Evaluation of the Validity of a Gestational Length Algorithm Based

upon Electronic Health Plan Data

Qian Li, Susan. E. Andrade, William O. Cooper, Robert L. Davis, Sascha Dublin, Tarek A. Hammad, Pamala. A. Pawloski, Simone P. Pinheiro, Marsha A. Raebel, Pamela E. Scott, David. H. Smith, Inna Dashevsky, Katie Haffenreffer, Karin E. Johnson, Darren Toh

18th Annual HMO Research Network Conference, Seattle WA

May 2, 2012

Funding Source & Conflict of Interest

Contracts HHSF223200510012C, HHSF223200510009C, and HHSF223200510008C from the U.S. FDA

Dr. Dublin funded by Paul Beeson Career Development Award from the National Institute on Aging, grant K23AG028954, and by Group Health Research Institute internal funds

Abstract not necessarily represent official views or endorsement of the FDA or the National Institute on Aging or the NIH

None of the other authors have conflict of interest

Background

Medication effects often specific to particular gestational period

Electronic health plan databases are increasingly used in pregnancy research

Valid prenatal exposure status Pharmacy dispensing data Pregnancy beginning & gestational length

Computerized algorithm (delivery date + preterm birth ICD-9-CM)

Objectives

To examine the validity of a common algorithm by comparing

algorithm-derived gestational length & prevalence of medication exposures during pregnancy “gold standard” measures in birth certificates

Data Source Medication Exposure in Pregnancy Risk

Evaluation Program (MEPREP) - U.S. Food and Drug Administration - HMO Research Network (8 health plans) - Kaiser Permanente California - Vanderbilt School of Medicine/Tenn Medicaid

MEPREP

- Enrollment - Demographics - Outpatient pharmacy dispensing - Outpatient and inpatient encounter Administrative and

Claims

- Socio-demographic (race/ethnicity) - Medical - Reproductive (parity, gestational age)

Birth Certificate

Study Population

Live born deliveries among women aged 15-45 years between Jan 1, 2001 and Dec 31, 2007

Availability of valid gestational length in linked birth certificate

Continuous enrollment and pharmacy benefit, 100 days before pregnancy through delivery

Gestational Length Algorithm based on Health Plan Data

ICD-9-CM code Definition Algorithm-derived gestational lengthWeeks Days

765.21 Less than 24 completed weeks of gestation24 168765.22 24 weeks of gestation

765.23 25-26 weeks of gestation 26 182765.24 27-28 weeks of gestation

28 196765.0-765.09 Extreme immaturity765.25 29-30 weeks of gestation 30 210765.26 31-32 weeks of gestation 32 224765.27 33-34 weeks of gestation 34 238765.28 35-36 weeks of gestation 36 252765.1-765.19 Other preterm infants

35 245765.20 Preterm with unspecified weeks of gestation644.21 Onset of delivery before 37 completed weeks of

gestation

Gestational length for deliveries without an ICD-9-CM code for preterm birth in the table was assumed to be 270 days.

“Gold Standard” Gestational Length

Birth certificate last menstrual period (LMP) clinical estimate (CE) / obstetric estimate

(OE) CDC’s National Center for Health

Statistics (NCHS) approach LMP primarily CE/OE, when LMP not

available 20-45 weeks (adapted from NCHS) compatible with birth weight

Medication Exposure

Long term Chronic basis

Antidepressants

FluoxetineSertraline

Short term Acute use

Antibiotics

AmoxicillinAzithromycin

Dispensing dates + days supplied ; 14-day grace period

Statistical Analysis Mean, range, proportion of

term/preterm deliveries Deliveries with two gestational lengths

differ within 0, ±1, ±2, ±3, ±4, or greater than ±4 weeks (stratified by plurality)

Prenatal medication exposure Sensitivity, specificity, PPV, NPV Any time in pregnancy or by trimester Stratified by term/preterm determined by

the algorithm

Study Results

Infants’ birth certificate files linked to health plan data in 92% deliveries

Gestational age missing/invalid in linked birth certificates in 0.4% deliveries

Final study population included 225,384 deliveries

Discussion

Algorithm underestimated gestational length by average 5.5 days Restricted to singleton deliveries (86% term)

270-day upper bound Not in multiple-gestation deliveries (36%

term) ICD-9-CM codes for preterm births

Algorithm underestimated prevalence of preterm deliveries 15% in study population > 12% nationally More women aged >35 years (21% vs. 14%)

Discussion

Algorithm correctly classified the antidepressants and antibiotics exposure status in most women Specificity and NPV close to 100% Poorer sensitivity and PPV for antibiotics

(sporadic) vs. antidepressants (chronic) Overestimate on antibiotics due to 14-

day grace period for dispensings

Discussion

Strengths Study population geographically and

demographically diverse, increasing generalizability

Reasonable gold standard of gestational length for majority of study population

Limitations Only evaluated 1 algorithm Only evaluated 2 antidepressants and 2

antibiotics, unknown for other medications Medication dispensed =?= medication use

Conclusion

Gestational length algorithm based on health plan data (delivery date + preterm birth diagnosis) classified prenatal medication use well

Performance slightly poorer for short-term drugs (e.g. antibiotic)

Thank you!Questions?

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