The design of the intervention corresponds to a classic RCT, a design that allows us to prospectively study pregnant women, in which it is intended to compare the effect of the intervention versus the control condition, to establish a cause-and-effect relationship. This design allows us to reduce the risk of comparability bias. The study will be carried out with pregnant women who control their pregnancy in Family Health Centers (CESFAM) of the Metropolitan Region (the capital city of Chile) and the Aconcagua Valley, Valparaiso Region (88 km to the north of the capital). The CESFAM work under the Comprehensive Health Model with a Family and Community Approach, focusing on prevention and health promotion, and are responsible for basic health care, including home care and health rehabilitation actions. These centers focus on families and communities, give importance to community participation, and work with a primary health team that attends to the whole family in health and sickness throughout the life cycle.

Pregnant women enrolled in the prenatal control program receive routine care at the CESFAM.

Pregnant women enrolled in the prenatal control program receive routine care at the CESFAM and messages on nutrition (intervention).

Chilean- or Spanish-speaking immigrant pregnant women older than 18 years who receive care at the 6 CESFAM in El Bosque, Metropolitan Region and in Segismundo Iturra CESFAM in San Felipe, Aconcagua Valley, Valparaiso Region; who have gestational ages ≤12 weeks (first trimester); who have a single pregnancy; who declare to have a normal pregnancy at the time of starting the intervention; who agree to be randomized; and who have voluntarily signed the informed consent can participate in this study. The pregnant women who participate in the study must have a mobile device that allows the use of MMS.

Exclusion criteria include multiple pregnancies, conditions requiring a special diet, participants with psychiatric illnesses or other prepregnancy pathology, and a history of recurrent miscarriages.

The total sample consists of 511 participants, which will be divided into 2 groups. In the El Bosque CESFAM, 280 pregnant women were recruited, with an estimated dropout rate of 30% (based on the pilot study carried out) to guarantee the required sample size of 210 pregnant women with a confidence level of 90% and a 5% error. At Segismundo Iturra CESFAM, 231 pregnant women were recruited, with the same estimated dropout rate, to ensure a sample size of 178 pregnant women with a confidence level of 90% and a 5% error. For the calculation of the sample size, the official records of the DEIS regarding the number of pregnant women between 20 and 44 years of age who were treated for prenatal control in the CESFAM of the El Bosque commune and Segismundo Iturra were considered. The recruitment period will be 6 months.

The pregnant women who meet the inclusion criteria are invited to participate in the study, as are those who accept and sign the informed consent form. These pregnant women receive the link to the diagnostic survey on their telephones and are then randomized to be included in the intervention. At the end of each month of the recruitment period, the researchers will randomize the pregnant women who were recruited during that month. A stratified randomization will be carried out to ensure a sample that is as balanced as possible. The sample will be divided into 4 strata according to their pregestational weight, classifying them as underweight (BMI<18.5 kg/m²), normal weight (BMI 18.5-24.9 kg/m²), overweight (25-29.9 kg/m²), and obese (BMI≥30 kg/m²). Simple random selection will be carried out then by generating a table of random numbers without repetition, from 1 to n, and deciding a priori that it will be read from left to right, with even numbers assigned to the control group and odd numbers to the intervention group.

A single-blind study will be carried out since the CESFAM personnel who will oversee the recruitment will be blinded to the randomization of the subjects to avoid bias in routine care.

The recruitment of pregnant women will be done for a period of 6 months. The study will end when all the participants with intervention have completed the 12-week message period.

Immediately after randomization, the researchers will send the MMS with the link that leads to a web-based survey. The survey will be the same for the control group and intervention group and will recollect demographic information, nutritional habits, and physical activity. Pregnant women in the intervention group who respond to the survey will receive the intervention messages by MMS.

Routine care visits will be scheduled usually by CESFAM’s midwifery professionals. Such visits should occur monthly until the 28th week of gestation, biweekly during the 28-36 weeks of gestation, and weekly until delivery. During prenatal control, the nutritional evaluation is carried out according to the technical standard, and a referral to a nutritionist is made if necessary. These care visits may also include participation in the “Elige Vivir Sano” and “Chile Crece Contigo” programs and everything associated with the prenatal control program.

The intervention consists of 3 MMS messages with nutritional information per week for 12 consecutive weeks. The messages were reviewed by a perinatal psychologist. The messages will be sent as follows: Monday at 3 PM, the message that addresses the cognitive domain will be sent; Tuesday at 3 PM, the message that addresses the affective domain will be sent; and Thursday at 3 PM, messages that address the psychomotor domain, together with the weekly user satisfaction survey, will be sent. This delivery scheme was validated in the pilot study that was carried out. The 12 topics related to nutrition during pregnancy will be addressed, 1 will be addressed per week, and 3 messages will be sent for each topic. At the beginning of each month, messages will be sent to pregnant women who were recruited during the immediately previous month. In the development of the project and to prevent pregnant women from incurring additional expenses for participating in the intervention, we will directly recharge the phones of the users who participate in the study.

The team of midwives will keep a record of the weight of the pregnant women who attend their prenatal checkups monthly. Therefore, the monitoring of the weight of both groups will be done through the midwives in order not to request sensitive data via MMS.

A record of the number of pregnant women who drop out of the study will be kept, as well as their characteristics for subsequent statistical analysis.

The primary outcome will be to assess the effectiveness of the mHealth mami-educ intervention in reducing the incidence of eGWG compared to routine care. Secondary outcomes will include identifying the barriers and facilitators influencing weight gain in pregnant women to compare the maternal outcome of pregnancy, in terms of complications developed during pregnancy (pre-eclampsia, gestational diabetes, and gestational hypertension), and the perinatal outcomes (prematurity and birth weight) of the pregnant women in the control and intervention groups.

The data analysis plan will be governed by the intention-to-treat principle, as we will include all participants who were randomly assigned after recruitment, assuming that participants who drop out are treatment failures. The effectiveness of the treatment will be measured using the chi-square test (χ²), comparing the intervention group with the control group in terms of the percentage of women who are classified as having excessive weight gain at the end of pregnancy. To confirm the effectiveness of the intervention, a significant decrease (P<.001) of women with eGWG in the intervened group will be expected. For data analysis, the statistical software GraphPad Instat 3.0b and GraphPad Prism 6.0f (GraphPad Software Inc) will be used. P<.001 (determined by a 2-sided test) will be considered statistically significant.

This research will be conducted in accordance with the Declaration of Helsinki. The study was approved by the Scientific Ethics Committee of the Aconcagua Health Service (protocol number: 26/2021, approved October 12, 2021) and the Scientific Ethics Committees of the South Metropolitan Health Service (protocol number: 07-27012022, approved February 7, 2022). Informed consent will be obtained from all participants invited to participate in the study before proceeding with the initial survey. The data will be treated respecting the ethical principles that guarantee the anonymity of the participants.

It is well known that pregestational obesity has been recognized as a risk factor for several perinatal complications, such as fetal macrosomia, gestational diabetes, hypertensive disorders, failed induction, premature rupture of membranes, and cesarean section [38]. Nevertheless, this risk is increased when eGWG is present [39,40]. Prevention strategies in primary care are key to fighting this problem; in this regard, strategies that target behavior change by promoting self-efficacy have been proposed [37]. A recent study conducted focus groups with 66 women between 16 and 24 weeks’ gestation [19], and the participants expressed that the difficulties in operationalizing the information in the guidelines and that provided by health care providers were one of the important barriers to self-care. For this reason, care providers’ advice on nutrition and physical activity was perceived as minimal and ineffective. We propose the integration of social cognitive theory with mHealth to provide nutritional information to pregnant women in primary care. In this study, the structure of the messages addresses 3 learning domains (cognitive, affective, and psychomotor) that promote self-efficacy [37]. The hypothesis of this study is that the mHealth intervention called mami-educ is effective in reducing eGWG in pregnant women who attend family health care centers in an urban area and another predominant rural area. From a public policy perspective, effective health communication is very important; mHealth provides fast, easy-to-use, and cost-effective communication. We designed this study to address the gap in evidence-based primary prevention strategies regarding the use of mHealth to reduce eGWG. Overall, this proposal has the potential to reduce the incidence of perinatal complications through adequate gestational weight gain. To ensure the reproducibility of the study for future research and reduce the risk of comparability bias, the design of the intervention corresponds to a classic RCT. This design allows us to carry out a prospective study of pregnant women in which it is intended to compare the effect of the intervention versus the control condition to establish a cause-and-effect relationship.

The results of this study may serve to implement evidence-based primary prevention strategies and help a broader group of pregnant women maintain adequate weight gain during pregnancy and prevent pregnancy pathologies associated with obesity. This would ultimately influence health care costs. In Chile, it has been described that the cost of overweight and obesity increases to US $455 million by year, representing 2% of the total health budget, which means that obesity costs 4-fold higher than normal weight health care [41]. Through this observation, the projected health costs for 2030 related to overweight and obesity will reach 3.4% of the total health budget (US $3 billion). Furthermore, it is estimated that a weight reduction of 7%-10% in the obese population would translate into a 40% decrease in spending on obesity-associated comorbidities [42]. Thus, promoting adequate weight gain during pregnancy in women with obesity could improve maternal, fetal, newborn, and offspring health and could significantly reduce public health care costs. Lastly, the data collected in this study can play a central role in the development of public policies based on mHealth directed exclusively to the population of pregnant women.

A limitation of this study is the reliance on smartphones to access interventions. In addition, the recruitment of pregnant women must occur during the first trimester of gestation, and this may be hindered because some pregnant women begin prenatal care in the second trimester. Another limitation is that the pregnant woman may decide not to interact with the messages by blocking the number of the intervention.