Introduction

Recent legislative decisions in the United States have encouraged discussion about national parental leave programs. Currently, over 47% of the United States workforce is female (“Women in the Workforce,” n.d.). However, the United States is the only nation of the 37 member countries in the Organization for Economic Co-Operation and Development (OECD) to have no national requirement for paid or unpaid maternity leave. Estonia offers the longest full-paid maternity leave of 85 weeks and Australia and New Zealand offer the shortest amount of full-paid leave time at 8 weeks (Length of Maternity Leave, Parental Leave and Paid Father-Specific Leave, n.d.). The Family Medical Leave Act (FMLA) of 1993 in the United States provides certain employees 12 weeks of unpaid, job-protected leave. FMLA time may be taken for the birth of a child, adoption or foster care processes, personal medical issues, or care of a family member. If a pregnant woman experiences any complications during pregnancy, she must use her FMLA time during pregnancy which decreases her job-protected leave time after the birth of her child.

To meet requirements of the FMLA, individuals must work at a company with 50 or more employees, have worked for the employer for at least 12 months with a cumulative total of 1250 h worked, and work at a location where the company employs 50 or more employees within 75 miles (Family and Medical Leave Act | U.S. Department of Labor, n.d.). In 2018, only 10% of all businesses in the private sector met these FMLA-requirements but employed 59% of private sector employees. Only 56% of all US employees meet FMLA qualifications and only 16% of the FMLA-eligible workforce take leave each year. For those that did take leave, 34% of them did not receive any form of payment (Gloria Sherman, 2019). Beginning October 1, 2020, the Federal Employee Paid Leave Act (FEPLA) offers 12 weeks of paid parental leave to federal employees. These employees must still meet the requirements outlines above for FMLA and guarantees 12 weeks of full paid leave (Gloria Sherman, 2019).

Financial strain from unpaid leave disproportionately impacts lower-income families. 54% of those with an average household income of $62,000 or less report receiving no pay while on FMLA compared to 18% of those with a household income greater than $62,000. Many individuals report difficulty making ends meet during unpaid leave time: cutting expenditures, using savings (either intended for leave or other purposes), delaying bill payments, obtaining loans, or relying on public assistance. More than one-third of all workers taking FMLA report cutting their leave time short because of the significant financial burden (Federal Employees Paid Parental Leave Act, 2013).

It is known that the first months of a child’s life are vital to their mental and physical wellbeing. For example, rapid brain development occurs with a child’s brain growing by 1% every day for the first three months of life (Wessel, 2019). Nurturing and responsive parenting is essential for proper brain development. Allowing women to take leave time without worry about financial or job security can positively impact child development. Stressors in early childhood can even lead to disruption in neurological, immunological, and metabolic processes (Robinson et al., 2017). An example of an early childhood stressor is a lack of secure emotional attachment to parent or caregiver (Audage& Middlebrooks, 2008) which can result from insufficient bonding time due to decreased parental leave. Breastfeeding, another benefit of maternal leave, has also been shown to enhance the mother–child bond (Krol & Grossmann, 2018).

In the postpartum period, a woman experiences significant mental and physical changes. Rapid hormonal changes following the delivery of the child predisposes women to experience heightened responses to stressors. 1 in 8 women will experience postpartum depression (Depression Among Women, 2020). Similarly, many women will experience low sleep duration and quality in the first few months following the birth of a child. Lack of sleep can further predispose a woman to experience symptoms of depression and anxiety (Creti et al., 2017). Return to regular daily activities can be difficult following birth, exacerbating depression and further hindering the recovery process.

A recent comprehensive review article outlines the importance of a national paid maternity leave policy in the United States to enhance maternal and infant mental and physical well-being (Van Niel et al., 2020). This study used only qualitative analyses to assess the data. In our study, we will expand upon their data to quantify the association between length of maternity leave and maternal and infant mental and physical health. We conducted a systematic review and meta-analysis to evaluate for the optimal length of maternity leave to enhance mental and physical well-being for women and their children.

In this study, outcomes for maternal mental health include postpartum depression, stress, and burnout. Outcomes for maternal physical health include the ability to complete activities of daily living. Infant mental health outcomes include maternal-child bonding and attachment style. Infant physical health outcomes include length of breastfeeding, pediatrician visits, and immunization status.

Methods

Data Sources and Search Strategy

We conducted a systematic literature search using electronic databases PubMed, Scopus, EMBASE and PsycINFO in December 2020. The search strategy was designed to include all published articles which dealt with the association between length of maternity leave and maternal and infant mental and physical health to accomplish the study objective. We applied various combinations of Boolean operators by using the following keywords for our search: [(“child mental health” OR “mother child bonding” OR “attachment” OR “breastfeeding” OR “pediatrician visits” OR “childhood immunizations” OR “infant morbidity” OR “infant mortality” OR “developmental milestones” “maternal mental health OR “maternal sleep disturbances” OR “maternal depression” OR “maternal anxiety” OR “maternal postpartum functioning” OR “postpartum sexual functioning” AND (“paid family leave” OR “paid maternity leave” OR “maternity leave”)]. As this study is a systematic review of the literature, it does not contain individual participant or patient data and is not based on clinical study. This study was not registered, and a protocol was not prepared.

Study Selection

Studies were eligible for inclusion if they met the following criteria: (1) originally published in English language; (2) include full information on the association either between child mental/physical health and paid family/maternity leave or between maternal mental/physical health and paid family/maternity leave; and (3) published as original investigation. The exclusion criteria for studies are as follows: (1) published in other than English language; (2) published as review, guideline, commentary, letter to the editor; (3) published as case reports with smaller numbers. Methods to assess bias in individual studies included using an established protocol for study identification and careful appraisal of each study prior to inclusion in the systematic review.

Data Extraction and Quality Assessment

An Excel data collection sheet was developed to extract all relevant information from the included eligible studies. Study characteristics involving last name of the first author of the study; year of publication; country of publication; sample size (total number of patients/subjects); average age (standard deviation/inter-quartile range); average BMI (standard deviation/inter-quartile range); paid maternity leave; period/length of maternity leave; race/ethnicity; educational status, locality (rural/urban); family type (nuclear/combined); status of any comorbidity (existing chronic illness and physical health problem such as ability to complete daily living activities) of the woman; existing mental health problems of the woman (postpartum depression, anxiety, stress, and sleep disorders); existing physical health issues of the newborn/infant; existing mental health issue of the newborn/infant; current physical health of the woman (ability to complete activities of daily living and restoration of sexual function), current mental health problems of the woman (postpartum depression, anxiety, stress, and sleep disorders), current physical health problems of the newborn/infant (pediatrician visits, immunization status, breastfeeding status, and infant morbidity and mortality) and current mental health problems of the newborn/infant (maternal child bonding, attachment, and achievement developmental milestones).

Statistical Analysis

STATA v.15 was used for statistical analysis. After careful data cleaning, a total of 21 studies between 1997 and 2020 were included in the analysis. We focused on overall depression status given the length of maternity leave, depression status specifically in short maternity leaves, any other form of mental illness given the length of maternity leave, and breast feeding associated with length of maternity leave. Odds ratios (OR) and 95% confidence intervals (CI) were used to describe the overall differences between depressed and non-depressed participants. A 95% confidence interval (CI) and p-values were calculated for each outcome. For certain studies where only frequencies were presented the OR, standard error (SE), and 95% confidence interval were calculated manually. OR were considered statistically significant at a p-value < 0.05. The magnitude of heterogeneity between-study was tested using The Moran’s I2 statistic (Dwivedi, 2017). A value of more than 50% of I2 will be known as significant heterogeneity. All statistical analyses were carried out with Stata software version 15 (StataCorp. 2017. Stata Statistical Software: Release 15. College Station, TX: StataCorp LLC).

Results

We identified 485 studies using the previously outlined search strategy. After initial screening with inclusion criteria and removing duplicates, 315 articles remained. A second screening for original investigation excluded an additional 282 articles. 12 of the remaining 33 articles were excluded due to insufficient data or irrelevance. The remaining 21 articles were analyzed. Flow of information is presented in the PRISMA diagram in Fig. 1. PRISMA checklist can also be found for this manuscript as Table 1.

Fig. 1
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Prisma flow diagram of included studies

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Table 1 PRISMA 2020 checklist
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The most common weakness among the studies used in this analysis was the lack of standardized reporting for some variables of interest, particularly among the mental health categories. For example, many clinicians use the Edinburgh Postnatal Depression Scale to assess for postpartum depression. However, not all studies that look at postpartum depression used this scale. This lack of standardization leads to the heterogeneity seen in the data. Study characteristics are summarized in Table 2. Racial and ethnic groups identification were not included in many of the included studies. Without this data, we cannot assess any differences in health outcomes in mothers or infants between racial and ethnic groups, especially in historically marginalized communities.

Table 2 Included studies
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Maternal Mental Health

Maternal mental health complications in this study include postpartum depression, stress, and burnout. We found seven articles addressing maternal mental health in relation to length of maternity leave. It is found that maternity leave of 8–12 weeks, in comparison to 6 weeks or less, is associated with lower rates of negative maternal mental health. Interestingly, one study (Kornfeind & Sipsma, 2018), found that for women taking 12 weeks or less of maternity leave, each week is associated with decreased rates of postpartum depression. However, for those taking 12 weeks of leave or more, additional leave time is not associated with less depressive symptoms. Another study by Dagher in 2014, found similar results using a benchmark of 6 months (Dagher et al., 2014). Overall, individuals with 8 to 12 weeks of maternity leave are less likely to experience depressive symptoms and burnout and more likely to have greater perceptions of support.

Our analysis (Figs. 2, 3) revealed that length of maternity leave is associated with lower levels of depression, OR 0.76 (0.52–1.11), and any maternal mental health condition, OR 0.87 (0.46–1.61). While these data do not hold statistical significance, clinical significance may be present. These results reflect the lack of homogeneity in the published literature.

Fig. 2
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Forest plot of overall depression status given the length of maternity leave

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Fig. 3
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Forest plot of presence of any mental health issue given the length of maternity leave

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Maternal Physical Health

Maternal physical health parameters in this study included rehospitalization after birth, self-rated physical health, and ability to participate in activities of daily living. We found three studies addressing maternal physical health in relation to length of maternity leave. Women that had paid leave of any duration are 51% less likely to be re-hospitalized for any reason in the year following birth. Additionally, those that took leave are found to be 1.8× more likely to engage in exercise. One Australian study looked at postpartum health of women before and after the enactment of a paid leave policy. This study showed that women had higher self-reported physical health after the enactment of the policy (Hewitt et al., 2017). Re-entry into the workplace in the postpartum period can be difficult, as assessed by Falletta et al. (2020). This study indicates that individuals with any length of maternity leave are associated with better self-reported physical health within the first month of work re-entry.

Infant Physical Health

Infant physical health parameters included infant mortality, hospitalizations, immunization status, and breastfeeding. Maternity leave is associated with lower rates of infant and child mortality. A European study found that an additional 10 weeks of maternity leave resulted in a 4.5–6.6% decrease in expected post-natal deaths (Ruhm, 2000). Another study conducted in the USA and other OECD countries found that any length of paid maternity leave is associated with a 4.1% decrease in post-natal mortality, 2.6% decrease in infant mortality and 3% decrease in child mortality (Tanaka, 2005). Similarly, an international study found a 10% lower infant and neonatal mortality with a 10 week increase in paid maternity leave (Heymann et al., 2011). The California Paid Leave Act, which provides financial assistance for six to eight weeks was passed in 2004. After the passage of this act, there was significant decrease in late immunizations for infants in California. Women that had 12 weeks or more of leave are more likely to initiate breastfeeding and maintain breastfeeding for at least 6 months (Mirkovic et al., 2016). Our analysis (Fig. 4) revealed that infants born to mothers with shorter maternity leave times are less likely to breastfeed for at least 6 months OR 1.49 (0.81–2.75).

Fig. 4
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Forest plot of breast-feeding status given the length of maternity leave

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Infant Mental Health

Infant mental health parameters included maternal-child attachment and achievement of childhood milestones. A cohort study using videotaped analysis of maternal-child interactions revealed that shorter maternity leaves, defined as 6 weeks or less, are associated with more negative maternal-child interactions (Kochanska et al., 1997). Another study found that length of maternity leave is significantly correlated with more positive maternal infant interactions, and eventually lead to higher rates of secure attachment, higher empathy, and academic success (Plotka & Busch-Rossnagel, 2018). One survey assessing the impact between maternity leave and infant developmental milestones found no significant difference in milestone achievement between various lengths of maternity leave (Baker & Milligan, 2010).

Discussion

The association between maternity leave length and impact on maternal and infant outcomes is a complex phenomenon. While each maternal-child dyad is different, it is known that the first few weeks of life are vital to the health of mother and infant. The nuanced discussion of maternity leave encompasses discussions of workplace culture and national politics. The United States remains the only OECD country to have no national requirement for paid maternity leave. This can lead to many unintended consequences in the realm of maternal-child health, including outcomes as dire as increased infant mortality. Our descriptive analysis revealed that longer maternity leave of 8–12 weeks, as compared to 6 weeks or less, may be correlated with better outcomes in maternal and child mental and physical health outcomes. While our analysis did not reveal statistically significant results, the data may be clinically significant. Longer maternity leave may lead to lower levels of maternal depression and longer periods of breastfeeding. The lack of research into this area, coupled with the lack of standardized reporting for these outcomes highlights the need for additional investigations in this area.

Despite data to substantiate the benefits of parental leave, many United States citizens do not enjoy the same parental leave benefits of those in other developed countries. The stipulations of mandated parental leave do not apply to many United States citizens. This demonstrates the need for policy changes in the US regarding parental leave. Grassroots organizations such as Moms Rising advocate for parental leave in the United States. These organizations fund research and governmental lobby to encourage family-friendly policies in the United States. A recent study by Moms Rising, in conjunction with Duke University, demonstrates that paid family leave is associated with better health for women and infants, as well as a more positive impact on the economy (Rowe-Finkbeiner et al., 2016).

Recently, there has been an increased interest surrounding family leave and childcare, shifting policies within the United States. The Build Back Better proposal initially included a universal family leave policy, but it failed to be enacted (President Biden Announces the Build Back Better Framework, 2021). This reflects the complicated nature of enacting laws in the United States but may be the first step towards change. Healthcare practitioners and public health professionals can use this information to advocate for family-centered policies at a local and national level. Understanding the changes that women and infants endure during the first weeks following childbirth are vital to creating a healthier country.

One limitation of this study is the lack of universal scales that yield data to objectively measure outcomes. The universal use of available validated scales, such as the Edinburgh Postnatal Depression Scale, could be useful to mitigate this limitation. Additionally, outcome measurements in some of the analyzed studies are subjective. This highlights the need for additional standardized scales in this realm of medical research. The lack of homogeneity in the current published literature illustrates the need for further study, including development of a comprehensive data set to include parental leave parameters and prospective research on these topics.

Conclusion

Further study is needed to determine a statistically significant quantitative link between the length of maternity leave and the impacts on maternal and infant mental and physical health. Standardized data gathering in primary studies addressing these topics will aid in further research used to guide local and national policies. Based on the data seen in this review, maternity leave of at least 12 weeks would confer the greatest benefit for mother and child.