Admission ultrasonography as a means of identifying unrecognized fetal compromise in term singleton pregnancies at the onset of labor - a feasibility study.

OBJECTIVES: Apparently uncomplicated low-risk pregnancies, especially first time births, account for a significant proportion of adverse birth outcomes. Improved risk stratification with a simple bedside scan on admission in early labor could potentially reduce adverse intrapartum outcomes. The aim of this feasibility study was to assess a cohort of low-risk subjects with admission ultrasonography at the onset of labor with a view to conducting a future randomized controlled trial (RCT). The objectives were three-fold; i) to determine the logistics of performing a labor admission ultrasound scan ii) to establish whether abnormal ultrasound features can be identified and iii) whether they are associated with emergency delivery and/or poor condition of the neonate at birth.

METHODS: We performed a prospective cohort study of 295 participants with term singleton cephalic pregnancies admitted in early labor or for labor induction with non-fetal indications. The setting was a university teaching hospital in Ireland with almost 8000 births annually. A bedside ultrasound scan was performed to assess fetal biometry, amniotic fluid volume and placental maturity. Patients and their babies were followed up until hospital discharge. The outcomes of interest included image quality, time to perform a scan, oligohydramnios (Single Deepest Pool ≤ 2 cm), small for gestational age (SGA; abdominal circumference <10th centile), mature placenta (Grannum 2 or 3), pathological CTG, emergency cesarean section (CS), fetal acidosis (cord arterial pH <7.10 or base excess <-12.0), low Apgar score <7 at 5 min and neonatal unit admission.

RESULTS: Image quality was optimal in 274 of the 295 scans (93%) and 271 (92%) were completed in less than 10 min. Of this low-risk population, 67 of 294 (23%) had oligohydramnios, 11 (4%) were small for gestational age and 87 (30%) had a mature placenta (Grannum grade 2). The incidence of pathological CTG and emergency CS was higher among patients with oligohydramnios than those with a normal scan but did not reach statistical significance; Odds Ratio 3.40 (95% Confidence Intervals 0.55 to 20.92) and OR 1.43 (95% CI 0.66 to 3.08) respectively. The mean birthweight was significantly lower in those with oligohydramnios -139 g (95% CI -248 to -30) and admission scan detected SGA -357 g (95% CI -557 to -137). Adverse perinatal outcomes were uncommon with a higher incidence of fetal acidosis (pH < 7.10) in the oligohydramnios group. The incidence of neonatal unit admission >24 h was higher in the oligohydramnios group but not statistically significant; OR 3.75 (95% CI 0.61 to 22.97). Results for SGA alone were non-significant and results for oligohydramnios and SGA combined were similar to those for oligohydramnios alone.

CONCLUSIONS: Admission ultrasonography is feasible in a routine clinical setting, but evidence of benefit is weak and does not currently justify a randomized controlled trial.