Pre-eclampsia

Chapter 6 Table 17: Performance of indicators for assisted delivery Assisted delivery Indicator Counta Min Sea Max Sea 1. Maternal height 5/13 0.30 0.52 2. Pre-pregnancy weight 3/10 0.30 0.42 3. Attained weight by month 5 2/11 0.38 0.67 4. Attained weight by month 7 2/11 0.30 0.33 5. Attained weight by month 9 1/12 0.35 0.35 6. Mid-upper-arm circumference 0/9 7. Weight gain: months 5 to 7 1/9 0.46 0.46 8. Weight gain: months 5 to 9 1/8 0.38 0.38 9. Weight gain: months 7 to 9 1/10 0.47 0.47 10. Weight gain: pp to month 5 0/9 11. Weight gain: pp to month 7 0/8 12. Weight gain: pp to month 9 0/8 13. Pre-pregnancy BMI 2/10 0.31 0.32 14. BMI month 5 1/10 0.31 0.31 15. BMI month 7 1/10 0.33 0.33 16. BMI month 9 1/10 0.32 0.32 a 'Count' gives the fraction of data sets in which the Se/Sp cri- terion was met. The absence of an asterisk, denotes that no indicator met this criterion (Se >0.3 and Sp >0.7) in more than 40% of the relevant studies. The observed maximum and mini- mum sensitivities across studies that meet the Se/Sp criterion are recorded in the final two columns. ered reliable indicators of a lowered probability of assisted delivery in the context of this study. It is perhaps surprising that maternal height does not emerge as a stronger indicator of assisted delivery, given service experience of risk associated with low maternal height (22). It will be recalled, however, that odds ratios calculated in this study are estimated on the basis of comparison of outcome frequency between the lower and upper quartiles of the indica- tor distribution. The 25th percentile cut-off would contain women of low, as well as critically low (<140 cm) stature, thus diluting the expected high risk of cephalo-pelvic disproportion and consequent need for assisted delivery. Analysis using upper and lower deciles do show a more powerful predictive capacity for maternal height. Pre-eclampsia Definition. No generally accepted definition for hypertensive disorders of pregnancy exists. The WHO Hypertensive Collaborative study recommen- ded the following diagnostic criteria: diastolic pres- sure >90 mmHg, proteinuria, and/or presence of oede- ma. Only 11 data sets were analysed with respect to this outcome-the WHO collaborative studies and the data from Colombia, to ensure equivalent definitions. Prevalence ranged from below 1% to 15% (see Table 8, Chapter 3, page 16). As oedema is associated with the development of pre-eclampsia, rapid weight gain during the latter half of pregnancy may be observed. As such, our analysis might be expected to show a low relative risk for those mothers with low weight gain in mid to late pregnancy. The summary table (Table 18) shows the range of combined ORs for each indicator in relation to this outcome. It is evident that none of the indicators are strongly predictive of risk for pre-eclampsia. The highest ORs are just above 1 and as such indicate negligible risk. The rest of the indicators have values below 1, including those based on late pregnancy weight gain as predicted above. The extreme exam- ple of this effect is weight gain from months 5 to 9, with an OR of 0.3 and a 95% CI of 0.2-0.4, suggest- ing that high weight gain, compared with low weight gain, over this period is associated with a threefold increase in the relative risk of developing pre- eclampsia. Excluding weight indicators in pregnancy as a whole, the ORs for maternal height, arm circum- ference, pre-pregnancy weight and BMI all have values of less than 1 (0.6-0.8), indicating a neutral or marginally negative relationship to pre-eclampsia. Evidently, poor maternal nutritional status is asso- ciated with a reduced risk of pre-eclampsia. Scien- tific evidence for nutritional factors in the etiology of pre-eclampsia is, however, weak (25). Table 18: Summary of the combined odds ratios for each Indicator. The ORs refer to the relative risk for pre- eclampsia for the lower quartile versus the upper quartile of the indicator's distribution. Odds ratio for Indicator pre-eclampsia Maternal height 0.8 Mid-upper-arm circumference 0.6 Pre-pregnancy weight 0.7 Attained weight by month 5 Attained weight by month 7 0.8 Attained weight by month 9 0.7 Pre-pregnancy BMI 0.7 BMI month 5 1.2 BMI month 7 0.9 BMI month 9 0.6 Weight gain: Pre-pregnancy to month 5 1.1 Pre-pregnancy to month 7 0.8 Pre-pregnancy to month 9 0.6 Month 5 to month 7 0.7 Month 5 to month 9 0.3 Month 7 to month 9 0.6 34 WHO Bulletin OMS: Supplement Vol. 73 1995 Maternal outcomes Fig. 18. The combined OR profiles for selected Indica- tors and pre-eclampsia are shown. Means (with 95% confidence interval) are estimated as: HT: 0.88 (0.7-1.0); MUAC: 0.69 (0.5-0.8); WTpp: 0.71 (0.6-0.8). The ORs are for mothers below the lowest quartile for the indicator ver- sus mothers above the highest quartile for the indicator. 0.5 1.0 1.5 Odds ratio Maternal height, pre-pregnancy weight and arm cir- cumference. Profiles for maternal height, MUAC and pre-pregnancy weight are jointly displayed in Fig. 18. Body mass index. Attained BMI by month 5 dis- plays the highest estimated OR for all indicators examined, 1.2, but the 95% confidence interval is 0.8 to 1.5; therefore a low BMI at this stage of pregnan- cy is effectively neutral with respect to this outcome. In contrast, pre-pregnancy BMI, and attained BMI Fig. 19. The combined OR profiles for attained BMI Indi- cators and pre-eclampsia are shown. Means (with 95% confidence interval) are estimated as: BMlpp: 0.7 (0.6-0.9); BMI/5: 1.2 (0.9-1.7); BMI/7: 0.9 (0.7-1.0); and BMI/9: 0.6 (0.5-0.8). The ORs are for BMI below the lowest quartile versus BMI above the highest quartile. 0 0.75 1.0 1.5 Odds ratio by months 7 and 9, all have small estimated mean ORs ranging from 0.6 to 0.9. The profile plot (Fig. 19) indicates that the profiles corresponding to pre- pregnancy and month 9 are well within the 0-1 range. Sensitivity and specificity Only BMI/9 (number 16) has a minimum study Se value of 0.05 (Fig. 20). However, several indicators show study sensitivities dropping below 0.1 WT/5 (number 3) has both the highest recorded Se and consequently the largest spread of values across studies. As will be noted from the specificity plot, a large proportion of study specificities-across nearly all indicators-fall below the 0.7 cut-off value. Table 19 shows the reliability of the Se/Sp characteristics across studies. It will be seen that for pre-eclampsia the single candidate (based on only 5 data sets) is the pre-pregnancy body mass index (reported OR is 0.75; 95% CI, 0.6-0.9). Pre-pregnan- cy weight (OR, 0.7; 95% CI, 0.6-0.8) achieved the Se/Sp criterion in only 2 out of 6 data sets. The overall conclusion is that maternal anthro- pometry is a poor predictor of increased risk of pre- eclampsia, in part because of the confounding effect of late pregnancy oedema on weight and weight gain. For this reason it could be concluded, at first sight, that the majority of indicators show a small protective effect for low nutritional status. It must be bome in mind, however, that if high weight status/ gain is a consequence of disease, rather than a cause, then low gain is not necessarily protective against this outcome. Fig. 20. Ranges in computed sensitivity (left side) and specificity (right side) across all relevant data sets for all indicators for pre-eclampsia. The indicators are num- bered 1 to 16 and follow the sequence shown in Table 19. 1.0 0.9 0.8 0.7 0.6 .5 ,, 0.5 cn 0.4 0.3 0.2 0.1 0 2.25 3.0 0 5 10 15 0 5 10 15 Indicators 1.0 0.9 0.8 0.7 0.6 -. 0.5 i, 0. 0.4 Ce 0.3 0.2 0.1 0 WHO 95096 WHO Bulletin OMS: Supplement Vol. 73 1995 0 35 Chapter 6 Table 19: Performance of indicators for pre-eclampsia. Asterisked indicators, having met the selection criteria, are considered candidates for 'best' indicator. Pre-eclampsia Indicator Counta Min Sea Max Sea 1. Maternal height 3/8 0.31 0.47 2. Pre-pregnancy weight 2/6 0.36 0.50 3. Attained weight by month 5 2/8 0.35 0.38 4. Attained weight by month 7 1/8 0.54 0.54 5. Attained weight by month 9 0/9 6. Mid-upper-arm circumference 0/9 7. Weight gain: months 5 to 7 0/6 8. Weight gain: months 5 to 9 0/6 9. Weight gain: months 7 to 9 0/7 10. Weight gain: pp to month 5 0/6 11. Weight gain: pp to month 7 0/6 12. Weight gain: pp to month 9 0/6 13. Pre-pregnancy BMI 3/5* 0.31 0.50 14. BMI month 5 1/8 0.35 0.35 15. BMI month 7 1/7 0.50 0.50 16. BMI month 9 0/7 a 'Count' gives the fraction of data sets in which the Se/Sp cri- teria was met. The asterisk denotes that the indicator met this criterion (Se >0.3, Sp >0.7) in over 40% of the studies. The observed maximum and minimum sensitivities across studies that meet the Se/Sp criterion are recorded in the final two columns. Where only one study has met the criteria, the min and max figure for Se will be the same. Postpartum haemorrhage Definition. Bleeding during the first 24 hours post- partum. As with prematurity, there is no known bio- logical basis for a relationship between maternal nutritional status and postpartum haemorrhage. Maternal anthropometric indicators are therefore examined solely for any predictive capacity. The six studies that had uniformly defined infor- mation on this condition are identified in Table 8, Chapter 3 (page 16), where it will be seen that the prevalence of this condition across studies is very low: 0.5-4.4%. Table 20 provides a summary of the combined odds ratios derived from the eligible stud- ies. As with assisted delivery and pre-eclampsia, all estimated ORs are below 1 with the exception of attained BMI indicators which show a marginal ele- vated risk (but with 95% CIs embracing 1.0) (Fig. 21). Apart from attained weight by month 9 and MUAC, confidence intervals for all other indicators include 1, suggesting that these are neutral in respect of risk prediction. Attained weight by month 9 has an OR of 0.6 with a 95% CI of 0.4-0.8 and MUAC has an OR of 0.6 with a 95% CI of 0.5-0.8, implying prediction Table 20: Summary of the combined odds ratios for each indicator. The ORs refer to the relative risk for post- partum haemorrhage for the lower quartile versus the upper quartile of the indicator's distribution. Odds ratio for postpartum Indicator haemorrhage Maternal height 0.7 Mid-upper-arm circumference 0.6 Pre-pregnancy weight 0.6 Attained weight by month 5 0.9 Attained weight by month 7 0.9 Attained weight by month 9 0.6 Pre-pregnancy BMI 0.8 BMI month 5 1.2 BMI month 7 1.1 BMI month 9 1.0 Weight gain: Pre-pregnancy to month 5 0.5 Pre-pregnancy to month 7 0.7 Pre-pregnancy to month 9 0.6 Month 5 to month 7 0.9 Month 5 to month 9 0.9 Month 7 to month 9 0.7 of a reduced risk, but more data would be required before this could be considered to be reliably deter- mined. For this reason a larger number of studies of Fig. 21. The combined OR profiles for attained weight and postpartum haemorrhage are shown. Means (with 95% confidence interval) are estimated as: WTpp: 0.6 (0.4-1.1); WT/5: 0.9 (0.4-1.7); WT/7: 0.9 (0.6-1.5); and WT/9: 0.6 (0.4-0.8). The ORs are for weight below the lowest quartile versus weight above the highest quartile. Pre-pregnancy Month 9 Month 7 Month 5 0 0.75 1.0 1.5 2.25 3.0 Odds ratio 36 WHO Bulletin OMS: Supplement Vol. 73 1995