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Prepregnancy Nutritional Status and its Impact on Birthweight

by Rae Galloway, Nutrition Advisor, MotherCare, John Snow Inc., 1616 N. Fort Myer Drive, 11th Floor, Arlington, VA 22209, and Mary Ann Anderson, Cognizant Technical Advisor, USAID, Office of Health

The nutritional status of a woman before conception is related to the birthweight of her child. Energy, fatty acids, and micronutrient deficiencies in women either before conception or very early in pregnancy have all been implicated in causing low birthweight in infants.

Babies born less than 2500 g are considered low in birthweight and usually fall into two categories: those that are premature (born before 37 weeks) or those with intrauterine growth retardation (IUGR)-babies who are full-term births but small-for-date. Most low birthweight in developing countries is due to IUGR which is caused predominately by maternal malnutrition, either before conception or during pregnancy. The effects of malnutrition during childhood or adolescence and during pregnancy probably have an additive negative impact on birthweight.

Birthweight is crucial to the survival of the infant. It has been estimated that normal infants in industrial countries have a mortality rate of 2/1,000 while low birthweight infants have a mortality rate of 86/1,000 (Wynn, et al, 1991). If low birthweight babies survive, they have greater rates of morbidity and poorer neurological development (poor vision, decreased educational attainment, and more cerebral palsy, deafness and autism). Damage to the nervous system increases as birthweight falls. Babies with weights greater than 3.5 kg have 6.8 cases of neurological problems per 1,000 live births compared to babies with weights less than 1.5 kg who have 200 cases of neurological problems per 1,000 live births (Hackney Hospital, 1991).

Prepregnancy Weight

For weight, an indicator used to measure protein-energy status, women in both developing and industrial countries who are heavier before pregnancy deliver heavier babies (Nisander and Gordon, 1972 in Wynn, et al., 1991; Kramer, 1987; Naeye, 1979; Kardjati, et al., 1988). Prepregnancy weight can thus be used to predict low birthweight. In a US study, women with a prepregnancy weight below 130 lbs or 59 kg were more than twice as likely to have low birthweight infants when compared to women with pregnancy weights >130 lbs or 59 kg (Taffel, 1980).

A recent meta-analysis of maternal anthropometry and pregnancy outcomes (WHO, forthcoming) confirmed that prepregnancy weight is a good predictor of low birthweight (less than 2.5 kg, odds ratio of 2.3) although attained weight at 5, 7, and 9 months of gestation (odds ratios of 2.4, 2.4 and 2.5, respectively) were also just as predictive of low birthweight. Combining either prepregnancy weight or maternal weight attained at 5, 7, and 9 months of gestation with maternal height, a measure of chronic protein-energy malnutrition, slightly increased the predictive power of these indicators (odds ratios of 2.5, 2.6, and 2.9, respectively). (The predictive power of height alone was not as good as weight, although height was highly predictive of the need for assisted deliveries.) Using as a cut-off the 10th centile of weight-for-gestational age, attained maternal weight at 5, 7, and 9 months of gestation had the greatest predictive power for low birthweight (odds ratios of 2.7, 3.0, and 3.1, respectively) although prepregnancy weight was also useful (odds ratio of 2.5).

Many researchers have found that using a prepregnancy weight of less than 40 kg is a useful cutoff to predict women who will deliver low birthweight babies. Tripathi, et al. (1987) found 60% of small-for-date Indian infants had mothers with prepregnancy weights less than 40 kg and a weight gain of less than 5 kg. Anderson (1989) estimated Indian women weighing less than 40 kg during the first 6 months postpartum had twice the risk of delivering low birthweight infants. This cutoff may only be relevant, however, to very poor countries in Asia and Latin America where the average height of low income women is around 150 cm. In Gujarat and Maharashtra, India, where women are both short and light, it is estimated that 56% and 63% of women, respectively, weigh less than 40 kg in the first trimester (Anderson, 1989). In industrial countries the proportion of women who weigh less than 40 kg is very low. Gopalan (1985) estimated that only 1% of US women weigh less than 40 kg. Women in Africa probably have mean weights that are higher than women in Asia, in part because they are taller. Table 1 shows mean heights and weights of women from a number of countries.

Micronutrients

Little work has been conducted to relate pre-pregnancy micronutrient intakes or status to low birthweight; however, Wynn, et al. (1991) suggests that acquiring a desirable weight and diet during the weeks before and around conception is highly recommended, especially in industrial populations where only subclinical micronutrient deficiencies exist. In developing countries, where a lifetime of very low intakes of micronutrients may exist, it is important to try to reverse these low intakes long before conception, but increasing intakes shortly before and during pregnancy may also help increase birthweight and survival chances of infants.

There is more evidence relating birthweight to micronutrient status or intake very early in pregnancy and over the course of pregnancy. A study in the UK found that birthweight and maternal nutrient intake during the first trimester, especially for 10 micronutrients, was significantly correlated for newborns weighing under the median (3,270g) (Wynn et al, 1991). It should be noted that inadequate intakes of certain micronutrients early in pregnancy have been related to other negative birth outcomes. For example, folic acid deficiency early in the first trimester is associated with neurological defects.

Trace elements in fetal tissue and blood correlate with infant weight and head circumference at birth (Hackney Hospital, 1991). Murphy, et al (1986) found that the frequency of low birthweight deliveries was greater in women with very low or very high hemoglobin levels during their second and third trimester. In a review of the literature, Scholl and Hediger (1994) found iron-deficiency anemia early in pregnancy was linked to low birthweight both in pre- and full-term deliveries. It should be noted, however, that many of the studies on anemia and low birthweight have been criticized because researchers use hemoglobin or other indicators of anemia in the third trimester when hemodilution is a confounding factor, and do not control for caloric intake which has a marked impact on birthweight (Kramer, 1987). However, a recent study in the UK found that inadequate maternal micronutrient and fiber intakes early in pregnancy were more important in determining low birthweights than low protein or energy intake (Wynn et al., 1991). In this study, women had intakes of fiber and ten of the micronutrients (riboflavin, niacin, pyridoxine, thiamin, folic acid, iron, magnesium, phosphorus, calcium, and zinc) that were more than 20% below the reference requirement.

Essential Fatty Acids

Essential fatty acids, needed for neural tissue growth, in fetal tissue and blood correlate with weight and head circumference of the infant at birth (Hackney Hospital, 1991). More work is needed to determine if maternal fatty acid intake or status prior to conception or early in pregnancy is related to birthweight of her infant.

Programmatic Approaches

Ideally, every effort should be made to obtain weights for women before they become pregnant and target education programs to those who are at risk for delivering low birthweight babies. Places to obtain these weights include secondary schools, marriage registration programs, places of work, family planning programs, and, for women who have had children already, through maternal and child health programs. Since adolescent girls deliver more low birthweight babies because they haven’t stopped growing (Garn, 1991), they may have a chance to gain weight the longer they defer marriage and conception. Family planning programs and education are essential to improving maternal nutritional status before the first pregnancy as well as later. For women who have had one or multiple children, adequate birth spacing (at least two years) is recommended so that women can replete their nutritional stores. Family planning and exclusive breastfeeding can assist with extending the birth interval.

Table 1. Mean Prepregnancy Heights and Weights of U.S. and Developing Country Women

Country

Sample Size

Height
(cm)

Weight
(kg)

Source

Bangladesh

2,161

147.9

40.4

Huffman et al., 1985

Indonesia

643

149.0

42.4

Kardjati et al., 1982

Nigeria

360

159.0

52.1

Morley et al., 1968

Senegal

2,088

162.5

58.3

Briend, 1985

Brazil

85

153.0

57.0

Desai et al., 1980

Guatemala

572

148.9

49.0

Lechtig et al., 1975, 1978

U.S.

NA

163.7

56.6

WHO, 1983

Note: Developing country women from these studies are from low socio-economic backgrounds while U.S. women are from average socio-economic backgrounds.

In countries where it is difficult to reach women before conception in order to measure prepregnancy weight but where utilization of antenatal care programs is good, it is possible to obtain weight as a predictor of risk for low birthweight early in pregnancy-up to the 13th week (Anderson, 1989). Those women who are at risk for delivering low birthweight babies should be given appropriate nutrition education messages. If women are not able to eat more because of limited family resources or national supplies of food, every effort should be made, through the community, to educate family members to share and thus reduce the woman’s workload (and thus decrease energy expenditure) during the second and third trimester.

In countries where women present for antenatal care only after the second or third trimester, a weight measurement at 5, 7 or 9 months should be obtained and compared with available references for maternal malnutrition. For women who are in their 5th or 7th month of pregnancy, appropriate measures to increase food intake or decrease workload are needed. If the woman is close to her delivery date, her weight should be measured, but the effectiveness of an intervention at this point to increase her weight is not great. Instead, if she is identified as “at risk” for delivering a low birthweight baby, procedures for referring her to a hospital before delivery should be reviewed with her in order to optimize the survival of the infant if it is born below 2.5 kg. Family members, traditional birth attendants, and other community members should be contacted to help make the referral process work smoothly. The Kangaroo Motherhood Method of caring for low birthweight infants by skin-to-skin contact and breastfeeding has been found to reduce illness and improve survival (MotherCare, 1993).

Because the prevalence of anemia is high and because of its link to poor birth and delivery outcomes and quality of life, all pregnant women in developing countries should receive iron-folate supplements. It has been recommended that in areas where prevalence of anemia is moderate or high, women should receive 2 pills per day containing 60 mg of elemental iron and 250 mcg of folic acid each from the fourth or fifth month of pregnancy (ACC/SCN, 1991). In areas where anemia is mild, women should receive 1 iron-folate pill per day. Women with severe anemia (hemoglobin less than 7 g/dl) should receive 3 iron-folate pills per day. Because of the possible link of prepregnancy iron status to birthweight, attempts should be made to find ways to improve iron-folic acid status before conception. Giving iron-folate pills will depend on national resources to purchase these pills. At the very least, governments should ensure the supply of these pills through the private sector and encourage women to purchase them. Providing iron-folate in oral contraceptives is another of way of ensuring increased intake before conception. For other micronutrients, increased dietary intake before conception through information, education and communication campaigns (EEC) is essential to improving the nutritional status of girls and the health and survival of their children before they become mothers.

Summary

The nutritional status of a woman before she becomes pregnant can determine the birthweight and survival of her future children. This is particularly true of women who have experienced protein-energy malnutrition at sometime during their lives. It may also be true of women who have had inadequate micronutrient intakes before conception although evidence for this is less clear. Programs should continue to address malnutrition in small children where most of the damage to growth is done, but efforts should also be made to ensure adequate intakes of energy and micronutrients of adolescent girls and delay pregnancy so they can maximize their growth before conception. If possible, women should be weighed prior to and during pregnancy to identify those at risk for delivering low birthweight babies. Interventions to increase energy and micronutrient intakes and decrease energy expenditure should help those at risk to optimize their weight and micronutrient status and survival chances of their infants.

References

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