# **_4.1 Prenatal risk factors_**

In the prenatal period, fetal growth is governed by the mother’s nutrition, endocrine and metabolic signals, and placental development. Newborn birth weight and gestational age reflect the intrauterine environment. While low birth weight (LBW, defined as < 2500g) is used as a proxy for undernutrition in utero, it really encompasses two related phenomena that have distinct underlying causes: small for gestational age (SGA)<sup>14</sup> and preterm delivery. SGA describes a fetus that is smaller than expected for the number of weeks in pregnancy and is closely associated with fetal growth restriction (FGR). Preterm denotes live births that occur before 37 weeks of completed gestation. Filipino newborns are among the world’s most likely to be born too small or too soon. An estimated 15 percent of live births in LMICs are LBW, with LBW prevalence highest in South Asia (25.6 percent), Sub-Saharan Africa (14.2 percent) and Southeast Asia (12.2 percent).<sup>15</sup> In the Philippines, the 2017 Demographic and Health Survey (DHS)<sup>16</sup> estimated 14.5 percent of live births were LBW, suggesting a significant drop since 2011 when LBW prevalence was estimated at 21.4 percent. Using data from the INTERGROWTH-21st project,<sup>17</sup> a recent study examined the global prevalence and burden of smallfor-gestational-age (SGA) and estimated that in 2012, 25.6 percent of Filipino newborns were SGA and that 22.7 percent of neonatal deaths were attributable to SGA (either term or preterm), placing the Philippines among the 10 countries globally with the highest SGA burden.<sup>18</sup> Recent global and national estimates<sup>19</sup> suggest preterm birth prevalence in the Philippines was in the range of 13.3 percent in 2014 and more than doubled since 2000.<sup>20</sup> Among SGA live births, 7 percent (or 1.8 percent among all live births) were also delivered preterm. The Philippines ranks 9th globally for the share of live births that are preterm and 3rd for the share of live births that are both SGA and preterm.

Using data from 19 birth cohorts and longitudinal studies representing countries in 3 LMIC regions (including the Cebu, Philippines cohort), Christian et al. explore the relationship between SGA and preterm birth with stunting between the ages of 12 and 60 months.<sup>21</sup> The study finds that the risk of stunting associated with LBW, SGA and preterm – even when adjusting for characteristics of the mother - is significantly elevated compared to appropriate for gestational age (AGA) and term births, with the risks being compounded for births that are both SGA and preterm. For example, for birth cohorts in the Southern/Eastern Asia region, the odds ratios (ORs) for stunting associated with LBW, SGA and preterm were 2.64, 2.13 and 1.34. Babies born both SGA and preterm had even higher odds of stunting (OR 3.63) compared to babies born AGA and term. Given that the study did not find significant variation in these associations by region, the authors consider highly plausible that the associations are biological. The combined population attributable risk for stunting from SGA was 0.16, suggesting that close to one-fifth of childhood stunting could have its origins in the fetal period.

Available evidence suggests that SGA (both term and pre-term) is strongly associated with maternal height and low BMI which are in turn associated with adolescent health and pregnancy. A pooled analysis of DHS data from 109 countries adjusting for socioeconomic characteristics, such as the wealth of the household and education of the mother, found a strong relationship between maternal height and stunting<sup>22</sup> : children of mothers measuring 145 cm or less had an 80.5 percent probability of being stunted, compared to 18.9 percent for children of mothers measuring 160 cm or more, controlling for other factors. Other studies have established links between maternal birth outcomes – such as birthweight and SGA – with offspring outcomes including stunting. A study using the Cebu longitudinal health and nutrition survey conducted between 1983 to 1995 in the Philippines reinforces this evidence, finding that the likelihood of stunting is inversely related to mother’s height and low birth weight.<sup>23</sup> 20