Low Risk Neonatal Nurse Exam

Every newborn assessment starts before birth. The maternal chart, prenatal tests, labor record and fetal heart rate tracing tell you which problems to expect and which screening and teaching the infant needs. Exam questions here usually give one or two maternal facts and ask what the nurse should anticipate or do first.

This chapter reviews the tests used to date a pregnancy, judge fetal well-being and screen for genetic conditions, and explains what an abnormal result means for the infant you will receive.

A first-trimester ultrasound measuring crown-rump length is the most accurate way to date a pregnancy. Without early dating, the newborn gestational age exam (Section 2) carries more weight, and an infant labeled "term" may actually be late preterm.

The nonstress test (NST) looks for fetal heart rate accelerations, which show an intact, well-oxygenated fetal nervous system. At 32 weeks or more, a reactive NST has at least two accelerations of 15 beats per minute lasting at least 15 seconds within 20 minutes (10 beats per minute for 10 seconds before 32 weeks). A nonreactive NST can reflect fetal sleep, medications or prematurity, so it leads to more testing.

The contraction stress test (CST) watches the fetal heart rate response to contractions (at least three in 10 minutes). A negative CST has no late decelerations and is reassuring. A positive CST has late decelerations with half or more of the contractions and suggests the fetus has little reserve to tolerate labor, which points toward uteroplacental insufficiency.

The biophysical profile (BPP) combines an NST with four ultrasound markers. Each of the five components scores 2 (normal) or 0 (abnormal), for a total of 10.

A score of 8 or 10 is normal, 6 is equivocal and 4 or less is abnormal. Acute hypoxia removes the NST, breathing, movement and tone first. Low amniotic fluid reflects chronic hypoxia, because the fetus redirects blood away from the kidneys and makes less urine. A fetus with a low BPP and oligohydramnios may be growth restricted and is at risk for hypoglycemia, polycythemia and poor temperature control after birth.

Memory Aid: Think of BPP as "four acute, one chronic." Breathing, movement, tone and NST reflect the fetus right now; fluid volume reflects the last several days to weeks.

Umbilical artery Doppler measures resistance to blood flow in the placenta. Normally there is forward flow during fetal diastole. When much of the placenta is damaged, end-diastolic flow becomes absent or reversed, a sign of severe placental insufficiency linked with growth restriction, earlier delivery and newborn hypoglycemia, polycythemia, thrombocytopenia, neutropenia and a higher NEC risk once feeds begin.

Amniocentesis samples amniotic fluid for chromosomal and genetic testing or infection. Lung maturity tests, such as a lecithin to sphingomyelin (L/S) ratio of 2.0 or more and phosphatidylglycerol, are now rarely used. The concept still matters: in an infant of a diabetic mother, high fetal insulin delays surfactant production, so a "mature" ratio may not prevent respiratory distress.

Cell-free DNA screening analyzes placental DNA fragments in maternal blood to estimate the chance of trisomy 21, 18 and 13 and sex chromosome differences. It is a screening test, not a diagnosis; a high-risk result needs confirmation by chorionic villus sampling, amniocentesis or newborn chromosomal testing.

Betamethasone (typically two doses of 12 mg IM 24 hours apart) given to the mother speeds fetal lung maturation and lowers the risk of respiratory distress syndrome, intraventricular hemorrhage and NEC. Benefit is greatest when birth occurs more than 24 hours after the first dose and within about 7 days. Courses are routinely offered from 24 to 33 6/7 weeks and may be offered in the late preterm period in selected women. Late preterm steroid exposure increases the risk of neonatal hypoglycemia.

• A reactive NST at 32 weeks or more is two accelerations of 15 beats per minute for 15 seconds in 20 minutes.
• A BPP of 8 or 10 is normal; low amniotic fluid signals chronic stress such as placental insufficiency.
• Absent or reversed end-diastolic flow on umbilical artery Doppler means severe placental insufficiency and a growth-restricted infant at risk for hypoglycemia, polycythemia and NEC.
• Cell-free DNA is a screening test only; confirmation requires diagnostic testing.
• Late preterm antenatal steroid exposure raises the infant's risk of hypoglycemia.