Title: Does Greater Exposure to WIC Affect Maternal Behavior and Improve Infant Health Evidence from the Pr
1Does Greater Exposure to WIC Affect Maternal
Behavior and Improve Infant Health? Evidence from
the Pregnancy Nutrition Surveillance System.
- Ted Joyce
- Cristina Yunzal
- Supported by a grant from the Institute for
Research on Poverty and the United States
Department of Agriculture (IRP-USDA) - Preliminary results. Not for citation.
2- WIC works, perhaps better than any other
government program in history. - USDA Secretary Dan Glickman, 1997
- The WIC Program results in significant Medicaid
savings that far outweigh the programs costs by
a ratio of 3 to 1. - - HHS Secretary Louis Sullivan, 1995
3What is WIC?
- The Special Supplemental Nutrition Program for
Women, Infants, and Children - Piloted by Congress in 1972, permanently
authorized in 1974 - Sources http//www.fns.usda.gov/wic/aboutwic/wica
taglance.htm - http//www.nutritionnc.com/wic/his
tory.htm
4Target Population
- Low-income, nutritionally at risk
- Pregnant women (through pregnancy and up to 6
weeks after birth or after pregnancy ends). - Breastfeeding women (up to infants 1st
birthday) - Nonbreastfeeding postpartum women (up to 6 months
after the birth of an infant or after pregnancy
ends) - Infants (up to 1st birthday). WIC serves 45
percent of all infants born in the United
States. - Children up to their 5th birthday.
- Source http//www.fns.usda.gov/wic/aboutwic/wicat
aglance.htm
5WIC Benefits
- Nutritional supplementation via checks/vouchers
to purchase specific foods that are high in
protein, calcium, iron, and vitamins A and C - Nutrition education and counseling
- Screening and referrals to other health, welfare
and social services - Source http//www.fns.usda.gov/wic/aboutwic/wicat
aglance.htm
6Funding and participation
- Overseen by the USDA and administered by 90 WIC
state agencies. - Not an entitlement program Congress authorizes a
specific amount of funds each year for it. - However, pregnant women receive highest admission
priority - In North Carolina, all eligible applicants from
1995 onwards were admitted into the program - 2005 funding 5.16 billion
- 2005 participation 8 million, from 88,000 in
1974 - Source http//www.fns.usda.gov/wic/aboutwic/wicat
aglance.htm
7Study objective
- Estimate the impact of North Carolinas prenatal
WIC program on singleton birth outcomes in
1996-2003
8Why focus on birth weight?
- LBW significant factor in infant mortality and
morbidity - In 2002, infant mortality in U.S. was 7 per 1,000
live births - Among low birth weight infants (lt2,500 grams),
rate was 60.3 per 1,000 live births - Birth weight well-documented on birth certificates
9Low birth weight trends, selected years
10Causes of low birth weight
- 1. Short gestational period (born preterm)
- Preterm infants are those born before 37 weeks of
gestation - 2. Intrauterine growth retardation (IUGR)
- Infants who have low birth weights for their
gestational age
11WIC Works Literature General Accounting
Office (GAO) Report (1992)
- Combined results of 17 existing WIC studies to
estimate WICs effect on reducing incidence of
low and very low birth weight (LBW is lt2500
grams VLBW is lt1500 grams). - Prenatal WIC participation reduced LBW by 25 and
VLBW by 44 - Each dollar spent on WIC for pregnant women saved
3.50 in medical disability costs
12WIC Works Literature Devaney, Bilheimer, and
Schore (1992)
13WIC Works Literature Gordon Nelson (1995)
14WIC Works Literature Bitler Currie (2005)
15WIC Works Criticism Besharov Germanis (2001)
- Review existing WIC studies and conclude that
findings on birth outcomes are unreliable. Most
research poorly designed and suffer from
selection bias, simultaneity bias, and lack of
generalizeability. - Argue that the program has suffered from
eligibility creep. Applicants must be income
eligible and be at nutrition risk. - Suggest that nutritional risk is assumed if
income criteria are met. States have used
generous cut-off points and loosely defined risk
criteria.
16WIC Works Criticism GAO (2001)
- Study of six local WIC agencies found that
individual nutrition education sessions did not
last long, ranging from 4-17 minutes. - Only two nutrition education contacts required
per 6-month certification period. - It is difficult to help prevent numerous
nutrition-related diseases with a few brief
nutrition education sessions.
17WIC Works Criticism Joyce, Gibson, Colman
(2005)
18Clinical literatureRush, Stein Susser (1980)
- Randomized controlled trial of women attending
clinic in a large black community in NYC
(1970-73). - Target population selected on grounds that the
lower the expected birth weight, the more likely
a better diet would help - Women lt 140 lbs at conception who fulfilled at
least one of the following - Low prepregnant weight (lt110 lbs) at conception
- Low weight gain up to recruitment
- At least one previous infant of low birth weight
- Protein intake lt50 grams in 24 hours before
registration (24-hour recall)
19Clinical literatureRush, Stein Susser (1980),
cont.
- Study groups
- Supplement Two 8-oz cans of beverage daily (40
grams of protein, 470 calories) - Complement Two 8-oz cans of beverage daily (6
grams of protein, 322 calories) - Control Regular clinic care
- Results
- Significant effects on weight gain limited to
those recruited early in pregnancy (lt15 weeks) - However, no impact on birth weight for this
cohort - Among full-term infants, mean birth weight not
significantly related to treatment in any cohort - Among preterm infants, mean birth weight lower in
Supplement than in Complement in 3 of 4 cohorts,
lower than Control
20Clinical literatureMetcoff, et al (1985)
- Impact of WIC supplement on birth weight tested
in a randomized, controlled trial involving a
population of women in midpregnancy at high risk
of having low birth weight infants. - No significant effect on birth weight when
midpregnancy weight added as a covariate - However, significant effect on smokers ( gt 10
cigarettes/day)
21Clinical literature
- Goldenberg Rouse (NEJM, 1998)
- Most interventions designed to prevent preterm
birth do not work, and the few that do are not
universally effective and are applicable only to
a small percentage of women at risk for preterm
birth. - Ancel (EJOG, 2004)
- Etiology of preterm delivery remains poorly
understood. - little support for the efficacy of nutritional
supplements, more intense prenatal monitoring,
and/or social support and limitation of risky
behaviour in reducing preterm deliveries.
22Expectations given the literature
- For a program to impact birth weight, must either
lengthen gestation or prevent fetal growth
retardation, or both. - Little evidence in clinical literature to
indicate that supplemental and referral programs
like WIC can lengthen gestation. Any impact of
WIC on gestation may be spurious and suggestive
of omitted variable bias. - Impact on fetal growth is more plausible through
nutritional supplementation-gtmaternal weight gain
23Our Data
- North Carolina Pregnancy Nutrition Surveillance
System (PNSS), 1996-2003 - Dataset combines rich administrative data from
the WIC program linked to birth certificates - More than 400,000 women in the database
- Size of sample allows us to stratify by race,
timing of prenatal care, etc. we can estimate
fully interacted models - All women in database are eligible for WIC and
have chosen to participate - Can compare outcomes for women who enrolled while
pregnant with women who did not join WIC until
the postpartum period
24WIC Eligibility
- Income lt 185 percent of U.S. Poverty Income
Guidelines. (Food Stamp/Medicaid/Temporary
Assistance for Needy Families recipients
adjunctively eligible.) - State residency
- Applicants determined to be at nutrition risk
by a health professional. - Medically-based risks such as anemia,
underweight, overweight, history of pregnancy
complications, or poor pregnancy outcomes. - Dietary risks, such as failure to meet the
dietary guidelines or inappropriate nutrition
practices - Source http//www.fns.usda.gov/wic/aboutwic/wicat
aglance.htm
25- Selected Characteristics, North Carolina WIC
Participantsa with Singleton Births, 1996-2003 - aExcluding prenatal women who do not return for a
follow-up visit
26Race/Ethnicity
27Mothers age
28Education (Mothers gt 20 years old)
29Prenatal care use
30Parity
31Program Evaluation
- Typical model
- Hit a0 a1WICit Xitß S?tYrt eit,
- where Hit infant/maternal outcome
- WICit dummy variable indicating WIC
participation - Xit matrix of other relevant
variables, including demographic characteristics
of the mother - Yrt year indicator
- ei error term, E(ei)0
- a1 average treatment effect of WIC on
health outcome
32Selection problem
- Decision to participate in WIC likely based on
factors that also affect Hit. - Women who enlist in WIC may be healthier and/or
more motivated to have healthy pregnancies a1
may overstate impact of WIC - Women may enroll in WIC because they are less
healthy and desire assistance a1 may
underestimate impact of WIC - Even after controlling for variables that
simultaneously impact Hit and WICit, cannot
guarantee that participants and nonparticipants
are similar on unobservables. - E(eitWICit) ? 0 and the estimator identifies
(sans other regressors) - E(?1) a1 E(eitWICit1) E(eitWICit0)
33Addressing selection bias
- Sample consists only of WIC women, differentiated
by trimester of pregnancy when they enrolled.
Comparison group is women who only enlist after
giving birth. - In lieu of usual WIC vs. non-WIC comparison, all
women in sample know of and have chosen to
participate in WIC - Focus on singleton births we exclude prenatal
enrollees who do not return for a WIC postpartum
visit - Use large sample to stratify into more
homogeneous subgroups
34Birth outcomes Means
35Birth outcomes Coefficients on WIC
36Birth outcomes Coefficients on WIC
37Birth outcomes Coefficients on WIC
38Comments on prenatal WIC coefficients
- WIC coefficient for birth weight unadjusted for
gestation (87 grams) fall in range of findings
by Devaney, et al (51-117). Larger than Gordon
Nelson (67.9), and Bitler Currie (63.65). - Marginal probit effect on LBW (-3.2) similar to
Devaney (-5.1 to 2.2) and slightly larger than
Bitler Curries (OR 0.726 LBW incidence in
our sample is 9.1). - Marginal probit effect on preterm birth (-3.9)
also similar to Devaney (-6.3 to 2.3) and
larger than Bitler Currie (OR 0.708 preterm
incidence in our sample is 10.6).
39Our model
- Hit a0 a1WIC1it a2WIC2it a3WIC3it Xitß
S?tYrt eit, - where
- WIC1it first-trimester WIC enrollment
- WIC2it second-trimester WIC enrollment
- WIC3it third-trimester WIC enrollment
40Our model, cont.
- We expect that the earlier a woman enlists in
WIC, the more favorable the outcome a1gta2gta3 - Following the clinical literature, we assume that
WIC cannot affect preterm birth/length of
gestation. Look for WIC impact that is primarily
driven by gestational age.
41Birth outcomes Birth weight (grams)
42Birth outcomes Birth weight, adjusted for
gestation
43Birth outcomes Length of gestation (weeks)
44Birth outcomes Low birth weight (lt2500 grams)
45Birth outcomes Small for gestational age
46Birth outcomes Preterm birth (lt37 weeks)
47Birth outcomes Term low birth weight (gt37
weeks lt2500 grams)
48Comments on WIC trimester coefficients
- WIC coefficients for birth outcomes that are
unadjusted for gestational age have relative
magnitudes a1lta2lta3. This suggests that WICs
impact is partly driven by the already lengthier
gestations of third-trimester enrollees. - Coefficients for birth outcomes adjusted for
gestational age (except term LBW) have the
expected relative magnitudes a1gta2gta3. For blacks
and Hispanics, significant results limited to 1st
and/or 2nd trimester.
49Maternal Inputs
- Smoking cessation
- Weight gain
- Breastfeeding
50Smoking during pregnancy(Birth certificates)
51Variables for generating smoking indicators
52Variables for generating smoking indicators
53Variables for generating smoking indicators
54Maternal smoking rates by race/ethnicity
(all questions)
55Maternal smoking rates by WIC Participation
56Smoking quit rates, by WIC participation
57Smoking quit rates, by WIC participation
58Maternal Inputs Smoking cessation during
pregnancy (all questions prenatal women only)
59Maternal Inputs Pregnancy weight gain
60Maternal Inputs Breastfeeding initiation
61Maternal Inputs Breastfeeding initiation, four
weeks after birth
62Birth outcomes Birth weight, adjusted for
gestation (early care, first births)
63Birth outcomes Small for gestational age (early
care, first births)
64Birth outcomes Term low birth weight (early
care, first births)
65Maternal Inputs Tried to quit smoking upon
learning of pregnancy
(early care, first births prenatal
women only)
66Conclusions
- WICs impact on birth weight smaller than implied
in previous research. Results partly driven by
third-trimester enrollment of women already
experiencing longer gestations. - Small effects on birth outcomes adjusted for
gestation. Largest effects among whites. Effects
among blacks and Hispanics limited to 1st and/or
2nd trimesters. - Weight gain effects limited to first- and
second-trimester enrollees. - Unreliably reported rates of smoking and smoking
cessation among WIC women, particularly
postpartum women, may confound results. - Impact on breastfeeding ranges from negative
(among whites and blacks) to substantial (among
Hispanics).