Selective versus universal third trimester ultrasound: Time for a rethink? An audit of current practices at a metropolitan Sydney hospital

Routine third-trimester ultrasound (T3US) is not recommended in evidence-based clinical guidelines despite occurring frequently. This study investigated the incidence, indication for, results and follow-up needs of T3US performed at a Sydney metropolitan teaching hospital.

Audit of T3US amongst singleton pregnancies at St George Hospital, Sydney: retrospective review October-December 2012, prospective cohort with clinician survey February-April 2013. Data included are as follows: maternal demographics, aneuploidy screening results, T3US ordering patterns, results, follow-up management and pregnancy outcomes. Comparison of demographic characteristics and pregnancy outcomes was performed for women undergoing T3US vs. no T3US.

One thousand and thirty-five women (623 retrospective, 412 prospective) were included, of whom 560 (54%) received at least one T3US. Characteristics of retrospective and prospective cohorts were similar, so combined data are presented. Most initial T3USs were for valid indications (463 of 560; 83%), most frequently low-lying placenta at morphology (19%), reduced fundal height (10%) and to follow-up fetal concerns at morphology ultrasound (9%). One hundred and sixty-two out of 560 (29%) of initial T3US were not normal, predominantly related to accelerated or reduced fetal growth. Detection of SGA babies was significantly higher in the T3US group (32% SGA babies detected vs. 0% if no T3US, P < 0.001). However, overall detection rates remained low, with 5.2% and 3.0% of babies who had a T3US unexpectedly <10^th and <3^rd centile birthweight, respectively.

The majority of women received at least one, usually indicated, T3US in routine practice at our metropolitan Sydney hospital. This may impact obstetric care, resource allocation and patient well-being. Detection of small for gestational age fetuses was poor.