Prematurity Workup

Updated: May 10, 2023
  • Author: Susan A Furdon, RNC, NNP-BC, MS; Chief Editor: Dharmendra J Nimavat, MD, FAAP  more...
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Laboratory Studies

Initial laboratory testing in cases of prematurity is performed to identify issues that, if corrected, improve the patient's outcome.

Blood tests

Obtain frequent blood glucose levels. This is crucial because hypoglycemia and hyperglycemia are very common in premature infants.

Complete blood cell (CBC) counts may reveal anemia or polycythemia that is not clinically apparent. A high or low white blood cell (WBC) count and numerous immature neutrophil types may also be found. An abnormal WBC count may suggest subtle infection.

Blood typing and antibody testing (Coombs test) 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 infant's risk for jaundice and kernicterus.

Serum electrolytes analysis

At birth, most serum electrolyte levels reflect those of the mother. For example, if the mother received magnesium sulfate to inhibit labor, the baby's respiratory effort may be compromised, and the serum magnesium value in the infant may be elevated.

The serum calcium may be low shortly after birth in small preterm babies.

Immature renal function, as well as limited bone and tissue reserves, result in the need for intravenous replacement of calcium, sodium, potassium, phosphate, and trace minerals in those infants who are taking nothing by mouth. Infants who can tolerate enteric nutrition receive adequate electrolytes and minerals from appropriate preterm formulas and fortified human milk.

Frequent laboratory determinations of serum sodium, potassium, calcium, and glucose levels in conjunction with monitoring of daily weight and urine output in extremely low birth weight (ELBW) infants assists the clinician in managing fluid and electrolytes.

Serum glucose concentrations

Serum glucose levels must be closely monitored because of the risk of hypoglycemia and hyperglycemia in preterm infants. The baby's gestational age and other medical conditions dictate the frequency of testing (see Hypoglycemia).

Metabolic screening

Every state has a metabolic screening program in the USA. All programs include testing of newborn blood spots for a minimum of phenylketonuria, hypothyroidism, and galactosemia. The timing of obtaining the sample varies and a few samples may be required at different intervals. Referring to state guidelines can be very helpful.

In general, false-positive results are most common in preterm babies. Early detection and intervention minimizes the long-term neurologic risk.

Investigational test

A systematic review and meta-analysis suggested the cervical phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) test has the potential to predict women with symptoms of preterm labor who will not deliver within 48 hours. [34] However, its overall predictive ability was limited for identifying symptomatic and asymptomatic women at risk for preterm birth.


Imaging Studies

Imaging studies are specific to the organ system affected. Chest radiography is performed to assess the lung parenchyma and heart size in newborns with respiratory distress. Cranial ultrasonography is performed to detect occult intracranial hemorrhage in extremely low birth weight (ELBW) premature newborns.

In a systematic review and meta-analysis, Conde-Agudelo and Romero found that changes in transvaginal ultrasonographic cervical length over time was not a clinically useful test to predict preterm birth in women with singleton or twin gestations. [35] Rather, a single cervical length measurement that was obtained between 18 and 24 weeks of gestation appeared to be a better test to predict preterm birth than changes in cervical length over time.



Lumbar puncture

Perform lumbar puncture in premature infants with positive blood cultures and in those who have clinical signs of central nervous system infection. Although the decision to perform lumbar puncture in extremely low birth weight (ELBW) premature infants may be a difficult one because of their size and the surrounding clinical circumstances, when feasible, lumbar puncture should be performed if CNS infection is suspected because this will help in determining the duration of antibiotic therapy.