Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (273 page)

   For patients with positive screening tests, amniotic fluid and chromosome analysis on chorionic villus sampling (CVS) may be performed and is diagnostic. Rapid detection of aneuploidy for chromosomes 13, 18, 21, X, and Y is available by CVS or amniotic fluid FISH.

Second trimester
(15w0d and 22w6d):

   Maternal Quad Screen (pregnancy-associated placental protein A, total hCG, nuchal translucency and inhibin A) and sonogram for genetic diseases should be offered if first-trimester screening or serial sequential screening was not performed (test between 16 and 18 weeks is optimal) (see Chapter
11
).

   For women who have had first-trimester screening, a repeat alpha-fetoprotein (AFP) at 16–18 weeks should be considered.

   Testing to rule out open neural tube defects may be performed on amniotic fluid by AFP testing.

   For women with diabetes in pregnancy, obtain a glucose tolerance test at 24–28 weeks.

At 36 weeks:

   Optional screen for group B streptococcus

   Laboratory Monitoring of the Neonate

The healthy term newborn requires minimal testing and only rarely develops hypoglycemia or hyperbilirubinemia. Preterm infants may require additional testing for hypoglycemia, and failure to grow in the neonatal intensive care unit with serum calcium and alkaline phosphatase. Preterm infants also have an increased rate of thrombocytopenia that may be alloimmune mediated due to maternal antibody or due to increased peripheral consumption. Platelets should be monitored and may drop as low as 10,000/μL.

Glucose monitoring should be performed in infants who are large for gestational age, have a diabetic mother, who require intensive care or are premature, have polycythemia or express tremors, hypotonia, irritability, lethargy, stupor, apnea, seizures, or hypothermia.

Infants should be monitored for jaundice at regular intervals of at least 8 hours and at discharge from the hospital. Bilirubin monitoring should be performed if jaundice is present within the first 24 hours. Transcutaneous bilirubin monitoring may be used to screen; however, elevated levels must be documented with serum.

Cord blood may be sent for blood typing and Coombs tests if the mother is Rh negative or if jaundice develops prior to 24 hours.

Microbiology and infectious disease studies for syphilis, HBV, and/or toxoplasma may be performed as clinically indicated.

Newborn screening for metabolic diseases is performed on the day of discharge or follow-up at age 4 days as mandated by state law (e.g., PKU, thyroid function tests, others).

INFANTS AT INCREASED RISK

Low birth weight infants are at increased risk for infection, necrotizing enterocolitis, respiratory distress syndrome, thrombocytopenia, intracranial bleed, and a number of other disorders. Infants with low birth weight ≤2,500 g, very low birth weight 1,500 g, or extremely low birth weight 1,000 g may be seen due to prematurity or intrauterine growth restriction. At the opposite extreme, infants with high birth weight (>4,000 g), and postmature infants are at risk for hypoglycemia, and increased perinatal mortality. Infants of high-risk mothers (toxemia, diabetes, drug addiction, cardiac or pulmonary disease) and those with polyhydramnios, oligohydramnios, and cesarean delivery are also at increased risk.

   Laboratory Monitoring for Infants at Increased Risk

During Labor and Delivery

   Monitoring fetal pH with a scalp monitor will indicate hypoxia during extended labor; pH <7.2 increases risk.

   Pulmonary immaturity may be recognized at the time of rupture of membranes by testing amniotic fluid for the lecithin/sphingomyelin ratio, lamellar body count, or phosphatidylglycerol.

   Amnionitis may be recognized by meconium-stained amniotic fluid at the time of rupture.