Maternal Height Nutritional Status and Dysfunctional Labor

Unlike in developed countries, where it is no longer a cause of maternal mortality, obstructed labor is a cause of death in 10-15% of women in the developing world [11]. The inverse relationship between maternal height and the risk of dystocia (difficult labor) due to cephalopelvic disproportion (CPD) obstructed labor due to a disparity between the dimensions of the fetal head and maternal pelvis or assisted/caesarean-section deliveries is frequently described but has been weak. A meta-analysis of nine studies found low sensitivity and specificity of low maternal height (<20th percentile) in predicting the risk of dystocia [74]. Because the prevalence of caesarean section in developing countries is low (at about 2%), the predictive value of low maternal height for caesarean section as an outcome is only 5%. Further, the relationship between maternal height and dystocia appears to be relative and not absolute. Height in the analysis was expressed in percentiles and, thus, the absolute value of a 20th percentile differed in different populations despite the risk of dystocia at that cutoff being of the same magnitude. In practical terms, therefore, using a single value of height as a cut-off would not be appropriate for predicting the risk of dysfunctional labor. In an earlier WHO meta-analysis of 16 studies, the odds of nonspontaneous deliveries, including caesarean section, was 60% higher among women in the lowest height quartile compared with those in the highest quartile [75].

The size of the fetus is also a cofactor in this relationship. Harrison et al. [76] showed that the risk of operative delivery was associated with both maternal height and the size of the baby; low maternal height and high birth weight increased the risk of operative delivery (Fig. 21.4).

However, maternal height, which is correlated with uterine volume, is a strong predictor of birth weight, and thus it is unlikely that the shortest women would produce truly large babies. But in underserved settings, the risk of obstructed labor may increase even at a birth weight that would be considered "normal" in a developed country [77]. Evidence that interventions such as food supplementation during pregnancy, aimed at improving birth weight in malnourished settings, can increase the risk of CPD or obstructed labor, however, is lacking. There was no evidence of an increased risk of CPD or complications in delivery in an antenatal food supplementation trial in the Gambia in which birth weight increases ranged from 100 to 200 g, [78]. The largest increase in head circumference, where head size was more strongly correlated with CPD than birth weight per se [13], was only 3 mm. This translates to an increase of only 1 mm in diameter, which is unlikely to raise the prevalence of CPD. Perinatal mortality was reduced due to maternal supplementation, further attesting to the lack of evidence for any harmful outcome as a result of the increase in birth weight but rather a benefit [78]. Whether these findings can hold in more malnourished South Asian settings where maternal stunting is more prevalent is

Maternal height (m)

Fig. 21.4. Rate of operative delivery by maternal height and birth weight. (From [76])

Maternal height (m)

  1. 21.4. Rate of operative delivery by maternal height and birth weight. (From [76])
  2. In two recent randomized controlled trials of antenatal multiple micronutrient supplementation in rural Nepal, mean birth weight improved by about 60-100 g [79, 80]. However, neonatal mortality was slightly, although not significantly, elevated in both studies, an increase that was significant when the data were pooled [81]. When treatment effects were examined by percentiles of birth weight in one of the studies, it was apparent that maternal multiple micronutrient supplementation increased birth weight both in the lower and upper tails of the distribution [82]. The increase on the upper tail may explain the increased risk of birth asphyxia and mortality in these infants as a result of maternal micronutrient supplementation [83]. However, other mechanisms may have also resulted in an adverse effect of the intervention on infant outcomes. Currently antenatal micronutrient supplementation beyond iron-folic acid is being evaluated for its safety and efficacy in the developing world.

Addressing the problem of short maternal stature and stunting is important for improving reproductive health in the developing world. However, few interventions are known to influence maternal height. Food supplementation between 6 and 24 or even up to 36 months of age may promote accelerated linear growth, but interventions beyond this period do not show further benefit [84]. Interventions during school age or adolescence appear to only modulate onset of menarche [5]. Based on adoption studies, relocation from environments that give rise to stunting may promote catch up growth but only among younger children (<2 years old) [84, 13]. In older adopted children accelerated maturation (early onset of menarche) resulted in a shorter growth period that led to little overall benefit in terms of attained height. Based on data from nine European countries, mean age at menarche has decreased in Europe by 44 days (18-58) as indicated by follow-ups of 5-year birth cohorts (youngest cohort: 1915-1919, oldest cohort: 1960-1964) [85]. Simultaneously, European women have grown taller over time, from 0.42 to 0.98 cm per 5-year birth cohort. However, women grew 0.31 cm taller when menarche occurred a year later due to the later closure of the epiphyseal plates of the long bones following onset of menarche. Will a decrease in the age of onset of menarche in the developing world as a result of nutrition interventions result in yet a shorter period of growth as suggested in adoption studies? This is an intriguing question.

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