The Effect of Prenatal Treatments on Offspring Events in the Presence of Competing Events: An Application to a Randomized Trial of Fertility Therapies

Internal validation of gestational age estimation algorithms in health-care databases using pregnancies conceived through fertility procedures

Fertility procedures recorded in health-care databases can be used to estimate the start of pregnancy, which can serve as a reference standard to validate gestational age estimates based on International Classification of Diseases codes. In a cohort of 17 398 US MarketScan pregnancies (2011-2020) in which conception was achieved via fertility procedures, we estimated gestational age at the end of pregnancy using algorithms based on (1) time (days) since the fertility procedure (the reference standard); (2) International Classification of Diseases, Ninth Revision (ICD-9)/International Classification of Diseases, Tenth Revision (ICD-10) (before/after October 2015) codes indicating gestational length recorded at the end of pregnancy (method A); and (3) ICD-10 end-of-pregnancy codes enhanced with Z3A codes denoting specific gestation weeks recorded at prenatal visits (method B). We calculated the proportion of pregnancies with an estimated gestational age falling within 14 days ($\pm$14 days) of the reference standard. Method A accuracy was similar for ICD-9 and ICD-10 codes. After 2015, method B was more accurate than method A: For term births, within-14-day agreement was 90.8% for method A and 98.7% for method B. Corresponding estimates were 70.1% and 95.6% for preterm births; 35.3% and 92.6% for stillbirths; 54.3% and 64.2% for spontaneous abortions; and 16.7% and 84.6% for elective terminations. ICD-10-based algorithms that incorporate Z3A codes improve the accuracy of gestational age estimation in health-care databases, especially for preterm births and non-live births.

Patterns of paternal medication dispensation around the time of conception

BACKGROUND

Past research on the safety of prenatal exposure to medications has focused on maternal use during gestation, with limited research into the potential effects of paternal use during the spermatogenic period preceding conception. Knowing the most common medications used by fathers around the time of conception can inform research priorities in this field.

OBJECTIVES

To identify the most common medications dispensed to fathers in the preconception period.

METHODS

Within the MarketScan research database of commercially insured individuals in the United States from 2011 to 2020, we identified pregnancies, estimated the date of conception, linked each pregnancy to the father using family enrolment information and required minimum enrolment period and prescription benefits. Then, we described the use of prescription medications by the father during the 90 days before conception based on pharmacy dispensation claims.

RESULTS

Of 4,437,550 pregnancies, 51.6% were linked with a father. Among the 1,413,762 pregnancies connected with a father that also met the inclusion criteria, the most common classes of medications dispensed were psychotropics (8.66%), antibiotics (7.21%), and analgesics (6.82%). The most frequently dispensed medications were amoxicillin (3.75%), azithromycin (3.15%), fluticasone (2.70%) and acetaminophen/hydrocodone (2.70%). Some fathers filled prescriptions for medications associated with foetal embryopathy when used by the mother, including mycophenolate (0.04%), methotrexate (0.03%) and isotretinoin (0.02%).

CONCLUSIONS

More than a third of fathers filled at least one prescription medication in the preconception period, and several of them are known to be embryotoxic, emphasizing the necessity for further investigation into the potential teratogenicity of paternal exposure.

Metformin Use in the First Trimester of Pregnancy and Risk for Nonlive Birth and Congenital Malformations: Emulating a Target Trial Using Real-World Data

BACKGROUND

Metformin is a first-line pharmacotherapy for type 2 diabetes, but there is limited evidence about its safety in early pregnancy.

OBJECTIVE

To evaluate the teratogenicity of metformin use in the first trimester of pregnancy.

DESIGN

In an observational cohort of pregnant women with pregestational type 2 diabetes receiving metformin monotherapy before the last menstrual period (LMP), a target trial with 2 treatment strategies was emulated: insulin monotherapy (discontinue metformin treatment and initiate insulin within 90 days of LMP) or insulin plus metformin (continue metformin and initiate insulin within 90 days of LMP).

SETTING

U.S. Medicaid health care administration database (2000 to 2018).

PARTICIPANTS

12 489 pregnant women who met the eligibility criteria.

MEASUREMENTS

The risk and risk ratio of nonlive births, live births with congenital malformations, and congenital malformations among live births were estimated using standardization to adjust for covariates.

RESULTS

A total of 850 women were in the insulin monotherapy group and 1557 in the insulin plus metformin group. The estimated risk for nonlive birth was 32.7% under insulin monotherapy (reference) and 34.3% under insulin plus metformin (risk ratio, 1.02 [95% CI, 1.01 to 1.04]). The estimated risk for live birth with congenital malformations was 8.0% (CI, 5.7% to 10.2%) under insulin monotherapy and 5.7% (CI, 4.5% to 7.3%) under insulin plus metformin (risk ratio, 0.72 [CI, 0.51 to 1.09]).

LIMITATION

Possible residual confounding by glycemic control and body mass index.

CONCLUSION

Compared with switching to insulin monotherapy, continuing metformin and adding insulin in early pregnancy resulted in little to no increased risk for nonlive birth among women receiving metformin before pregnancy. Under conventional statistical criteria, anything between a 49% decrease and a 9% increase in risk for congenital malformations was highly compatible with our data.

PRIMARY FUNDING SOURCE

National Institutes of Health.

Association of platinum-based chemotherapy with live birth and infertility in female survivors of adolescent and young adult cancer

OBJECTIVE

To estimate the effect of platinum-based chemotherapy on live birth (LB) and infertility after cancer, in order to address a lack of treatment-specific fertility risks for female survivors of adolescent and young adult cancer, which limits counseling on fertility preservation decisions.

DESIGN

Retrospective cohort study.

SETTING

US administrative database.

PATIENTS

We identified incident breast, colorectal, and ovarian cancer cases in females aged 15-39 years who received platinum-based chemotherapy or no chemotherapy and matched them to females without cancer.

INTERVENTION

Platinum-based chemotherapy.

MAIN OUTCOME MEASURES

We estimated the effect of chemotherapy on the incidence of LB and infertility after cancer, overall, and after accounting for competing events (recurrence, death, and sterilizing surgeries).

RESULTS

There were 1,287 survivors in the chemotherapy group, 3,192 in the no chemotherapy group, and 34,147 women in the no cancer group, with a mean age of 33 years. Accounting for competing events, the overall 5-year LB incidence was lower in the chemotherapy group (3.9%) vs. the no chemotherapy group (6.4%). Adjusted relative risks vs. no chemotherapy and no cancer groups were 0.61 (95% confidence interval [CI] 0.42-0.82) and 0.70 (95% CI 0.51-0.93), respectively. The overall 5-year infertility incidence was similar in the chemotherapy group (21.8%) compared with the no chemotherapy group (20.7%). The adjusted relative risks vs. no chemotherapy and no cancer groups were 1.05 (95% CI 0.97-1.15) and 1.42 (95% CI 1.31-1.53), respectively.

CONCLUSIONS

Cancer survivors treated with platinum-based chemotherapy experienced modestly increased adverse fertility outcomes. The estimated effects of platinum-based chemotherapy were affected by competing events, suggesting the importance of this analytic approach for interpretations that ultimately inform clinical fertility preservation decisions.

Causal relationships between pain, medical treatments, and knee osteoarthritis: A graphical causal model to guide analyses

OBJECTIVE

Randomized controlled trials (RCTs) are a gold standard for estimating the benefits of clinical interventions, but their decision-making utility can be limited by relatively short follow-up time. Longer-term follow-up of RCT participants is essential to support treatment decisions. However, as time from randomization accrues, loss to follow-up and competing events can introduce biases and require covariate adjustment even for intention-to-treat effects. We describe a process for synthesizing expert knowledge and apply this to long-term follow-up of an RCT of treatments for meniscal tears in patients with knee osteoarthritis (OA).

METHODS

We identified 2 post-randomization events likely to impact accurate assessment of pain outcomes beyond 5 years in trial participants: loss to follow-up and total knee replacement (TKR). We conducted literature searches for covariates related to pain and TKR in individuals with knee OA and combined these with expert input. We synthesized the evidence into graphical models.

RESULTS

We identified 94 potential covariates potentially related to pain and/or TKR among individuals with knee OA. Of these, 46 were identified in the literature review and 48 by expert panelists. We determined that adjustment for 50 covariates may be required to estimate the long-term effects of knee OA treatments on pain.

CONCLUSION

We present a process for combining literature reviews with expert input to synthesize existing knowledge and improve covariate selection. We apply this process to the long-term follow-up of a randomized trial and show that expert input provides additional information not obtainable from literature reviews alone.

Estimating Post-treatment Recurrence After Multidrug-Resistant Tuberculosis Treatment Among Patients With and Without Human Immunodeficiency Virus: The Impact of Assumptions About Death and Missing Follow-up

BACKGROUND

Quantification of recurrence risk following successful treatment is crucial to evaluating regimens for multidrug- or rifampicin-resistant (MDR/RR) tuberculosis (TB). However, such analyses are complicated when some patients die or become lost during post-treatment follow-up.

METHODS

We analyzed data on 1991 patients who successfully completed a longer MDR/RR-TB regimen containing bedaquiline and/or delamanid between 2015 and 2018 in 16 countries. Using 5 approaches for handling post-treatment deaths, we estimated 6-month post-treatment TB recurrence risk overall and by HIV status. We used inverse-probability weighting to account for patients with missing follow-up and investigated the impact of potential bias from excluding these patients without applying inverse-probability weights.

RESULTS

The estimated TB recurrence risk was 7.4/1000 (95% credible interval: 3.3-12.8) when deaths were handled as non-recurrences and 7.6/1000 (3.3-13.0) when deaths were censored and inverse-probability weights were applied to account for the excluded deaths. The estimated risks of composite recurrence outcomes were 25.5 (15.3-38.1), 11.7 (6.4-18.2), and 8.6 (4.1-14.4) per 1000 for recurrence or (1) any death, (2) death with unknown or TB-related cause, or (3) TB-related death, respectively. Corresponding relative risks for HIV status varied in direction and magnitude. Exclusion of patients with missing follow-up without inverse-probability weighting had a small impact on estimates.

CONCLUSIONS

The estimated 6-month TB recurrence risk was low, and the association with HIV status was inconclusive due to few recurrence events. Estimation of post-treatment recurrence will be enhanced by explicit assumptions about deaths and appropriate adjustment for missing follow-up data.

Accounting for Twins and Other Multiple Births in Perinatal Studies Conducted Using Healthcare Administration Data

The analysis of perinatal studies is complicated by twins and other multiple births even when they are not the exposure, outcome, or a confounder of interest. Common approaches to handling multiples in studies of infant outcomes include restriction to singletons, counting outcomes at the pregnancy-level (i.e., by counting if at least one twin experienced a binary outcome), or infant-level analysis including all infants and, typically, accounting for clustering of outcomes by using generalised estimating equations or mixed effects models. Several healthcare administration databases only support restriction to singletons or pregnancy-level approaches. For example, in MarketScan insurance claims data, diagnoses in twins are often assigned to a single infant identifier, thereby preventing ascertainment of infant-level outcomes among multiples. Different approaches correspond to different causal questions, produce different estimands, and often rely on different assumptions. We demonstrate the differences that can arise from these different approaches using Monte Carlo simulations, algebraic formulas, and an applied example. Furthermore, we provide guidance on the handling of multiples in perinatal studies when using healthcare administration data.

Preconception contraceptive use and miscarriage: prospective cohort study

Objectives

To evaluate the association between preconception contraceptive use and miscarriage.

Design

Prospective cohort study.

Setting

Residents of the United States of America or Canada, recruited from 2013 until the end of 2022.

Participants

13 460 female identified participants aged 21-45 years who were planning a pregnancy were included, of whom 8899 conceived. Participants reported data for contraceptive history, early pregnancy, miscarriage, and potential confounders during preconception and pregnancy.

Main outcome measure

Miscarriage, defined as pregnancy loss before 20 weeks of gestation.

Results

Preconception use of combined and progestin-only oral contraceptives, hormonal intrauterine devices, copper intrauterine devices, rings, implants, or natural methods was not associated with miscarriage compared with use of barrier methods. Participants who most recently used patch (incidence rate ratios 1.34 (95% confidence interval 0.81 to 2.21)) or injectable contraceptives (1.44 (0.99 to 2.12)) had higher rates of miscarriage compared with recent users of barrier methods, although results were imprecise due to the small numbers of participants who used patch and injectable contraceptives.

Conclusions

Use of most contraceptives before conception was not appreciably associated with miscarriage rate. Individuals who used patch and injectable contraceptives had higher rates of miscarriage relative to users of barrier methods, although these results were imprecise and residual confounding was possible.

Estimating post-treatment recurrence after multidrug-resistant tuberculosis treatment among patients with and without HIV: the impact of assumptions about death and missing follow-up

Background

Quantification of recurrence risk following successful treatment is crucial to evaluating regimens for multidrug- or rifampicin-resistant (MDR/RR) tuberculosis (TB). However, such analyses are complicated when some patients die or become lost during post-treatment-follow-up.

Methods

We analyzed data on 1,991 patients who successfully completed a longer MDR/RR-TB regimen containing bedaquiline and/or delamanid between 2015 and 2018 in 16 countries. Using five approaches for handling post-treatment deaths, we estimated the six-month post-treatment TB recurrence risk overall, and by HIV status. We used inverse-probability-weighting to account for patients with missing follow-up and investigated the impact of potential bias from excluding these patients without applying inverse-probability weights.

Results

The estimated TB recurrence risk was 6.6 per 1000 (95% confidence interval (CI):3.2,11.2) when deaths were handled as non-recurrences, and 6.7 per 1000 (95% CI:2.8,12.2) when deaths were censored and inverse-probability weights were applied to account for the excluded deaths. The estimated risk of composite recurrence outcomes were 24.2 (95% CI:14.1,37.0), 10.5 (95% CI:5.6,16.6), and 7.8 (95% CI:3.9,13.2) per 1000 for recurrence or 1) any death, 2) death with unknown or TB-related cause, 3) TB-related death, respectively. Corresponding relative risks for HIV status varied in direction and magnitude. Exclusion of patients with missing follow-up without inverse-probability-weighting had a small but apparent impact on estimates.

Conclusion

The estimated six-month TB recurrence risk was low, and the association with HIV status was inconclusive due to few recurrence events. Estimation of post-treatment recurrence will be enhanced by explicit assumptions about deaths and appropriate adjustment for missing follow-up data.

Emulating Target Trials to Avoid Immortal Time Bias - An Application to Antibiotic Initiation and Preterm Delivery

BACKGROUND

Randomized trials in pregnancy are extremely challenging, and observational studies are often the only option to evaluate medication safety during pregnancy. However, such studies are often susceptible to immortal time bias if treatment initiation occurs after time zero of follow-up. We describe how emulating a sequence of target trials avoids immortal time bias and apply the approach to estimate the safety of antibiotic initiation between 24 and 37 weeks gestation on preterm delivery.

METHODS

The Tsepamo Study captured birth outcomes at hospitals throughout Botswana from 2014 to 2021. We emulated 13 sequential target trials of antibiotic initiation versus no initiation among individuals presenting to care <24 weeks, one for each week from 24 to 37 weeks. For each trial, eligible individuals had not previously initiated antibiotics. We also conducted an analysis susceptible to immortal time bias by defining time zero as 24 weeks and exposure as antibiotic initiation between 24 and 37 weeks. We calculated adjusted risk ratios (RR) and 95% confidence intervals (CI) for preterm delivery.

RESULTS

Of 111,403 eligible individuals, 17,009 (15.3%) initiated antibiotics between 24 and 37 weeks. In the sequence of target trials, RRs (95% CIs) ranged from 1.04 (0.90, 1.19) to 1.24 (1.11, 1.39) (pooled RR: 1.11 [1.06, 1.15]). In the analysis susceptible to immortal time bias, the RR was 0.90 (0.86, 0.94).

CONCLUSIONS

Defining exposure as antibiotic initiation at any time during follow-up after time zero resulted in substantial immortal time bias, making antibiotics appear protective against preterm delivery. Conducting a sequence of target trials can avoid immortal time bias in pregnancy studies.

Reevaluating the protective effect of smoking on preeclampsia risk through the lens of bias

Preeclampsia is a hypertensive disorder that is usually diagnosed after 20 weeks' gestation. Despite the deleterious effect of smoking on cardiovascular disease, it has been frequently reported that smoking has a protective effect on preeclampsia risk and biological explanations have been proposed. However, in this manuscript, we present multiple sources of bias that could explain this association. First, key concepts in epidemiology are reviewed: confounder, collider, and mediator. Then, we describe how eligibility criteria, losses of women potentially at risk, misclassification, or performing incorrect adjustments can create bias. We provide examples to show that strategies to control for confounders may fail when they are applied to variables that are not confounders. Finally, we outline potential approaches to manage this controversial effect. We conclude that there is probably no single epidemiological explanation for this counterintuitive association.

The Role of Maternal Preconception Adiposity in Human Offspring Sex and Sex Ratio

We evaluated relationships between preconception adiposity and human offspring sex and sex ratio. Using data from a prospective preconception cohort nested within a randomized controlled trial based at 4 US clinical sites (2006-2012), we used logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for male:female sex ratio, and log-identity regression to estimate risk differences (RDs) and 95% CIs for male and female livebirth according to preconception adiposity measures. Inverse-probability weights accounted for potential selection bias. Among 603 women attempting pregnancy, there were meaningful reductions in sex ratio for the highest category of each adiposity measure. The lowest sex ratios were observed for obesity (body mass index of ≥30, calculated as weight (kg)/height (m)2, OR = 0.48, 95% CI: 0.26, 0.88) relative to normal body mass index, and the top tertiles (tertile 3) of serum leptin (OR = 0.50, 95% CI: 0.32, 0.80) and skinfold measurements (OR = 0.50, 95% CI: 0.32, 0.79) relative to the lowest tertiles. Reductions were driven by 11-15 fewer male livebirths per 100 women (for obesity, RD = -15, 95% CI: -23, -6.7; for leptin tertile 3, RD = -11, 95% CI: -20, -3.2; and for skinfolds tertile 3, RD = -11, 95% CI: -19, -3.3). We found that relationships between preconception adiposity measures and reduced sex ratio were driven by a reduction in male births.

Effectiveness and safety of intrauterine insemination vs. assisted reproductive technology: emulating a target trial using an observational database of administrative claims

OBJECTIVE

To compare the effectiveness and safety of 1 cycle of assisted reproductive technology (ART) vs. 3 cycles of intrauterine insemination (IUI).

DESIGN

Target trial emulation using observational data.

SETTING

A healthcare claims database (2011-2015).

PATIENT(S)

The patients were 29,021 women aged 18-45 years with an infertility diagnosis and no history of IUI or ART within the past 12 months.

INTERVENTION(S)

One ART cycle immediately, with no more cycles of ART or IUI within the next 4 months; or 1 IUI cycle immediately, with 2 additional consecutive cycles of IUI within the next 4 months unless pregnancy occurred.

MAIN OUTCOME MEASURE(S)

Live births, multiple births, congenital malformations, preterm births, small-for-gestational-age newborns, large-for-gestational-age newborns, admission to neonatal intensive care unit (NICU), gestational diabetes, preeclampsia, and gestational hypertension.

RESULT(S)

The probability of live birth was 27.3% for ART and 26.3% for IUI. The observational analogue of per-protocol risk difference (95% confidence interval) for ART compared with IUI was 1.0% (-0.1%, 2.2%) for live births, 4.3% (3.7%, 4.9%) for multiple births, 3.4% (2.8%, 4.0%) for preterm births, 1.5% (0.9%, 2.1%) for NICU admissions, and 0.6% (0.2%, 1.0%) for gestational diabetes. The risk differences for the other outcomes were <0.5%. The results of the 2 strategies were similar in women ≤40 years, but in women >40 years the probability of live birth was greater for ART (14.4%) than for IUI (7.4%).

CONCLUSION(S)

Compared with 3 cycles of IUI, 1 cycle of ART was estimated to have a similar probability of live birth but slightly higher risks of multiple gestations, preterm births, and NICU admissions.

Study design flaws and statistical challenges in evaluating fertility treatments

Health interventions should be tested before being introduced into clinical practice, to find out whether they work and whether they are harmful. However, research studies will only provide reliable answers to these questions if they are appropriately designed and analysed. But these are not trivial tasks. We review some methodological challenges that arise when evaluating fertility interventions and explain the implications for a non-statistical audience. These include flexibility in outcomes and analyses; use of surrogate outcomes instead of live birth; use of inappropriate denominators; evaluating cumulative outcomes and time to live birth; allowing each patient or couple to contribute to a research study more than once. We highlight recurring errors and present solutions. We conclude by highlighting the importance of collaboration between clinical and methodological experts, as well as people with experience of subfertility, for realising high-quality research.

Lay summary

We do research to find out whether fertility treatments are beneficial and to make sure they don't cause harm. However, research will only provide reliable answers if it is done properly. It is not unusual for researchers to make mistakes when they are designing research studies and analysing the data that we get from them. In this review, we describe some of the mistakes people make when they do research about fertility treatments and explain how to avoid them. These include challenges which arise due to the large number of things that can be measured and reported when looking to see if fertility treatments work; failure to check whether the treatment increases the number of live births; failing to include all study participants in calculations;challenges in studies where participants may have more than one treatment attempt. We conclude by highlighting the importance of collaboration between clinical and methodological experts, as well as people with experience of fertility problems.

A potential outcomes approach to defining and estimating gestational age-specific exposure effects during pregnancy

Many studies seek to evaluate the effects of potentially harmful pregnancy exposures during specific gestational periods. We consider an observational pregnancy cohort where pregnant individuals can initiate medication usage or become exposed to a drug at various times during their pregnancy. An important statistical challenge involves how to define and estimate exposure effects when pregnancy loss or delivery can occur over time. Without proper consideration, the results of standard analysis may be vulnerable to selection bias, immortal time-bias, and time-dependent confounding. In this study, we apply the “target trials” framework of Hernán and Robins in order to define effects based on the counterfactual approach often used in causal inference. This effect is defined relative to a hypothetical randomized trial of timed pregnancy exposures where delivery may precede and thus potentially interrupt exposure initiation. We describe specific implementations of inverse probability weighting, G-computation, and Targeted Maximum Likelihood Estimation to estimate the effects of interest. We demonstrate the performance of all estimators using simulated data and show that a standard implementation of inverse probability weighting is biased. We then apply our proposed methods to a pharmacoepidemiology study to evaluate the potentially time-dependent effect of exposure to inhaled corticosteroids on birthweight in pregnant people with mild asthma.

The implications of outcome truncation in reproductive medicine RCTs: a simulation platform for trialists and simulation study

BACKGROUND

Randomised controlled trials in reproductive medicine are often subject to outcome truncation, where the study outcomes are only defined in a subset of the randomised cohort. Examples include birthweight (measurable only in the subgroup of participants who give birth) and miscarriage (which can only occur in participants who become pregnant). These outcomes are typically analysed by making a comparison between treatment arms within the subgroup (for example, comparing birthweights in the subgroup who gave birth or miscarriages in the subgroup who became pregnant). However, this approach does not represent a randomised comparison when treatment influences the probability of being observed (i.e. survival). The practical implications of this for the design and interpretation of reproductive trials are unclear however.

METHODS

We developed a simulation platform to investigate the implications of outcome truncation for reproductive medicine trials. We used this to perform a simulation study, in which we considered the bias, type 1 error, coverage, and precision of standard statistical analyses for truncated continuous and binary outcomes. Simulation settings were informed by published assisted reproduction trials.

RESULTS

Increasing treatment effect on the intermediate variable, strength of confounding between the intermediate and outcome variables, and the presence of an interaction between treatment and confounder were found to adversely affect performance. However, within parameter ranges we would consider to be more realistic, the adverse effects were generally not drastic. For binary outcomes, the study highlighted that outcome truncation could cause separation in smaller studies, where none or all of the participants in a study arm experience the outcome event. This was found to have severe consequences for inferences.

CONCLUSION

We have provided a simulation platform that can be used by researchers in the design and interpretation of reproductive medicine trials subject to outcome truncation and have used this to conduct a simulation study. The study highlights several key factors which trialists in the field should consider carefully to protect against erroneous inferences. Standard analyses of truncated binary outcomes in small studies may be highly biassed, and it remains to identify suitable approaches for analysing data in this context.

Long-term risk of epilepsy, cerebral palsy and attention-deficit/hyperactivity disorder in children affected by a threatened abortion in utero

BACKGROUND

The birth of a child affected by a threatened abortion (TAB) in utero is associated with autism spectrum disorder; association with other neurological disorders is unknown.

METHODS

This nationwide registry-based cohort study included singletons live-born in Denmark (1979-2010), followed through 2016. The outcomes were epilepsy, cerebral palsy (CP) and attention-deficit/hyperactivity disorder (ADHD). We used Cox regression to compute hazard ratios (HRs), adjusted for birth year, birth order, parental age, morbidity, medication use and maternal socio-economic factors. To remove time-invariant family-shared confounding, we applied sibling analyses.

RESULTS

The study population included 1 864 221 singletons live-born in 1979-2010. Among the TAB-affected children (N = 59 134) vs TAB-unaffected children, at the end of follow-up, the cumulative incidence was 2.2% vs 1.6% for epilepsy, 0.4% vs 0.2% for CP and 5.5% vs 4.2% for ADHD (for children born in 1995-2010). The adjusted HRs were 1.25 [95% confidence interval (CI) 1.16-1.34] for epilepsy, 1.42 (95% CI 1.20-1.68) for CP and 1.21 (95% CI 1.14-1.29) for ADHD. In the sibling design, the adjusted HRs were unity for epilepsy (full siblings: 0.96, 95% CI 0.82-1.12; maternal: 1.04, 95% CI 0.90-1.20; paternal: 1.08, 95% CI 0.93-1.25) and ADHD (full: 1.08, 95% CI 0.92-1.27; maternal: 1.04, 95% CI 0.90-1.20; paternal: 1.08, 95% CI 0.93-1.25). For CP, HRs shifted away from unity among sibling pairs (full: 2.92, 95% CI 1.33-6.39; maternal: 2.03, 95% CI 1.15-3.57; paternal: 3.28, 95% CI 1.36-7.91).

CONCLUSIONS

The birth of a child affected by TAB in utero was associated with a greater risk of CP, but not epilepsy or ADHD.