This prospective cohort study was carried out at the Fernandes Figueira National Institute of Women, Children and Adolescent Health, Oswaldo Cruz Foundation, Rio de Janeiro (RJ), Brazil. The study was approved by the IRB CEPIFF from Instituto Fernandes Figueira/Fiocruz Human Research Ethics Committee (CAAE 50773615.5.1001.526). Parent consent forms were obtained before data was collected from the newborn and infants. The Clinicaltrials.gov registration number is NCT00875251.
The study included mothers and their newborns born during gestational week 37 or later and hospitalized in the well-baby nursery room of the Institute’s hospital from March 2016 to August 2017. Patients with congenital malformations, genetic syndromes, exposure to TORCH congenital infections, human immunodeficiency virus and Zika virus, multiple gestations, and newborns with blood incompatibility who required phototherapy were excluded from the study.
Gestational age at birth was determined based on the first-trimester ultrasonography or the date of the last menstrual period .
The exposure variable was gestational weight gain, calculated as the difference between the pregestational weight and weight at the last prenatal visit before birth (38 ± 2 weeks). Both weights were obtained from prenatal records. The pregestational weight is the last known weight before knowledge of the pregnancy and was provided by the woman at her first prenatal appointment.
The body mass index (BMI) was obtained by dividing the mother’s pre-pregnancy weight by height squared (kg/m2) . This criterion establishes the following: for low-weight women (BMI < 18.5 kg/m2), the appropriate gestational weight gain is from 12.5 to 18 kg; for eutrophic women (BMI: 18.5–24.9 kg/m2), 11.5 to 15.9 kg; for overweight women (BMI: 25.0–29.9 kg/m2), 7 to 11.5 kg; and for obese women (BMI ≥ 30.0 kg/m2), 5 to 9 kg. Gestational weight gain was then classified as insufficient, appropriate or excessive according to the pregestational BMI based on the 2009 Institute of Medicine (IOM) criteria .
Newborn and infant growth and body composition were evaluated in the first 96 h of life and at 1, 2 and 4 months of life. Trained researchers evaluated each infant’s weight, height, head circumference (grams and Z score) and BMI, as well as FM and FFM (in grams and %).
Air displacement plethysmography (PeaPod Infant Body Composition System Life Measurement, Inc., Concord Canada, CA) was used to estimate the body composition by densitometry. Body density was used in a two-compartment model to calculate the percentage of fat mass and fat-free mass. By definition, the density of the whole body is the body mass divided by body volume. The PeaPod® is a noninvasive technique that is not only accurate and easily used by operators but also comfortable and adequate for serial evaluations of infants between birth and 6 months of age or for infants weighing up to 8 kg [14, 15]. The weight in grams was obtained using the PeaPod® high precision scale. Body length (in centimeters) was measured on a specific anthropometric scale. The head circumference (in centimeters) was measured in millimeters using an inextensible measuring tape that was well-adjusted on the supraorbital region, in front of the head and over the occipital prominence, and on the back of the head. INTERGROWTH recommendations were used for the anthropometric measurements .
The Z-score was calculated for the weight/age, height/age, and head circumference/age indexes based on growth curves proposed by the WHO in 2006 using WHO Anthro software (version 3.2.2 January 2011).
Data on the newborns and infants, such as gestational age, birth weight, sex, Apgar score and type of feeding, and maternal data, such as demographic data, occupational data, educational level, socioeconomic status, presence of chronic diseases during gestation, type of delivery, parity and smoking status, were collected from the information recorded in the medical records and prenatal card and through interviews with the puerperal women.
Gestational hypertension was defined as a systolic blood pressure ≥ 140 mmHg or diastolic blood pressure ≥ 90 mmHg at two different times during gestation [17, 18]. Gestational diabetes mellitus was characterized using the following cutoff points: fasting plasma glucose ≥92 mg/dl; one-hour plasma glucose, after the oral glucose tolerance test (OGTT) ≥ 180 mg/dl; or two-hour plasma glucose, after OGTT ≥153 mg/dl, at any time during gestation [19, 20].
A sample size of 124 participants was calculated considering the results observed by Hull et al.21 for the neonatal % fat mass (mean 11.2 ± 5,3% fat mass in the appropriate gestational weight gain group and 12,7 ± 4,6% fat mass in the excessive gestational weight gain group); the difference between the groups was 2,5% fat mass. An 80% power and 95% confidence interval were considered.
Data storage was performed using EpiData software version 3.1. The SPSS 22 program was used for data treatment and all statistical analyses.
Descriptive analysis was performed with absolute and relative frequencies for the categorical variables and measurements of central tendency and dispersion for the numerical variables. Bivariate analysis was carried out using the categories of gestational weight gain with maternal and neonatal characteristics. To evaluate the statistically significant associations, the chi-square test was used for categorical variables, and analysis of variance (ANOVA) was used for numerical variables. A linear regression model was performed to evaluate the relationship between maternal factors (gestational weight gain, gestational diabetes, gestational hypertension, and pregestational BMI) and neonatal FM and FFM. For all analyses, a significance level of 0.05 was used to identify statistically significant differences.