Maternal hemoglobin concentration and adverse pregnancy outcomes at low and moderate altitudes in Peru

Higher oxygen content and transport characterize high-altitude ethnic Tibetan women with the highest lifetime reproductive success

We chose the "natural laboratory" provided by high-altitude native ethnic Tibetan women who had completed childbearing to examine the hypothesis that multiple oxygen delivery traits were associated with lifetime reproductive success and had genomic associations. Four hundred seventeen (417) women aged 46 to 86 y residing at ≥3,500 m in Upper Mustang, Nepal, provided information on reproductive histories, sociocultural factors, physiological measurements, and DNA samples for this observational cohort study. Simultaneously assessing multiple traits identified combinations associated with lifetime reproductive success measured as the number of livebirths. Women with the most livebirths had distinctive hematological and cardiovascular traits. A hemoglobin concentration near the sample mode and a high percent of oxygen saturation of hemoglobin raised arterial oxygen concentration without risking elevated blood viscosity. We propose ongoing stabilizing selection on hemoglobin concentration because extreme values predicted fewer livebirths and directional selection favoring higher oxygen saturation because higher values had more predicted livebirths. EPAS1, an oxygen homeostasis locus with strong signals of positive natural selection and a high frequency of variants occurring only among populations indigenous to the Tibetan Plateau, associated with hemoglobin concentration. High blood flow into the lungs, wide left ventricles, and low hypoxic heart rate responses aided effective convective oxygen transport to tissues. Women with physiologies closer to unstressed, low altitude values had the highest lifetime reproductive success. This example of ethnic Tibetan women residing at high altitudes in Nepal links reproductive fitness with trait combinations increasing oxygen delivery under severe hypoxic stress and demonstrates ongoing natural selection.

Accuracy of HemoCue301 portable hemoglobin analyzer for anemia screening in capillary blood from women of reproductive age in a deprived region of Northern Peru: An on-field study

OBJECTIVE

We aim to assess the accuracy and effectiveness of the HemoCue 301, a point-of-care (POC) device for measuring hemoglobin levels, and detecting anemia among individuals living in Tumbes, a rural, underserved area in Northern Peru.

METHODS

Baseline analysis of a clinical trial aimed at assessing the effect of multi-fortified bread (NCT05103709). Adult women with capillary blood HemoCue 301 readings below 12 g/dL were recruited in coastal city of Tumbes, Peru. A total of 306 women took part of the study, venous blood samples were taken and analyzed with an automated hematology analyzer. Serum samples were used to measure ferritin, serum iron and C reactive protein.

RESULTS

Capillary blood measured by the Hemocue 301 has a bias of 0.36 ± 0.93 g/dL respect to the automated Hb. More than 50% of women with normal ferritin values were classified as anemics according to the HemoCue 301. Automated Hb cut-off of 10.8 g/dL [AUC 0.82 (0.77-0.88)] had a specificity of 0.817 and a sensitivity 0.711 while with the HemoCue 301 cut-off of 11.1 g/dL [AUC 0.71 (0.62-0.79)] had a specificity of 0.697 and a sensitivity 0.688. The performance of the automated Hb cut-off was significantly better than the HemoCue (p<0.001).

CONCLUSION

Caution must be taken when using POC devices, especially with values around the threshold. Cut-off values found in our study could be used as surrogate means when no confirmatory tests are available. Clinical outcomes should be prioritized when diagnosing iron deficiency anemia in women of reproductive age to ensure proper diagnosis.

Adverse pregnancy and perinatal outcomes in Latin America and the Caribbean: systematic review and meta-analysis

Objective.

To estimate the point prevalence and likely ranges of pregnancy-induced hypertension, pre-eclampsia, gestational diabetes, low birth weight and preterm delivery in Latin America and the Caribbean, and evaluate the heterogeneity of the estimates.

Methods.

We conducted a systematic review and meta-analysis of observational studies reporting the prevalence of maternal and perinatal adverse outcomes in populations in Latin American and the Caribbean published between 2000 and 2019 in English, Spanish, or Portuguese. We searched PubMed, Embase, and LILACS. We estimated the point prevalence and evaluated overall heterogeneity and, in sub-group analyses, heterogeneity by study design and level of bias.

Results.

Of 1087 records retrieved, 50 articles were included in the review: two on hypertensive disorders of pregnancy, 14 on pre-eclampsia, six on gestational diabetes, nine on low birth weight and 19 on preterm birth. No meta-analysis for hypertensive disorders of pregnancy could be done because of the small number of studies. Point prevalence estimates and 95% confidence intervals (CIs) for pre-eclampsia, gestational diabetes, low birth weight, and preterm birth were: 6.6% (95% CI: 4.9%, 8.6%), 8.5% (95% CI: 3.9%, 14.7%), 8.5% (95% CI: 7.2%, 9.8%), and 10.0% (95% CI: 8.0%, 12.0%), respectively. We observed substantial heterogeneity overall and by study design. No major differences in estimates were observed by level of bias.

Conclusions.

The results of this study provide updated estimates of some of the most prevalent adverse pregnancy and perinatal outcomes in Latin America and the Caribbean. They highlight that important heterogeneity exists in prevalence estimates, which may reflect the diversity of populations in the region.

Repeatability of adaptive traits among ethnic Tibetan highlanders

OBJECTIVES

Connecting traits to biological pathways and genes relies on stable observations. Researchers typically determine traits once, expecting careful study protocols to yield measurements free of noise. This report examines that expectation with test-retest repeatability analyses for traits used regularly in research on adaptation to high-altitude hypoxia, often in settings without climate control.

METHODS

Two hundred ninety-one ethnic Tibetan women residing from 3500 to 4200 m in Upper Mustang District, Nepal, provided three observations of hemoglobin concentration, percent of oxygen saturation of hemoglobin, and pulse by noninvasive pulse oximetry under conditions designed to minimize environmental noise.

RESULTS

High-intraclass correlation coefficients and low within-subject coefficients of variation reflected consistent measurements. Percent of oxygen saturation had the highest intraclass correlation coefficient and the smallest within-subject coefficient of variability; measurement noise occurred mainly in the lower values. Hemoglobin concentration and pulse presented slightly higher within-subject coefficients of variation; measurement noise occurred across the range of values. The women had performed the same measurements 7 years earlier using the same devices and protocol. The sample means and SD observed across 7 years differed little. Hemoglobin concentration increased substantially after menopause.

CONCLUSIONS

Analyzing repeatability features of traits may improve our interpretation of statistical analyses and detection of variation from measurement or biology. The high levels of measurement repeatability and biological stability support the continued use of these robust traits for investigating human adaptation in this altitude range.

Maternal hemoglobin associates with preterm delivery and small for gestational age in two Finnish birth cohorts

OBJECTIVE

To test whether maternal hemoglobin during pregnancy associates with offspring perinatal outcomes in a developed country. Changes in maternal hemoglobin concentration during pregnancy are partly physiological phenomena reflecting alterations of maternal blood volume. Especially hemoglobin measures outside the physiological range may influence maternal health and fetal growth with long-lasting consequences.

STUDY DESIGN

We studied an unselected sample drawn from two regional birth cohorts born 20 years apart: The Northern Finland Birth Cohorts 1966 and 1986. These are two mother-and-child population-based birth cohorts together comprising 21,710 mothers and their children. After exclusions, the sample size of the current study was 20,554. Concentrations of maternal hemoglobin at first and last antenatal visits were categorized as low (lowest 10%), medium (reference) or high (highest 10%). Multinomial logistic regression analyses for categories of maternal hemoglobin and perinatal outcomes such as preterm delivery and full-term small and large for gestational age were conducted with adjustments for maternal cofactors.

RESULTS

Low maternal hemoglobin at early pregnancy associated with decreased risk of full-term small for gestational age (adjusted OR 0.73, 95% CI [0.58, 0.93], p = 0.010). At late pregnancy, low maternal hemoglobin associated with increased risk of preterm delivery (adjusted OR 1.60, 95% CI [1.26, 2.02], p < 0.0005) whereas high maternal hemoglobin associated with increased risk of full-term small for gestational age (adjusted OR 1.29, 95% CI [1.07, 1.56], p = 0.009). Maternal hemoglobin did not show constant association with risk of large for gestational age.

CONCLUSION

The results from this study support evidence that both low and high maternal hemoglobin associate with adverse perinatal outcomes. Low maternal hemoglobin associated with preterm delivery and high with full-term small for gestational age. Association was mainly present when maternal hemoglobin was measured during the third trimester. These results indicate that it is important to monitor both extremes of maternal hemoglobin throughout the pregnancy.

Preconception Hb concentration and risk of preterm birth in over 2·7 million Chinese women aged 20-49 years: a population-based cohort study

Evidence on the association between maternal Hb concentration and preterm birth (PTB) risk is inconclusive. This paper aimed to explore whether women with anaemia or high Hb level before pregnancy would be at higher risk of PTB. We conducted a population-based cohort study with 2 722 274 women aged 20-49 years, who participated in National Free Pre-Pregnancy Checkups Project between 2013 and 2015 and delivered a singleton before 2016 in rural China. Logistic models were used to estimate OR and 95 % CI after adjusting for confounding variables. Restricted cubic spline models were applied to evaluate the dose-response relationships. A total of 192 819 (7·08 %) women had preterm deliveries. Compared with women with Hb of 110-149 g/l, the multivariable-adjusted OR for PTB was 1·19 (95 % CI 0·98, 1·44) for women with Hb<70 g/l, 1·01 (95 % CI 0·97, 1·03) for 70-99 g/l, 0·96 (95 % CI 0·95, 0·98) for 100-109 g/l, 1·04 (95 % CI 1·01, 1·06) for 150-159 g/l, 1·11 (95 % CI 1·05, 1·17) for 160-169 g/l and 1·19 (95 % CI 1·11, 1·27) for ≥170 g/l, respectively. The multivariable-adjusted OR for very PTB (VPTB) was 1·07 (95 % CI 1·03, 1·12) and 1·06 (95 % CI 1·01, 1·12) for women with Hb <110 and ≥150 g/l, compared with those with Hb of 110-149 g/l, respectively. Our study identified a U-shaped relationship between maternal preconception Hb concentration and PTB risk. Both preconception anaemia and high Hb level can significantly increase VPTB risk. Appropriate intervention for women with abnormal Hb levels before pregnancy is very necessary.

Hemoglobin levels during the first trimester of pregnancy are associated with the risk of gestational diabetes mellitus, pre-eclampsia and preterm birth in Chinese women: a retrospective study

BACKGROUND

Hemoglobin (Hb) measurement is a standard test among pregnant women during the first perinatal visit that is used to evaluate physical status and anemia. However, studies focusing on Hb levels and pregnancy outcomes are scarce. This study aimed to determine whether Hb levels in early pregnancy were associated with the risk of gestational diabetes mellitus (GDM), pre-eclampsia (PE) and preterm birth.

METHODS

A hospital-based retrospective study was conducted among 21,577 singleton, non-smoking pregnancies between June 2013 and January 2015. The demographic data and medical information of each participant were collected individually through questionnaires and patient medical records. Odds ratios were generated using a multivariate logistic regression analysis to evaluate the relative risk of GDM, PE and preterm birth continuously and across different hemoglobin ranges in the overall population and in women from different pre-pregnancy body mass index (BMI) categories, respectively. The level of statistical significance was set at 0.05.

RESULTS

(1) For women who were underweight, normal-weight, overweight and obese, early pregnancy Hb levels were 127.8 ± 10.1 g/L, 129.6 ± 9.7 g/L, 132.2 ± 9.5 g/L and 133.4 ± 9.4 g/L, respectively. (2) Women with GDM and PE had significantly increased Hb levels during early pregnancy compared with controls, whereas women with preterm birth processed significantly decreased Hb levels. (3) After adjusting for confounders, the risks for GDM and PE increased with high maternal Hb (OR: 1.27 for Hb 130-149; OR: 2.06 for Hb ≥ 150 g/L), and the risk for preterm birth decreased with high maternal Hb (OR: 1.30 for Hb 130-149; OR: 2.38 for Hb ≥ 150 g/L) and increased with low maternal Hb (OR: 1.41 for Hb <  110 g/L). Among women whose BMI was < 24 kg/m2, high GDM (OR: 1.27 for Hb 130-149; OR: 1.84 for Hb ≥ 150 g/L) and low preterm rates (OR: 0.77 for Hb 130-149; OR: 0.23 for Hb ≥ 150 g/L) were observed with high Hb, whereas in women whose BMI was ≥24 kg/m2, only high GDM rates were observed with Hb > 150 g/L (OR: 2.33).

CONCLUSION

These findings suggest that Hb levels during early pregnancy play a role in predicting the risk of GDM, PE and preterm birth.

Ethnically Tibetan women in Nepal with low hemoglobin concentration have better reproductive outcomes

Background and objectives: Tibetans have distinctively low hemoglobin concentrations at high altitudes compared with visitors and Andean highlanders. This study hypothesized that natural selection favors an unelevated hemoglobin concentration among Tibetans. It considered nonheritable sociocultural factors affecting reproductive success and tested the hypotheses that a higher percent of oxygen saturation of hemoglobin (indicating less stress) or lower hemoglobin concentration (indicating dampened response) associated with higher lifetime reproductive success.

Methodology: We sampled 1006 post-reproductive ethnically Tibetan women residing at 3000–4100 m in Nepal. We collected reproductive histories by interviews in native dialects and noninvasive physiological measurements. Regression analyses selected influential covariates of measures of reproductive success: the numbers of pregnancies, live births and children surviving to age 15.

Results: Taking factors such as marriage status, age of first birth and access to health care into account, we found a higher percent of oxygen saturation associated weakly and an unelevated hemoglobin concentration associated strongly with better reproductive success. Women who lost all their pregnancies or all their live births had hemoglobin concentrations significantly higher than the sample mean. Elevated hemoglobin concentration associated with a lower probability a pregnancy progressed to a live birth.

Conclusions and implications: These findings are consistent with the hypothesis that unelevated hemoglobin concentration is an adaptation shaped by natural selection resulting in the relatively low hemoglobin concentration of Tibetans compared with visitors and Andean highlanders.

Mild anemia during pregnancy upregulates placental vascularity development

The connection between maternal hematological status and pregnancy outcome has been shown by many independent researchers. Attention was initially focused on the adverse effects of moderate and severe anemia. Interestingly, some studies revealed that mild anemia was associated with optimal fetal development and was not affecting pregnancy outcome. The explanation for this phenomenon became a target for scientists. Hemodilution, physiologic anemia and relative decrease in hemoglobin concentration are the changes observed during pregnancy but they do not explain the reasons for the positive influence of mild anemia on a fetomaternal unit. It is hypothesized that hemodilution facilitates placental perfusion because blood viscosity is reduced. Subsequently, it may lead to a decline in hemoglobin concentration. Anemia from its definition implies decreased oxygen carrying capacity of the blood and can result in hypoxemia and even hypoxia, which is a common factor inducing new blood vessels formation. Therefore, we raised the hypothesis that the lowered hemoglobin concentration during pregnancy may upregulate vascular growth factor receptors expression such as VEGFR-1 (Flt-1) and VEGFR-2 (FLK-1/KDR). Consecutively, increased fetoplacental vasculogenesis and angiogenesis provide further expansion of vascular network development, better placental perfusion and hence neither fetus nor the mother are affected.

Maternal haemoglobin concentrations before and during pregnancy and stillbirth risk: a population-based case-control study

Background

Results of previous studies on the association between maternal haemoglobin concentration during pregnancy and stillbirth risk are inconclusive. It is not clear if haemoglobin concentration before pregnancy has a role. Using prospectively collected information from pre-pregnancy and antenatal visits, we investigated associations of maternal haemoglobin concentrations before and during pregnancy and haemoglobin dilution with stillbirth risk.

Methods

In a population-based case–control study from rural Golestan, a province in northern Iran, we identified 495 stillbirths (cases) and randomly selected 2,888 control live births among antenatal health-care visits between 2007 and 2009. Using logistic regression, we estimated associations of maternal haemoglobin concentrations, haemoglobin dilution at different stages of pregnancy, with stillbirth risk.

Results

Compared with normal maternal haemoglobin concentration (110–120 g/l) at the end of the second trimester, high maternal haemoglobin concentration (≥140 g/l) was associated with a more than two-fold increased stillbirth risk (OR = 2.31, 95 % CI [1.30–4.10]), while low maternal haemoglobin concentration (<110 g/l) was associated with a 37 % reduction in stillbirth risk. Haemoglobin concentration before pregnancy was not associated with stillbirth risk. Decreased haemoglobin concentration, as measured during pregnancy (OR = 0.61, 95 % CI [0.46, 0.80]), or only during the second trimester (OR = 0.75, 95 % CI [0.62, 0.90]), were associated with reduced stillbirth risk. The associations were essentially similar for preterm and term stillbirths.

Conclusions

Haemoglobin concentration before pregnancy is not associated with stillbirth risk. High haemoglobin level and absence of haemoglobin dilution during pregnancy could be considered as indicators of a high-risk pregnancy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12884-016-0924-x) contains supplementary material, which is available to authorized users.

Maternal and cord blood vitamin D status in high-altitude pregnancy

OBJECTIVE

We aimed to explore the risk factors that may lead to vitamin D deficiency in pregnant women living in moderately high-altitude regions.

METHODS

The study was conducted prospectively between November 2012 and July 2013. City of Erzurum is located at an altitude of 1900-2200 m, north Turkey at 39°4' latitude. Healthy mothers that gave birth after completing 37th week of their pregnancies and healthy neonates weighting >2500 g were included in the study. For 25-hydroxyvitamin D (25(OH)D) analyses venous blood samples of 2 ml were obtained from the umbilical cord and the mother. Questionnaires were developed covering the demographical characteristics and possible risk factors for mothers.

RESULTS

Totally 81 mothers and neonates were included into the study. The mean 25(OH)D level of mothers was 7.1 ± 6.5 ng/ml. It was noted that 45 (55.7%) mothers had severe deficiency. Multivariate linear regression analysis showed that the dressing style and the level of sunlight received by the house were independent factors affecting the level of 25(OH)D.

CONCLUSION

Our findings showed that cultural factors had significant effects on vitamin D levels. We believe that appropriate dose of vitamin D prophylaxis should be administered to pregnant women, considering the risk factors as well as the geographical features.

Evaluation of Premature Infants Hospitalized in Neonatal Intensive Care Unit between 2010-2012

OBJECTIVE

With continuing developments in the field of neonatology, survival rates of low birth weight and small for gestational age infants have increased, which in turn has brought important prematurity-related problems. The aim of this study was to evaluate retrospectively the prematurity problems that are the significant causes of morbidity and mortality.

MATERIALS AND METHODS

613 premature infants hospitalized in the neonatal intensive care unit of Ataturk University Medical Faculty Hospital between January 2010 and January 2012 were included in this study. Infants were divided into groups according to their birth weight and gestational age.

RESULTS

323 infants were male (52.6%) and 290 were female (47.4%). 63.9% of infants weighed ≥1500 grams, and 58.5% had a gestational age of ≥33 weeks. Respiratory distress syndrome (RDS) was detected in 249 (40.6%), bronchopulmonary dysplasia (BPD) in 124 (20.2%), necrotizing enterocolitis (NEC) in 41 (6.6%), retinopathy of prematurity (ROP) in 202 (32.9%), and intracranial hemorrhage (ICH) in 15 (2.4%). RDS, BPD, NEC, ROP, and ICH rates were inversely proportional to decreases in gestational age and birth weight, and were found to be statistically significant.

CONCLUSION

Mortality and morbidity rates were similar to the other data published from our country, but the rates were above those reported in developed countries. We believe that our morbidity and mortality rates can reach levels comparable to those of developed countries with improved antenatal care, regular follow-up of pregnancy and increased numbers of physicians and health care personnel per patient.

Causes of and factors associated with stillbirth in low- and middle-income countries: a systematic literature review

BACKGROUND

Annually, 2.6 million stillbirths occur worldwide, 98% in developing countries. It is crucial that we understand causes and contributing factors.

METHODS

We conducted a systematic review of studies reporting factors associated with and cause(s) of stillbirth in low- and middle-income countries (2000-13). Narrative synthesis to compare similarities and differences between studies with similar outcome categories.

MAIN RESULTS

A total of 142 studies with 2.1% from low-income settings were investigated; most report on stillbirths occurring at health facility level. Definition of stillbirth varied; 10.6% of studies (mainly upper middle-income countries) used a cut-off point of ≥22 weeks of gestation and 32.4% (mainly lower income countries) used ≥28 weeks of gestation. Factors reported to be associated with stillbirth include poverty and lack of education, maternal age (>35 or <20 years), parity (1, ≥5), lack of antenatal care, prematurity, low birthweight, and previous stillbirth. The most frequently reported cause of stillbirth was maternal factors (8-50%) including syphilis, positive HIV status with low CD4 count, malaria and diabetes. Congenital anomalies are reported to account for 2.1-33.3% of stillbirths, placental causes (7.4-42%), asphyxia and birth trauma (3.1-25%), umbilical problems (2.9-33.3%), and amniotic and uterine factors (6.5-10.7%). Seven different classification systems were identified but applied in only 22% of studies that could have used a classification system. A high percentage of stillbirths remain 'unclassified' (3.8-57.4%).

CONCLUSION

To build capacity for perinatal death audit, clear guidelines and a suitable classification system to assign cause of death must be developed. Existing classification systems may need to be adapted. Better data and more data are urgently needed.

Adaptation to High Altitude: Phenotypes and Genotypes

Populations residing for millennia on the high-altitude plateaus of the world started natural experiments that we can evaluate to address questions about the processes of evolution and adaptation. A 2001 assessment in this journal summarized abundant evidence that Tibetan and Andean high-altitude natives had different phenotypes, and the article made a case for the hypothesis that different genetic bases underlie traits in the two populations. Since then, knowledge of the prehistory of high-altitude populations has grown, information about East African highlanders has become available, genomic science has grown exponentially, and the genetic and molecular bases of oxygen homeostasis have been clarified. Those scientific advances have transformed the study of high-altitude populations. The present review aims to summarize recent advances in understanding with an emphasis on the genetic bases of adaptive phenotypes, particularly hemoglobin concentration among Tibetan highlanders. EGLN1 and EPAS1 encode two crucial proteins contributing to oxygen homeostasis, the oxygen sensor PHD2 and the transcription factor subunit HIF-2α, respectively; they show signals of natural selection such as marked allele frequency differentiation between Tibetans and lowland populations. EPAS1 genotypes associated in several studies with the dampened hemoglobin phenotype that is characteristic of Tibetans at high altitude but did not associate with the dampened response among Amhara from Ethiopia or the vigorous elevation of hemoglobin concentration among Andean highlanders. Future work will likely develop understanding of the integrative biology leading from genotype to phenotype to population in all highland areas.

Risk factors and consequences of maternal anaemia and elevated haemoglobin levels during pregnancy: a population-based prospective cohort study

BACKGROUND

To determine sociodemographic and life style-related risk factors and trimester specific maternal, placental, and fetal consequences of maternal anaemia and elevated haemoglobin levels in pregnancy.

METHODS

In a population-based prospective cohort study of 7317 mothers, we measured haemoglobin levels in early pregnancy [gestational age median 14.4 weeks (inter-quartile-range 12.5-17.5)]. Anaemia (haemoglobin ≤11 g/dl) and elevated haemoglobin levels (haemoglobin ≥13.2 g/dl) were defined according to the WHO criteria. Maternal blood pressure, placental function and fetal growth were measured in each trimester. Data on gestational hypertensive disorders and birth outcomes was collected from hospitals.

RESULTS

Older maternal age, higher body mass index, primiparity and European descent were associated with higher haemoglobin levels (P < 0.05). Elevated haemoglobin levels were associated with increased systolic and diastolic blood pressure throughout pregnancy (mean differences 5.1 mmHg, 95% confidence interval [CI] 3.8, 6.5 and 4.1 mmHg, 95% CI 3.0, 5.2, respectively) and with a higher risk of third trimester uterine artery notching (RR 1.3, 95% CI 1.0, 1.7). As compared with maternal normal haemoglobin levels, not anaemia, but elevated haemoglobin levels were associated with fetal head circumference, length, and weight growth restriction from third trimester onwards (P < 0.05). Elevated haemoglobin levels were associated with increased risks of gestational hypertensive disorders (RR 1.4, 95% CI 1.1, 1.8) and adverse birth outcomes (RR 1.4, 95% CI 1.1, 1.7).

CONCLUSIONS

In a low-risk population, various sociodemographic and life style factors affect haemoglobin levels during pregnancy. Elevated haemoglobin levels are associated with increased risks of maternal, placental, and fetal complications.

Correcting haemoglobin cut-offs to define anaemia in high-altitude pregnant women in Peru reduces adverse perinatal outcomes

PURPOSE

To determine if correction of cut-offs of haemoglobin levels to define anaemia at high altitudes affects rates of adverse perinatal outcomes.

METHODS

Data were obtained from 161,909 mothers and newborns whose births occurred between 1,000 and 4,500 m above sea level (masl). Anaemia was defined with or without correction of haemoglobin (Hb) for altitude as Hb <11 g/dL. Correction of haemoglobin per altitude was performed according to guidelines from the World Health Organization. Rates of stillbirths and preterm births were also calculated.

RESULTS

Stillbirth and preterm rates were significantly reduced in cases of anaemia calculated after correction of haemoglobin for altitude compared to values obtained without Hb correction. At high altitudes (3,000-4,500 masl), after Hb correction, the rate of stillbirths was reduced from 37.7 to 18.3 per 1,000 live births (p < 0.01); similarly, preterm birth rates were reduced from 13.1 to 8.76 % (p < 0.01). The odds ratios for stillbirths and for preterm births were also reduced after haemoglobin correction.

CONCLUSION

At high altitude, correction of maternal haemoglobin should not be performed to assess the risks for preterm birth and stillbirth. In fact, using low altitude Hb cut-off is associated with predicting those at risk.

Maternal and perinatal outcomes in second hemoglobin measurement in nonanemic women at first booking: effect of altitude of residence in peru

Objective. To determine changes in hemoglobin concentration at second measurements after a normal hemoglobin concentration was detected at first booking during pregnancy at low and at high altitudes. Methods. This is a secondary analysis of a large database obtained from the Perinatal Information System in Peru which includes 379,816 pregnant women and their babies from 43 maternity units in Peru. Results. Most women remained with normal hemoglobin values at second measurement (75.1%). However, 21.4% of women became anemic at the second measurement. In all, 2.8% resulted with moderate/severe anemia and 3.5% with erythrocytosis (Hb>14.5 g/dL). In all cases Hb was higher as altitude increased. Risk for moderate/severe anemia increased associated with higher gestational age at second measurement of hemoglobin, BMI <19.9 kg/m(2), living without partner, <5 antenatal care visits, first parity, multiparity, and preeclampsia. Lower risk for moderate/severe anemia was observed with normal high Hb level at first booking living at moderate and high altitude, and high BMI. Conclusion. Prevalence of anemia increases as pregnancy progress, and that a normal value at first booking may not be considered sufficient as Hb values should be observed throughout pregnancy. BMI was a risk for anemia in a second measurement.