Correction: Effectiveness of Home Visits in Pregnancy as a Public Health Measure to Improve Birth Outcomes

There are a number of errors in Table 2. Please see the corrected Table 2 here. 
 
 
 
Table 2 
 
Baseline characteristics and outcomes of the home-visit program 
 
 
 
There are a number of errors in Table 4. Please see the corrected Table 4 here. 
 
 
 
Table 4 
 
Effects of home-visit program on birth outcomes

Implementation of a home-visit program during pregnancy is a comprehensive strategy to prevent adverse birth outcomes [26,27]. Although the exact mechanism of this approach is not well clarified, many previous studies have suggested that providing tangible in-home or one-on-one psychosocial support, and improving linkages to medical providers, social services and nutrition support can encourage healthy prenatal behaviors [28][29][30][31]. However, previous randomized controlled trials (RCTs) of home-visit programs and pregnancy outcomes showed inconsistent results [32][33][34][35]. For example, Lee and colleagues [36] found that home visits before 30 weeks' gestation for women (Black and Hispanic: 65%; under 18 years old: 24.6%) were effective for preventing LBW (5.1% versus 9.8%; p = 0.022), however McLaughlin and colleagues [37] found home visits for women (Black women: 35%, mean age: 21.8 years old) showed no significant effect in reducing LBW incidence. This is likely due to several factors, including differences in the characteristics of target participants and methods of program delivery, the reluctance of high-risk women to participate, and variation in the timing of home-visit implementation between trials [38,39]. Therefore, an assessment of the effectiveness of home visits for a wide range of high-risk women, and the timing of implementation, is needed.
Japan has a unique data collection and prenatal support system that was first established by the Maternal and Child Health (MCH) Act and MCH Law in 1965 for the promotion of maternal, newborn, and infant health. The Act promotes continuity of care through the MCH Handbook [40], which is provided for free to expectant mothers who submit a notice of pregnancy to their local government office. Women in Japan are supposed to register their pregnancy within the 11th gestational week [41]. The Handbook unifies maternal and child health into one resource, serving as a maternal health record during pregnancy and a child health record from 0-6 years, which parents can keep and take with them to appointments. In addition to the MCH Handbook, which has almost 100% coverage [40] for expectant mothers, the Act also provides health guidance to pregnant and postpartum women, and health check-ups for newborns and infants at local government health centers.
In July 2011, Kyoto city in Japan established the population-based home-visit program for all high-risk pregnant women. High-risk pregnant women were defined as teenage girls (range 14-19 years old), women with a twin pregnancy, women who registered their pregnancy late, had a physical or mental diseases, were of single marital status, non-Japanese women who were not fluent in Japanese, or elderly primiparas. At the time of pregnancy registration at the public health center, public health nurses assessed the risk level of pregnant women by conducting an interview in person using a registration questionnaire. As some women receive the home-visit program and others do not, we were provided with the opportunity to conduct a quasi-experimental study on the effectiveness of the home-visit program. As the baseline information is known at registration, the propensity of receiving the home-visit program can be assessed.
The objective of this study is to evaluate the effectiveness of the home-visit program conducted by public health nurses to high-risk pregnant women to prevent adverse birth outcomes (preterm, LBW, and SGA) by using the propensity score-matching model. We also investigated whether timing of program implementation had an effect on adverse birth outcomes.

Ethics statement
We used secondary administrative data from Kyoto city government in this study, which did not contain identifying information about individuals. In addition, public health nurses obtained written informed consent from pregnant women. We obtained written informed consent from Kyoto city government's ethical committee to use this secondary administrative data which did not contain identifying information about individuals, and published an announcement about this study on the official homepage of Kyoto city government. The announcement stated that if individuals who met the inclusion criteria did not want their own data to be used, even though it was anonymised, they could request for their data to be omitted by calling the Kyoto city government. However, no one requested for their data to be omitted from the study. The study was approved by the Kyoto University Graduate School and Faculty of Medicine Ethics Committee (E1833).

Study design and population
This was a quasi-experimental cohort study using administrative data collected in Kyoto, Japan. Data was obtained from the Department of Child and Maternal Health in Kyoto, including the baseline questionnaire conducted at pregnancy registration in public health centers, MCH handbook data, which includes data from prenatal checkups, delivery, child development, vaccinations, and home-visits. The population of Kyoto is around 1,467,000. During the period of 1 July 2011 to 30 June 2012, 11,749 women registered their pregnancy at public health centers in Kyoto. Trained public health nurses conducted interviews in person at the public health center using unified standard questionnaires to assess high-risk pregnancy. Target participants of our study were all high-risk pregnant women who registered their pregnancy in Kyoto city. High-risk pregnant women were administratively defined as follows: 1) women who had past or current physical or mental illness; 2) primiparas under the age of 20; 3) primiparas over the age of 35 with some unfavorable conditions such as poverty; 4) women who were pregnant with twins; 5) women who were late to register their pregnancy (i.e. after the 22 nd week of gestation) or women who were unhappy about being pregnant; 6) women with single marital status (unmarried or divorced); 7) non-Japanese women who were not fluent in Japanese, and 8) women who were assessed by public health nurses at registration as requiring any additional support including both medical, psycho-social, nutrition counseling.
The target population of high-risk prenatal mothers in this project was 1,023 women, and all data were used in the initial analysis to calculate propensity scores for receiving the homevisit program. That is, all high-risk pregnant women were supposed to receive home visits from public health nurses; however, 594 women (58.1%) did not receive any visits because they were not reachable. This group was used as a control sample (Fig 1).

Home-visit programs for pregnant women in Kyoto
In this program, trained public health nurses were to make at least 1 home visit to high-risk pregnant women lasting for more than 1 hour during mid-or late-term pregnancy (mean gestational age: 27.2 (SD = 6.9) weeks, range: 7-40 weeks). Nurses received specific training about home visiting about once a year and were expected to consult with supervisors about difficult cases. The contents of the home visit were as follows: 1) checking women's social support status and linking them to other services in the community, if needed; 2) providing information about appropriate nutrition during pregnancy, prenatal care, dental care, and child care, and 3) asking women about their physical or psychological health and linking them to medical facilities if needed. If nurses concluded that the women required more support, they provided follow-up support by phone, made another home visit, or introduced women to further social services support. Detailed components of the home visit are shown in Table 1.

Outcomes
Birth outcomes, birth weight (crude value) and gestational age were obtained from birth records in the MCH handbook. Z-scores of birth weight (ZBW) were calculated and we adjusted for gestational age, sex, and parity [42]. Binary indicators were low birth weight, defined as less than 2500g; preterm birth, defined as less than 37 weeks, and small for gestational age, defined as <10 percentile. Covariates and independent variables The following covariates were obtained from baseline questionnaires and interviews from trained public health nurses at the time of pregnancy registration: maternal age, paternal age, employment status during pregnancy, living with family members, marital status, parity, history of miscarriage and stillbirth, experiences of fertility treatment, late submission of pregnancy registration (over 22 weeks), twin pregnancy, maternal smoking or alcohol consumption, smoking among women's family members, maternal physical or mental illness, limited Japanese ability among non-Japanese women, unintended pregnancy, worries about childrearing, finances, and relationship with partner, having someone to consult with on child care, experiences of good relationships with parents, subjective economic status, maternal and paternal attitudes to child-rearing, and experiences of child-rearing. Categorical variables were used for childcare services ("Yes", "Rarely", or "Never") and knowing someone with experience of child-rearing ("Yes, many people", "Yes, a few people", or "No, do not know anyone"). The remaining variables were binominal (see Table 2).

Statistical analysis
Of the 1,023 baseline samples, we excluded participants who had missing birth-outcome data (home-visit program: n = 19, no home-visit program: n = 40, 5.8% in total participants) from the analysis (total N = 964 women, home-visit program: n = 410, no home-visit program: n = 554). Then, propensity score-matched analysis was performed to reduce potential bias on receiving the home-visit program. The probability of home-visit participation was estimated by all baseline characteristics using logistic regression, because these characteristics possibly associate with participation in the home-visit program. Propensity-score matching was performed by using the following algorithm: 1:1 nearest-neighbor match method with a caliper of 0.4 SD and no replacement. Finally, 311 women who received the home-visit program and 311 women who did not were included in the analysis (that is, N = 622). Variables used to estimate the propensity to participate in the program were sufficiently high, with C-statistics at 0.77. No significant difference was observed between the baseline characteristics of the home-visit program group and the no home-visit group ( Table 2, right columns). The propensity-matched pairs were compared using logistic regression analysis, and multivariate regression analysis after adjusting for all baseline variables. In addition, sub-group analysis was performed for the timing of home-visit implementation, which was divided into two subgroups (home visits  at <28 gestational weeks, home visits at 28 weeks). Missing data of covariates such as alcohol consumption (n = 4), experiences of fertility treatment (n = 12), physical or mental illness (n = 2), employment status (n = 25), living with family members (n = 162), experiences of good relationships with parents (n = 25), maternal and paternal attitudes of child rearing (n = 32) and experiences of child-rearing (n = 12) were treated as dummy variables. Where paternal age was missing in the data, the mean age was imputed. Stata version 13 was used to perform the analysis between January 2014 and June 2014.

Effectiveness of Home Visit in Pregnancy on Birth Outcomes
Results Table 2 shows the baseline characteristics of prenatal mothers at pregnancy registration in the home-visit group (n = 410) and the no home-visit group (n = 554) before propensity-score matching. Mean gestational age for infants of mothers in the home-visit group was 27.2 (SD = 6.9) weeks. Pregnant women who received home visits were more likely to be experiencing their first pregnancy (n = 333, 81.2%), diagnosed with a disease (n = 163, 39.8%), and worried about child-rearing (n = 192, 46.8%) or relationships with neighbors (n = 64, 15.6%) compared with women who did not receive home visits. Pregnant women who did not receive home visits were more likely to smoke (n = 111, 20.0%), drink alcohol (n = 67, 12.1%), be unmarried (n = 197, 35.6%), feel unhappy about their pregnancy (n = 111, 20.0%), or had partners who were unhappy about their pregnancy (n = 85, 15.3%) compared with women in the home-visit group. After performing propensity-score matching with the comparison group, no significant difference was observed between variables (see Table 2). Table 3 shows the birth outcomes before and after propensity-score matching. Before propensity-score matching, women from the home-visit group had a heavier birth weight (2905.3 g, SD = 499.5 g), longer gestational age (38.7 weeks, SD = 1.8 weeks), higher ZBW (-0.04, SD = 1.1), less LBW infants (n = 85, 19.2%), less preterm birth (n = 40, 9.8%), and less SGA infants (n = 52, 11.7%) compared to participants who did not receive the home-visit program. After propensity-score matching, women from the home-visit group had a heavier birth weight (2933.3 g, SD = 473.4 g), longer gestational age (38.6 weeks, SD = 1.8 weeks), and less preterm birth (n = 34, 10.9%) compared to women who did not receive the home-visit program. Table 3. Description of outcomes of home-visit program vs. no home-visit program.

P Value
Birth weight, mean (SD), g 2905. 3 Table 4 shows the coefficient and odds ratios (ORs) of the home-visit program for birth outcomes. Before propensity-score matching was conducted in the univariate model, women in the home-visit program during their pregnancy had a significantly heavier birth weight (coefficient: 138.3g, 95% confidence interval [CI]: 63.2 to 213.4), longer gestational age (coefficient: 0.67 week, 95% CI: 0.33 to 1.00), higher ZBW (coefficient: 0.25, 95% CI: 0.11 to 0.38), LBW (OR: 0.70, 95% CI: 0.49 to 0.98), preterm birth (OR: 0.62, 95% CI: 0.41 to 0.94), SGA (OR: 0.62, 95% CI: 0.43 to 0.91) than women who did not receive the home-visit program. These associations remained significant in the multivariate adjusted model, except for ZBW and SGA. Further, in the propensity-matched sample for the home-visit group, a heavier birth weight, longer gestational age, and lower odds of preterm birth remained significant during pregnancy, although odds of LBW became non-significant. In the final model-the multivariate adjustment of the propensity-score matched sample-pregnant women in the home-visit group delivered infants with a heavier birth weight of 99.1g (95% CI: 20.5 to 177.6) and a longer gestational age of 0.61 weeks (95% CI: 0.25 to 0.96), and were 74% less likely to deliver preterm, compared to pregnant women who did not receive home visits. Table 5 shows the subgroup analyses of the effectiveness of the home-visit program by timing of implementation (i.e. whether the program was implemented before or after 28 weeks' gestation). In the propensity-score matched sample, women who entered the home-visit program late (after 28 gestational weeks, n = 159) showed a longer gestational age (coefficient: 0.65 weeks, 95% CI: 0.09 to 1.20) compared to women who did not receive home visits. Further, a marginal protective effect on preterm birth was found among women who entered the program late compared to women who were registered in the program earlier (OR: 0.57, 95% CI: 0.31 to 1.06). However, early implementation of the home-visit program (before 28 gestational weeks, n = 145) failed to show longer gestational age nor a protective effect on preterm than women in the comparison group, suggesting that joining the home-visit program after 28 weeks' gestation was more effective to achieve longer gestational age and to be protective for preterm.

Discussion
The present study evaluated the effectiveness of the home-visit program for high-risk pregnant women in Japan on birth outcomes (birth weight, gestational age, Z-scores of birth weight) using a propensity-score matched sample. We found that home visits from trained public health nurses at least once during pregnancy were effective to prevent preterm birth, but not small for gestational age among high-risk pregnant women in Japan. To our knowledge, this is the first study to investigate the effectiveness of the home-visit program for a wide range of high-risk pregnant women as a public healthcare measure. However, two randomized controlled trials of home-visit programs [36,37], which investigated the efficacy of birth outcomes, suggested that the effectiveness of such programs is still inconsistent, while two recent observational studies conducted in the United States (US) using propensity score-matched analysis found home-visit programs to be effective [33,43]. Both US studies concluded that participating in the home-visit program reduced the risk of adverse birth outcomes in disadvantaged populations (i.e. people who received Medicaid). Our finding is consistent with these previous studies in showing the effectiveness of the home-visit program in preventing adverse birth outcomes, although the definition of disadvantaged population is different (i.e. our definition of 'high-risk pregnant women' did not only focus on economic status but on medical conditions, social disadvantages and other factors).
In the Japanese healthcare system, all pregnant women are screened by public health nurses at registration of their pregnancy, or within 11 weeks' gestation. In addition, high-risk women receive comprehensive support and are referred to appropriate follow-up services [44]. This system enables high-risk women to be followed-up from the prenatal to postnatal period, and facilitates the first contact between public health services and high-risk pregnant women. Some components of the home-visit program, such as consultations on maternal anxiety, nutrition education and health-check ups, might improve birth weight. Although we tried to provide the home-visit program for all high-risk pregnant women, approximately half of the high-risk women (n = 554) were not reachable and showed worse risk factors, such as smoking and drinking alcohol, for poor birth outcomes. It is another challenge to support the super-highrisk pregnant women who were not reachable in general health care system.
We found that late admission to the home-visit program was effective to prevent preterm birth, although early admission to the home-visit program did not. The reason for this difference is unknown. It is possible that perinatal care or advice from public health nurses might be more effective closer to delivery. Further study is needed to elucidate the mechanism on why receiving home visits later in pregnancy is more effective to prevent preterm birth. This study has some limitations. First, this study was of a quasi-experimental cohort design, so there may be unobserved variables and unknown confounding factors, such as maternal personality or characteristics. These factors may affect birth outcomes despite adjusting for baseline variables using the propensity score. Second, potential selection bias exists because approximately 5.8% (59/1023) of the data was omitted due to missing outcome data. However, there were no significant differences in the baseline characteristics between analyzed and omitted samples, so the present results represent the overall sample data. Finally, we could not count the dosage of the program and the number of times nurses visited participants' homes. Further study is needed to investigate the association between outcomes and dosage of the program.
Despite these limitations, we found that the home-visit program for high-risk pregnant women by public health nurses significantly prevented preterm birth. Further studies with larger sample sizes are needed to measure the timing and dosage of the intervention in order to clarify the dose-response relationship in the home-visit program.

Conclusion
Our findings suggest that home visits by public health nurses for high-risk pregnant women in Japan might be effective in preventing preterm birth, but not SGA. This study adds to the evidence of the effectiveness of population-based home-visit programs as a public healthcare measure.