Service applications

8. Service applications Introduction Some 30% to 80% of births in the developing world take place in the home, usually assisted by a birth attendant who is illiterate and without formal train- ing. Under these conditions there is often little contact with the health system prior to pregnancy, while the first antenatal visit is often delayed until the third trimester and is not always repeated. At this point it is critical for the peripheral worker to take full advantage of any opportunity to determine the woman's health and nutritional status, to detect any existing abnormality, and to determine the risk of adverse outcome for the mother and the fetus. Based on such an assessment, a decision can be made regarding the need for special attention and for refer- ral to higher levels of care at the appropriate time. It is also the key opportunity to provide information and guidance on self-care and to emphasize the need to continue service contacts and make arrangements for safe delivery. Obstetrical monitoring and assessment of risk are based on a series of routine observations made during the antenatal visit. Age, parity, history, physi- cal health, and gestational progress are basic clinical observations, while nutritional status assessment pro- vides essential corollary information which further improves risk prediction. Such assessment must be carried out at the lowest level in the health care system if the principles of early detection and timely intervention are to be applied. Given that the major- ity of primary care systems operate under basic con- ditions and that nutritional status is an important source of fetal and matemal risk, it is essential to identify which indicators can be used under different service conditions. Such conditions include the timing and frequency of antenatal contact, the avail- ability of weighing scales, the ability of the worker to carry out simple calculations and to make decisions based on defined thresholds. All of this presupposes the existence of effective interventions that can be applied at the lowest possible level in the system. Selection of indicators: practical considerations For the above reasons it is appropriate to examine the range of indicators identified in terms of com- mon constraints on their use under field conditions, using the same operational framework discussed in Chapter 1 (Table 2, page 3). As previously, Table 23 identifies situations characterized by: (i) contact frequency - ranging from a one- time only attendance at a clinic to two or more opportunities for measurement; (ii) technical equipment - the availability or not of reliable weighing scales for routine use; and (iii) service delivery - which may be con- strained by late registration (around 30 weeks), restricted outreach, and limited ability or inadequate training of the health worker. In Table 23 the 'worst case scenario' corresponds to case A: a single contact late in pregnancy, with no weighing scales available; this rules out the use of all weight indicators regardless of the health worker's competence. A more typical situation is illustrated by a single contact in the second half of pregnancy, with weighing scales available and measurements made by a minimally trained worker (case C). In such a setting, weight attained by month 7 (24-27 weeks) or month 9 (32-35 weeks) are feasible meas- urements; however, weight gain or early pregnancy weight cannot be considered unless pre-pregnancy weight can be accurately predicted from arm circum- ference (see Chapter 9, pages 48-50). An optimal situation would be multiple contacts starting in pre- pregnancy or early in pregnancy, taking place at a health centre that had weighing scales and was staffed, for example, by an auxiliary nurse midwife with basic numerical skills (case H). Detailed com- ments are presented in and below Table 23. 1. No scales/one or more contacts! constraints: yes/no Rows A & B and E & F (Table 23). If no scales are available, only matemal height and arm circumfer- ence measurements are feasible. Neither of these in- dicator variables were asterisked in the second stage of the analysis as they did not meet the Se/Sp criteri- on in more than 40% of the data sets for any of the three outcomes. Height as an indicator for LBW and IUGR comes closest but the odds ratios are not notably high for either outcome (Chapter 5, see pp. 21, 24). For preterm birth, both variables have lower confidence limits of 1 or just above 1 and so may be regarded as neutral. Clearly, for case F, there is no advantage in repeatedly measuring either height or MUAC. 2. Scales available/one contact/delivery constraints Row C (Table 23). Assuming scales are available, but the first service contact is at about 30 weeks of pregnancy, attained weight by month 7 (WT/7) and WHO Bulletin OMS: Supplement Vol. 73 1995 43 Chapter 8 Table 23: Preferred Indicators for predicting Increased relative risk for the specified outcomes for different opera- tional settingsa Frequency Service of contact Scales delivery LBW IUGR PTB SINGLE No scales Some constraints A HT HT No constraints B HT HT MUAC Scales Some constraints C WT/7 WT/9 WT/9 WT/7 No constraints D WTpp WT/pp WT/pp WT/5,/7,/9 WT/5 BMIpp BMIpp WT/9 WT/7 MULTIPLE No scales Some constraints E Not applicable Not applicable Not applicable No constraints F HT, MUAC HT, MUAC Scales Some constraints G As C As C WTg/7-9/HT WTg/7-9/HT - or WTpp or WTpp No constraints H As D As D As D WTg/7-9/HT WTg/pp-9 WTg/5-7/HT or WTpp WTg/5-7 WTg/pp-9/HT WTg/pp-5 WTg/pp-7 a Within each cell, the indicators are listed in preferred order, i.e., (i) indicators in bold type meet the final selection criterion discussed in Chapter 4, p. 20 (Se > 0.35 and Sp > 0.7, in .40% relevant data sets); and (ii) indicators in italics that do not reach the full selection requirements, but represent the best available alternatives. Outcomes and indicators are shown as abbreviations (PTB: pre-term birth), with numbers referring to lunar months (WTg/7-9: weight gain between lunar months 7 and 9). Line F indicators do not require multiple measurements. by month 9 (WT/9) are the preferred indicators for LBW with ORs of 2.41 and 2.59, respectively. Weight by month 9 (WT/9) is the only acceptable indicator for IUGR with an OR of 3.09 because weight by month 7 does not meet the final selection criterion. No month 9 indicator has been considered for predictive purposes for PTB as a significant pro- portion of such deliveries will have occurred by this time. 3. Scales available/one contact! no constraints Row D (Table 23). With scales available and a first contact occurring in the first or second trimester (prior to 20 weeks) or even pre-pregnancy, there are three preferred indicators for both LBW and IUGR: pre-pregnancy weight and weight by months 5 and 9, with weight by month 7 also for LBW. ORs are as follows: for LBW - WTpp, 2.3; WT/5, 2.4; WT/7, 3.0; WT/9, 2.5; and for IUGR - WTpp, 2.5; WT/5, 2.7; WT/9, 3.0. For PTB, pre-pregnancy weight and pre-pregnancy BMI were asterisked, with estimated ORs of 1.4 and 1.3, respectively. Row E (Table 23) for IUGR, LBW and preterm birth. In a setting with no scales and service delivery con- straints, it is assumed that no possibility exists for multiple contacts. 4. Scales available/multiple contacts/ delivery constraints Row G (Table 23). For IUGR, LBW and PTB the preferred indicators are as in case C. The late contact rules out any viable indicator for preterm birth. Possible altematives for LBW and IUGR (not asterisked, but with a reasonable percentage meeting the selection criterion across studies, see Chapter 5, pages 23, 27) are weight gain between months 7 and 9, for mothers of below average maternal height or pre-pregnancy weight. 5. Scales available/multiple contacts/ no constraints Row H (Table 23). For IUGR, LBW and PTB, if the first contact is either pre-pregnancy or in the first or second trimester (prior to 20 weeks), case D selec- WHO Bulletin OMS: Supplement Vol. 73 199544 Service applications tion applies; no additional indicators met the final selection criterion for any of the three outcomes. Though falling somewhat short of the cross-study specification, several weight gain indicators are listed which might be considered as alternatives. In the case of IUGR and LBW, these indicators met the selection criterion in 25% of relevant data sets, whereas for preterm birth the percentages recorded are around 17% (see Chapter 5). It is rather striking that no weight gain or sub- group indicators met the selection criterion for the final list in Table 23; some were close and may be worth considering if local experience suggests as much. Although having comparatively higher ORs, these indicators do not often have the required joint levels of specificity and sensitivity which are felt to be desirable. Implications for primary health care: use as a screening test All selected indicators have only moderate sensitivi- ties, usually between 0.35 and 0.55. The implications of this may be conveniently explored by supposing that 100 mothers attend an antenatal clinic where the chosen indicator (e.g., weight attained by month 5) has the following characteristics: Se = 0.4, Sp = 0.78. If the prevalence of IUGR is 20%, then the results of this screening test are as set out in Table 24, with the relevant measures shown below the Table. Se and Sp are pre-defined; because Se is rela- tively low, the positive predictive value (PPV, or proportion of those screened positive who were truly positive) of this test is poor and will decrease further where the prevalence of IUGR is lower for the same Se/Sp. On the other hand, because Sp is reasonably good, the negative predictive value (NPV, or propor- tion of those screened negative who were truly nega- tive) of this test is quite high at 0.84. The overall test efficiency (eff), i.e., the proportion of mothers cor- rectly classified by the test is 0.71. Twelve of the twenty mothers eventually delivering an IUGR infant would be missed by being improperly screened as negative for IUGR in this situation - a function of low test sensitivity. On the other hand, as specificity is 78%, 17 of the 25 mothers screened positive will eventually deliver a non-IUGR infant and may receive an inappropriate intervention. As most nutri- tion interventions are relatively innocuous this does not pose a therapeutic hazard; however, they could have serious cost implications and constitute an inef- ficient use of limited resources. For the same pre-set specificity and prevalence rates, improved sensitivity and positive predictive value could only be obtained in theory by raising the Table 24: Hypothetical results of an anthropometric screening test for IUGR with Se = 0.4, Sp = 0.78, and an outcome prevalence level of 20%a IUGR Non-IUGR Infant Infant Total Screen positive (below 25th centile) 8 (TP) 17 (FP) 25 Screen negative (above 25th centile) 12 (FN) 63 (TN) 75 Total 20 80 100 a TP true positives; FP. false positives; FN, false negatives; TN, true negatives; PPV, positive predictive value; NPV, negative predictive value; eff, efficiency; N, total number. TP Se = TP + FN TN Sp = TN + FP x 100 = 0.40 x 100 = 0.78 TP PPV= x 100 = 0.32 TP + FP TN NPV = TN + FN TP + TN eff = N x 100 = 0.84 x 100 = 0.71 cut-off point for a positive screen - for example, to perhaps the 30th percentile (Se would now equal 0.65 with PPV = 0.43), at a cost of increasing the number of mothers apparently needing intervention. In practice, a higher cut-off point for these indicators will improve sensitivity but will also result in a reduction in specificity and consequently in a higher rate of false positives. For the meta-analysis, estimated ORs and the conclusions based upon these have been a function of the comparison between mothers with anthropo- metric measurements in the lowest quartile as com- pared to an assumed low-risk category, i.e., those mothers with measurements in the highest quartile of the relevant indicator's distribution. From further analysis undertaken, but not reported here, alterna- tive comparisons of predictive capacity, e.g., 10th centile versus the highest quartile, may result in larger ORs and higher specificities. Certainly, high- er ORs were computed for the 10th centile cut-off point for various indicators and outcomes, but were less satisfactory in that the estimates are much less WHO Bulletin OMS: Supplement Vol. 73 1995 45 Chapter 8 reliable. Also, as discussed in some detail above, higher specificity is usually gained only at the expense of lower sensitivity. Conclusions This meta-analysis has brought together a significant number of data sets from around the world and has attempted to quantify and compare the performance of a number of commonly used indicators in relation to selected infant and maternal outcomes. The first stage of the analysis confirmed the inherent value of maternal weight (measured before and during preg- nancy), height, arm circumference, and body mass index as predictive of specific infant and/or maternal outcomes, while subsequent analysis considered indicator sensitivity and specificity so that these indi- cators could be ranked in order of preference for primary health care planners and managers. Pre- pregnancy weight and attained weight by months 5, 7 and 9 were found by and large to meet the selec- tion criteria for LBW and IUGR. Of the remaining indicators, weight gain (months 5-7 or 7-9, in mothers with low maternal height), while not match- ing the full selection requirements, represented the best of the alternatives; however, the prediction of maternal risk was found to be relatively weak, with the exception of assisted delivery. Some of the con- straints for field application of these indicators with typical levels of Se and Sp were presented to illus- trate the limitations of anthropometry alone as a screening tool. In considering these conclusions, there are a number of caveats to bear in mind re- garding the scope of the analysis and the application of the guidelines proposed: (1) Although some 25 data sets were incorpora- ted into this meta-analysis, it is unclear whether this is a sufficient number to guarantee a representative sample embracing varied operational settings and responses of relevance to the project and its conclu- sions. Several further data sets have been acquired since the analysis began, and it is intended to incor- porate these into the data bank and to continue build- ing on the available information to refine the results discussed above and to address other important issues. (2) Several other anthropometric indicators (e.g., various skinfold thicknesses and limb circum- ferences) are currently proposed as feasible and use- ful alternatives to the standard indicators. Also, other combinations of the traditional measurements of height and weight are now being recommended (27) in certain settings. To our knowledge, no meta- analysis has yet been conducted on the utility of these indicators. (3) This analysis has been confined to relatively simple models, ignoring the relevant confounding effects relating to the mother's demographic profile and obstetric history, etc. As was made clear in the statement of the objectives, the specific concern of this work was to investigate the predictive power of anthropometry per se, irrespective of other factors. On the other hand, the unique advantage of this pro- ject has been the ability to wield a large measure of control over the definition of variables, choice of cut-off points, and modes of analysis. Accepting these caveats, this meta-analysis has indicated the strength of maternal anthropometry in predicting fetal outcomes and its relative weakness, apart from height for assisted delivery, in predicting the selected maternal outcomes. The strength of maternal anthropometry to predict other important maternal outcomes such as lactation performance and general morbidity, for which a clear biological relationship exists, is beyond the scope of this study but could be of great importance to maternal health and reproduction in a wider perspective. The fetal outcome of most importance to maternal and child health services is intrauterine growth retar- dation for which acceptable and effective interventions exist. Indicators useful for IUGR can also be applied to LBW where IUGR is prevalent, as in poor popula- tions. This analysis has confirmed that pre-pregnancy weight and attained weight at 5, 7, and 9 lunar months are useful predictors of fetal risk. Weight gain can also be useful, particularly if the pre-pregnancy weight is available. It did not, however, offer any major advan- tages over attained weight, while the requirement for two measurements increases the operational complex- ity. The application of these indicators to the low height and weight subgroups clearly strengthens the predictive capacity, even though it adds to the com- plexity of assessment. The study also noted (discussed in Chapter 9, pages 48-50) the poor precision of arm circumference as a predictor of pre-pregnancy weight for individual mothers. The study raised the interesting possibility of indicators of reduced risk for maternal outcomes. There is a reasonable biological argument for sup- posing that conditions that may be favourable to the mother in the short term (low risk of assisted deliv- ery) will be unfavourable to the fetus and newborn in the longer term (increased morbidity and mortality in the first year). These "reduced risk" indicators will require further consideration and an examination of the short and long term trade-offs between maternal and infant health and survival. The simple procedures and equipment required to apply the indicators selected by this meta-analysis in a service context make them particularly suitable for use by community health workers. The related WHO Bulletin OMS: Supplement Vol. 73 199546 Service applications interventions to prevent and correct IUGR are effec- tive and feasible at the primary care level. This study systematically applied the lower quartile as the cut-off point for each indicator, which may limit specificity and produce a yield for inter- vention that is in excess of resources. The use of more stringent criteria, such as a 10% cut-off, would increase the power and specificity of these indicators on the one hand and, on the other, limit the demand for intervention to those most seriously in need. However, these are clearly decisions best made at a regional or local level based on identified needs and service conditions. The study has also provided practical informa- tion on optimal and minimal pregnancy weight-gain values that can be applied to the design and use of maternal health records, particularly home-based models. Gestational weight-gain curves will enable community health workers to track the nutritional response to pregnancy in a simple and reliable man- ner. They will also provide valuable material for health education of the mother and family on repro- ductive health. The operational value of the findings of this study can only be demonstrated through their suc- cessful application in service settings on a large scale. Information collected systematically from pro- gramme sources will verify the assumptions and con- clusions derived from the meta-analysis of project data. In turn, however, the successful application of these indicators will be critically dependent on the availability of effective interventions. A substantial body of knowledge has been accumulated on the fetal and maternal response to food and nutrient sup- plementation at different stages of pregnancy; how- ever, much less is known of the efficiency of nutri- tion interventions prior to pregnancy or in the first trimester. Similarly the value of indirect interven- tions, such as infectious disease and parasite control and the reduction of energy expenditure in late preg- nancy, needs to be established under a range of oper- ational conditions. The programme effectiveness of the indicators derived from this analysis should be demonstrated in the more efficient use of resources and by the improvement in conventional outcome measures of maternal, fetal and infant health. It will be the task of service directors, in collaboration with national and international agencies, to undertake a comprehensive review of these long-term effects in the coming years. The work discussed here must be seen as the first critical step in a two-stage process. For the sec- ond stage, these results will provide the means for analysing and quantifying the expected benefits of specific interventions for selected situations. WHO Bulletin OMS: Supplement Vol. 73 1995 47