Ultrasound for fetal assessment in early pregnancy

Abstract

Background

Diagnostic ultrasound is a sophisticated electronic technology, which utilises pulses of high‐frequency sound to produce an image. Diagnostic ultrasound examination may be employed in a variety of specific circumstances during pregnancy such as after clinical complications, or where there are concerns about fetal growth. Because adverse outcomes may also occur in pregnancies without clear risk factors, assumptions have been made that routine ultrasound in all pregnancies will prove beneficial by enabling earlier detection and improved management of pregnancy complications. Routine screening may be planned for early pregnancy, late gestation, or both. The focus of this review is routine early pregnancy ultrasound.

Objectives

To assess whether routine early pregnancy ultrasound for fetal assessment (i.e. its use as a screening technique) influences the diagnosis of fetal malformations, multiple pregnancies, the rate of clinical interventions, and the incidence of adverse fetal outcome when compared with the selective use of early pregnancy ultrasound (for specific indications).

Search methods

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 March 2015) and reference lists of retrieved studies.

Selection criteria

Published, unpublished, and ongoing randomised controlled trials that compared outcomes in women who experienced routine versus selective early pregnancy ultrasound (i.e. less than 24 weeks' gestation). We have included quasi‐randomised trials.

Data collection and analysis

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. We used the Review Manager software to enter and analyse data.

Main results

Routine/revealed ultrasound versus selective ultrasound/concealed: 11 trials including 37,505 women. Ultrasound for fetal assessment in early pregnancy reduces the failure to detect multiple pregnancy by 24 weeks' gestation (risk ratio (RR) 0.07, 95% confidence interval (CI) 0.03 to 0.17; participants = 295; studies = 7), moderate quality of evidence). Routine scans improve the detection of major fetal abnormality before 24 weeks' gestation (RR 3.46, 95% CI 1.67 to 7.14; participants = 387; studies = 2, moderate quality of evidence). Routine scan is associated with a reduction in inductions of labour for 'post term' pregnancy (RR 0.59, 95% CI 0.42 to 0.83; participants = 25,516; studies = 8), but the evidence related to this outcome is of low quality, because most of the pooled effect was provided by studies with design limitation with presence of heterogeneity (I² = 68%). Ultrasound for fetal assessment in early pregnancy does not impact on perinatal death (defined as stillbirth after trial entry, or death of a liveborn infant up to 28 days of age) (RR 0.89, 95% CI 0.70 to 1.12; participants = 35,735; studies = 10, low quality evidence). Routine scans do not seem to be associated with reductions in adverse outcomes for babies or in health service use by mothers and babies. Long‐term follow‐up of children exposed to scan in utero does not indicate that scans have a detrimental effect on children's physical or cognitive development.

The review includes several large, well‐designed trials but lack of blinding was a problem common to all studies and this may have an effect on some outcomes. The quality of evidence was assessed for all review primary outcomes and was judged as moderate or low. Downgrading of evidence was based on including studies with design limitations, imprecision of results and presence of heterogeneity.

Authors' conclusions

Early ultrasound improves the early detection of multiple pregnancies and improved gestational dating may result in fewer inductions for post maturity. Caution needs to be exercised in interpreting the results of aspects of this review in view of the fact that there is considerable variability in both the timing and the number of scans women received.

Plain language summary

Routine compared with selective ultrasound in early pregnancy

Ultrasound is an electronic technology that uses the reflection of pulses of high‐frequency sound to produce an image. Ultrasound may be used in a variety of circumstances during pregnancy. It has been assumed that the routine use of ultrasound in early pregnancy will result in the earlier detection of problems and improved management of pregnancy complications when compared with selective use for specific indications such as after clinical complications (e.g. bleeding in early pregnancy), or where there are concerns about fetal growth.

The focus of this review is routine early pregnancy ultrasound (before 24 weeks). We included 11 randomised controlled trials involving 37,505 women. Early ultrasound improved the early detection of multiple pregnancies and improved gestational dating, which may result in fewer inductions for post maturity. The detection of fetal malformation was addressed in detail in only two of the trials. There was no evidence of a significant difference between the screened and control groups for perinatal death. Results do not show that routine scans reduce adverse outcomes for babies or lead to less health service use by mothers and babies. Long‐term follow‐up of children exposed to scans before birth did not indicate that scans have a detrimental effect on children's physical or intellectual development. Studies were carried out over three decades and technical advances in equipment, more widespread use of ultrasonography, and increased training and expertise of operators may have resulted in more effective sonography.