Risk stratification for small for gestational age for the Brazilian population: a secondary analysis of the Birth in Brazil study

Abstract

Risk-stratification screening for SGA has been proposed in high-income countries to prevent perinatal morbidity and mortality. There is paucity of data from middle-income settings. The aim of this study is to explore risk factors for SGA in Brazil and assess potential for risk stratification. This population-based study is a secondary analysis of Birth in Brazil study, conducted in 266 maternity units between 2011 and 2012. Univariate and multivariate logistic regressions were performed, and population attributable fraction estimated for early and all pregnancy factors. We calculated absolute risk, odds ratio, and population prevalence of single or combined factors stratified by parity. Factors associated with SGA were maternal lupus (ORadj 4.36, 95% CI [2.32–8.18]), hypertensive disorders in pregnancy (ORadj 2.72, 95% CI [2.28–3.24]), weight gain < 5 kg (ORadj 2.37, 95% CI [1.99–2.83]), smoking at late pregnancy (ORadj 2.04, 95% CI [1.60–2.59]), previous low birthweight (ORadj 2.22, 95% CI [1.79–2.75]), nulliparity (ORadj 1.81, 95% CI [1.60–2.05]), underweight (ORadj 1.61, 95% CI [1.36–1.92]) and socioeconomic status (SES) < 5th centile (ORadj 1.23, 95% CI [1.05–1.45]). Having two or more risk factors (prevalence of 4.4% and 8.0%) was associated with a 2 and fourfold increase in the risk for SGA in nulliparous and multiparous, respectively. Early and all pregnancy risk factors allow development of risk-stratification for SGA. Implementation of risk stratification coupled with specific strategies for reduction of risk and increased surveillance has the potential to contribute to the reduction of stillbirth in Brazil through increased detection of SGA, appropriate management and timely delivery.

Performances of birthweight charts to predict adverse perinatal outcomes related to SGA in a cohort of nulliparas

“…These differences may contribute to the higher incidence of SGA neonates born to nulliparous women. A possible reason for the poor accuracy in identifying SGA neonates with adverse outcomes born to nulliparous women is that although this population is associated with a higher risk of SGA [ 4 ], those neonates may comprise both constitutionally small and growth-restricted infants. Nulliparous women may be more likely to have constitutionally small infants with mild/no increase in risk of neonatal morbidity [ 29 ].…”

“…Birthweight centiles were calculated using international population charts such as the birthweight chart from Intergrowth-21 st , the birthweight chart from WHO-Fetal Growth Charts (WHO-FGC) [ 8 , 9 ], the Birth in Brazil population chart [ 4 ] and the GROW customised birthweight chart (GROW) [ 11 ]. Assuming the representativeness of the Brazilian population, the Birth in Brazil chart was considered the reference method for comparison.…”

“…Many factors are known to be associated with an increased risk of SGA, such as nulliparity, malnutrition, extremes of maternal age, and tobacco and/or drug use, among others. According to a study based on a large Brazilian population, nulliparity was a significant risk factor for SGA (OR 1.81, 95%CI: 1.60–2.05) with a population attributable fraction of 24%, meaning that 24% of SGA could be attributed to nulliparity [ 4 ].…”

“…International birthweight standards, such as the Intergrowth-21 st study charts and the WHO-Fetal Growth Charts study, are based on a ‘healthy’ sample composed of well-nourished pregnant women, without important risk factors for fetal growth abnormalities [ 8 , 9 ]. The birth weight chart from the Birth in Brazil study is a population standard developed and based on a retrospective analysis that excluded high-risk pregnancies from a large cohort recruited through a complex sampling strategy to represent the Brazilian population [ 10 ]. In addition, there are customised growth charts that use a pregnancy-related optimal weight (GROW) software [ 11 ], adjusting not only for neonatal but also maternal characteristics including age, maternal weight, maternal height, parity and ethnicity to provide an individual assessment of fetal growth [ 12 ].…”

“…The current study aimed to describe the prevalence of SGA in nulliparous women according to different birthweight charts from the INTERGROWTH-21 st Project [ 9 ], the birth weight chart from World Health Organization—Fetal Growth Charts (WHO-FGC) [ 8 ], the Birth in Brazil population chart [ 4 ] and the GROW-customised growth chart [ 12 ] and evaluate the diagnostic performance of these charts to identify adverse perinatal outcomes using different thresholds to define small infants using a cohort of nulliparous women.…”