Abstract
Objective: Pregnancy considerably increases iron needs in a mother and her fetus. The purpose of this study was to assess the relationship between maternal hemoglobin concentration in labor with neonatal birth weight.
Methods: A population-based study in Shahid Sadughi Hospital in Yazd, Iran, was performed by comparing 1842 singleton term pregnancies of patients with and without anemia and their newborns. Maternal characteristics, including hemoglobin values, were recorded at the labor visit. Maternal anemia was defined as hemoglobin concentration lower than 10 g/dl during pregnancy. Main outcome measures included birth weight and Apgar score. Linear and logistic regression models were used to analyze data.
Results: Anemia (Hb<10 g/dl) was associated with a significantly increased risk of low birth weight (<2500 g). High hemoglobin (>13 g/dl) increased the risk of low birth weight but it was not significant. The risk of a low Apgar score was significantly increased in women with anemia. The minimum incidence of low birth weight occurs in association with a hemoglobin concentration of 10–13 g/dl.
Conclusions: Maternal anemia was significantly associated with effect on birth weight. Also Hb>13 g/dl was also associated with an increased risk of low birth weight.
Introduction
Pregnancy increases considerably the iron needs in a mother and her fetus. During pregnancy, the fetal demand for iron increases maternal iron requirements by about 1 g.Citation1,Citation2 Plasma volume increases by 10 to 15% at 6 to 12 weeks of gestation, and expands rapidly until 30 to 34 weeks, after which there is only a modest rise. The total gain at term, in the most successful pregnancies, is a 50% expansion of plasma volume. The red blood cell mass begins to increase at 8 to 10 weeks of gestation and steadily rises, in women taking iron supplements, by 20 to 30% above non-pregnant levels by the end of pregnancy. A greater increase in intravascular volume compared to red cell mass results in the dilutional or physiologic anemia of pregnancy. This becomes most apparent at 30 to 34 weeks of gestation when plasma volume peaks in relation to red cell volume.Citation3
The average daily diet in the developed world contains about 10–14 mg iron, but not all of this can be absorbed.Citation2In women who are not given supplemental iron, the hemoglobin concentration of the maternal blood falls from an average of 13·3 g/dl in non-pregnant women to an average of 11·0 g/dl at 36 weeks gestation. The fall is steepest up to 20 weeks of gestation; the hemoglobin concentration remains fairly constant up to 30 weeks and then rises slightly thereafter.Citation4
A high proportion of women in both industrialized and developing countries become anemic during pregnancy. Estimates from the World Health Organization report that from 35 to 75% (56% on average) of pregnant women in developing countries, and 18% of women from industrialized countries are anemic.Citation5 Anemia is one of the most prevalent nutritional deficiency problems afflicting pregnant women. Anemia during pregnancy, was defined as hemoglobin concentration <10 g/dl.Citation6 Anemia that complicates pregnancy threatens the life of both the mother and the fetus. The extent which maternal anemia affects maternal and neonatal health is still uncertain.Citation2 Relationships between anemia and adverse birth outcomes have been inconsistent. Some studies have found anemia to significantly increase the risk of low birth weight and preterm delivery.Citation7–Citation9 In controversy some studies, did not find any association between maternal anemia and adverse pregnancy outcome.Citation10–Citation12 The importance of adequate plasma volume expansion in allowing adequate fetal growth is attested to by several studies that showed an increased incidence of low birth weight in association with either a high maternal hemoglobin concentration.Citation13Most studies indicated a U-shaped curve relationship between the maternal hemoglobin concentrations, according to the trimesters of pregnancy. Thus the risk of low birth weight newborns was approximately doubled in pregnant women with moderate-to-severe anemia during the first and second trimesters, while this relationship was reversed during the third trimester.Citation14
Since anemia is considered to be one of the most common medical disorders during pregnancy, this association is of main importance. Thus, this study was performed to assess the relation of maternal hemoglobin concentration in third trimester of pregnancy with neonatal birth weight.
Materials and Methods
This study was performed on 1842 singleton term pregnant women who were hospitalized in Shahid Sadughi Hospital in Yazd, Iran for delivery from 2009 to 2010. Maternal hemoglobin concentration was measured during the first stage of labor using Coulter counter method. Maternal anemia was defined as hemoglobin concentration lower than 10 g/dl during pregnancyCitation15,Citation16 and low birth weight defined as neonatal birth weight <2500 g.Citation17 Patients with hemoglobinopathies such as thalassemia were excluded from the analysis. Also twin pregnancy, maternal systemic diseases such as hypertension, diabetes and renal diseases, IUFD, smoking and oligohydramnios were excluded.
Data were collected by questionnaire and comprised information collected uniformly according to pre-defined criteria at admission time by a first year resident. The following information was extracted from the medical charts: age, gestational age (by using last menstrual dates), self-reported pre-pregnancy weight, BMI (kg/m2), maternal education, parity, hemoglobin concentration and infant birth weight.
Data were analyzed by SPSS 15·0 software with Chi-square test, unpaired t-test, and Mann-Whitney test, as appropriate. P<0·05 is considered statistically significant.
Results
During the study period there were 2045 deliveries in Shahid Sadughi Hospital in Yazd, Iran.
A total of 1842 fulfilled the inclusion criteria. Three hundred and twenty-eight (17·8%) of deliveries occurred in patients with hemoglobin concentration lower than 10 g/dl, 916 (49·7%) with Hb = 10–13 g/dl and 598 (32·5%) with Hb>13 g/dl that classified according to their hemoglobin concentration (in three groups) for study and comparison (). The demographic and socioeconomic characteristics of these three groups are shown in . The mean age of anemic women was slight higher than other two groups. The BMI of women in three groups was similar. The majority of the women in three groups were housewives.
Table 1. Study population grouping according to maternal hemoglobin concentration
Table 2. Demographic and socioeconomic characteristics of the study population
shows that anemia (Hb<10 g/dl) was associated with a significantly increased risk of low birth weight (<2500 g). High hemoglobin (>13 g/dl) increased the risk of low birth weight but it was not significant. The risk of low Apgar score was significantly increased in women with anemia. The minimum incidence of low birth weight occurs in association with a hemoglobin concentration of 10–12 g/dl.
Table 3. A comparison of neonatal weight and Apgar according to maternal hemoglobin concentration in study population
shows the number of low birth weight in each group.
Table 4. Incidences of low birth weight according by maternal hemoglobin concentration in study population
Discussion
Plasma volume expansion in normal pregnancy causes a drop in maternal hemoglobin to concentrations commonly regarded as indicating anemia (physiologic anemia).Citation3 Anemia during pregnancy, defined as hemoglobin concentration <10 g/dl.Citation6 Traditionally, anemia was associated with sub-optimal pregnancy outcome mainly due to lower birth weight and preterm delivery.Citation13
Since anemia is considered to be one of the most common medical disorders during pregnancy, this association is of main importance. Thus, this study was performed to assess the relation of maternal hemoglobin concentration in third trimester of pregnancy with neonatal birth weight. Birth weight is the single biggest determinant of mortality in the first year of life, and has therefore a strong claim to being a good indicator of the efficiency with which a woman has supported her fetus.Citation18Our study has shown the striking association of birth weight with hemoglobin concentration. The prevalence of anemia during the study pregnancy was 17·8%. Anemia (Hb<10 g/dl) was associated with a significantly increased risk of low birth weight (<2500 g). High hemoglobin (> or = 13 g/dl) increased the risk of low birth weight but it was not significant.
The prevalence of anemia during the study pregnancy was 17·8% and was similar to Bánhidy’s reported (16·7%).Citation14 Iron deficiency is the most common cause for anemia during pregnancy.Citation19 Unfortunately, we do not have data regarding neither iron nor ferritin levels in our database, but many studies indicated that routine iron supplementation during pregnancy may have beneficial effects on pregnancy outcome.Citation7
However, some researchers believe that the extent to which maternal anemia affects maternal and neonatal health is still uncertain, other reported low maternal hemoglobin levels are associated with increased risk of LBW babiesCitation2,Citation4,Citation7–Citation9and Apgar score <5 at 1 minute birth.Citation2Rasmussen reported that strong evidence exists for an association between maternal hemoglobin concentration and birth weight as well as between maternal hemoglobin concentration and preterm birth. It was not possible to determine how much of this association is attributable to iron-deficiency anemia in particular. In this study both low birth weight and preterm birth occurred at maternal hemoglobin concentrations below the 11 g/dl.Citation11 Lone showed ‘Maternal hemoglobin values during pregnancy are associated with birth weight and preterm birth in a U-shaped relationship with high rates of babies who are small at low and high concentrations of maternal hemoglobin’.Citation2 In contrast, some studies reported that anemia is an independent risk factor for the development of adverse outcome of pregnancy or LBW.Citation6,Citation10,Citation13
This study has found an increased incidence of LBW in association with maternal hemoglobin concentration higher than 13 g/dl. Like this Chang et al.Citation9 also reported an increased incidence of LBW and preterm birth in association with either a high maternal hemoglobin concentration or high hematocrit. This result is very interested; because, although there may be other reasons to offer women supplemental iron during pregnancy, the currently available evidence from studies with designs appropriate to establish a causal relationship is insufficient to support or reject this practice for the specific purposes of raising birth weight or lowering the rate of preterm birth. Further studies are needed to assess the effects of routine antenatal supplementation with iron or a combination of iron and folic acid on clinically important maternal and infant outcomes. Also, future studies should focus on the biological mechanisms responsible for the relationship between high hemoglobin concentrations and adverse birth outcomes. Our database does not include information regarding the precise week of anemia diagnosis, nor of compliance of patients with treatment. Thus, maternal iron status was not accurately known. Since adequate counseling is an important determinant of compliance, future inquiries about the effectiveness of iron/folic acid supplementation in other countries should focus on the nature of the interaction between midwives and patients during the prenatal visit and on midwives’ training and knowledge about anemia.
Conclusion
In conclusion, the current study indicated the association of maternal anemia in pregnancy with increased risk of delivery of LBW babies. On the other hand, Hg>13 g/dl was also with risk of low birth weight. Certainly, iron supplements improve the iron status of the mother during pregnancy, even in women who enter pregnancy with reasonable iron stores. The advisability of routine iron supplementation during pregnancy has been needed if the mother is anemic, but it may be not necessary if maternal Hb at first trimester is increased.
This study resulted from a medical student thesis of Shahid Sedughi University of Medical Sciences. The authors are thankful to the maternity ward and laboratory personnel of Shahid Sedughi Hospital for their assistance.
References
- Bashiri A, Burstein E, Sheiner E, Mazor M. Anemia during pregnancy and treatment withintravenous iron: current review of the literature. EurJ Obstet Gynecol Reprod Biol 2003;110:2–7.
- Lone FW, Qureshi RN, Emanuel F. Maternal anaemia and its impact on perinataloutcome. Trop Med Int Health 2004;9:486–90.
- Bernstein IM, Ziegler W, Badger GJ. Plasma volume expansion in early pregnancy. ObstetGynecol 2001;97:669–74.
- Steer PJ. Maternal hemoglobin concentration and birthweight. Am J Clin Nutr 2000;71:1285S–7S.
- Lindsay HA. Anemia and iron deficiency: effects on pregnancyoutcome. Am J Clin Nutr 2000;71:1280S–4S.
- Levya A, Frasera D, Katzc M, Mazorc M, Sheiner E. Maternal anemia during pregnancy is an independentrisk factor for low birthweight and preterm delivery. EurJ Obstet Gynecol Reprod Biol 2005;122:182–6.
- El Guindi W, Pronost J, Carles G, Largeaud M, El Gareh N, Montoya Y, et al.. Severe maternal anemia and pregnancyoutcome. J Gynecol Obstet Biol Reprod 2004;33:506–9.
- Bisai S, Mahalanabis D, Sen A, Bose K, Datta N. Maternal early second trimester pregnancyweight in relation to birth outcome among Bengalee Hindus of Kolkata, India. AnnHum Biol 2007;34:91–101.
- Chang SC, O’Brien KO, Nathanson MS, Mancini J, Witter FR. Hemoglobin concentrations influence birthoutcomes in pregnant African-American adolescents. JNutr 2003;133:2348–55.
- Levario-Carrillo M, Hernández M, Vásquez ME, Chávez D, Sánchez C, Corral M. Effects of iron-deficiency anemia on placentaand birth weight. Ginecol Obstet Mex 2003;71:75–81.
- Rasmussen KM. Is there a causal relationship between irondeficiency or iron-deficiency anemia and weight at birth, length of gestationand perinatal mortality? J Nutr 2001;131:590S–603S.
- Milman N. Iron and pregnancy—a delicate balance. AnnHematol 2006;85:559–65.
- von Tempelhoff GF, Heilmann L, Rudig L, Pollow K, Hommel G, Koscielny J. Mean maternal second-trimester hemoglobinconcentration and outcome of pregnancy: a population-based study. ClinAppl Thromb Hemost 2008;14:19–28.
- Bánhidy F, Ács N, Puhó EH, Czeizel AE. Iron deficiency anemia: pregnancy outcomeswith or without iron supplementation. Nutrition 2011;27:65–72.
- Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC, Hauth JC, Wenstrom KD. Williams obstetrics. 23rd ed. NewYork: McGraw-Hill; 2009.p. 1080–1.
- Shah PS, Ohlsson A. Effects of prenatal multimicronutrient supplementationon pregnancy outcomes: a meta-analysis. CMAJ 2009;180:E99.
- Martin JA, Kung HC, Mathews T. Annual summary of vital statistics: 2006. Pediatrics 2008;121:788–801.
- Hack M, Flannery DJ, Schluchter M, Cartar L, Borawski E, Klein N. Outcomes in young adulthood for very-low-birth-weightinfants. N Engl J Med 2002;346:149–57.
- Lawrence P. Iron deficiency in pregnancy. ObstetricMedicine 2010;3:17–24.