Discussion
Main findings
Our study found that both increased duration and intensity of breastfeeding following a GDM-affected pregnancy were associated with a reduction in the risk of developing GDM in a subsequent pregnancy. Furthermore, breastfeeding duration and intensity influenced the glucose levels of the OGTT performed during the subsequent pregnancy.
There is a growing body of evidence demonstrating the association between breastfeeding and a reduction in type 2 diabetes.13, 20, 21 Stuebe (2015) hypothesized that early, high intensity lactation may be crucial in the ‘resetting’ of an endocrine balance from an insulin-resistant state in pregnancy, and, without the lactation-mediated reset, there may be long-term cardiometabolic health consequences.22 Studies have demonstrated that with a greater lifetime-years of maternal breastfeeding there is a corresponding risk reduction for type 2 diabetes.12, 23 Research using data from the Nurses’ Health Study found that for every extra lifetime-year of breastfeeding, there was a 15% reduction in the risk of type 2 diabetes for women who had a pregnancy in the last 15 years.20
In a study that included both post-GDM (n = 300) and non-GDM (n = 220) women, O’Reilly et al. (2011) found that hyperglycemia was more frequent at the postpartum OGTT in women who were not breastfeeding compared to women who were, with breastfeeding reducing the incidence of postpartum hyperglycemia by 60%.24 The SWIFT study was the first prospective investigation of breastfeeding intensity and hyperglycemia.25 It found an association between higher intensity breastfeeding and improved postpartum OGTT levels. As early as 6–9 weeks postpartum, a greater intensity of breastfeeding in women with GDM resulted in a lower mean fasting plasma glucose level as measured at their postpartum OGTT and a dose response to improved homeostasis model assessment (HOMA-IR). The SWIFT study also demonstrated that there was a dose-protective response of intensity and length of breastfeeding for type 2 diabetes risk two years after the GDM pregnancy.25
A lower HbA1c is associated with greater lengths of breastfeeding postpartum.13 There is also evidence that breastfeeding improves insulin sensitivity, with women who breastfed at high intensity having a lower HOMA-IR at 6–10 weeks’ postpartum, though this may only be evident in obese women.26
Although there are benefits of breastfeeding for women who have had GDM, evidence suggests that these women have greater difficulty breastfeeding than unaffected women.27, 28 Women with GDM have more issues establishing breastfeeding, experience delayed lactogenesis and breastfeed for a shorter duration than other women.29Oza-Frank et al. (2017) found that women with GDM experienced practices in hospital that are known to negatively impact on long-term breastfeeding.30 For example, they were less likely to breastfeed in the first hour after birth and it was more likely that their baby received formula in hospital than women without GDM. The importance of breastfeeding for women with GDM therefore requires greater understanding for effective, targeted lactation support. Careful consideration needs to be given to protocols whereby babies of women with gestational diabetes are routinely admitted to special care nurseries as this may negatively impact breastfeeding success.30
Breastfeeding intensity and duration can be improved through appropriate education and consistent advice that ideally includes both antenatal and postnatal care.31 Novel engagement with the use of text-based support has been trialled, with one study suggesting the best predictor for exclusive breastfeeding was strong engagement in the first two weeks postpartum utilising two-way lactation consultant texting support.32 Stuebe et al. (2016) found GDM women were less likely to stop breastfeeding or introduce formula (adjusted HR 0.50, 95% CI 0.34–0.72) at six weeks when provided with a pre- and postnatal lifestyle intervention program that included breastfeeding text-based support.33 A recent (2017) Cochrane review found that lactation support for women improved breastfeeding intensity for up to six months.34
Provision of comprehensive lifestyle and breastfeeding support for GDM women requires investment in additional staff time and resources. However, our study and others have demonstrated that optimal breastfeeding for women with a history of a GDM pregnancy reduces the risk of the mother developing type 2 diabetes and other cardiometabolic disorders. A reduction in hyperglycemia in a subsequent pregnancy also negates some of the maternal and fetal risks associated with GDM. The savings from this are likely to offset the investment in the provision of breastfeeding support. It is a financially judicious use of health resources to support early prevention for cardiometabolic disease and a unique opportunity to engage women in health intervention programs that include breastfeeding support during pregnancy and the postpartum period.
We are not aware of any published methods for the routine assessment of breastfeeding intensity. This is important as duration of breastfeeding by itself does not necessarily reflect early breastfeeding issues. Low intensity breastfeeding may occur early postpartum, however a small percentage of mothers will persist despite extreme difficulties (Table 2). Women who breastfeed more successfully with greater intensity tend to breastfeed for longer.35 The BLISS check is therefore a novel means of assessing breastfeeding intensity through a maternal recall questionnaire. Evaluation of previous breastfeeding is an important component of the pregnancy and postpartum evaluation, and this can easily be established as a routine tool for use by clinicians. The findings of our study suggest that the BLISS check score may be a useful clinical tool.
We are continuing to validate the BLISS check in a larger cohort for antenatal lactation counselling referral purposes and research. It is important to work towards standardizing the assessment of breastfeeding intensity in a manner that is clinically useful and capable of informing both care and research. Defining and standardizing breastfeeding terminology for both clinical and research purposes will assist with comparison of data and patient management.36
Strengths and limitations
The high participation rate of women gave our study strength and reduced potential recruitment bias. This suggests that women are interested in breastfeeding and are keen to discuss their breastfeeding history and associated problems. This also suggests the need for more antenatal breastfeeding support that provides an appropriate clinical avenue for breastfeeding counselling and information. Ethnic diversity is an additional strength of our study and informs the capacity to extrapolate the results to other populations.
The major weakness of our study is potential recall bias. In the literature, however, maternal recall of breastfeeding history has been validated as a reliable method to determine infant feeding history.37, 38 In a Norwegian study, recall of duration of breastfeeding was found to be accurate after 20 years with a median over-estimation of only two weeks.38 The recall bias in our BLIiNG study would be less, as all participants had only one previous pregnancy and feeding details to remember. The same recall limitation would exist for both GDM and non-GDM groups and the mean time between births was three years for both groups.
Interpretation
There is concern about the high incidence of GDM and its recurrence. Much of the focus amongst women who have had GDM is to reduce obesity and improve lifestyle in between pregnancies. However programs aimed at these risk factors are challenging, resource intensive, and have in general met with little success.39-41 On the other hand, breastfeeding is already encouraged, and for the majority of women, is acceptable, and can be undertaken successfully. Yet this has largely been neglected in the GDM and diabetes prevention literature.
Conclusions
Our study has demonstrated that a greater intensity of breastfeeding can improve glycemia and reduce recurrent GDM in pregnant women who have had a previous GDM-affected pregnancy. Breastfeeding may potentially reduce future type 2 diabetes and cardiovascular disease risk for the mother, as well as providing known benefits to the health of the infant. Thus, the promotion and support of breastfeeding should be routinely implemented as an important intervention for the prevention of recurrent GDM and type 2 diabetes.
Disclosure of interest
None declared. All authors declare they have no conflict of interest which may arise from being named as an author on the manuscript.
Author Contributions
The research idea was conceived by SJM and LW. The study was designed by SJM, LW, MS, IA, SP and WC. AK performed the statistical analysis, SJM interpreted the data and wrote the initial drafts with supervision from WC and DP. Invaluable support was given by IA, WC, DP, LW, MS, SP, VS and AK for final interpretation of findings, and critical revision of the article. All authors reviewed and approved the final version of the article submitted for publication.

Details of ethics approval

The study was approved by the Western Sydney Local Health District (WSLHD) Human Research and Ethics Committee (LNR/16/WMEAD/404; 1 February 2017), all participants provided informed consent.
Funding
This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.

Acknowledgments

We acknowledge and appreciate the contribution to the study of data custodian Monica Hook and the assistance with data collection by Sarah Tapp.

Data sharing

No additional data is available in compliance with WSLHD Human Research and Ethics Committee regulations.
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Table 1 Characteristics of women who were diagnosed with recurrent
gestational diabetes (GDM) in their second pregnancy