Ethnic and environmental factors affecting fetal growth in Papua New Guinea

Cause of fetal growth restriction during high-altitude pregnancy

High-altitude pregnancy increases the incidence of fetal growth restriction and reduces birth weight. This poses a significant clinical challenge as both are linked to adverse health outcomes, including raised infant mortality and the development of the metabolic syndrome in later life. While this reduction in birth weight is mostly understood to be driven by the hypobaric hypoxia of high altitude, the causative mechanism is unclear. Moreover, it is now recognized that highland ancestry confers protection against this reduction in birth weight. Here, we analyze the evidence that pregnancy at high altitude reduces birth weight and that highland ancestry confers protection, discussing mechanisms contributing to both effects.

Azithromycin-containing intermittent preventive treatment in pregnancy affects gestational weight gain, an important predictor of birthweight in Papua New Guinea - an exploratory analysis

In Papua New Guinea, intermittent preventive treatment with sulphadoxine-pyrimethamine and azithromycin (SPAZ-IPTp) increased birthweight despite limited impact on malaria and sexually transmitted infections. To explore possible nutrition-related mechanisms, we evaluated associations between gestational weight gain (GWG), enrolment body mass index (BMI) and mid-upper arm circumference (MUAC), and birthweight. We investigated whether the increase in birthweight associated with SPAZ-IPTp may partly be driven by a treatment effect on GWG. The mean GWG rate was 393 g/week (SD 250; n = 948). A 100 g/week increase in GWG was associated with a 14 g (95% CI 2.6, 25.4) increase in birthweight (P = 0.016). Enrolment BMI and MUAC also positively correlated with birthweight. SPAZ-IPTp was associated with increased GWG [58 g/week (26, 900), P < 0.001, n = 948] and with increased birthweight [48 g, 95% CI (8, 880), P = 0.019] when all eligible women were considered (n = 1947). Inclusion of GWG reduced the birthweight coefficient associated with SPAZ-IPTp by 18% from 44 to 36 g (n = 948), although SPAZ-IPTp was not significantly associated with birthweight among women for whom GWG data were available (P = 0.13, n = 948). One month post-partum, fewer women who had received SPAZ-IPTp had a low post-partum BMI (<18.5 kg m(-2) ) [adjusted risk ratio: 0.55 (95% CI 0.36, 0.82), P = 0.004] and their babies had a reduced risk of wasting [risk ratio 0.39 (95% CI 0.21, 0.72), P = 0.003]. SPAZ-IPTp increased GWG, which could explain its impact on birthweight and maternal post-partum BMI. Future trials of SPAZ-IPTp must incorporate detailed anthropometric evaluations to investigate mechanisms of effects on maternal and child health.

Causes of preterm delivery and intrauterine growth retardation in a malaria endemic region of Papua New Guinea

AIM

To identify causes of preterm delivery and intrauterine growth retardation (IUGR) in a malaria endemic region of Papua New Guinea.

METHODS

Independent predictors of preterm delivery and birthweight in term infants were identified using multiple regression analysis in a prospective study of 987 singleton live births delivered in Madang Hospital.

RESULTS

Overall, Plasmodium falciparum infection of the placenta was associated with a reduction in birthweight of 130 g. Malaria was significantly more common in primigravidae than multigravidae and probably contributed to both preterm delivery and IUGR. Maternal haemoglobin concentrations were significantly lower in malaria infected than noninfected women and reduced haemoglobin was the main determinant of preterm delivery. Poorer maternal nutritional status and smoking were associated with both prematurity and IUGR. Greater antenatal clinic attendance predicted increased birthweight in term infants.

CONCLUSIONS

Protection against malaria during pregnancy, especially in primigravidae, improved nutrition in women and discouragement of smoking would probably reduce both preterm delivery and IUGR. Greater use of existing antenatal clinics might increase birthweight in term infants.

Anaemia- and malaria-attributable low birthweight in two populations in Papua New Guinea

We studied 7300 singleton births in the highlands and 4881 in coastal Papua New Guinea in order to examine the separate contribution of anaemia or malaria to low birthweight. The highland sample was selected from a non-malarious area (Goroka) and the coastal sample from an area with perennial malaria transmission (Madang). There was an approximately three-fold increased risk of low birthweight (< 2500 g) in live-births in Madang compared to Goroka. The prevalence of anaemia in the two areas was strikingly different, with 29.2% of Goroka and 89.0% of Madang women anaemic. There was a trend towards increased low birthweight with decreasing haemoglobin levels in both areas, but this was significant only for Madang. It was assumed that for a given haemoglobin level the increased low birth weight percentage in Madang compared to Goroka was due to malaria exposure, and on this basis relative risk values were estimated for the effect of malaria exposure on low birthweight. Using this approach separate estimates for anaemia and malaria population-attributable risk for low birth weight in Madang were calculated. These indicated that up to 40% of low birthweight babies born in malarious areas may be attributable to malaria and less than 10% attributable to severe anaemia (Hb < 7.0 g dl-1). The magnitude of the malaria effect estimated in this analysis places a high priority on malaria control in pregnancy as a strategy for improving birthweight and child survival.

Longitudinal weight growth patterns in the highland fringes of West Sepik Province, Papua New Guinea: a comparison of three groups

Longitudinal weight growth data from three groups in West Sepik Province, Papua New Guinea, are compared. A form of analysis based on the four-parameter Jenss curve is adopted, to allow intelligible comparisons of parameter means despite irregular weighing schedules for individual children. Although many weighing records include notes of a child's ill-health (e.g. malaria), omission of these weighings does not have a large effect on the results. Some significant sex differences were found, but do not appear to be importantly confounded with group differences. Of the three groups compared, the East Mianmin live at moderate altitude, the Imnai live at low altitude, and the West Mianmin are a migrant group from moderate to low altitude. In principle the analysis could have shown the groups to be differentiated by altitude of current residence (suggesting the influence of environmental factors), by altitude of ancestral residence (suggesting the influence of genetic and/or cultural factors) or by some interaction of causal factors. Findings on most parameters suggest interaction. Neither moderate nor low-altitude conditions appear consistently more favourable to rapid growth; it is suggested that the advantage of a more favourable disease environment at moderate altitude may be at least partially offset by a nutritional disadvantage. The effect of environmental conditions may also be non-uniform, especially for young infants, since infants of the migrant group, the West Mianmin, are born heaviest but grow more slowly in the early months than infants of either non-migrant group.