Ultrasound for fetal assessment in early pregnancy
Routine ultrasound scanning during pregnancy increased the chances of detection of multiple pregnancy before 24 weeks of gestation and was associated with a reduction in the incidence of labour induction for "post-term" pregnancy. There was also some evidence of earlier detection of fetal abnormalities. However, routine scans did not appear to reduce adverse outcomes for babies or the frequency of use of health-care service by mothers and babies.
RHL Commentary by Belizán JM and Cafferata ML
1. INTRODUCTION
The use of ultrasound in early pregnancy is increasing unabated in developing countries as it is vigorously promoted not only by manufacturers but also in publications coming from developed countries (1). This implies higher health-care costs for developing countries (in terms of purchasing of equipment and training of technicians and physicians), and an undervaluing and less use of clinical examination. The universal use of ultrasound scanning in early pregnancy should be based on a clear demonstration of high benefits that outweigh the logistical and financial implications before introduction of routine ultrasound use is considered
Sometimes women who do not have any risk factors for their pregnancy experience adverse pregnancy-related outcomes. Because of this, it has been be assumed that routine use of ultrasound in all pregnancies is beneficial. However, such screening would be justified only if routine ultrasound use could detect clinical conditions that place the fetus or mother at high risk, which could not have been detected by other means, such as clinical examination, and for which subsequent management would improve perinatal outcome. The objective of this Cochrane review (2) was to assess whether routine use of ultrasound in early pregnancy 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 selective use (i.e. for specific indications) of ultrasound in early pregnancy.
2. METHODS OF THE REVEIW
The review authors searched the literature with the help of the Trials Search Co-ordinator of the Cochrane Pregnancy and Childbirth Group’s Trials Register. The authors also searched for cited references in the literature, abstracts, letters to the editor, and editorials for additional studies. Where necessary, they contacted the primary investigators directly to obtain further data. The searches were conducted without any language restrictions.
Randomized and quasi-randomized controlled trials that had compared routine with selective early pregnancy ultrasound were eligible for inclusion. Also considered were abstracts that contained a detailed description of the results and sufficient information to assess eligibility and risk of bias. The methodological quality of the included trials was assessed by two review authors independently using the Cochrane Handbook for Systematic Reviews of Interventions criteria. Differences between the findings of individual authors were solved by consensus. The search strategy for identification of the studies and data sources was appropriate and complete as was the assessment of the trials' methodological quality.
The primary outcomes considered were the detection of: major fetal abnormality prior to 24 weeks’ gestation, multiple pregnancy by 24 weeks’ gestation, and induction of labour for "post-term" pregnancy and perinatal death. A complete and clear analysis of the outcomes has been presented in the review.
3. RESULTS OF THE REVIEW
Eleven trials involving 37 505 women were included in the review. Only two trials (17 158 pregnancies) reported on the detection of fetal abnormalities before 24 weeks among screened and unscreened women. A total of 387 fetal abnormalities were recorded in the two trials, with most being undetected at 24 weeks (346, 89% not detected by 24 weeks). Women in the screened group were more likely to have abnormalities detected by 24 weeks compared with controls (unweighted percentages 16% versus 4%) [risk ratio (RR) 3.46, 95% confidence interval (CI) 1.67–7.14).
The risk of failure to detect multiple pregnancies before 24 weeks was lower in the screened group compared with the unscreened group (seven studies, RR 0.07, 95% CI 0.03–0.17). With respect to women being induced for post-maturity, women who received early routine ultrasound were less likely to be induced (RR 0.59, 95% CI 0.42–0.83); however, there was a high level of heterogeneity between the studies for this outcome. There was no evidence of a significant difference for perinatal mortality and low birth weight between the screened and the unscreened groups.
4. DISCUSSION
4.1. Applicability of the results
Routine ultrasound scanning during pregnancy increased the chances of detection of multiple pregnancy before 24 weeks' gestation and was associated with a reduction in the incidence of labour induction for "post-term" pregnancy. There was also some evidence of earlier detection of fetal abnormalities. However, routine scans did not appear to reduce adverse outcomes for babies or the frequency of use of health-care service by mothers and babies.
The introduction of routine ultrasound scanning in a resource-constrained health-care setting could place a large burden on available resources, detracting from other more beneficial services. Although clear benefits of routine use of ultrasound scanning have not been established, there are some circumstances in developing countries in which selective use of ultrasound scanning in early pregnancy could be considered. One such circumstance would be in the case of women for whom it is not known when the last menstrual period occurred. However, it should be kept in mind that in developing countries many women do not consult a health-care worker for early antenatal care and this fact would limit this possible advantage.
4.2. Implementation of the intervention
On the basis of the information provided by this review routine use of ultrasound scanning in early pregnancy would not be warranted in under-resourced settings.
4.3. Implications for research
All but one of the studies included in this review were performed in high-income countries. Taking into consideration the differences between under-resourced-settings and high-income settings, routine ultrasound scanning in early pregnancy could show different results in the former. For example, the availability of routine ultrasound early in pregnancy may encourage women to consult a health-care worker sooner for antenatal care or the use of ultrasound may help to detect a multiple pregnancy early and it may be possible to plan the delivery in hospital. Thus, whether introduction of routine ultrasound scanning leads to increased use of antenatal services could be researched in under-resourced settings. The development of portable ultrasounds equipment and whether it could be used by non-medical staff in under-resourced settings would also be of interest.
References
- Hofmeyr GJ. Routine ultrasound examination in early pregnancy: is it worthwhile in low-income countries? Ultrasound in Obstetrics and Gynecology 2009; 34: 367–370.
- Whitworth M, Bricker L, Neilson JP, Dowswell T. Ultrasound for fetal assessment in early pregnancy. Cochrane Database of Systematic Reviews 2010; Issue 4. Art. No.: CD007058; DOI: 10.1002/14651858.CD007058.pub2
This document should be cited as: Belizán JM and Cafferata ML. Ultrasound for fetal assessment in early pregnancy : RHL commentary (last revised: 1 September 2011). The WHO Reproductive Health Library; Geneva: World Health Organization.