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Low Birth Weight: Risk Factors, Prognosis and Interventions

Women's Health, Infant and Children | April 2, 2015 | Author: The Super Pharmacist

women, infant

Low Birth Weight: Risk Factors, Prognosis and Interventions

Birthweight is a key indicator of infant health and a principal determinant of a baby's chance of survival and good health. At birth, most babies weigh 3000 to 3500 grams (6 to 8 pounds). Low birthweight has been defined by the World Health Organization (WHO) as weight at birth of less than 2,500 grams (5.5 pounds). This practical cut-off for international comparison is based on epidemiological observations that infants weighing less than 2,500 g are approximately 20 times more likely to die than heavier babies. 

Babies born in remote areas and babies born in the lowest socioeconomic groups were more likely to be of low birthweight than babies born in major cities and babies born in the highest socioeconomic groups. It is widely recognised that weight at birth is an important indicator of foetal and neonatal health for both individuals and populations. Birthweight in particular is strongly associated with foetal, neonatal, and postneonatal mortality, inhibited long term growth and cognitive development, and chronic diseases later in life.

What Causes Low Birth Weight?

What Causes Low Birth Weight?Birth weight is determined by two processes: the duration of gestation and the rate of foetal growth. A baby’s low weight at birth is either the result of preterm birth (before 37 weeks of gestation) or of restricted foetal (intrauterine) growth. Thus, a fetus or newborn can have a birth weight of less than 2,500 grams either because he/she is born early (preterm birth) or is born small for his/her gestational age due to intrauterine growth restriction (IUGR).

Risk factors for preterm birth

Risk factors for preterm birth include the following:

  • Previous preterm birth
  • Being pregnant with twins, triplets, or more (called “multiple gestations”); one study showed that more than 50% of twin births occurred preterm, compared with only 10% of births of single infants.
  • Certain abnormalities of the reproductive organs (e.g. women who have a short cervix or whose cervix shortens in the second trimester of pregnancy instead of the third trimester)
  • Certain developmental abnormalities in the foetus

Age and certain medical conditions in the mother:

  • Age of the mother: The incidence of LBW is higher among mothers under the age of 18 or over the age of 35.
  • Urinary tract infections
  • Sexually transmitted infections
  • Certain vaginal infections, such as bacterial vaginosis and trichomoniasis
  • High blood pressure
  • Bleeding from the vagina
  • Pregnancy resulting from in vitro-fertilisation
  • Being underweight or obese before pregnancy
  • Short time period between pregnancies (less than 6 months between a birth and the beginning of the next pregnancy)
  • Placenta previa (when the placenta grows in the lowest part of the uterus and covers all or part of the opening to the cervix)
  • Being at risk for rupture of the uterus (when the wall of the uterus rips open); rupture of the uterus is more likely after a prior cesarean delivery or after removal of a uterine fibroid
  • Diabetes (high blood sugar) and gestational diabetes (which occurs only during pregnancy)
  • Blood clotting problems

Certain lifestyle and environmental factors can also be a risk factor. These includie

  • Risk factors for preterm birthSmoking
  • Late or no health care during pregnancy
  • Strong dose-dependent risk factor for LBW
  • Increases the risk of preterm birth although it appears to affect foetal growth more than gestational duration
  • Drinking alcohol
  • Using illegal drugs
  • Domestic violence, including physical, sexual, or emotional abuse
  • Lack of social support
  • Stress
  • Long working hours with long periods of standing
  • Exposure to certain environmental pollutants

Risk factors for intrauterine growth restriction (IUGR)

Risk factors for IUGR (intrauterine growth restriction) include certain medical conditions in the mother, maternal lifestyle factors, certain medications, and congenital foetal abnormalities. The three major risk factors that account for nearly two-thirds of all growth-retarded infants (IUGR) are cigarette smoking during pregnancy, low maternal weight gain and low pre-pregnancy weight.

Medical conditions that predispose to IUGR:

  • Chronic hypertension
  • Pre-eclampsia in early pregnancy
  • Diabetes mellitus
  • Systemic lupus erythematosus
  • Chronic renal disease
  • Inflammatory bowel disease
  • Severe hypoxic lung disease
  • Infections
    • Syphilis
    • Cytomegalovirus
    • Toxoplasmosis
    • Rubella
    • Hepatitis B
    • Herpes simplex virus 1
    • Herpes simplex virus 2
    • HIV

Maternal factors which may cause IUGR include:

  • Smoking
  • Alcohol use
  • Cocaine use
  • Medications (eg, warfarin, phenytoin)
  • Malnutrition
  • Prior history of pregnancy with IUGR
  • Residing at an altitude above 5000 feet

Congenital causes of IUGR include:

  • Trisomy 21
  • Trisomy 18
  • Trisomy 13
  • Turner's syndrome

Prognosis for Low Birth Weight Infants

Studies have demonstrated higher rates of both major developmental handicaps such as cerebral palsy, mental retardation, blindness, and deafness, and less severe developmental handicaps such as learning disabilities and attention deficits, in children born preterm and/or with low birth weights. Research has consistently demonstrated a greater risk for learning-related problems in preterm, low birth weight children as they progress through infancy, preschool, and elementary school. Studies have also indicated a greater incidence of social-emotional and behavior problems associated with prematurity and low birth weight, such as internalising (e.g. depression, anxiety) and externalising (e.g. aggression) problems. LBW has also been found to be associated with increased risk of cardiovascular disease, hypertension, type 2 diabetes mellitus, and stroke. The associations are present across populations, and research has identified plausible biological mechanisms that mediate the associations.

What Interventions Can Help Prevent Low Birth Weight?

Unquestionably, prenatal medical care can benefit certain mothers and their babies enormously. All women, pregnant or not, should get preventive and regular medical care.

What Interventions Can Help Prevent Low Birth Weight?But standard prenatal care cannot be expected to improve aggregate birth outcomes because most treatable medical conditions during pregnancy affect only a small proportion of women. A recent comprehensive review found no evidence that prenatal educational or psychosocial services, home visiting programs, or any medical interventions, even those to prevent infections, prevented either preterm birth or fetal growth retardation. 

One promising way to reduce aggregate rates of low birth weight is to reduce smoking and improve nutrition. 

Interventions to Improve Developmental Outcomes in LBW Children

Many early intervention programs have been developed to enhance the cognitive development of low birthweight infants and to improve their school readiness. A broad review of such interventions found modest success overall, with the most effective programs involving parents as well as children. 

One such “two-generation” intervention, the Infant Health and Development Program (IHDP), targeted low birthweight premature infants and provided family support, including home visits and parent group meetings. Researchers have evaluated the effects of the IHDP program. One study found that the mean IQ of the intervention group at age three was 93.6, while that of the control group was 84.2; and that heavier low birth weight infants benefited more than lighter infants (those weighing less than 2,000 grams). Children whose mothers had a high school education or less gained more from the intervention than those whose mothers had attended college, with the latter showing no significant enhancement in IQ scores at age three. 

Several studies found that the intervention improved cognitive scores at ages twenty-four months and thirty-six months, and one found lower (more favorable) behavior problem scores at twenty-four and thirty-six months. Children who had large gains on IQ score, cognitive skills, school achievement, and behavior at age three, however, generally did not sustain the gains at age eight, although the heavier low birth weight intervention group still outscored the control groups on measures of cognition and school achievement. A recent review of interventions targeting socially deprived families concluded that home visits accompanied by early stimulation in the neonatal unit, as well as by preschool placement, appeared to improve the cognitive development of low birthweight and premature children.

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