Designing Trials for and with Breastfeeding Mothers*

Published on Monday, 03 August 2026

Breast milk and breastfeeding benefit mother, child, economy and environment, yet breastfeeding rates remain suboptimal globally, and particularly so in the UK. With rising chronic disease burden and health inequalities, there is an urgent need for high-quality evidence for and with breastfeeding women to identify barriers and strategies to promote breastfeeding and improve outcomes.

Research Inclusion

Women's health research is already underrepresented, and breastfeeding women face further exclusions. They are routinely excluded from drug trials by default due to concerns about infant safety, leaving women and clinicians to make decisions without essential information on risks and benefits of a medicine during breastfeeding. As a result, women may avoid needed treatment, take an incorrect dose or stop breastfeeding altogether. There's a recent push from the WHO, European Medicines Agency, researchers and others for the inclusion of pregnant and breastfeeding people in clinical trials with special considerations outlined, including undertaking lactation studies to determine drug transfer as a first step. This should mean fewer women are unnecessarily excluded from research or discouraged from breastfeeding, and better data to inform appropriate clinical practice.

Mothers Matter Too

Breastfeeding research and public health messaging often focus on benefits to the infant. However, extensive evidence shows that women benefit too, including reduced risks of breast and ovarian cancers and type 2 diabetes. Trials should ask how an intervention could benefit the mother. One example of this is evidence from randomised controlled trials showing that breastfeeding relaxation interventions reduce maternal stress, alter breast milk composition, improve infant growth and potentially result in more favourable infant behaviour, across different settings and populations. One such trial was undertaken at the NPEU CTU investigating the use of a relaxation audio for mothers expressing milk for their very preterm infant.

Practical Considerations

There are several further practical points trial teams should address:

Design: consider barriers to participation, including the demanding postpartum period, lack of support, and cultural hesitancy or mistrust in research. Involving mothers, breastfeeding charities, and partners/families in the study planning would help identify and reduce these barriers. It is also worth considering how a study itself could interfere with breastfeeding. The DOLFIN trial, which investigated a nutritional supplement for neonates, provides a good example of how to manage this. The study developed breastfeeding-specific resources (videos, leaflets), offered different delivery methods (syringe, teat, finger, cup) and engaged national breastfeeding charities to ensure that breastfed infants could be included without the supplement interfering with feeding.

Outcomes: there is currently no core outcome set for breastfeeding outcomes, with considerable variation in the endpoints, time points and definitions used, making it difficult to pool data or compare findings across studies.

Exclusive breastfeeding status is often assessed by maternal recall over varying periods (24-hours, 7-days or since birth) so exact definitions and time points should always be reported for transparency.

Milk volume is another outcome of interest, often assessed by feeding diaries or test-weighing. However, these techniques can be time-consuming and burdensome. Where possible, isotope techniques such as deuterium oxide dose-to-mother offer a more objective method, and can also assess exclusive breastfeeding status more reliably than maternal recall which is prone to recall and social desirability biases.

Trials investigating breast milk itself also need to account for its dynamic nature, since composition changes within a feed, throughout the day and across time. Standardising sampling techniques to account for time of day, expression method, and breast fullness and emptying improves both internal validity and comparability across studies.

Data collection: collect data at home visits or during routine appointments whenever possible; offer flexibility around feeding schedules and routine care; provide spaces to feed or express milk and allow for longer visit times to reduce participation barriers.

Dissemination: share findings back in collaboration with breastfeeding mothers.

Overall, there is a need for trials that are designed with and for breastfeeding women in mind to ensure their inclusion and representation in research and data, and to improve breastfeeding and other health outcomes.

*We use the term 'breastfeeding women' and 'breastfeeding mother' to refer to those who are providing breast milk. We acknowledge that not all people who provide breast milk identify as women or mothers, and it is important that evidence-based care for maternity, perinatal and postnatal health is inclusive.

Sarah Dib, PhD, RD

NIHR Development and Skills Enhancement Award Fellow, undertaking a placement at the National Perinatal Epidemiology Unit Clinical Trials Unit (NPEU CTU)

Honorary Research Fellow, UCL Great Ormond Street Institute of Child Health

Research Associate, Leicester Diabetes Centre and NIHR Leicester Biomedical Research Centre