Expanding Prenatal Care to Unauthorized Immigrant Women and the Effects on Infant Health

Abstract

Objective

To measure the result of access to prenatal care on unauthorized and low-income, new legal permanent resident immigrant women and their offspring.

Methods

We used a difference-in-difference design that leverages the staggered rollout of Emergency Medicaid Plus by county from 2008 to 2013 as a natural experiment to estimate the effect on health service utilization for women and health outcomes for their infants. Regular Medicaid pregnancies were used as an additional control in a triple difference design.

Results

Our sample included pregnancies covered by Emergency Medicaid (34,319), Emergency Medicaid Plus (12,344), and Medicaid (163,537). After expansion of access to prenatal care, there was an increase in prenatal visits (7.2 more visits, 95% CI 6.46 to 7.98), receipt of adequate prenatal care (28% increased rate, CI 26 to 31), rates of diabetes screening (61% increased rate, CI 56 to 65) and fetal ultrasounds (74% increased rate, CI 72 to 77). Maternal access to prenatal care was also associated with an increased number of well-child visits (0.24 more visits, CI 0.07 to 0.41), increased rates of recommended screenings and vaccines (0.04 increased probability, CI 0.002 to 0.074), and reduced infant mortality (-1.04 per 1000, CI -1.45 to -0.62) and rates of extremely low birth weight (<1000g) (-1.5 per 1000, CI -2.58 to -0.53).

Conclusion

Our results provide evidence of increased utilization and improved health outcomes for unauthorized immigrants and their children who are United States citizens after introduction of prenatal care expansion in Oregon. This study contributes to the debate around reauthorization of the Children's Health Insurance Program in 2017.

Introduction

Prenatal care is an important component of preventive health care, with multigenerational consequences for women and their families. For the woman, prenatal care promotes health, helps prepare for birth, and prevents and detects complications including anemia, hypertensive diseases of pregnancy and infection.^1–4 For the neonate, regular prenatal care is associated with decreased incidence of low birth weight and neonatal deaths.^1,3,5

Barriers to accessing prenatal care are greatest among the populations who would be expected to benefit most from preventive health care: low-income women. Medicaid is the largest payer for obstetric care nationally. Throughout the United States (US), standard Medicaid provides coverage for all pregnancy related care, encompassing the antenatal period, childbirth and postpartum. In contrast, Emergency Medicaid, a federal safety net program for those poor enough to qualify for Medicaid but who cannot meet the citizenship requirements, covers only acute life-threatening events and obstetric admissions.^6,7

Under federal law, authorized immigrants in their first five years in the US and unauthorized immigrants are ineligible to participate in full-scope Medicaid using federal funds. For this immigrant population, Emergency Medicaid covers the cost of a birth but not prenatal care or postpartum contraception. Obstetric diagnoses are the majority of claims paid by Emergency Medicaid, accounting for greater than 80% of claims in North Carolina and Oregon.^7,8 States can choose to spend their own funds to provide additional health services for immigrants. The Emergency Medicaid population is often considered highly vulnerable.⁹ Indeed, data from California and North Carolina suggests that of the Emergency Medicaid users in those states 91% and 99% are unauthorized immigrants, respectively.^7,10

An “unborn child” option in the Children's Health Insurance Program (CHIP) enacted in 2002 and the Child Health Insurance Program Reauthorization Act (CHIPRA) enacted in early 2009, gave states new options to provide prenatal care coverage with federal matching funds for extending coverage to immigrant children and pregnant women, regardless of their legal status or date of entry to the US.^11–13 In response, Oregon began piloting a program to expand access to prenatal care for all recent and unauthorized immigrant women in 2008 called CAWEM Plus (Citizen/Alien Waived Emergent Medical Care). In this study, we refer to this program as Emergency Medicaid Plus.

Oregon's structured expansion of Emergency Medicaid Plus provides us with a suitable and rare natural experiment to study the result of providing access to prenatal care for a vulnerable immigrant population. With the introduction of Emergency Medicaid Plus, immigrant women suddenly had access to comprehensive prenatal care. Importantly, the expansion to Emergency Medicaid Plus through a staggered rollout statewide did not change the pool of women who had access to the newly covered care. Moreover, women could not self-select into Emergency Medicaid Plus because eligibility was tied to the county of residence. As shown in Figure 1, the first counties offered Emergency Medicaid Plus in 2008 with stepwise expansion to all 36 counties by 2013.

Figure 1.

Rollout of Emergency Medicaid Plus Prenatal across Oregon counties.

Previous studies of prenatal care have compared groups with high and low utilization.^3,14–16 In this study we isolate the effect of access to prenatal from self-selection biases by utilizing the exogenous variation in access to prenatal care that stems from the staggered rollout of the Emergency Medicaid Plus program in a difference-in-difference framework. Our objective was to measure the result of access to prenatal care on unauthorized and low-income, new legal permanent resident immigrant women and their offspring. We specifically examined whether expanding access to prenatal care resulted in utilization of services by women and their infants including prenatal visits, recommended pregnancy care, well-child checks and vaccines. We also assessed effects on infant health outcomes including low birth weight, preterm birth, and infant death. In a separate study, we plan to present the associated maternal health outcomes.

Materials and Methods

Medical claims data from January 1, 2003 through October 1, 2015, were obtained through Oregon Health Authority's Department of Health Analytics for all Medicaid claims, encompassing pregnancies under standard Medicaid as well as Emergency Medicaid and Emergency Medicaid Plus. The Oregon Health Authority provided three different types of quarterly data: recipient, claims, and prescription. We used administrative records and personal communication with the Oregon Health Authority to confirm start dates for the expansion of Emergency Medicaid Plus in each of Oregon's 36 counties (see Appendix 1).

The Institutional Review Boards at Oregon Health & Science University (Protocol 15633) and Stanford University (Protocol 40907) approved this research.

Our population consists of reproductive aged women (12-51), and their offspring aged 0-1 years. The Emergency Medicaid and Emergency Medicaid Plus sample include low-income immigrant women who are either unauthorized or have fewer than 5 years of legal permanent residency. We refer to individuals in this sample as unauthorized immigrants as they predominantly use these programs.^7,17 Our unit of analysis was a pregnancy and only singleton pregnancies were included. To identify each pregnancy episode, we developed an algorithm building on prior literature modified for the Oregon Medicaid claims data (see Appendix 2).¹⁸ In addition, we relied on a matching algorithm using a validated household identification number in the beneficiary file and other auxiliary information to match pregnancies and infants (see Appendices 3 and 4).¹⁹

We examined outcomes related to health service utilization as well as infant health outcomes. Outcomes for utilization by women included: prenatal visits and receipt of adequate prenatal care (defined as one visit in the first pregnancy trimester plus a total of nine or more visits overall).²⁰ A prenatal visit was defined as having one or more claims for prenatal supervision on a distinct day of service. To capture visits not billed as prenatal care, we also counted all outpatient visits during pregnancy, though measures of adequacy are based on prenatal supervision visits only. Routine prenatal care services measured included: ultrasound during pregnancy, vaccination for Tetanus, Diphtheria and Pertussis (Tdap), Rhesus (Rh) immunoglobulin administration (for women with Rh negative blood type), and diabetes screening. (See Appendix 5). Given the limitation of the database, we were unable to identify women with Rh negative blood type, so results for Rh immunoglobulin administration are for all pregnancies.

We examined several markers of infant utilization of health care services in the first year of life. These included: the number of well-child checks, outpatients visits, and urgent care or emergency room visits, as well as receipt of standard vaccinations and screenings in the first year of life. We identified the number of emergency room and urgent care visits using a service location identifier code included in the claims database. A list of Current Procedural Terminology (CPT) codes was used to identify receipt of routine screening and vaccines that are recommended in the first year of life. (Appendices 6-8)

We measured several infant health outcomes including: low birth weight (<2,499 grams), very low birthweight (<1,499 grams), extremely low birth weight (<1,000 grams), preterm birth (< 37 weeks), and infant death. Death in the first year of life was identified using the recipient database.

Table 1 shows the naïve comparison of mean outcomes between pregnancies under Emergency Medicaid and Emergency Medicaid Plus. While illustrative, this comparison does not adjust for potential confounding.

Table 1. Descriptive Statistics: Maternal and Infant Outcomes by Insurance Group.

	Emergency Medicaid	Emergency Medicaid Plus Prenatal
Insurance:	(EM)	(EMP)	Medicaid	EM vs. EMP
No. of supervision visits (count)	0.24	8.53	6.11	8.29
	± 1.23	± 5.21	±4.17	[8.20-8.38]
No. of outpatient visits (count)	0.30	12.25	11.04	11.95
	±1.76	±7.27	±8.69	[11.82-12.08]
Early visit (0/1)	0.02	0.50	0.56	0.48
	±0.13	±0.50	±0.50	[0.47-0.49]
Early visit and 9 or more visits (0/1)	0.01	0.43	0.41	0.43
	±0.08	±0.50	±0.49	[0.42-0.44]
Rh immunization (per 1,000)	7.55	22.44	89.14	14.89
	±86.54	±148.11	±284.95	[12.12-17.66]
Tdap vaccination (0/1)	0.01	0.31	0.27	0.31
	±0.07	±0.46	±0.45	[0.30-0.32]
Glucose testing (0/1)	0.02	0.73	0.74	0.71
	±0.14	±0.45	±0.44	[0.70-0.71]
Fetal ultrasound (0/1)	0.04	0.87	0.88	0.83
	±0.21	±0.33	±0.33	[0.82-0.83]
No. of well child checks (count)	4.92	5.22	4.37	0.29
	±2.57	±2.94	±2.51	[0.23-0.35]
No. of outpatient visits (count)	9.14	10.27	9.53	1.13
	±5.84	±5.82	±6.06	[1.01-1.25]
No. of emergency room visits (count)	3.30	3.57	3.12	0.27
	±2.18	±2.14	±2.32	[0.23-0.32]
Screenings and vaccinations (0/1)	0.82	0.90	0.79	0.08
	±0.39	±0.30	±0.41	[0.08-0.09]
Low birth weight (per 1,000)*	49.97	58.97	61.20	9.00
	±217.89	±235.58	±239.69	[4.25-13.75]
Very low birth weight (per 1,000) †	3.79	3.32	4.60	-0.47
	±61.43	±57.54	±67.66	[-1.67-0.74]
Extremely low birth weight (per 1,000) ‡	1.75	0.65	1.76	-1.10
	±41.78	±25.45	±41.93	[-1.73- -0.47]
Preterm birth < 37 weeks (per 1,000) §	67.08	74.77	79.00	7.69
	±250.16	±263.03	±269.75	[2.35-13.03]
Death in first 365 days (per 1,000)‖	1.11	0.32	1.33	-0.78
	±33.26	±18.00	±36.49	[-1.26- -0.31]

EM- Emergency Medicaid. EMP- Emergency Medicaid Plus Prenatal. Columns 2-4 show means with standard deviations in parentheses. Column 5 shows the difference in means between EM and EMP with robust 95% confidence intervals. N = 34319 for EM; N = 12344 for EMP; N= 163537 for Medicaid.

^*N=1715 for EM; N=728 for EMP; N=10008 for Medicaid.

^†N=130 for EM; N=41 for EMP; N=752 for Medicaid

^‡N=60 for EM; N=8 for EMP; N=288 for Medicaid

^§N=2302 for EM; N=923 for EMP; N=12920 for Medicaid

^‖N=38 for EM; N=4 for EMP; N=218 for Medicaid

To isolate the effect of expanding access to prenatal care from confounding characteristics we utilized a difference-in-differences approach that exploits the staggered rollout of the Emergency Medicaid Plus. Difference-in-difference methodology is increasingly employed as a tool in observational studies of health policy.²¹ Studies using a more traditional pre- and post-policy comparison of outcomes are likely to be confounded by a secular trend unrelated to the policy change. Researchers can thus mistake an improvement in an outcome as resulting from a policy change when it could simply be the continuation a pre-existing trend.²¹ In contrast, a difference-in-difference approach better isolates the changes associated with a policy by comparing an outcome for exposed and unexposed groups before and after policy implementation. This design controls for unobserved common-shocks and time-invariant characteristics.

We estimate the following baseline specification

$$Y_{\mathit{\text{ijt}}}=\alpha +\pi {\mathrm{Z}}_{\mathit{\text{ijt}}}+\theta {\mathrm{K}}_{\mathit{\text{ijt}}}+{\beta }_c+{\beta }_t+{\beta }_{cj}{T}_t+{\varepsilon }_{\mathit{\text{ijt}}}$$

where Y_ijt is an outcome of interest for pregnancy i in county j and month t, Z_ijt is a treatment indicator, coded 1 if Emergency Medicaid Plus was offered in the county where the women was enrolled at the end of pregnancy i, and 0 otherwise, K_ijt is a vector of time varying controls (including an age polynomial and fixed effects for race categories, ethnicity categories, and gravidity, defined as the number of pregnancies identified between 2003-2015), β_c are county-level fixed effects, β_t are monthly period fixed effects, β_cjT_t are county specific time trends, and ε is the error the term.

County fixed effects account for all time-invariant county level confounders, period fixed effects account for all common confounders that vary by month, and county-specific time trends account for any changes in unobserved confounders that vary at the county level and affect outcomes smoothly over time. The quantity of interest is the coefficient π that identifies the intention-to-treat effect of providing access to prenatal care by switching from Emergency Medicaid to Emergency Medicaid Plus. We clustered standard errors at the level of the county. We also block bootstrapped standard errors as a sensitivity analysis and found a minimal difference in our results. To check the robustness of our results, we also extend this baseline specification to a triple differences framework and include a third comparison group by adding pregnancies that used standard Medicaid in the same counties and at the same time. The triple difference model ensures robustness to potentially confounding trends within the same county that are specific to the immigrant population that utilized Emergency Medicaid and correlated with the introduction of Emergency Medicaid Plus in a given county.

All analyses, unless otherwise stated, were pre-registered and posted in a pre-analysis plan with Evidence in Governance and Politics (EGAP).²² EGAP is a research network with the aim of strengthening research and evidence-based policy making. Members can register relevant analysis plans to help prospectively clarify goals and avoid post-hoc data mining.

Results

Our sample included pregnancies covered by Emergency Medicaid (34,319), Emergency Medicaid Plus (12,344), and Medicaid (163,537) (see Appendix 9 for descriptive statistics). Women in Emergency Medicaid and Emergency Medicaid Plus were predominantly Hispanic ethnicity (80% and 77%, respectively), whereas the Medicaid population was predominantly non-Hispanic (80%).

Figure 2 compares the use of prenatal care coverage and the number of prenatal visits before and after the rollout of the Emergency Medicaid Plus program. The program was rapidly adopted with more than 95% of unauthorized immigrant pregnancies billed to the new program after its rollout. There was also a marked increase in the number of prenatal visits from an average of zero to about 12 outpatient visits during the pregnancy period.

Figure 2.

Uptake of Emergency Medicaid Plus Prenatal. A and B show the average jump in usage of prenatal care associated with the introduction of Emergency Medicaid Plus Prenatal. The figures are in event time and aggregate the stepwise introduction from 2008 to 2013 to time 0 where the program became active. A shows that the share of pregnancies in the Emergency Medicaid sample that use the Emergency Medicaid Plus Prenatal (EMP) insurance increases rapidly after the rollout of the EMP program across Oregon counties. B shows that the number of outpatient visits per pregnancy similarly increases. Blue lines denote monthly means with 95% CIs.

Table 2 shows estimates of the intention-to-treat effect from the difference-in-differences and the triple differences models. After expansion to Emergency Medicaid Plus, there was an increase in the number of prenatal visits (7.22 additional visits per pregnancy, 95% CI 6.46 to 7.98) and the number of outpatient visits (9.81 additional visits, CI 9.03 to 10.59) for unauthorized immigrant women. There was also an increase in the probability that unauthorized immigrant women had at least one prenatal visit in the first trimester (32 percentage point increase from baseline of 2%, CI 29 to 36) and received adequate prenatal visits (28% increase from baseline of 1%, CI 26 to 31). Moreover, with expansion to Emergency Medicaid Plus there was an increased likelihood of having Rh immunoglobulin administration during pregnancy (0.8% increase above baseline rate of 0.8%, CI 0.4 to 1.2), vaccination for Tdap (19% increase from baseline of 1%, CI 13 to 25), diabetes screening with oral glucose tolerance testing (61% increase from baseline of 2%, CI 56 to 65) and fetal ultrasound (74% increase from baseline of 4%, CI 72 to 77). These estimates were consistent using both the difference-in-differences and triple differences specifications, although the effect on Rh immunoglobulin administration is not consistent across specifications and the effect on Tdap vaccinations shrinks.

Table 2. Effect of Emergency Medicaid Plus Prenatal on Utilization for Women.

Outcome:	DID Model Effect 95 % CI	Triple DID Model Effect 95 % CI
No. of supervision visits (count)	7.22 [6.46-7.98]	8.03 [7.00-9.06]
No. of outpatient visits (count)	9.81 [9.03-10.59]	9.32 [8.62-10.02]
Early visit (0/1)	0.32 [0.29-0.36]	0.35 [0.31-0.39]
Early visit and 9 or more visits (0/1)	0.28 [0.26-0.31]	0.29 [0.24-0.34]
Rh immunization (per 1,000)	7.87 [4.22-11.52]	-2.26 [-9.53-5.02]
Tdap vaccination (0/1)	0.19 [0.13-0.25]	0.09 [-0.00-0.18]
Glucose testing (0/1)	0.61 [0.56-0.65]	0.71 [0.67-0.74]
Fetal ultrasound (0/1)	0.74 [0.72-0.77]	0.78 [0.75-0.80]

Effect estimates from difference-in-differences model (DID) and triple differences model (Triple DID) model with robust 95% confidence intervals (clustered by county) in parentheses. Rh- Rhesus and Tdap- Tetanus, Diptheria and Pertussis. All models include county fixed effects, month fixed effects, county specific time-trends, and covariates (age polynomial, race fixed effects, ethnicity fixed effects, and gravidity fixed effects (defined as the number of pregnancies identified between 2003-2015)). N = 46666 for DID models and N=210206 for Triple DID models.

Table 3 shows the effects on the utilization of care for infants of unauthorized immigrant women. With expansion of Emergency Medicaid Plus, there was an increase in the number of well-child checks (0.24 more visits, CI 0.07 to 0.41), the number of emergency department and urgent care visits (0.24 more visits, CI 0.07 to 0.41), and the probability of receiving recommended screenings and vaccinations (4% increase from a baseline of 82%, CI 0.2 to 7.4) during the first year of life. These estimates were consistent using both the difference-in-differences and triple differences specifications, but with important exceptions. The effect on the number of outpatient visits is slightly larger in the triple difference model (0.72 more visits, CI 0.35 to 1.10) and the effect on emergency department and urgent care visits is no longer significant in the triple differences model (0.09 more visits, -0.24 to 0.42).

Table 3. Effect of Emergency Medicaid Plus Prenatal on Utilization and Health Outcomes for Infants.

Outcome:	DID Model Effect 95 % CI	Triple DID Model Effect 95 % CI
Well child check (0/1)	0.01 [-0.00-0.02]	0.01 [0.01-0.01]
No. of well child checks (count)	0.24 [0.07-0.41]	0.29 [0.14-0.44]
No. of outpatient visits (count)	0.19 [-0.09-0.48]	0.72 [0.35-1.10]
No. of emergency room visits (count)	0.24 [0.07-0.41]	0.09 [-0.24-0.42]
Screenings and vaccinations (0/1)	0.04 [0.002-0.074]	0.05 [0.02-0.07]
Low birth weight (per 1,000)	-0.34 [-9.95-9.27]	3.69 [-1.16-8.54]
Very low birth weight (per 1,000)	1.07 [-0.65-2.79]	-0.66 [-1.56-0.25]
Extremely low birth weight (per 1,000)	-1.55 [-2.58--0.53]	-1.35 [-2.25--0.44]
Preterm birth < 37 weeks (per 1,000)	0.83 [-9.78-11.44]	8.40 [0.88-15.92]
Death in first 365 days (per 1,000)	-1.04 [-1.45--0.62]	-1.46 [-1.99--0.93]

Effect estimates from difference-in-differences model (DID) and triple differences model (Triple DID) model with robust 95% confidence intervals (clustered by county) in parentheses. Low birth weight- 2,499 g or less; very low birth weight- 1500 g and less; extremely low birth weight- 1000 g or less. Emergency room visits include urgent care. All models include county fixed effects, month fixed effects, county specific time-trends, and covariates (age polynomial, race fixed effects, ethnicity fixed effects, and gravidity fixed effects (defined as the number of pregnancies identified between 2003-2015)). N = 46663 for DID models and N=210200 for Triple DID models.

As shown in Table 3, there were also several improved health outcomes for infants after the rollout of the Emergency Medicaid Plus. There was a decrease in the probability of extremely low birth weight infants (-1.55 reduction in extremely low birth weight per 1000 live births, CI -2.58 to -0.53) and a decrease in infant mortality in the first year of life (-1.04 reduction in infant mortality per 1000 live births, -1.45 to -0.62). Both of these results were consistent across the difference-in-differences and triple differences specifications. We found no consistent effects on the probability of low and very low birth weight, and preterm birth.

We conducted a number of non-prespecified sensitivity tests. To examine whether providing prenatal care changed the population utilizing Emergency Medicaid, we estimated the effect of Emergency Medicaid Plus expansion on the covariates replicating the differences-in-differences and triple differences specifications. The results indicated no substantive compositional shifts in age, number of pregnancies, race or ethnicity of the population (Appendix 10). To examine the robustness of the mortality results, we expanded the time horizon to estimate the effects on infant death per 1000 infants at two and three years after birth. The differences-in-differences and triple differences estimates were significant and consistently negative across these additional time intervals, corroborating the reduction in infant mortality (Appendix 11). Second, we conducted Fisher exact tests which showed that the infant mortality rate significantly declined after the Emergency Medicaid Plus expansion for mortality measured at one, two, and three years after birth (Appendices 12-14). The tests also showed that during the same time frame, infant mortality, if anything, increased for the standard Medicaid pregnancies (Appendices 15-17).

Discussion

Understanding how expanding access to prenatal care influences both health outcomes and costs is of national relevance as states strive to meet the triple aim of increasing quality and access care, while simultaneously reducing the costs.²³ As of 2015, thirty-two states and the District of Columbia have opted to provide some level of prenatal care for unauthorized immigrant women through Medicaid or CHIP.¹² Funding for CHIP is extended through 2017 and the scope of the program at renewal is likely to be a topic of debate.

To inform these policy debates, we leveraged a rare natural experiment where unauthorized immigrant women eligible for Emergency Medicaid gained access to prenatal care coverage by the expansion of the Emergency Medicaid Plus program in Oregon. We found that expanding access to prenatal care considerably increased both utilization of and quality of prenatal care and women were much more likely to receive adequate care and recommended preventive health services. Since the infants are US citizens by birth, they have the same access to care regardless of whether their mothers had prenatal care or not. Yet, we found a significant increase in infants receiving recommended preventive health services and improved health outcomes after expansion of prenatal care. A possible explanation for this finding is that increased contact with the health system during pregnancy led women to be more connected with care after their children were born. Future research is needed to determine the precise mechanisms driving this effect.

We also found a significant decrease in both the probability of extremely low birth weight infants and infant deathwith access to prenatal care. Our estimates suggest that pregnancies covered underEmergency Medicaid Plus saw a reduction in infant mortality by about 1.04 per 1000. As a point of comparison, this reduction is greater than the 30-year reduction in infant mortality from Sudden Infant Death Syndrome (SIDS) associated with the “Back to Sleep” campaign.^24,25 This reduction in infant mortality linked to access to prenatal care represents a meaningful gain in a public health metric where the US lags behind other developed countries.²⁶ The reduction we observed in extremely low birth weight infants likely contributes to the decrease in infant mortality rate in our population. While we were unable to stratify preterm birth for this analysis, extremely low birth weight (<1,000 grams) is correlated with early prematurity and high mortality.^24,27

Previous studies of expansion coverage for immigrants through CHIP and CHIPRA have shown increased utilization of prenatal care but have been unable to differentiate between foreign-born women who may already have insurance coverage and those who are affected by the expansion.^12,13 Our study corroborates these important findings related to prenatal care access, which a growing body of literature links to improved health and economic indicators in the subsequent generation.²⁸ Moreover, because we are able to specifically isolate immigrant women who gain coverage through Oregon's expansion, we are better able to measure related health outcomes.

Our study has a number of limitations. As with any study using claims data, input errors or omissions could have affected our results. The claims database did not include information on socio-economic status, education or other obstetric risk factors that might help better contextualize the results. Women ineligible for Emergency Medicaid Plus may have obtained prenatal care through self-pay or uncompensated care that would not be reflected in the claims database. While this may mean we overstate the increase in utilization for women, the bias on health outcomes for infants is toward the null. We captured infant mortality by using the date of death recorded in the claims recipient database rather than a death registry, which would have been more comprehensive and identified more deaths.²⁷ If, as the results suggest, women with access to prenatal care were more connected to the health care system and more likely to bring in their children for preventive services, then we would be more likely to also identify the death of their infants and this would bias the infant mortality effects towards the null. Our results should be interpreted with some caution in application to other states as Oregon has a relatively small population with significant demographic differences from other regions of the US, and has also adopted a number of reforms, such as Medicaid expansion under the Affordable Care Act, that may indicate a favorable environment for expansion of government-sponsored insurance. However, as the expansion is statewide, it does encompass economic, health system and environmental heterogeneity that increases generalizability.

In sum, our results provide evidence of an unusual success story in preventive care with excellent uptake in the target population and subsequent reduction in morbidity and mortality in the next generation. Policy makers can use this information as they decide the fate of similar programs.