The Future of Children, Princeton - Brookings: Providing research and analysis to promote effective policies and programs for children.

For prenatal care to prevent low birth weight deliveries, women at risk of giving birth to preterm or intrauterine growth-retarded infants need to be identified in an accurate and timely manner and to receive effective interventions to reduce preventable risks. Unfortunately, the high risk assessment screening systems that are currently available are neither sensitive nor specific enough to be of great clinical value.^5,8 Further, many incorporate risk factors that are immutable, for example, ethnicity, which limits the potential impact of prevention-oriented prenatal care efforts aimed at modifying amenable risk characteristics.⁸ To appraise the potential impact of universal access and use of prenatal care on reducing the current rates of low birth weight, we must consider the degree to which the currently known determinants of low birth weight and its subcomponents, preterm delivery and intrauterine growth retardation, are potentially preventable or mutable. This needs to be done to estimate a low birth weight percentage that is likely to be achieved through prenatal care interventions. One approach for estimating this target is to determine the proportion of the low birth weight problem in a population which is potentially modifiable.

Establishing the relative prevalence and strength of the known precursors of intrauterine growth retardation (IUGR) and preterm birth is difficult because so little is known about their direct causes.^52-54 In developed countries, the predominant risk factors in order of importance are: (1) cigarette smoking; (2) low maternal weight gain; (3) low prepregnancy weight; (4) first births; (5) female sex; (6) short maternal stature; (7) black race/ethnicity; (8) maternal low birth weight and prior low birth weight history; and (9) general morbidity.^52-54 The top three risk factors can potentially be modified and have been suggested to be involved in nearly two-thirds of IUGR births. Although these estimates suggest that we have a relatively good knowledge base for developing programs to improve fetal growth, these efforts may have only a marginal impact on neonatal and infant mortality in developed countries.⁵⁴

In contrast, very little is known about the risk factors for preterm birth. For preterm births in developed countries, the primary risks are: (1) cigarette smoking; (2) prior preterm birth and spontaneous abortion; (3) low prepregnancy weight; and (4) in utero exposure to diethylstilbestrol (DES), a miscarriage deterrent used primarily in the 1950s in the United States.^52-54 More than two-thirds of preterm deliveries could not be explained by known risk factors, and the proportion of preterm births attributed in this analysis to modifiable risk factors—that is, to smoking, low prepregnancy weight, and DES—was approximately 25%. (It should be noted that, while DES was identified as a contributor to low birth weight, its continued impact on birth weight may be time-limited. Its mention serves as a reminder that well-intended prenatal treatments can inadvertently or indirectly increase the risk of delivering a low birth weight infant.)

These results indicate that the most likely known targets for prenatal interventions to prevent low birth weight rates are (1) smoking (aimed at reduction or cessation); (2) nutrition (aimed at increasing prepregnancy weight and/or ensuring adequate weight gain during pregnancy); and (3) medical care (aimed at reducing overall morbidity).^52-54 These data also emphasize that an appreciable proportion of low birth weight deliveries in developed countries is due to unknown causes or is related to factors that cannot be modified during pregnancy. Some of these factors, for example, ethnicity, may be indicative of the long-term influence of adverse socioeconomic conditions which may be difficult to overcome with prenatal care.

Lowering Individual Risks

Although we do not know the primary causes for low birth weight and preterm birth, we do know at least three important steps that can be taken to reduce the rate of low birth weight. A short discussion of these factors is presented below. (For a more detailed discussion of individual lifestyle factors, see the article by Chomitz in this journal issue.)

Smoking Cessation

Smoking is a major preventable risk factor for low birth weight.⁵ In the wake of growing acceptance of the evidence linking smoking to adverse health effects, smoking is declining among women, although not as fast as among men. Some women report that they cease smoking on their own when they become pregnant (18% to 20%), and others reduce the amount they smoke (27% to 36%). However, about 25% of women who are pregnant continue to smoke throughout their pregnancy.⁵⁵ It has been estimated that as much as one-quarter of low weight births could be prevented if smoking during pregnancy were eliminated.⁵⁶

Some clinical trials of smoking cessation interventions have reported significant effects on increasing birth weight.^57,58 Smoking cessation methods during pregnancy generally include health education, self-help techniques, or counseling programs. Some include home visits, and the more recent approaches include feedback to the woman of her own serum nicotine metabolites. Quit rates during pregnancy have ranged from 9% to 27%, and reduction rates, from 17% to 28%.^59-61

Smoking cessation methods are found to be modestly effective at getting women to stop or reduce smoking, except where interventions merely involve routine advice or when advice was not given to all smokers.^62,63 Reduced smoking, as confirmed by biochemical tests during pregnancy, has been associated with improved mean birth weight in a number of intervention trials.^57,58,64-66 However, most studies of interventions to stop smoking during pregnancy have been too small to detect differences in low birth weight or infant mortality rates. Many clinicians are not thoroughly trained in, nor do they have the time to provide, individualized smoking cessation counseling or reinforcement. Haddow and colleagues found that there was a 30% reduction in low birth weight in pregnancies managed by physicians who had the highest rates of completing the study's smoking cessation intervention.⁶⁴ There was little impact on those managed by physicians with lower rates of completing the intervention.⁶⁴

Women who find the risks of smoking acceptable are least likely to quit.⁶⁷ Some women refer to their previous positive birth outcomes to refute the risks of smoking for them. Others, when trying to quit smoking, point out the unhealthy effects that their coping behaviors have on themselves and others.⁶⁸ In a group of British women who had given birth to low birth weight babies, 38% believed smoking was a cause of low birth weight, but only 10% thought smoking had anything to do with the fact that they had a low weight baby.⁶⁹ Overcoming the factors that lead to these beliefs is a challenge to prenatal care providers.

There is much to be done to disseminate smoking cessation programs within prenatal care.^61,70 Given the substantial proportions of women who continue to smoke during pregnancy or relapse after stopping, developing and disseminating effective cessation programs that are practical for prenatal care settings offers one potentially fruitful approach to address this preventable precursor to low birth weight. In view of recent findings that the infants of mothers with passive smoke exposure during pregnancy are also at risk, efforts to modify smoking habits of family members of pregnant women may be further indicated.⁷¹

Nutritional Care

While there is substantial evidence associating low maternal weight gain and low prepregnancy weight with low birth weight,^72-74 research studies do not clearly indicate that prenatal nutritional interventions will reliably prevent low birth weight deliveries. Randomized trials of supplementation have not found any particular supplement associated with reliable and appreciable improvements in birth weight.⁷⁴ The equivocal research findings regarding the impact of supplementation on birth weight in adequately nourished populations make it difficult to assume that assessment and counseling efforts alone will be highly associated with birth weight improvements.⁷⁴ Overall, the available research on the influence of nutrient supplementation of pregnant women on improved birth weight suggests that benefits may be largely limited to women who are chronically undernourished.⁷⁵

Medical Care

Although a specific medical condition may have a large individual effect on birth weight, most medical conditions affect only a small proportion of pregnant women and, therefore, may contribute little to overall low birth weight rates.^5,76 Infections, sexually transmitted diseases, maternal hematological status, diabetes, and hypertension-related complications all heighten the risk of low weight births.⁵ While high-risk medical care in general, rather than specific medical interventions for specified conditions, might have a measurable impact on low weight births, not all medical interventions reduce the chances of low birth weight. High-risk, acute care to reduce IUGR or lower chances of preterm birth are limited in application and effect. Indeed, under specific conditions—for example, uncontrolled diabetes or severe hypertension—the appropriate intervention may be to induce labor and delivery even though doing so may increase the risk of a low weight birth.

Interventions to minimize the risks of intrauterine growth retardation must give specific attention to fetal growth. A Public Health Expert Panel recommended that maternal risk factors for impaired fetal growth be identified during prenatal screening.⁷² These factors include maternal hypertension, renal disease, heart disease, third trimester bleeding, multiple pregnancy, and sickle cell disease. In the presence of such risk factors and an abnormally low fundal height (abdominal measurement of the mother) for a reliably determined gestational age, an ultrasound examination of the fetus, placenta, and amniotic fluid and monitoring of fetal well-being can aid in the management of a pregnancy for optimal fetal growth. There is little evidence that early delivery improves outcome, except for prevention of fetal death.⁷²

It is important to acknowledge that certain risks of low birth weight may be immutable once a woman is pregnant and has decided not to terminate the pregnancy. At the individual level, the effect of demographic risk factors on birth weight tends to be smaller than medical condition effects. Nevertheless, demographic risks affect larger numbers of women and may be more difficult to alter or ameliorate.⁷⁶ For example, limitations in the size and weight of newborns associated with the mother's or father's size (underweight and short) or the mother's birth weight are not likely to be reversible or may reflect natural variation that is unrelated to mortality. However, the higher rates of very low birth weight among teenage mothers and black mothers may indicate that some demographic risk factors are partly amendable by population-based comprehensive preconception and prenatal interventions. The following discussion concentrates on the role of prenatal care in reducing low birth weight rates by implementing effective features of comprehensive care in populations rather than on a case-by-case basis.

Lowering Population Risks

Improving the nation's low birth weight rates will require more than simply improving the content of prenatal care and changing individual risk factors. System level approaches to impact the accessibility and appropriateness of delivery of health care services to entire groups of women with specifically identified characteristics associated with preventable risks of low birth weight also may be needed. Although observational studies often accompany population-based interventions, there is a paucity of information from more rigorously designed evaluations to assess the impact of these innovations. A number of population-based interventions aimed at motivating and enabling women to optimize their health behaviors and maximize the benefits they might draw from health care services like prenatal care have been developed. Although the available evidence to support their efficacy is equivocal, they are areas for further investigation.

Improving the Use of Prenatal Care

Much attention has been given to the possibility that, in the absence of randomized trials of prenatal care, the observed association between adequate prenatal care utilization and lower rates of low weight births may, in part, reflect the individual and social characteristics of women who choose to use prenatal care early and often. Thus, an important area for continuing inquiry is the exploration of what maternal, paternal, and social factors contribute to the adequate use of prenatal care. Interventions that improve compliance with advice to obtain prenatal care early and continuously throughout pregnancy may be found to improve compliance with other advice given during prenatal care visits, for example, to stop smoking. It has already been reported that belief in the benefits of prevention in general and prenatal care specifically is associated with adequate care use.^77,78 In addition, women who receive adequate prenatal care are also more likely to get preventive care for their infants.⁷⁸

Women who get inadequate amounts of prenatal care do so for a variety of reasons related to characteristics of the health care system, provider practices, and their own individual and social characteristics.⁷⁹ Numerous financial, cultural, and system barriers to prenatal care access have been identified.⁷⁹ In a national study of low-income women, 71% of the women experienced a problem getting prenatal care and, on average, indicated three distinct barriers.⁸⁰ Those who received the least prenatal care cited finances as the "most important reason" for not getting prenatal care sooner or more often. However, as these women were more likely to cite multiple access problems, improving prenatal care access and use may require more than overcoming health care system financial barriers. Women next cited transportation and child care as additional barriers to prenatal care access.

Motivating positive attitudes toward pregnancy is important.⁸¹ Women whose pregnancy is unwanted, who have negative attitudes about being pregnant, or who unintentionally became pregnant are more likely to delay prenatal care or to miss appointments.^82,83 Women who obtain late or no prenatal care are more likely to have considered abortion than adequate prenatal care users.⁸⁴ A recent study found that, prior to the availability of abortion, women who indicated that they or their husbands were unhappy, resentful, or upset about the pregnancy, who did not want the pregnancy, or who had a mistimed pregnancy were more than twice as likely to have a neonatal death, though not a low birth weight baby.⁸⁵ Denial and depression have also been associated with poor use of prenatal care, especially among adolescents.⁸⁶ The woman's partner and family social support network have also been found to be associated with use of adequate care, though findings conflict because of differing definitions of social support and differences in the populations studied.⁸⁷ Women living with the father or a sexual partner were more likely to receive adequate prenatal care visits than women living with adult relatives.⁸⁸ However, conflict or problems with the father of the baby have been found to act as deterrents to early and continuous prenatal care use.^89,90 Familial support and discussions of pregnancy and prenatal care have been shown to have only modest or no measurable effects on a woman's actual use of care.^77,86,91

Patient satisfaction with health care in general is a current aim of quality assurance efforts in the United States.⁹² What is most important to pregnant women in their care has only recently been studied. Women who are satisfied with their care and view their physicians as competent and concerned about their welfare are more likely to receive adequate amounts of care.⁸⁴ On the other hand, negative attitudes toward health care and health care providers may lead women to reject the importance of prenatal care and seek care less often.

Women who disagree with their physicians regarding health risks are less likely to get care.⁹³ Having a baby too soon or too small is of concern to most women, but their own perceptions of when is too soon, what is too small, and what is a problem vary. A small baby in and of itself is not considered a risk by women in general. When asked, many women will respond that a smaller baby is easier in labor and delivery. A British study of pregnant women who had previously had a low birth weight baby—one of the few studies to look at women's views of the risks of low birth weight—found that more than a third of women (37%) did not see low birth weight as a problem.⁶⁹ Yet 63% of these women said that the baby had been in an intensive care unit, and 72% said that the child had problems after birth. Some 15% said they did not think the child was developing normally and 42% said they had continuing worries about the child's development.

Clearly, the determinants of prenatal care use are varied and range from obvious financial, geographic, and support barriers to more subtle cultural and attitudinal characteristics. Through the expansion of Medicaid eligibility, nationwide efforts to reduce the financial barriers to prenatal care access have been under way for some years.⁹⁴ Preliminary reports indicate that these efforts have increased prenatal care use.^95,96 These reports are encouraging given the established benefits that prenatal care can provide in the areas of maternal morbidity and mortality and the potential to encourage subsequent health care utilization.⁷⁸ Nevertheless, between 1981 and 1991, the incidence of low birth weight in the United States increased.⁹⁷ Further, the proportion of women getting no care or starting prenatal care in the third trimester also increased.⁹⁷

To the extent that managed care plans under Medicaid will increasingly become the usual source of care for low-income pregnant women, some of the current providers of enhanced perinatal services may be displaced. Publicly funded agencies, maternal and infant care projects, and health departments, typically seen as having the capacity and experience to provide the ancillary services that enhance the comprehensiveness of prenatal care, have traditionally provided prenatal care services to segments of the population at higher risk. The maintenance or transfer of this capacity and experience under managed care or a health care reform scenario is a matter for policy attention.

Providing Preconception Care

Continuous access to health care, not only early in pregnancy but also before and after pregnancy, has been advocated as a means to improve health outcomes of pregnancy, although there is a paucity of rigorous evidence to establish the potential impact of this proposal. Availability of abortion services and, to a lesser extent, family planning services has been associated with lower rates of low weight births.^98,99 In addition, preconception care is currently practiced in some places as a part of maternal and fetal medical care, family planning, and ongoing primary care.¹⁰⁰ Many low birth weight risks predate a woman's pregnancy, and specific interventions exist to reduce prepregnancy risks such as smoking, alcohol and drug use, inadequate weight for height, poor nutritional status, and chronic or recurrent diseases, including sexually transmitted diseases, reproductive tract infections, hypertension, and diabetes.^5,73 Women should be immune to rubella before pregnancy. Although outbreaks of rubella are relatively rare, congenital rubella syndrome effects on fetuses can be devastating in early stages of pregnancy. Women should also be queried about the need for genetic counseling prior to becoming pregnant.

The role of preconception care in improving pregnancy outcomes in general and low birth weight rates in particular remains a topic for investigation. There are well-established methods for determining the relative value of screening tests and treatment in women of varying risks. It is important to assess the individual and cumulative benefit to prepregnancy screening and treatment for conditions with high risk of low birth weight.

Delivering Specialized Prenatal Care

Teenage pregnancy programs serve a population group at distinct high risk of low weight births and are generally a mix of health care, education, and social services in coordination with local agencies. Core services include prenatal, postpartum, and pediatric health care, remedial education, employment training and counseling, family planning services, life planning assistance and life skills training, and parenting education. In addition, many comprehensive care programs have featured a case management approach in which individualized service plans are developed on the basis of individual needs assessments.¹⁰¹ The programs are usually based in schools, health facilities, or the teens' homes. Besides providing psychosocial, nutritional, medical, and health education services, these programs also offer parenting education, encourage continued schooling, urge adolescents to delay subsequent pregnancies, prepare them for employment, and assist them with legal, family, and financial problems. In nonrandomized studies, some of these programs have been found to be associated with higher-than-expected birth weights.²⁹

Prenatal home visiting programs are designed to take aspects of prenatal care into the homes of women who live in high-risk communities. The use of both nurses and lay health workers as home visitors has been revived in recent years as attention has been paid to psychosocial and environmental risk factors for low weight births of the socially disadvantaged. Home visiting is routine in many European countries, where it is usually conducted by midwives. However, many recent pilot projects in this country have used lay health workers from the community. While this intervention has attracted considerable attention as a potentially viable approach to improving birth weights, the evidence regarding its effectiveness remains open to debate.^8,10,102

Involving Cultures and Communities in Developing Prenatal Care

A vital area for reducing low birth weight rates may lie with improving socioeconomic conditions. Improvement in low birth weight rates might be expected if the health, well-being, resources, and prenatal care of the advantaged women in this country could be more widely distributed and if improvements in education, employment, and child care opportunities could be achieved.⁵ Focusing culturally competent outreach and prenatal care efforts in disadvantaged communities may also be a potentially viable area for the improvement of low birth weight rates.⁷⁹ Cultural and community-based enhancements of prenatal care have not been evaluated for their impact on low weight births.

Community empowerment is a process of enabling groups to develop the authority to act, control, or influence consequences that are important to their members. Since the beginnings of the development of prenatal care, it has been recognized that community conditions such as poverty and racism can create circumstances in people's lives that heighten the risks of morbidity, mortality, and the inadequate use of preventive resources.¹⁰³ Empowerment is improving the distribution of the political resources conducive to health and well-being. The concept of empowerment of neighborhoods has led to a recent revival of the ideas of community health workers and community health centers, whose broader role is seen as family life community centers. The notion of empowerment has become entwined with the activities of the culturally focused movements to promote family conditions and parental competencies and behaviors that contribute to maternal and infant health and development.^104,105

The persistent lower rates of low weight births in certain cultural groups, even after adjustments for known differences in risk factors among these groups, have raised concerns that prenatal care should be adapted to specific cultures to be most effective. Culturally sensitive services are those in which there is an appreciation or admiration for the cultural characteristics of a group, and culturally competent services refer to those that accept, respect, and give attention to cultural differences in knowledge, values, beliefs, and customs.^106,107 At the programmatic level, it is recognized that realignments of agency efforts are needed to collaborate with communities in the joint development of goals and directions and to share responsibility for goals, resource development, risks, and rewards.¹⁰⁸