Newborn Assessment and Maternal Factors Influencing Neonatal Outcomes
Assessment of the Newborn: Chapter 2 – Maternal Factors
Maternal Factors
Any condition that leads to the interference with placental blood flow or the transfer of oxygen to the fetus can cause an adverse outcome.
Ultrasonography
Uses high-frequency sound waves to obtain a picture of the infant in utero. This allows the physician to:
- View the position of the fetus and placenta.
- Measure fetal growth.
- Identify possible anatomical anomalies.
- Qualitatively assess the amniotic fluid.
Amniocentesis
Involves direct sampling and quantitative assessment of amniotic fluid. Amniotic fluid may be inspected for meconium (fetal bowel contents) or blood. Lung maturation can be assessed with amniocentesis. The lecithin-to-sphingomyelin ratio involves the measurement of two phospholipids, lecithin and sphingomyelin. At 34 to 35 weeks gestation, the L/S ratio abruptly rises above 2:1, and this ratio indicates stable surfactant production and mature lungs.
Phosphatidylglycerol (PG) is another lipid found in the amniotic fluid that is used to assess fetal lung maturity. PG first appears at approximately 35 to 36 weeks gestation. If the PG is more than 1% of the total phospholipids, then the risk of respiratory distress syndrome is less than 1%.
Fetal Heart Rate Monitoring
Involves the measurement of fetal heart rate and uterine contractions during labor. Normal fetal heart rate is between 120 to 160 b/m. Fetal tachycardia can be a sign of fetal hypoxemia, prematurity, or maternal fever. Temporary drops in fetal heart rate are called decelerations and can be mild (<15), moderate (15 to 45), or severe (>45). Decelerations are classified by their occurrence in the uterine contraction cycle.
- Early decelerations occur when the fetal heart rate drops at the beginning of the contraction and are secondary to the compression of the fetal head in the birth canal.
- Late decelerations occur when the heart rate drops 10 to 30 seconds after the onset of contractions and are produced by impaired maternal placental blood flow, or uteroplacental insufficiency.
- Variable decelerations are the most common of the three and are probably related to umbilical cord compression.
A completely monotonous heart rate tracing may be indicative of fetal asphyxia. A healthy fetus will have two accelerations within a 20-minute period.
Fetal Blood Gas Analysis
Fetal blood pH can be used to determine the severity of potential problems during labor and delivery. Normally, fetal blood is obtained from a capillary sample taken usually from the scalp. Normal fetal capillary pH ranges from 7.35 to 7.25, with lower values occurring late in labor. A pH below 7.20 may indicate fetal asphyxia.
Evaluation of the Newborn
The initial assessment of the newborn includes a specific sequence of steps following delivery. These are drying, warming, positioning, and suctioning. If the newborn has not begun breathing, lightly flicking the newborn’s heel or vigorously rubbing the back provides physical stimulation.
Apgar Score
The Apgar score is performed at one and five minutes post-delivery. It has five components: heart rate, respiratory effort, muscle tone, reflex irritability, and skin color. In general, infants scoring 7 or higher at 1 minute are responding normally. An infant with a score of 7 may require supportive care, such as oxygen or stimulation to breathe. Infants with a 1-minute Apgar score of 6 or less may require more aggressive care.
Assessment of Gestational Age
Determination of gestational age involves the assessment of multiple physical characteristics and neurological signs. Two common systems are used for the determination of gestational age:
- The Dubowitz scales that involve the assessment of 11 physical and 10 neurological signs.
- The Ballard scales include 6 physical and 6 neurological signs.
Infants born between 38 to 42 weeks are considered term gestation. Infants born before 38 weeks are preterm, while those born after 42 weeks are postterm. All newborns weighing less than 2500 grams are called low birth weight (LBW). Newborns less than 1500 grams are called very low-birthweight (VLBW). Infants whose weight falls between the 10th and 90th percentile are appropriate for gestational age (AGA). Those above the 90th percentile are large for gestational age (LGA), while those below the 10th percentile are small for gestational age (SGA).
Respiratory Assessment of the Infant
Normal newborn respiratory rate is 40 to 60 breaths/minute. Tachypnea (>60 b/m) can occur because of hypoxemia, acidosis, anxiety, or pain. In premature newborns, causes of slow respiratory rates include medications, hypothermia, or neurological impairment.
Physical Assessment
Normal infant heart rates vary between 100 and 160 b/m. Heart rate can be assessed by auscultation of the apical pulse (5th intercostal space, midclavicular line). Alternatively, the brachial and femoral pulses may be used. Weak pulses indicate hypotension, shock, or vasoconstriction. A strong brachial pulse in the presence of a weak femoral pulse suggests either a patent ductus arteriosus (PDA) or coarctation of the aorta.
Physical Assessment
Infants in respiratory distress typically exhibit one or more key physical signs: nasal flaring, cyanosis, expiratory grunting, tachypnea, retractions, and paradoxical breathing. The Silverman score is a system for grading the severity of lung disease.
Retractions
Represent the drawing in of the chest wall between bony structures. Retractions can occur in the suprasternal, substernal, and intercostal regions. Retractions indicate an increase in the work of breathing, especially because of decreased pulmonary compliance. The infant with paradoxical breathing tends to draw in the chest wall.