Introduction

Obesity represents a significant health burden, and WHO recognises the importance of preventing weight gain and subsequent development of obesity among adults who are within the healthy weight range. Women of reproductive age have demonstrated high rates of weight gain during pregnancy placing them at risk of becoming overweight or obese. We will evaluate the effects of dietary and physical activity advice on maternal, fetal and infant health outcomes, among pregnant women of normal body mass index (BMI).

Methods and analysis

We will conduct a randomised controlled trial, consenting and randomising women with a live singleton pregnancy between 10⁺⁰ and 20⁺⁰ weeks and BMI 18.5–24.9 kg/m² at first antenatal visit, from a tertiary maternity hospital. Women randomised to the Lifestyle Advice Group will receive three face-to-face sessions (two with a research dietitian and one with a trained research assistant) and three telephone calls over pregnancy, in which they will be provided with dietary and lifestyle advice and encouraged to make change using a SMART goals approach. Women randomised to the Standard Care Group will receive routine antenatal care. The primary outcome is infant birth weight >4 kg. Secondary outcomes will include adverse infant and maternal outcomes, maternal weight change, maternal diet and physical activity changes, maternal quality of life and emotional well-being, fetal growth and costs of healthcare. We will recruit 624 women to detect a reduction from 8.72% to 3.87% (alpha 0.05 (two-tailed); power 70%) in infants with birth weight >4 kg. Analyses will be intention to treat with estimates reported as relative risks and 95% CIs.

Ethics and dissemination

Ethical approval has been obtained from the Women’s and Children’s Hospital ethics committee. Findings will be disseminated widely via journal publication and conference presentation(s), and participants informed of results.

Trial registration number

ACTRN12614000583640.