# Presentation: 252925

## Maternal Smoking During Pregnancy and the Risk for Clubfoot

- <date/time>

- Data from North Carolina: 1999-2003
- Kathryn C. Dickinson
- North Carolina Birth Defects Monitoring Program

## Background

- Talipes equinovarus (TEV) results in:
- forefoot adduction, hindfoot inversion, and hindfoot equines
- abnormal foot bones, muscles, and ligaments, and abnormal ankle bones
- Occurs in approx. 1 in 1,000 live births
- Requires medical treatment, often surgery, for correction
- Picture from: http://www.footandanklecolorado.com/practiceSpecialties.html

## Background

- Proposed causes of TEV include:
- intrauterine compression
- vascular insufficiency
- abnormal myogenesis
- intrauterine infections
- neurologic abnormalities
- genetics

## Background

- Risk factors that have been examined:
- Infant’s sex (  male)
- Maternal age (  /  )
- Maternal education level (  /  )
- Maternal Race/Ethnicity (  non-Hispanic
-    white?)
- Parity (  /  )
**Maternal smoking during pregnancy **

## Background

- Previous Studies:
- Shiono et al. (1986) showed OR 0.7 (95% CI 0.6, 0.9)
- Malloy et al. (1989) found OR 1.02
- Van den Eeden et al. (1990) showed RR of 1.4 (95% CI 1.0, 2.0)
- Alderman et al. (1991) found OR 2.8 (95% CI 1.6, 5.1) for male infants and OR 1.8 (95% CI 0.8, 4.4) for female infants
- McDonald (1992) demonstrated the risk as being slightly elevated for women who smoked 1-9 cigarettes per day (OR 1.06), but found that the risk decreased as the number of cigarettes smoked increased
- Honein et al. (2000) showed OR 1.34 (95% CI 1.04, 1.72)
- Skelly et al. (2002) found dose-response of ORs 1.5-3.9

## Background

- Why the different results?
- case definition
- specific vs. general
- isolated vs. syndromic

## Study Question

- Is maternal smoking associated with an increased risk of clubfoot in infants?

## Methods

- Data sources
- North Carolina Birth Defects Monitoring Program
- vital statistics from the State Center for Health Statistics
- the “BabyLove” file, also from the SCHS
- 1999-2003

## Methods

- Case Selection
- dx of talipes equinovarus or clubfoot, nos (BPA codes 754.500 or 754.730)
- only singleton births
- only isolated cases
- cases with other major malformations were excluded, but minor malformations did not lead to exclusion (i.e. polydactyly)
- excluded cases with missing smoking data
- total cases= 443

## Methods

- Control Selection
- SRS of birth certificate data
- only singleton births
- linked to NCBDMP data to exclude controls with birth defects
- excluded controls with missing smoking data
- ratio of 10:1, controls to cases
- total controls= 4,492

## Case/Control Selection

## Methods

- Smoking ascertainment
- from the birth certificate (yes/no)
- reliability?
- Compared smoking data from BC to WIC data
- p<0.001
- Compared smoking data from BC to NCPRAMS data
- Kappa statistic= 0.769
- approx. 95% agreement

## Methods

- Other variables of interest:
- maternal age
- maternal race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, other)
- maternal marital status (married/not married)
- maternal educational attainment (<HS, HS, >HS)
- parity (# prev. live births)
- Medicaid status
- WIC status
- month prenatal care began
- infant’s sex
- weeks of gestation
- birthweight
- death of the infant

## Results: Selected Frequencies

- Smoking
- 18.3% cases
- 13.1% controls
- Male infant
- 65.7% cases
- 50.5% controls
- White, non-Hispanic
- 68.2% cases
- 60.7% controls
- Maternal age ≥30
- 28.0% cases
- 33.6% controls

## Results: Selected Unadjusted                 ORs (95% CIs)

- Smoking
- 1.49 (1.15, 1.92)
- Sex of the infant, male
- 1.87 (1.52, 2.30)
-  Maternal Race/Ethnicity
- Non-Hispanic black: 0.68 (0.53, 0.88)
- Hispanic: 0.84 (0.61, 1.15)
- Other: 0.61 (0.33, 1.14)
- Maternal Age, <20
- 1.48 (1.07, 2.05)

## Results: Final Model

- 1.40 (95% CI 1.07, 1.83)
- When controlling for sex of the infant, maternal age, maternal race/ethnicity, and timing of prenatal care initiation, women who smoke during pregnancy have a 40% increased risk of having an infant with clubfoot compared to women who don’t.

## Conclusion

- This study is consistent with the hypothesis that smoking during pregnancy is associated with a slightly increased risk of an infant being born with clubfoot.

## Acknowledgements

- Thank you to Bob Meyer and Jonathan Kotch for their help with this project!

## References

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- Alderman BS, Takahashi ER, LeMier MK. 1991. Risk indicators for talipes equinovarus in Washington state, 1987-1989.  Epidemiology 2:289-292.
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## References cont’d

- Malloy MH, Kleinman JC, Bakewell JM, Schramm WF, Land GH. 1989. Maternal smoking during pregnancy: no association with congenital malformations in Missouri 1980-83. Am J Public Health 79:1243-1246.
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- Shiono PH, Klebanoff MA, Berendes HW. 1986. Congenital malformations and maternal smoking during pregnancy. Teratology 34:65-71.
- Skelly AC, Holt VL, Mosca VS, Alderman BW. 2002. Talipes equinovarus and maternal smoking: a population-based case-control study in Washington state. Teratology 66:91-100.
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- Wynne-Davies R. 1972. Genetic and environmental factors in the etiology of talipes equinovarus. Clin Orthop 84:9-13.