Postnatal growth outcomes and influence of maternal gestational weight gain: a prospective cohort study in rural Vietnam

Women who enter pregnancy with a sub-optimal body mass index (BMI) and gain either too little or too much weight have an increased risk of delivery of low birth weight and small-for-gestational age (SGA) infants, intra-uterine growth restriction, neonatal mortality, preterm delivery, still birth and congenital defects [1‐6]. Limited studies have examined the effect of gestational weight gain extending past the neonatal period into infancy or childhood, and those that are available have been conducted in high-income countries [7‐10]. Mounting evidence suggests that growth patterns in early life reflect body composition in adulthood [11], and are associated with increased risk of metabolic syndrome and the development of chronic diseases such as hypertension, coronary heart disease, and high cholesterol [12‐14].

Currently the recommended weekly weight gain during the second and third trimesters of pregnancy is 0.8 to 1 kgs/week for women with a normal pre-pregnancy BMI (18.5–24.9 kg/m²), 1 to 1.3 kgs/week for women who are underweight (pre-pregnancy BMI < 18.5 kg/m²), and 0.5 to 0.7 kgs/week for women who are overweight (pre-pregnancy BMI ≥25 kg/m²⁾ [15]. However these recommendations are based on data collected from developed countries, where the main focus is on the adverse consequences of excess weight gain during pregnancy.

In Vietnam, underweight prevalence remains significantly higher than in other South East Asian countries, with around 20% of women reported to have low BMI (<18.5 kg/m²) [16]. Determining predictors of gestational weight gain, and its influence on early infant postnatal growth, would provide an opportunity to better understand the nutritional programming of body composition in resource poor settings. This may enable appropriate targeting of preventive measures in early or pre-pregnancy, to improve child growth and development and reduce disease risk in later life.

We therefore conducted a prospective cohort study in a rural province of Vietnam that aimed to identify maternal predictors of rate of weight gain in pregnancy, and to determine the influence of rate of weight gain during pregnancy on infant growth outcomes at birth and 6 months of age.

The study flow diagram is presented in Figure 1. A total of 1258 pregnant women were enrolled into the original cluster randomised trial, 1042 women were seen at 32 weeks, and gestational rate of weight gain was available on 1041 women (82.8%). 965 infants were seen at the 6 month visit. The three arms of the trial were equally represented among infants followed until 6 months of age. Twenty-six percent (329/1257) of women were underweight at baseline (BMI < 18.5 kg/m²), and 1.4% (18/1257) were classified as overweight (BMI > 30 kg/m²). Average weekly weight gain was 0.4 kg/week [SD 0.13].

Baseline maternal characteristics according to baseline maternal BMI status are presented in Table 1. Mid upper arm circumference, meat intake during pregnancy and use of traditional supplements in early pregnancy were associated with maternal BMI at baseline.

Our findings indicate that rate of gestational weight gain was significantly associated with infant birth (weight and length) and growth outcomes at 6 months of age (weight for age, length for age, weight for length z scores weight gain velocity). We also documented a high prevalence of pregnant women residing in rural Ha Nam Province, Vietnam with a low BMI in early pregnancy. Maternal tertiary education and office-based occupation, as well as use of nutritional supplementation in early pregnancy predicted increased rate of weight gain during pregnancy. To our knowledge, this is the first study in a lower-income country to examine the influence of rate of gestational weight gain on postnatal growth outcomes.

Growth patterns in early infancy have been shown to make a significant contribution to body composition in later life, which may influence the future health and disease development in the child [11, 21]. Previous studies have demonstrated that undernutrition during the in utero period can permanently change the physiology and composition of the body either through direct effects on the cell, or as a result of altered concentrations of growth factors, hormones, distribution of cell types, metabolic activity and organ structure. These changes can then in turn increase the risk of disease such as coronary heart disease, stroke, diabetes and hypertension in adult life [12, 22‐26].

The majority of previous studies in the literature have focussed on the association between weight gain during pregnancy and outcomes at birth [1‐4, 27‐29]. Using data from seven population based cohort studies, Black et al. have shown that low maternal BMI during the pregnancy period significantly increases the risk of having a small for gestational age baby [30]. In a large cohort study in Vietnam, Ota et al. estimated the risk of giving birth to an infant too small or too large for gestational age as a function of maternal gestational weight gain and BMI, and demonstrated that a low maternal BMI and a weight gain of < 10 kg during pregnancy significantly increased the risk of delivering a small for gestational age baby [3]. Liu et al. found that women who were overweight/obese and had high weight gain, as well as those who were underweight and had a low weight gain, had a significantly higher risk of adverse pregnancy outcomes including large or small for gestational age, low birth weight and pre-eclampsia in a large cohort of singleton term pregnancies (n = 292, 568) [31]. Our findings extend those of Heerman et al. who demonstrated that the combined effect of pre-pregnancy BMI and maternal gestational weight gain was significantly associated with infant growth trajectory throughout the first year of life [32]. We also demonstrated an inverse association between baseline maternal body mass index and rate of gestational weight gain, and this has also been shown by Rode et al. who found that gestational weight gain decreased with increasing body mass index [33].

Undernutrition at different times during the gestational period has been shown to result in varying effects on growth [12, 22‐25]. Barker et al. demonstrated that undernutrition during late gestation leads to disproportionate growth, whilst undernutrition during early gestation leads to proportionate loss of body size [22]. Disproportionate growth has been shown to result in an increased risk of coronary artery disease and other non-communicable diseases [23]. Our findings strengthen the need for an urgent public health focus on improving the nutrition of pregnant women in Vietnam, and this is of particular importance in lower and middle income countries where overweight is an emerging problem and morbidity and mortality from non-communicable diseases is increasing [34].

In our study, we demonstrated a direct link between rate of weight gain during pregnancy and early infant weight gain velocity. Emerging evidence has shown that children who are undernourished or have poor weight gain during the first 2 years of life, are at significantly higher risk of chronic diseases in adulthood [14, 35, 36]. For example Hale et al. have previously proposed a thrifty ‘phenotype hypothesis’ where poor nutrition in fetal and early infant life predisposes to the later development of Type 2 diabetes through defects in the structure and function of Beta cells of the islets of Langerhans [37, 38]. Further follow up of our cohort of infants beyond the early infancy period will therefore be important, to determine the long-term adverse consequences related to inadequate gestational weight gain in this setting.

We found that nearly 30% of women had low BMI in early pregnancy, which is an indicator of chronic energy deficiency and has been shown to be related to body fat mass and fat-free mass [39]. Although the prevalence of low maternal BMI has declined globally over the past twenty years, maternal under-nutrition is still of major concern in Asia and Africa [30]. Vietnam has achieved significant and rapid economic growth in the last decade, resulting in a reduction in the prevalence of the total population living under the poverty line, and a transformation in nutritional profile of the country [17]. Over the last two decades, a significant increase in the consumption of meat, total fat and eggs among the population has been documented, and underweight prevalence (BMI <18.5 kg/m²) in women aged 20–49 years has reduced from 33.1% in 1990 to 20.5% in 2005 [16]. However, the rapid economic growth within the country has served to widen the socio-economic gap, with many of the rural population still facing significant inequities in economic, development and health burdens.

The strengths of our study are that infant anthropometric outcomes were followed past the neonatal period to six month of age, and that we measured BMI and weight gain directly, rather than rely on participant self-reporting as in many previous studies. In addition, our study was conducted in a rapidly developing rural area, representative of many areas of Vietnam, and thus our findings may be generalizable to other parts of the country.

Limitations of our study are that weight during pregnancy was only measured at enrolment and during late pregnancy (range 31–39 weeks; mean gestational age 33.4 weeks), and therefore we were unable to estimate total weight gain during pregnancy; and that maternal early pregnancy dietary habits were not accurately quantified. However despite this, the large sample size, and rigorous trial design of the original cluster randomised controlled trial, have allowed us to measure a comprehensive set of factors during the pregnancy period that predict rate of gestational weight gain, and to determine the critical influence of rate of weight gain during pregnancy on infant anthropometric outcomes.

Our findings highlight the important issue of low BMI in early pregnancy and the influence of gestational weight gain on infant outcomes in rural Vietnam. Rate of weight gain during pregnancy was found to be significantly associated with postnatal growth at six months of age, which may have adverse consequences for the infant that extend into childhood and beyond. Public health programs should be targeted towards improving nutritional status and weight gain in pregnant women in rural Vietnam.