Prematurity

Practice Essentials

Prematurity is a term for the broad category of neonates born at less than 37 weeks’ gestation. For premature infants born with a weight of less than 1000 g, the 3 primary causes of mortality are respiratory failure, infection, and congenital malformation.

Essential update: Study indicates that dexamethasone may affect hearing and intelligence in preterm infants

A meta-analysis by Ruolin et al indicated that dexamethasone use in preterm infants may have significant deleterious effects on hearing and intelligence. The study looked at ten randomized, controlled trials involving a total of 1038 preterm infants, including 512 who received intravenous dexamethasone and 526 who received a placebo. The investigators found a significantly lower intelligence quotient in patients who received dexamethasone treatment within seven days following birth, compared with the placebo group.

In infants who began treatment with dexamethasone more than seven days after birth, the incidence of hearing loss was significantly greater than in the controls, although the change in intelligence quotient was comparable to that in the placebo group. The investigators also found that the incidence of cerebral palsy and visual impairment were similar in the dexamethasone and placebo groups whether dexamethasone was received within seven days following birth or later.

Signs and symptoms

Confirmation of gestational age is based on physical and neurologic characteristics. The Ballard Scoring System remains the main tool clinicians use after delivery to confirm gestational age by means of physical examination. The major parts of the anatomy used in determining gestational age include the following:

  • Ear cartilage (eg, a preterm infant at 28 weeks’ gestation has a small amount of ear cartilage and/or a flattened pinna)
  • Sole (eg, a preterm infant at 33 weeks’ gestation has only an anterior crease on the sole of the foot)
  • Breast tissue (eg, a preterm infant at 28 weeks’ gestation has no breast tissue, and the areolae are barely visible)
  • Genitalia

Diagnosis

Laboratory studies

Initial laboratory studies in cases of prematurity are performed to identify issues that, if corrected, improve the patient’s outcome. Such tests include the following:

  • Complete blood count (CBC): May reveal anemia or polycythemia that is not clinically apparent
  • White blood cell (WBC) count: A high or low WBC count and numerous immature neutrophil types may be found; an abnormal WBC count may suggest subtle infection
  • Blood type and antibody testing (Coombs test): These studies are performed to detect blood-group incompatibilities between the mother and infant and to identify antibodies against fetal red blood cells (RBCs); such incompatibilities increase the risk for jaundice and kernicterus
  • Serum electrolyte levels: Frequent determination of serum sodium, potassium, and glucose concentrations, in conjunction with monitoring of daily weight and urine output in extremely low birth weight (ELBW) infants, assist the practitioner in determining fluid requirements

Imaging studies

Imaging studies are specific to the organ system affected. Chest radiography is performed to assess lung parenchyma in newborns with respiratory distress. Cranial ultrasonography is performed to detect occult intracranial hemorrhage in ELBW newborns. Prematurity itself is not an indication for an imaging study.

Lumbar puncture

Lumbar puncture is performed in infants with positive blood cultures and in those who have clinical signs of infection (presumed sepsis) and for whom a full course of antibiotic coverage is planned.

Management

Stabilization in the delivery room with prompt respiratory and thermal management is crucial to the immediate and long-term outcome of premature infants, particularly extremely premature infants.

Respiratory management

  • Recruitment and maintenance of adequate or optimal lung volume; in infants with respiratory distress, this step may be accomplished with early continuous positive airway pressure (CPAP) given nasally, by mask (Neopuff), or by using an endotracheal tube when ventilation and/or surfactant is administered
  • Avoidance of hyperoxia and hypoxia by immediately attaching a pulse oximeter and, using an oxygen blender, keeping the oxygen saturation (SaO2) between 86% and 93%
  • Prevention of barotrauma or volutrauma by using a ventilator that permits measurement of the expired tidal volume and by keeping it at 4-7 mL/kg
  • Administration of surfactant early (< 2 hr of age) when indicated and prophylactically in all extremely premature neonates (< 29 wk)

Thermoregulation

In the intensive care nursery, radiant warmers may be used to compensate for heat loss in the premature infant. Incubators are more efficient than radiant warmers because the heated environment decreases heat loss due to conduction, convection, and radiation. In all nurseries, the environmental temperature should be maintained at more than 70°F (>21°C).

Fluid and electrolyte management

Preterm infants need intense monitoring of their fluid and electrolytes because of increased transdermal water loss and immature renal function in these infants, as well as various environmental issues (eg, radiant warming, phototherapy, mechanical ventilation). The degree of prematurity and the infant’s specific medication problems dictate initial fluid therapy. However, the following general principles apply to all preterm infants:

  • Initial fluid should be a solution of glucose and water
  • Electrolytes should not be added until the infant is 24 hours of age, when urine output is adequate
  • Infants who develop acute tubular necrosis (ATN) should be treated with fluid restriction that equals insensible water loss plus urine output
  • Hyponatremia and weight gain should be treated with decreasing fluid administration

The patient’s weight should be followed up every 24 hours. Results of laboratory monitoring and change in weight dictate changes in fluid and electrolyte support.

Background

Prematurity refers to the broad category of neonates born at less than 37 weeks’ gestation. Although the estimated date of confinement (EDC) is 40 weeks’ gestation, the World Health Organization (WHO) broadened the range of full term to include 37-42 weeks’ gestation.

Premature newborns have many physiologic challenges when adapting to the extrauterine environment. Most articles in the neonatology section discuss in detail the most serious of these problems. Serious morbidities occur in extremely low birth weight (ELBW) infants. The near-term neonate (34-36 weeks’ gestation) has issues of prematurity that include feeding immaturity, temperature instability, and prolonged jaundice. This article provides a general overview of the premature infant.

Pathophysiology

Before birth, the placenta serves 3 major roles for the fetus: provision of all the nutrients for growth, elimination of fetal waste products, and synthesis of hormones that promote fetal growth.

With the exception of most electrolytes, the maternal circulation contains more substrate (eg, blood glucose) than the fetal circulation. In addition, the placenta is metabolically active and consumes glucose. Waste products of fetal metabolism (eg, heat, urea, bilirubin, carbon dioxide) are transferred across the placenta and eliminated by the mother’s excretory organs (ie, liver, lung, kidneys, skin).

In addition, the placenta acts as a barrier to infection through mucosal macrophages and by allowing transfer of maternal immunoglobulins (immunoglobulins such as immunoglobulin G [IgG]) to the fetus beginning at 32-34 weeks’ gestation. Placental dysfunction is involved in the transfer of IgG. Antibacterial activity of the amniotic fluid improves as gestational age advances.

Each of the immature organs of a premature infant has functional limitations. The tasks of caregivers in neonatal intensive care units (NICUs) are to recognize and monitor the needs of each infant and to provide appropriate support until functional maturity can be achieved.

History

In assessing prematurity, gestational age dating by using the mother’s history can be unreliable because of uncertainty of the dates.

About 20% of women have an uncertain last menstrual period (LMP).

Gestational age assessment begins prenatally with obstetric ultrasonography in the first trimester.

Discovery of many fetal anomalies, unsuspected multiple gestation, location of the placenta, and an accurate dating of the pregnancy are additional major benefits of early ultrasonography.

Physical

Confirmation of gestational age is based on physical and neurologic characteristics. In 1979, the Dubowitz scoring system for determining gestational age based on neurologic and physical parameters was revised to include 12 items.  The Ballard Scoring System, revised again to include extremely low birth weight (ELBW) infants, remains the main tool clinicians use after delivery to confirm gestational age by means of physical examination.

The major parts of the anatomy for physical characteristic markers are ear cartilage, sole creases, breast tissue, and genitalia.

This examination should be performed immediately after stabilization and before the expected weight loss occurs on the first day.

Hittner et al reported that regression of the vascularity of the lens capsule is an excellent tool to confirm a gestational age of 28-34 weeks.

Neurologic criteria include muscle tone of the trunk and extremities and joint mobility.

Reassessing the neurologic criteria 18-24 hours after birth is best to allow for recovery from maternal medication (eg, magnesium sulfate, analgesics), which may decrease tone and responsiveness.

Causes

Premature delivery can be the result of preterm labor and preterm premature rupture of the membranes (PPROM) or can be due to maternal indications (eg, pregnancy-induced hypertension).

Chorioamnionitis

Amniocentesis that demonstrates bacteria, WBCs, and a low glucose concentration confirms the diagnosis of chorioamnionitis and is an indication for delivery.

A decrease in the biophysical score or profile in association with chorioamnionitis is associated with fetal infection.

Rates of perinatal mortality, neonatal infection, and respiratory distress syndrome (RDS) increase in the presence of maternal fever and chorioamnionitis.

Intrauterine growth restriction (10th percentile for birth weight)

This is significantly associated with perinatal mortality and long-term morbidity.

Low socioeconomic status

Programs offering additional social support for at-risk pregnant women have not been demonstrated to reduce the numbers of ELBW or preterm infants.

Maternal diabetes

Pregnancies complicated by diabetes and poor glycemic control are associated with a high incidence of prematurity, macrosomia, malformation, fetal death, and neonatal death.

The rate of preterm birth (< 37 weeks’ gestation) is 20-22% of persons with insulin-dependent diabetes.

In women with diabetes diagnosed before pregnancy, the frequency of preeclampsia is increased as the severity of diabetes increases.

Multiple gestation pregnancies

Women with multiple gestation pregnancies are at high risk of preterm labor and delivery and account for increasing percentage of preterm births and ELBW infants

With advances in assisted reproductive technology, multiple gestation pregnancies have increased.

Preterm birth rate for twins has increased from 40.9% in 1981 to 55% in 1997. Multiple births related to infertility treatment have dramatically increased.

Prepregnancy counseling of prospective parents regarding the risks related to multiple gestations is important.

Preterm birth (< 35 weeks’ gestation) occurs in 26% of twins compared with 3% of singletons.

Triplet pregnancies are associated with an increased incidence of preterm labor and delivery at a decreased gestational age and birth weight, compared with singletons and twins. When the data are controlled for gestational age, outcomes are similar for singletons, twins, and triplets.

Maternal age

In women aged 13-15 years, the rate of preterm birth is 5.9%. This rate declines to 1.7% in women aged 18-19 years and 1.1% in women aged 20-24 years.

The rate of preterm births increases in pregnancies in which the mother is older than 40 years. The scoring system for the risk of preterm delivery uses a criterion of age older than 40 years.

Tobacco use

Approximately 15-20% of pregnant women smoke tobacco.Tobacco use is a risk factor for placental abruption and accounts as a factor for 15% of preterm births and 20-30% of ELBW infants.

Source: emedicine.medscape.com

 

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