We set out to determine the effect of routine ultrasound scans early in pregnancy (before 24 weeks). This was in comparison to no scan at all, or scans only when a clinical problem was suspected, such as if the woman has vaginal bleeding, or the baby is at high risk of having an abnormality.
What is the issue?
Ultrasound scans send out high-frequency sound waves directed to the area being examined, and use the reflected sound to make an image. This review considers two types of scan in the first half of pregnancy. Early scans (before 14 weeks) mainly aim to count the number of babies, to check they are growing in the correct place and check the pregnancy dates. Later scans, typically done around 18 to 24 weeks, recheck all the above, and also examine the baby's anatomy and whether the placenta (afterbirth) is in the correct place. Both types of scan may cause parental anxiety and a false positive diagnoses could lead to harm. The aim of this review is to compare routine with selective or no scans.
Why is this important?
It has been assumed that routine scans before 24 weeks' gestation will result in the earlier detection of problems and improve management and the pregnancy outcome. The alternative is selective scans for specific reasons.
What evidence did we find?
We searched for randomised controlled trials. We found 13 studies including 85,265 women. We included two main comparisons.
Routine early scanning
Ultrasound scans in the first 14 weeks reduced short-term maternal worries about the pregnancy. There was no evidence of a clear effect on induction of labour to prevent the pregnancy going overdue, loss of the baby, early birth (before 34 weeks) or mothers choosing termination for baby abnormalities.
Routine later scanning
Second trimester scans, at 14 to 24 weeks, increased detection of baby abnormalities, and more women chose termination of pregnancy for this reason. There was no evidence of an effect on perinatal loss. Induction of labour to prevent the pregnancy going overdue was reduced. No studies reported how it affected maternal anxiety. Multiple pregnancies were more likely to be detected by 24 weeks. Long‐term follow‐up of children exposed to these scans did not indicate that they were harmful to children's physical or intellectual development.
We also found one trial from a group of low and middle income countries, comparing a combination of two scans and specialist training of health professionals and referral of women with complications, with selective scans and routine care. The intervention did not alter the number of women delivering in a hospital with caesarean section facility. Nor did it appear to reduce maternal deaths or the numbers of low-birthweight babies, although the evidence was very uncertain.
We also found one trial where all women underwent scans but the results were revealed to the health care professionals in half the cases. This trial showed no important effect of revealing the scan results but the evidence was very uncertain.
Most studies were carried out relatively early in the development of scan technology and when training in its use was less advanced. In most trials a large proportion of women in the control groups received a scan too.
What does this mean?
Early scans probably reduce maternal worries about the baby in the short term. Later scans may reduce labour induction to prevent the pregnancy going overdue. They may also improve detection of major abnormalities in the baby and increase the number of women who choose pregnancy termination for this reason. They may also reduce the number of undetected twin pregnancies. All these findings accord with common sense.
Although neither type of scan appears to alter other important outcomes, our review may underestimate the effect in modern practice because the trials were mostly from relatively early in the development of scan technology, and many participants in the control arms also had scans.
Early scans probably reduce short term maternal anxiety.
Later scans may reduce labour induction for post-maturity. They may improve detection of major fetal abnormalities and increase the number of women who choose termination of pregnancy for this reason. They may also reduce the number of undetected twin pregnancies. All these findings accord with observational data.
Neither type of scan appears to alter other important maternal or fetal outcomes, but our review may underestimate the effect in modern practice because trials were mostly from relatively early in the development of the technology, and many control participants also had scans. The trials were also underpowered to show an effect on other important maternal or fetal outcomes.
Ultrasound examination of pregnancy before 24 weeks gestation may lead to more accurate dating and earlier diagnosis of pathology, but may also give false reassurance. It can be used to monitor development or diagnose conditions of an unborn baby. This review compares the effect of routine or universal, ultrasound examination, performed before 24 completed weeks' gestation, with selective or no ultrasound examination.
To assess the effect of routine pregnancy ultrasound before 24 weeks as part of a screening programme, compared to selective ultrasound or no ultrasound, on the early diagnosis of abnormal pregnancy location, termination for fetal congenital abnormality, multiple pregnancy, maternal outcomes and later fetal compromise.
To assess the effect of first trimester (before 14 weeks) and second trimester (14 to 24 weeks) ultrasound, separately.
We searched Cochrane Pregnancy and Childbirth’s Trials Register, ClinicalTrials.gov, and the World Health Organization's International Clinical Trials Registry Platform (ICTRP) on 11 August 2020. We also examined the reference lists of retrieved studies.
We included randomised controlled trials (RCTs), quasi-RCTs, cluster-RCTs and RCTs published in abstract form. We included all trials with pregnant women who had routine or revealed ultrasound versus selective ultrasound, no ultrasound, or concealed ultrasound, before 24 weeks' gestation. All eligible studies were screened for scientific integrity and trustworthiness.
Two review authors independently assessed trials for eligibility and risk of bias, extracted data and checked extracted data for accuracy. Two review authors independently used the GRADE approach to assess the certainty of evidence for each outcome
Our review included data from 13 RCTs including 85,265 women. The review included four comparisons. Four trials were assessed to be at low risk of bias for both sequence generation and allocation concealment and two as high risk. The nature of the intervention made it impossible to blind women and staff providing care to treatment allocation. Sample attrition was low in the majority of trials and outcome data were available for most women. Many trials were conducted before it was customary for trials to be registered and protocols published.
First trimester routine versus selective ultrasound: four studies, 1791 women, from Australia, Canada, the United Kingdom (UK) and the United States (US).
First trimester scans probably reduce short-term maternal anxiety about pregnancy (risk ratio (RR) 0.80, 95% confidence interval (CI) 0.65 to 0.99; moderate-certainty evidence). We do not have information on whether the reduction was sustained.
The evidence is very uncertain about the effect of first trimester scans on perinatal loss (RR 0.97, 95% CI 0.55 to 1.73; 648 participants; one study; low-certainty evidence) or induction of labour for post-maturity (RR 0.83, 95% CI 0.50 to 1.37; 1474 participants; three studies; low-certainty evidence).
The effect of routine first trimester ultrasound on birth before 34 weeks or termination of pregnancy for fetal abnormality was not reported.
Second trimester routine versus selective ultrasound: seven studies, 36,053 women, from Finland, Norway, South Africa, Sweden and the US.
Second trimester scans probably make little difference to perinatal loss (RR 0.98, 95% CI 0.81 to 1.20; 17,918 participants, three studies; moderate-certainty evidence) or intrauterine fetal death (RR 0.97, 95% CI 0.66 to 1.42; 29,584 participants, three studies; low-certainty evidence).
Second trimester scans may reduce induction of labour for post-maturity (RR 0.48, 95% CI 0.31 to 0.73; 24,174 participants, six studies; low-certainty evidence), presumably by more accurate dating.
Routine second trimester ultrasound may improve detection of multiple pregnancy (RR 0.05, 95% CI 0.02 to 0.16; 274 participants, five studies; low-certainty evidence).
Routine second trimester ultrasound may increase detection of major fetal abnormality before 24 weeks (RR 3.45, 95% CI 1.67 to 7.12; 387 participants, two studies; low-certainty evidence) and probably increases the number of women terminating pregnancy for major anomaly (RR 2.36, 95% CI 1.13 to 4.93; 26,893 participants, four studies; moderate-certainty evidence).
Long‐term follow‐up of children exposed to scans before birth did not indicate harm to children's physical or intellectual development (RR 0.77, 95% CI 0.44 to 1.34; 603 participants, one study; low-certainty evidence).
The effect of routine second trimester ultrasound on birth before 34 weeks or maternal anxiety was not reported.
Standard care plus two ultrasounds and referral for complications versus standard care: one cluster-RCT, 47,431 women, from Democratic Republic of Congo, Guatemala, Kenya, Pakistan and Zambia.
This trial included a co-intervention, training of healthcare workers and referral for complications and was, therefore, assessed separately.
Standard pregnancy care plus two scans, and training and referral for complications, versus standard care probably makes little difference to whether women with complications give birth in a risk appropriate setting with facilities for caesarean section (RR 1.03, 95% CI 0.89 to 1.19; 11,680 participants; moderate-certainty evidence). The intervention also probably makes little to no difference to low birthweight (< 2500 g) (RR 1.01, 95% CI 0.90 to 1.13; 47,312 participants; moderate-certainty evidence). The evidence is very uncertain about whether the community intervention (including ultrasound) makes any difference to maternal mortality (RR 0.92, 95% CI 0.55 to 1.55; 46,768 participants; low-certainty evidence).
Revealed ultrasound results (communicated to both patient and doctor) versus concealed ultrasound results (blinded to both patient and doctor at any time before 24 weeks): one study, 1095 women, from the UK.
The evidence was very uncertain for all results relating to revealed versus concealed ultrasound scan (very low-certainty evidence).