CASE-CONTROL STUDIES:AN EXAMPLEEP 711

November 8, 2011

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Issues in Study Design and Interpretation• Type of study• Case definition• Control definition• Sources of exposure information• Exposure definition• Potential confounders• Potential sources of bias

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Louik C et al: N Engl J Med 2007;356:2675-83

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Background• ≥10% of pregnant women experience depressive

symptoms in pregnancy• Medications represent one treatment option• SSRIs first marketed in 1988 and gained widespread

acceptance• RDD survey in 2005 indicated that among women aged 18-44,

~8% used an SSRI in the week preceding interview

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Background• Advantages of SSRIs

• Established efficacy• Favorable side effect profile• Serum monitoring not required• Toxicity/overdose not a major problem

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Background• SSRIs include

• Fluoxetine (Prozac)• Sertraline (Zoloft)• Paroxetine (Paxil)• Citalopram (Celexa)• Fluvoxamine (Luvox)• Escitalopram (Lexapro)

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Background• Congenital malformations

• Major defects affect about 2-3% of livebirths• Encompasses a wide variety of defects• Some are extremely rare, e.g. limb reduction defects (2-4/10,000)• Others are more common, e.g. cleft lip (1/700), neural tube defects

(1/1000)• Heart defects occur about 1/200 births

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Background• Initial studies

• Small cohorts from pregnancy registries• Results reassuring with respect to birth defects overall

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Background• Later studies

• Larger• Found no increased risk for birth defects overall, but

• Increased risk for some specific defects• 3 independent studies reported increased risk for heart defects

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Objectives• Examine 1st trimester use of specific SSRIs in relation to

specific birth defects• Test existing hypotheses

• Craniosynostosis• Omphalocele• Heart defects

• Explore other defects not yet reported

• Focus on specificity to help reduce misclassification

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Choice of Study Design• Birth defects occur in 2-3% of livebirths (not uncommon)• Short latent period (9 months)• So why not cohort??

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Choice of Study Design• “Birth Defects” is NOT a single outcome, and individually,

THEY ARE RARE• Major birth defects affect 2-3% of newborns• However, specific defects typically affect only ~2/1000 to 1/10,000

• Known teratogens typically increase the risk of a specific defect or a group of related defects (syndrome or sequence)

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Choice of Study Design• Therefore, a case-control approach is better suited to our

research question looking at specific defects.

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Types of Case-Control Studies

Specific Semi-Specific Non-Specific

Methods

• Study subjects• Infants with any of a wide range of malformations (isolated

minor defects excluded)• Sample of non-malformed infants from same birth hospitals

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Methods

• Identified in 5 study centers• Study staff review clinic/surgical logs,

admission/discharge lists, contact newborn nursery and labor/delivery rooms

• In 2 study centers, use statewide birth defects registries

• Nonmalformed infants identified at study hospitals• In Mass., population-based random sample of

newborns

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Methods

• Mothers interviewed within 6 months of birth• Trained study nurses• By telephone• Questions address

• Demographics• Reproductive history• Medical history• Lifestyle habits• Detailed medication history (includes prescription, over-the-counter,

and herbal products)

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Case definition--Theory• Specific as possible• Strict criteria• Should be reasonable to think that they have a common

etiology

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Case Definition--Applied• Cases are infants with heart defects

• Concerns• No rigorous definition• Not homogeneous

• Solution• Blind review of all infants with a heart-related defect• Sub-classify into embryologically meaningful groups to increase

homogeneity

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Case Definition--Applied

• Case subgroups• Looping, laterality, and single ventricle defects• Conotruncal defects• Atrioventricular canal defects• Right ventricular outflow tract obstruction defects• Left ventricular outflow tract obstruction defects• Septal defects• Anomalous pulmonary venous return

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Normal Heart

Pulmonary Valve Stenosis

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Ventricular Septal Defect

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Control Definition--Theory• Sample of the population that produced the cases• Sampled independently of exposure status

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Control Definition--Applied• Infants with other malformations

• Advantages• From same population as cases• Should remember pregnancy events similarly to cases

• Disadvantages• May not reflect exposure status in population that gave rise to cases, i.e.

exposure may be associated with increased risk of these defects too

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Control Definition--Applied• Nonmalformed infants

• Advantages• From same population as cases• Should reflect exposure status in the population that gave rise to cases

• Disadvantages• May remember pregnancy events differently than cases (recall bias)

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Control Definition--Applied• We will use nonmalformed controls

• Address disadvantages by• Asking focused exposure questions (evidence exists that this enhances

recall)• Considering other antidepressants (recall bias, if present, should apply

to these too)

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Exposure Assessment--Theory• Need sufficient detail of nature, duration, and timing of

exposure• Accuracy is critically important• Sources of Information

• Biomarkers• Records• Interviews

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Exposure Assessment--Applied• Biomarkers—not applicable• Records

• Medical records• Multiple providers• Prescription ≠ Consumption• Complete?

• Pharmacy• No OTC meds, herbals• Dispense ≠ Use

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Exposure Assessment--Applied• Interview

• Greater detail available• Potentially includes all drugs• Relies on mother’s recollection

• Because we chose to use nonmalformed controls, may differ between cases and controls (recall bias)

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Source of Selected Prescription Drugs 5,435

Mothers; Boston, Philadelphia, Toronto, Iowa, 1976-1984

Total

Source (in %)

Drug

Users Physician’s Prescription

Other

Bendectin

859

98

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Valium 135 82 18 Fiorinal 105 96 4 Hydrodiuril 76 97 3 Clomid 66 100 0 Compazine 59 91 9 Darvon 42 78 22 Seconal 42 95 5 Diuril 27 85 11

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Mitchell AA, Cottler LB, Shapiro S. Effect of questionnaire design on recall of drug exposure in pregnancy. Am J Epidemiol 1986;123:670‑6.

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Exposure Assessment

J Womens Health (Larchmt). 2008 Sep;17(7):1073-80.

Prescription medication borrowing and sharing among women of reproductive age.

Petersen EE, Rasmussen SA, Daniel KL, Yazdy MM, Honein MA.

National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

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Exposure Assessment

• Overall, 28.8% of women and 26.5% of men reported ever borrowing or sharing prescription medications.

• Women of reproductive age were more likely to report prescription medication borrowing or sharing (36.5%) than women of nonreproductive age (>or=45 years) (19.5%)

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A quarter of new prescriptions go unfilled, study findsFebruary 18, 2010

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Exposure Assessment

More than a quarter of new prescriptions are unfilled, especially when the drugs are for symptomless conditions, researchers from Boston's Brigham and Women's Hospital have found. Physicians have long been concerned that many patients fill new prescriptions one time, then never get refills. But it has been impossible in the past to determine adherence to new prescriptions. The new study was made possible by the implementation of an electronic-prescribing initiative by two Massachusetts health plans.

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Exposure Assessment—Evidence of Completeness*

• False negatives• Valium reports—1975

• Medical records—1.2%• Maternal interview—5.8%

• 20% from sources other than physician

• Bendectin—late 1970’s, used exclusively in pregnancy• Manufacturer’s data—25%• Interview data—24%

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*Mitchell AA, Cottler LB, Shapiro S. Effect of questionnaire design on recall of drug exposure in pregnancy. Am J Epidemiol 1986;123:670‑6.

Exposure Assessment—Evidence of Completeness*

• False positives• Elamar

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*Mitchell AA, Cottler LB, Shapiro S. Effect of questionnaire design on recall of drug exposure in pregnancy. Am J Epidemiol 1986;123:670‑6.

Exposure Assessment—Addressing Recall Bias

• If recall is complete, recall bias cannot exist• Enhancement of recall will diminish recall bias

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Reported Drug Use by Question Asked532 Women; Boston - 1975, and Toronto - 1978

Drug

Percent Ascertained by

Total Users

Open-ended Indication Name (n)

Prescription Drugs

Valium 21 55 26 (90)

Fiorinal 37 35 28 (43)

Darvon 23 45 32 (40)

Non-Prescription Drugs

Aspirin 1 79 20 (377)

Acetaminophen 2 55 43 (177)

Am J Epidemiol 1986; 123:670-6.

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Exposure Assessment

•Series of questions about medications used any time from 2 months prior to LMP through the pregnancy• Illnesses they may have had, and medications used

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Exposure Assessment• List of indications for which medications might be used

• Anxiety, depression, other psychological conditions

• Use of specific medications• Prozac, Zoloft, Paxil, Effexor, Elavil, Celexa, Luvox, Lexapro,

Wellbutrin

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Exposure Assessment—Details• Timing

• First trimester• 28 days prior to LMP through the 4th lunar month

• Nature• Any SSRI• Specific SSRI• Non-SSRI antidepressants

• Helps assess presence of recall bias• Helps assess “confounding by indication”

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Exposure Assessment• Referent group

• Women who reported no exposure to any antidepressant at any time (56 days prior to LMP through the pregnancy)

• Exclusions• Women whose only exposure was either 28-56 days prior to LMP

or after the 4th lunar month

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Potential confounders• Factors related to exposure and to outcome that explain

results• Maternal age Parity• Maternal race/ethnicity History of seizures,

diabetes, hypertension• Maternal education Infertility• Smoking history Folic acid use• Alcohol consumption LMP year• Family history of birth defects Study center• BMI

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Results

• 5,860 nonmalformed infants• Rate of exposure to any SSRI in controls—2.8%

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Results• 3,724 infants with congenital heart defects (100

exposed)• 186 looping, laterality defects (2 exposed)• 620 conotruncal defects (13 exposed)• 164 atrioventricular defects (0 exposed)• 363 RVOTO (15 exposed)• 482 LVOTO defects (15 exposed)• 1161 septal defects (32 exposed)• 17 anomalous pulmonary venous return (0 exposed)

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All cardiac defects

Cases Controls OR

(95% CI)

Any SSRI 2.7% 2.7% 1.2

(0.9, 1.6)

Non SSRI

Antidepressant

0.6% 0.8% 0.8

(0.5, 1.5)

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Results• Create more homogeneous classes

• Specific cardiac defects• Septal defects• RVOTO defects

• Specific SSRIs• Fluoxetine• Sertraline• Paroxetine

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Septal defects

Cases Controls OR

95% CI

Fluoxetine 0.9% 1.1% 1.0

(0.5, 2.2)

Sertraline 1.1% 0.8% 2.0

(1.2, 4.0)

Paroxetine 0.5% 0.5% 0.8

(0.3, 2.2)

Non-SSRI

Anti-depressants

0.9% 0.9% 1.1

(0.6, 2.4)

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RVOTO Defects

Cases Controls OR

(95% CI)

Fluoxetine 1.1% 1.0% 1.0

(0.2, 3.4)

Sertraline 0.8% 0.8% 2.0

(0.6, 6.8)

Paroxetine 1.7% 0.5% 3.3

(1.3, 8.8)

Non-SSRIAnti-depressants

0.6% 0.8% 0.9

(0.2, 3.8)

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Interpretation

• Possible explanations for findings• Selection bias• Information bias• Confounding• Chance• “Real”

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Interpretation

• Selection bias• Not population-based, so must be considered• Is entry into study related to exposure

• “medicalization”? • These are serious defects, unlikely to escape detection

• Differential effects among SSRIs and no effect for non-SSRI antidepressants

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Interpretation

• Information bias• Interviewers “blind” to hypothesis• Recall bias

• Structured interview• Antidepressants used on a regular basis• Antidepressants used for non-trivial indications

• Null effect for non-SSRI antidepressants

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Interpretation

• Confounding• Many demographic, medical, reproductive, and

administrative variables “controlled” for in analysis• “confounding by indication”

• No increased risk for non-SSRI antidepressants

• Uncontrolled confounding by factors not considered is always possible

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Interpretation

• Chance• Can never be ruled out• In this study, many comparisons were made, so

possibility of chance findings are increased• Place greatest reliance on those findings that are

consistent with other studies

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RVOTO Defects (NBDPS data)

Fluoxetine Sertraline Paroxetine

No. of infants

No. Adjusted OR

(95%CI)

No. Adjusted OR

(95%CI)

No. Adjusted OR

(95%CI)

RVOTO 669 4 0.9

(0.4-2.1)

4 0.8

(0.3-2.3)

7 2.5

(1.0-6.0)

Controls 4092 29 32 18

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Alwan S, Reefhuis J, Rasmussen SA, Olney RS, Friedman JM. Use of selective serotonin-reuptake inhibitors in pregnancy and the risk ofbirth defects. N Engl J Med 2007; 356:2684-92

Conclusions• This study does not support overall effect with cardiac

defects, but does find evidence of associations for specific SSRIs with specific cardiac defects• Paroxetine and RVOTO • Sertraline and septal

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Conclusions• Specific SSRIs may increase the risk of specific birth

defects• Absolute risks still small

• Baseline prevalence of RVOTO: about 5.5 cases per 10,000 livebirths

• 4-fold increase in risk means that the absolute risk is only 0.2%.

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Conclusions

• Depression in pregnancy is not a good thing for the mother or her infant.

• As with any therapeutic decision, one must weigh the risk of possible adverse outcomes with the benefits of treating depressed women with any SSRI and with specific SSRIs.

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Source of Selected Prescription Drugs 5,435

Mothers; Boston, Philadelphia, Toronto, Iowa, 1976-1984

Total

Source (in %)

Drug

Users Physician’s Prescription

Other

Bendectin

859

98

1

Valium 135 82 18 Fiorinal 105 96 4 Hydrodiuril 76 97 3 Clomid 66 100 0 Compazine 59 91 9 Darvon 42 78 22 Seconal 42 95 5 Diuril 27 85 11

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Am J Epidemiol 1986; 123:670-6.

Fetal Circulation

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Circulation after birth

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