What are the recommended screening tests and interventions for premature maturity?

Screening Tests for Premature Maturity

For pregnancies at risk of preterm delivery, routine ultrasound screening before 24 weeks' gestation should be performed to accurately date the pregnancy and detect multiple gestations, which reduces unnecessary inductions for post-maturity and improves early detection of complications. 1, 2

Gestational Age Assessment and Dating

Accurate gestational age determination is the foundation of managing premature maturity risk:

• Ultrasound cephalometry (biparietal diameter measurement) provides the most reliable prediction for fetal age determination and should be performed in early pregnancy, ideally before 14 weeks. 3

• First trimester ultrasound (before 14 weeks) improves gestational dating accuracy, which subsequently reduces inductions for presumed post-maturity by approximately 40-50%. 2

• If gestational age changes by 2 or more weeks after ultrasound examination, screening test results must be reinterpreted with the corrected dates. 4

Fetal Growth and Development Monitoring

Ultrasound Surveillance for Growth Restriction

• Fetal growth restriction should be defined as ultrasonographic estimated fetal weight or abdominal circumference below the 10th percentile for gestational age. 4

• Population-based fetal growth references (such as Hadlock curves) should be used for determining fetal weight percentiles rather than customized standards. 4

• Serial ultrasound assessment of fetal biometry (biparietal diameter, head circumference, abdominal circumference, and femur length) should be performed at 2-week intervals minimum when growth restriction is suspected. 4

Doppler Assessment

• Once fetal growth restriction is diagnosed, serial umbilical artery Doppler assessment should be performed to detect deterioration. 4

• With decreased end-diastolic velocity or severe fetal growth restriction (estimated fetal weight less than 3rd percentile), weekly umbilical artery Doppler evaluation is recommended. 4

• Doppler assessment should increase to 2-3 times per week when umbilical artery absent end-diastolic velocity is detected. 4

Fetal Lung Maturity Assessment

When preterm delivery is anticipated or being considered:

• Assessment of fetal lung maturity through lecithin/sphingomyelin (L/S) ratio in amniotic fluid is more reliable than gestational age indicators alone for determining readiness for delivery. 3

• The L/S ratio determination via thin layer chromatography correlates well with rapid semiquantitative foam stability tests and reliably predicts respiratory distress syndrome risk. 3

• In maternal diabetes mellitus, lung maturity is often reached later than in normal pregnancies, requiring direct assessment rather than relying on gestational age alone. 3

Aneuploidy and Structural Anomaly Screening

Second Trimester Maternal Serum Screening

• Multiple marker screening (AFP, hCG, uE3 with or without inhibin-A) should be offered to all women between 16-18 weeks gestation unless amniocentesis is already indicated or first trimester screening was performed. 4

• Maternal serum AFP (MSAFP) screening should be offered optimally between 16-18 weeks for detection of open neural tube defects and anencephaly. 4

Ultrasound for Structural Anomalies

• Second trimester ultrasound (14-24 weeks) increases detection of major fetal abnormalities before 24 weeks (3.45-fold increase) and enables informed decision-making about pregnancy continuation. 2

• A detailed obstetrical ultrasound examination should be performed with early-onset fetal growth restriction (<32 weeks gestation) to evaluate for structural anomalies. 4

Genetic Testing Considerations

• Fetal diagnostic testing including chromosomal microarray analysis should be offered when fetal growth restriction is detected alongside fetal malformation or polyhydramnios, regardless of gestational age. 4

• Prenatal diagnostic testing with chromosomal microarray analysis should be offered for unexplained isolated fetal growth restriction diagnosed at <32 weeks gestation. 4

• Screening for toxoplasmosis, rubella, or herpes is not recommended in pregnancies with fetal growth restriction absent other specific risk factors. 4

Hormone Testing in At-Risk Populations

For cancer survivors or those with treatment exposures affecting ovarian function:

• Prepubertal females age ≥11 years who fail to initiate or progress through puberty require laboratory evaluation of FSH and estradiol levels. 4, 5

• Postpubertal females treated with alkylating agents and/or radiotherapy with potential ovarian exposure who present with menstrual dysfunction should undergo hormone testing for premature ovarian insufficiency. 4, 5

Screening Tests NOT Recommended

Several proposed screening modalities lack sufficient evidence for routine use:

• Salivary estriol testing carries high false-positive rates and should not be used for predicting preterm delivery. 4

• Bacterial vaginosis screening and treatment has insufficient data to support routine use in low-risk or high-risk populations for preventing preterm birth. 4

• Fetal fibronectin testing has limited usefulness in low-risk women, though negative results may help rule out preterm delivery within 2 weeks in symptomatic high-risk patients. 4

• Transvaginal cervical length measurement by ultrasound, while predictive, is not recommended for routine screening due to lack of effective preventive interventions. 4

Critical Timing Considerations

• Antenatal corticosteroids for fetal lung maturation should be administered between 24+0 and 34+0 weeks gestation when preterm delivery is anticipated. 4

• Magnesium sulfate for fetal neuroprotection should be given before 32 weeks gestation if preterm delivery is imminent. 4

• Long-term follow-up studies show no detrimental effects of prenatal ultrasound exposure on children's physical or cognitive development. 1, 2