review of both epidemiological contributions in the past and approaches to advance the field in the future. After considering also their limitations, we conclude that modern epidemiologic approaches are invaluable to advance our understanding of risk factors for human birth defects, and that interdisciplinary collaborations will also be essential to further our knowledge.

Genetic contribution to postpartum haemorrhage in Swedish population: cohort study of 466,686 births.

OBJECTIVE: To investigate the familial clustering of postpartum haemorrhage in the Swedish population, and to quantify the relative contributions of genetic and environmental effects. DESIGN: Register based cohort study. SETTING: Swedish population (multi-generation and medical birth registers). MAIN OUTCOME MEASURE: Postpartum haemorrhage, defined as >1000 mL estimated blood loss. PARTICIPANTS: The first two live births to individuals in Sweden in 1997-2009 contributed to clusters representing intact couples (n = 366,350 births), mothers with separate partners (n = 53,292), fathers with separate partners (n = 47,054), sister pairs (n = 97,228), brother pairs (n = 91,168), and mixed sibling pairs (n = 177,944). METHODS: Familial clustering was quantified through cluster specific tetrachoric correlation coefficients, and the influence of potential sharing of known risk factors was evaluated with alternating logistic regression. Relative contributions of genetic and environmental effects to the variation in liability for postpartum haemorrhage were quantified with generalised linear mixed models. RESULTS: The overall prevalence of postpartum haemorrhage after vaginal deliveries in our sample was 4.6%. Among vaginal deliveries, 18% (95% confidence interval 9% to 26%) of the variation in postpartum haemorrhage liability was attributed to maternal genetic factors, 10% (1% to 19%) to unique maternal environment, and 11% (0% to 26%) to fetal genetic effects. Adjustment for known risk factors only partially explained estimates of familial clustering, suggesting that the observed shared genetic and environmental effects operate in part through pathways independent of known risk factors. There were similar patterns of familial clustering for both of the main subtypes examined (atony and retained placenta), though strongest for haemorrhage after retained placenta. CONCLUSIONS: There is a maternal genetic predisposition to postpartum haemorrhage, but more than half of the total variation in liability is attributable to factors that are not shared in families.