The investigators know that being overweight during pregnancy increases the health risks to both mum and baby. There is good evidence that diet or exercise, or both, during pregnancy can reduce excessive weight gain. The Best Start study aims to test the theory that obese pregnant women with a Body Mass Index (BMI) of 30 or over who participate in a structured programme of nutrition and lifestyle advice (Foodwise in Pregnancy ™) will achieve the recommended weight gain during pregnancy of no less than 5kg and no more than 9.1kg.

The investigators would like to find out if pregnant women with a BMI of 30 or over who receive the Best Start intervention are more likely to effectively manage weight gain during pregnancy. To achieve this, the investigators will undertake a trial that randomly puts participants into an experimental group, or a control group, which will compare those who receive the intervention to those who continue with routine antenatal care. The investigators are aiming to recruit around 500 women during the study period. 250 will receive the Best Start intervention, and 250 will continue with routine antenatal care.

The investigators would also like to find out if women who gain the recommended weight during pregnancy have better outcomes, compared to women who gain more or less weight. To do this the investigators will look at the routine information collected during antenatal and postnatal care, for both mum and baby. To do this regardless of the group clients are randomised to, the investigators will ask for permission to look at the routine information within the participants maternity record. This information includes, weight gained during pregnancy, whether the baby is born early, the type of labour and delivery, and any complications during the pregnancy or delivery that may have resulted in the need for additional care for mum or baby.

The results of the study will be prepared for publication in scientific journals, and for presentation at scientific conferences. All participants will be able to obtain a copy of the results once they have been published and any information that could identify participants will be removed.

The intervention will invite obese pregnant women with a BMI ≥30 to participate in a research study where participants may be offered a programme of nutrition and lifestyle advice, unless participants meet the exclusion criteria.

The programme of nutrition and lifestyle advice will comprise a series of weekly 7 x 2 hour group sessions, which will be delivered in community venues by trained Healthy Lifestyle Support Workers (HLSWs) employed within the maternity service.

The group sessions will follow the scripted "Foodwise in PregnancyTM" manual of nutrition information; practical cooking sessions; and information on low impact exercise e.g. walking. 'Foodwise in PregnancyTM' has been developed by a group of NHS Dietitians and Midwives and is adapted from the existing Foodwise for Life programme. Pedometers will be provided at session three to raise participants awareness of the benefits of physical activity. The programme is participative in its approach to experiential learning.

The group sessions will also promote breastfeeding (All Wales Maternity Strategy Key Performance Indicator/Measure) to assist healthy weight gain for babies, healthy weaning and the importance of play and physical activity. Delivery of the sessions will be quality assured by a specialist public health dietitian and public health midwife employed within Cwm Taf University Health Board.

Because eligible women will initially be referred by a midwife, all midwives will be trained by a public health dietitian on the "Eating for 1, Healthy and Active for 2" Royal College of Midwives accredited compact training, to ensure a sensitive and effective conversation (using motivational interviewing techniques) that raises the issue of excess weight in pregnancy. The Healthy Lifestyle Support Workers, delivering the intervention, will also attend this training.

Inclusion Criteria:

• Pregnant women who at their early pregnancy dating scan (optimum time 12 weeks gestation, but with a tolerance of up to 16 full weeks gestation for women who book late) have a BMI of 30 or over and reside in Cwm Taf University Health Board area.
• Aged over 16.
• Capable of giving informed consent.
• Singleton and multiple pregnancies.

Exclusion Criteria:

• Pregnant women who at their early pregnancy dating scan (optimum time 12 weeks gestation, but with a tolerance of up to 16 full weeks gestation for women who book late) have a BMI of less than 29.9 and reside in Cwm Taf University Health Board area.
• Aged under 16.
• Incapable of giving informed consent.
• Any women who have pre-existing diabetes, or develop gestational diabetes during their pregnancy.
• Any health condition that means the health professional looking after the patient feels would contra-indicate involvement in this programme (e.g. losing the ability to consent during the programme)

Study findings will be disseminated via The Burdett Trust for Nursing, Cwm Taf University Health Board, Public Health Wales NHS Trust, health boards and interested clinicians and submission of a paper to a scientific journal for peer-review e.g. the British Journal of Midwifery.

The results of our study will be prepared for publication in scientific journals, and for presentation at scientific conferences. All participants will be able to obtain a copy of the results once they have been published, no patient identifiable information will be included.

It is anticipated that the initial study findings will be available for dissemination by approximately January 2021.

The final Statistical Analysis Plan (SAP) is still to be determined.

Access criteria is still to be determined.