Discussion
In this prospective facility-based cohort study of 1089 pregnant women receiving antenatal care and delivering at a tertiary care hospital in rural Haiti, 36% of women had preterm birth, compared with 14%–25% reported in retrospective analyses in urban Haiti,8 10 and 26% of live births resulted in a neonate that was SGA. Although there are no national estimates in Haiti for the prevalence of SGA, a large pooled analysis of nine low-income and middle-income countries found that SGA was observed in 19.3% of live births.15 We found that age less than 20 or greater than 34 years and severe household food insecurity were independently associated with greater risk of preterm birth; that age greater than 34 years, twin pregnancy and first pregnancy were independently associated with greater risk of an infant born SGA; and that number of prior abortions was independently associated with a reduced risk of an infant born SGA.
Among these factors, food insecurity, defined as a persistent lack of access to food in adequate quantity or quality,16 stands out as an important addition to the understanding of the risk of preterm birth. While food insecurity has been closely linked to a number of adverse health outcomes independent of wealth in a variety of settings and through multiple pathways beyond simply nutritional deficiency,16 17 few studies have evaluated the relationship between food insecurity and preterm birth. One recent study of 674 healthy pregnant women in urban Iran found a twofold increase in the odds of preterm birth among mothers living in food insecure households.18 Similarly, a cohort study in urban South Africa found an independent association between food insecurity and gestational age.19 Another study in the USA found an association between food insecurity and preterm birth among parous women.20
There are a number of plausible pathways by which food insecurity may increase risk of preterm birth. Food insecurity is often characterised by extended periods of time without eating, and one study in the USA found an increased risk of preterm birth for women who experienced periods without food longer than 13 hours.21 Food insecurity is associated with worse mental health and an increased stress response during pregnancy,22 23 which in turn are associated with higher risk of preterm birth.24–26 Food insecurity is likewise associated with chronic inflammation,27 28 which is also thought to play a role in preterm birth.29 In some cases, food insecurity may lead to poor maternal nutrition, a well-described risk factor for preterm birth.4 Consequences of food insecurity may be exacerbated during pregnancy because of higher nutrient demands, a greater effort required for food preparation and the possibility that pregnant women are obligated to leave the workforce, especially late in pregnancy.22
The role of food insecurity in preterm birth is especially important in Haiti, one of the most food insecure countries in the world, where more than half of the total population is chronically food insecure.30 31 While the impact of interventions targeting food insecurity on preterm birth in low-income countries has not been extensively studied, food assistance programmes in high-income countries have been associated with a reduction in preterm birth and infant mortality,32 and in this context, our findings suggest that food support has an important role to play for pregnant women who are food insecure in low-income settings. Interventions targeting food insecurity should be evaluated and implemented with a goal of improving birth outcomes, while existing food assistance programming targeting pregnant women (like that by the World Food Programme in Haiti) should be emphasised and strengthened.
The independent association we found between history of abortion and reduced risk of SGA has been previously reported once in a high-income setting and may relate to abortion being a proxy measure for socioeconomic status.33 In Haiti, women with higher socioeconomic status are much more likely to report having had an abortion, with women in the middle wealth quintile having a 3.3 times greater odds of reporting a prior abortion, and women in the top two wealth quintiles having a 7.4 times greater odds, compared with women in the bottom two wealth quintiles.34 Other studies have found a decreased risk of SGA for women from wealthier households.5 Women who have had abortions may also have longer interpregnancy periods, perhaps leaving them healthier or with increased resources during a subsequent pregnancy.
We identified a number of risk factors for preterm birth and SGA that have been reported in other settings, indicating some consistency between rural Haiti and other settings ranging from rural to urban and low to high income. The association between low and high maternal age and preterm birth has been well documented,4 although the underlying reason for this association is unknown. For older mothers, it may relate in part to a higher prevalence of other comorbidities that increase risk of preterm birth, like hypertension, diabetes and thyroid disease.4 High maternal age (potentially for similar reasons as with preterm birth), twin pregnancy (because of shared uterine environment) and first pregnancy (for both social and biological reasons) have all been found to confer increased risk for SGA in settings other than Haiti as well.5
This study is subject to some limitations. Our findings are among women who attended a facility for delivery and may not be generalisable to Haitian women who do not have a facility delivery. Women living in rural Haiti face impoverishment and limited public infrastructure and services, impacting their ability to consistently access healthcare. It is possible that women with high-risk pregnancies are more strongly encouraged to come to HUM for delivery, and thus overall rates of PTB and SGA may not reflect rates in the entire population. In a separate analysis, we found that participants who had a facility delivery had a lower probability of poverty and food insecurity compared with those who did not.14 As a result, there is risk of selection bias attenuating the identified relationship between food insecurity and preterm birth. We do not know the percent of eligible women who participated in the study or the reasons that eligible women who did not participate were not included; this may impact the generalisability of our findings. Because this study was originally intended to assess for arbovirus prevalence in pregnant women, we did not comprehensively collect maternal comorbidities and were unable to determine the specific contributions of these conditions to preterm birth and SGA. We also do not have information about maternal nutrition, which may be an important mediator between food insecurity and preterm birth. There may be additional unmeasured variables that confound the relationships between the risk factors identified in this study and preterm birth or SGA, including length of interpregnancy period, psychosocial stress, mental health, pregnancy-related factors like pre-eclampsia and others.