• To assess the effectiveness of a brief intervention to encourage healthy weight gain during pregnancy.

Secondary objectives

• To assess the difference in weight gain per weeks of pregnancy between the groups.
• To compare the difference in change in total weight gain during pregnancy between the groups.
• To compare the difference in changes in psychological health, physical activity and diet quality between the groups.
• To compare the occurrence rates of common complications of pregnancy (e.g. c-section, hypertension in pregnancy and gestational diabetes) between the groups.

Study design

This study is a two group RCT with participants allocated to receive usual antenatal care only or usual antenatal care plus the intervention. Participants will be individually randomised to the trial groups. See Fig.

for trial flow

Fig. 4

Study flow diagram

Outcome measures

The primary outcome is the proportion of participants per group who exceed the IOM guidelines for gestational weight gain according to their early pregnancy BMI category from baseline to 38 weeks of pregnancy. Secondary outcomes are the difference in weight gain per weeks of pregnancy between the groups difference in total weight from baseline to 38 weeks of pregnancy between the groups and difference in changes in psychological health, physical activity and diet quality between the groups from baseline to 38 weeks of pregnancy.

Identification and recruitment of pregnant women

Women will receive the participant information leaflet from their community midwife at their first antenatal appointment or by post. Women will be advised to read the leaflet and that they may be approached to participate in the study after they have had their dating scan at 10 –14 weeks of pregnancy.

Eligible women who do not consent

The researcher at the scan clinics will record the number of women each day who are eligible but do not provide consent to participate when approached. With the verbal consent of the woman the researcher making the approach will log the BMI status, ethnicity and age of eligible women approached who do not consent to participate in the study.

Recruitment

This trial is multisite with participants recruited from four maternity centres in the UK; Birmingham Women’s NHS Foundation Trust, The Dudley Group NHS Foundation Trust, Oxford University Hospitals NHS Trust (OUH) and South Warwickshire NHS Foundation Trust where there are 7670, 4610, 6500 and 3456 births per year respectively (total yearly births 22, 236). Of these 97 % ( = 21, 568) will be of either healthy weight, overweight or obese at booking, and of these we conservatively expect 55 % to be confirmed as receiving community midwife led care ( = 12, 230) and fully eligible, demonstrating there is a very large population available from which we can recruit. We plan to enrol 610 pregnant women.

Sample size

We will recruit 610 participants, with 305 randomised to each group.

Planned inclusion criteria

• Aged 18 years or more
• Between 10+0 and 14+6 weeks of pregnancy
• Singleton pregnancy with a BMI ≥18.5 kg/m2 at the time of recruitment planned to receive community midwife led care or shared care where it is anticipated any consultant appointments will be in addition to community midwife appointments, at the time of recruitment. This criteria is included because it is important that women enrolled into the study who are randomised to the intervention group receive all the intervention contacts with their community midwife.

Planned exclusion criteria

• Women referred for consultant led care where it is anticipated that midwife appointments will be substituted by consultant appointments
• Unable to understand English or provide informed consent
• Women who are attending a weight management programme (i.e. Slimming World Whilst Pregnant)
• Current severe mental illness, known history of eating disorders or dependent on illicit drugs or alcohol

Randomisation and blinding

The telephone randomisation service at the Primary Care Clinical Research Trials Unit (PCCRTU) will be used to randomly allocate participants to trial groups. The randomisation list will be developed by a statistician within the Trials Unit using NQuery Advisor. Participants will be individually randomised to usual care plus intervention or usual care only on a 1:1 basis using random permuted blocks of random size. The list will be stratified by BMI category at recruitment (healthy weight, overweight, obese) and maternity site (Birmingham, Oxford, Dudley & Warwick). The primary outcome is measured by community midwives at routine 38 week pregnancy appointments, therefore they will not be blinded to group allocation but we have no reason to believe midwives will not record these data accurately. The trial statistician will remain blinded to group allocation until analysis is completed.