Audit of the appropriateness of the indication for obstetric sonography in a tertiary facility in Ghana
Kobina Mesi Edzie1,&, Klenam Dzefi-Tettey2, Philip Narteh
Gorleku1, Edmund Kwakye Brakohiapa3, Benard
Ohene Botwe4, Adu Tutu Amankwa5, Ewurama Andam Idun6,
Henry Kusodzi1, Abdul
1Department of Medical Imaging, School of Medical Sciences, College of Health and Allied Sciences, University of Cape Coast, PMB, Cape Coast, Ghana, 2Department of Radiology, Korle Bu Teaching Hospital. P. O. BOX KB 77 Korle Bu, Accra, Ghana, 3Department of Radiology, University of Ghana School of Medicine and Dentistry, College of Health Sciences, University of Ghana. P. O. BOX GP 4236, Accra, Ghana, 4Department of Radiography, School of Biomedical and Allied Health Sciences, College of Health Sciences, University of Ghana, Accra, Ghana, 5Department of Radiology, School of Medical Sciences, College of Health Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, 6Department of Radiology, 37 Military Hospital, Neghelli Barracks Liberation Road 37, Accra, Ghana
Emmanuel Kobina Mesi Edzie, Department of Medical Imaging, School of Medical Sciences, College of Health and Allied Sciences, University of Cape Coast, PMB, Cape Coast, Ghana
the use of ultrasound is one of the most vital tools in the management of pregnancies and contributes significantly in improving maternal and child health. Certain indications in pregnancy, guide the obstetrician as to which obstetric scan deems appropriate. The full realization of the benefits of ultrasound depends on whether it is being used appropriately or not, and hence this study aimed at auditing for the appropriate indications for obstetric ultrasound.
a review of all request forms for obstetric scan between June 2019 and
July 2020 was performed to assess the appropriateness of requests for
obstetric ultrasound at the Cape Coast Teaching Hospital. The data obtained
using SPSS (SPSS Inc. Chicago, IL version 20.0). A Chi-squared test of
independence was used to check for statistically significant differences between
at p ≤ 0.05.
three hundred and fourteen (314) out of the 527 request forms had clinical indications stated. 174 (81.7%) of requests from Cape Coast Teaching Hospital and 39 (18.3%) from other health centers did not indicate patients clinical history/indication on the request forms. Majority 76 (68.5%) of scans in the first trimester were done without indications/history. Only 29 of requests with clinical history were inappropriate.
practitioners should be mindful of adequately completing request forms
for obstetric investigations since e a large number of practitioners
do not state the history/indications for the scans. There should be continuous
medical education on the importance
of appropriate indication for obstetric ultrasound.
The application of ultrasound imaging in obstetric care has contributed
significantly to the improvement of maternal health through the
early diagnosis of complications like placenta previa, ectopic pregnancy,
problems with the uterus .
Aside pregnancy complications, obstetric ultrasonography is a routine practice
in radiology, performed to evaluate intrauterine gestation in
early pregnancy, fetal anatomy at mid-term or to assess fetal growth at
Obstetric ultrasonography is commonly used to evaluate issues
of fetal viability, anomalies and fetal well-being .
For instance, an early ultrasound scan (before 13 weeks and 6 days gestation)
is normally performed to confirm a viable intrauterine pregnancy
second trimester ultrasound examinations are used for fetal anatomic
survey, ideally performed between 18-20 weeks and third trimester examinations
for detailed fetal growth evaluations, usually performed after
of pregnancy .
Basically, an obstetric ultrasound examination gives an accurate
and safe clinical evaluation of the gravid uterus throughout a
pregnancy . The American College of Radiology (ACR),
the American College of Obstetricians and Gynecologists (ACOG),
and the American Institute of Ultrasound in Medicine (AIUM) jointly
updated practice guidelines in 2013 for performing an obstetric
ultrasound examinations. For high quality of patients care, these
guidelines have described
indications and key elements for an obstetrical ultrasound examination.
According to these guidelines, “a standard obstetrical ultrasound
in the second and third trimester includes determination of amniotic
fluid volume, cardiac activity, placental position, fetal number,
fetal biometry, and fetal anomaly scan” .
In general, screening for pathological conditions with ultrasound, helps improve
maternal and prenatal healthcare due to the radiation free visualization
of the fetus, uterus and placenta . These applications
show the appropriate uses of ultrasound technology, since they
provide a clear and early diagnosis of potential problems .
The challenge with ultrasonography is where useful clinical information
from the requesting practitioners are missing, which may affect
the accuracy of the ultrasound procedure as well as the interpretation
of results ,
thereby creating the possibility of patient mismanagement. In a
study conducted in Norway, majority of obstetricians reported that
even in the absence of medical
indications, pregnant women will always expect to undergo an ultrasound
examination . Most sonographers on the other hand,
particularly in a private diagnostic facilities, do not bother
about the clinical indications because of the economic gains derived
from the procedure .
Even though there is no conclusive evidence of harm in human studies,
if used imprudently, diagnostic ultrasound could be capable of
Ultrasound is arguably, the most commonly used diagnostic procedure
in obstetrics . In our setting, a recent study
conducted by Edzie et al. to assess the imaging modalities available
in radiological practices in Ghana, discovered that Digital Ultrasound
commonest among all imaging modalities available .
Therefore, it is important to adhere to the protocols for requesting
an obstetric ultrasound and maintain vigilance to ensure the continued
safe use of ultrasound and this is exactly what “as low as reasonably
(ALARA) recommends . However, it is assumed that
the subjective opinions of midwives and obstetricians will influence
their requests for ultrasound examination leading to inappropriate
In this study, we audited for the appropriateness of indications
for obstetric ultrasound in a tertiary facility in Ghana. Most
have laid down guidelines for professional ultrasound practice
in obstetrics. The present study compared the findings to the ACR-AIUM-ACOG
guidelines for the use of obstetrical ultrasound as the yardstick
for the appropriateness of requests.
This retrospective study reviewed all request forms of clients who
had an obstetric scan at the imaging center of the Cape Coast Teaching
Hospital between ( CCTH) June 2019 and July 2020. The facility
is a public tertiary facility
that receives referrals from all tiers of health care delivery
centers in the region. All the scans were done using a Toshiba
ultrasound machine (Nemio
XG Toshiba American Medical system, Inc. Tustin California) fitted
with curvilinear transducers with frequency of 2.5MHz. Three consultant
of at least 15 years experience in obstetric ultrasonography performed
all the scans.
The reports for all the requests were retrieved from the electronic
records; Picture Archiving and Communications System (PACS) by
the radiologists after permission from the hospital authorities. The clinical
age of the gravid women were recorded as indicated on the request
forms, and the maturity of pregnancies were recorded. Forms were only included
if their corresponding scan report were retrievable, or otherwise
All request forms were checked to differentiate requests from CCTH
and those from outside CCTH. All requests were classified as either appropriate
inappropriate. Two radiologists who are both authors of this study
independently evaluated the appropriateness of each request by comparing
details or history provided on the request forms to the composite
American College of Radiology (ACR) - American Institute of Ultrasound in
(AIUM) - American College of Obstetricians and Gynecologists (ACOG)
practice guidelines for the performance of obstetrical ultrasound .
Two criteria of appropriateness were considered. First, all request
forms without history/indication were considered as inappropriate and those
history/indication were considered as appropriate. For request
forms with clinical history/indication, a second measure of appropriateness
A request was classified as appropriate if the indications of the
scans requested and the maturity of pregnancies conform to the ACR- AIUM
Data obtained (clinical history/indication, gestational age, origin
of requests, and demographics) were entered in SPSS (SPSS Inc.
Chicago, IL version 20.0) software for windows and analyzed using
and presented in appropriate tables and charts. We compared the
appropriateness of request forms (with or without history) and
scan indications from CCTH
and outside CCTH using Chi-square. A p-value ≤ 0.05 was considered
statistically significant in all inferential analyses.
The study was approved by the Ethical Review Board of Cape Coast Teaching Hospital with clearance number CCTHERC/EC/2020/057. Anonymity and confidentiality were maintained throughout the study.
A total of 527 request forms were retrieved and reviewed for this study. The mean age was 29.96±5.070 ranging from 14 to 50 years. Majority (45.5%) of the scans were done in the third trimester (Table 1).
Overall, 314 out of the 527 request forms had clinical indications stated. The number of requests that were appropriate was 295 (93.3%) largely from CCTH practitioners. However, a significant number 174 (81.7%; p< 0.001)
of the request forms without clinical history/indication
were from CCTH. Also, out of the 58 request forms from other health centers, 39 of them did not write the history of the patient. For request forms with clinical history, only a few 29 (9.2%) were inappropriate. Comparative analysis using Chi-squared test showed that inappropriate requests from the other health centers were significantly higher than requests from practitioners within CCTH (P < 0.001) (Table 1 and Table 2).
A total of 111, 176 and 240 scans were recorded in the first, second
and third trimester respectively. Majority 76 (68.5%) of scans in the first
trimester were done without indications. In the second and third trimesters,
most practitioners stated indications for the scan [116 (65.9%) in the second
trimester and 164 (68.3%) in the third trimester] (Table
1 and Figure 1).
Majority of the obstetric request forms with the appropriate indications
were high across all the trimesters, with the third trimester scans having
the lowest frequency (6.7%) of inappropriate requests (Figure
2). Fetal anatomy was the commonest indication in the second trimester
85(73.3%) and requests for fetal measurements, lie, presentation, liquor and
placental assessment were the common indications in the third trimester 107(65.2%)
3). Out of the 314 request forms with scan indications, fetal anomaly
and pregnancy dating were the only two indications that were requested outside
the required/ideal gestational period (Table
The advent of ultrasound in medical practice has had a significant
influence on patient management due to its accuracy in diagnosing
medical conditions . The clinical application of
ultrasound does not involve the use of ionising radiation, hence
poses insignificant risk to the developing fetus .
Despite the clinical benefits of ultrasound and minimal risk, there
is the need to check
for the appropriate use of ultrasound, especially for obstetrical
the best of our knowledge, this study is the first of its kind
conducted in a tertiary facility in our setting and provides important
the utilization of obstetric ultrasound. The ACR, ACOG and AIUM
are all specialized bodies dedicated to advancing the safe and
effective use of
ultrasound in medicine through professional and public education
These practice guidelines have been developed for use by practitioners
performing obstetric ultrasound. According to the ACR, ACOG-AIUM,
obstetric ultrasound examination should be performed only when
there is a valid medical
reason . However, these guidelines are not intended
to establish a legal standard of care, but for the purposes of
providing high quality ultrasound examination for the betterment of patient
We found that 40.4% of the request forms had no clinical history/indication
1). Several studies have shown flaws of practitioners in filling
of radiological request forms [18, 19].
An analysis of request forms from a previous study showed that
a significant proportion of requests forms had no clinical information
It was established that clinicians who request an imaging examination
frequently experience several difficulties in getting the clinical
history of the patient,
mainly due to little/no information described in clinical records
of patients and delay in laboratory results . Request
forms serve as media of communication between clinicians and diagnostic
providers. Some clinicians underestimate the importance of request
forms and hence either do not provide them at all or provide inadequate
history/indications when making a radiological request. This may
result in medical
delay in instituting appropriate treatment . In
this study, except for not indicating the clinical history on request
forms, the patients´ names and ages were provided on all request forms.
Even though this was not an objective for this study, we however
found that practitioners
from Ghana are doing well compared to other practitioners from
other African countries. Similar studies in Ghana on analysis of
request forms showed
a 99% completion rate of request forms in terms of the patient´s name
and age . In a study conducted in South Africa
and Nigeria, a parameter like patient age was reported to be filled
in as low as 29% and 68% of request forms respectively [23, 24].
The American College of Radiologists (ACR) stipulates that for
a better understanding of the patient´s condition, all forms should
be adequately completed  to aid in the proper management
of patients. Likewise, the ACR-ACOG-AIUM, practice guidelines require
written request for an obstetrical ultrasound examination should
information to demonstrate the medical necessity of the examination” .
For request forms that had clinical history/indications, only a few (29 out of 314) were inappropriately requested based on the ACR-ACOG-AIUM guidelines (Table 1). These inappropriate requests were made for the purpose of dating pregnancy with maturity of 26W + 0 D gestation for 1 request form, fetal anomaly for pregnancies with maturity of < 13W gestation in 3 of the request forms and maturity > 22W gestation in 25 of the request forms (Table 4). Pregnancy dating is accurately determined in first-trimester ultrasound (ultrasound before 13 weeks and 6/7 days) and second trimester ultrasound (before 22 0/7 weeks) since an error of dating advanced
pregnancy by ultrasound can be significantly enormous . Third-trimester ultrasound (beyond 28 0/7 weeks) is the most inaccurate method for pregnancy dating with an accuracy of +/- 21 to 30 days . In the first trimester, an average of three crown-rump length measurement is used to improve accuracy. When crown-rump length exceeds 84 mm (approximately 14 weeks and 0/7 days), the accuracy decreases, and full fetal biometry is used to approximate gestational age . One major concern with third trimester ultrasound dating is underestimating the gestational age of a growth-restricted fetus . Decisions on pregnancy management using a third-trimester ultrasound alone can be difficult for this reason.
Using ultrasound to assess fetal anomaly is now a routine obstetric
practice because of the important component it has in prenatal care .
According to the ACR, AIUM, ACOG practice guidelines, second trimester (weeks
18 to 22) is the ideal time for screening for structural defects in pregnancy
due to a proper visualization of structures at this period .
The majority of fetal anomalies can be diagnosed in late first or early
second trimester of pregnancy . Though early first
trimester ultrasound can aid in evaluating fetal anatomy, in most instances
it is not technically feasible for normal pregnancies 
and hence inappropriate. The second trimester scan has a higher rate (ranging
from 21% to 85%) of detecting major structural anomalies compared to the
first trimester scan (13% to 43.6%) [29-32]. Initiating
anatomy scans in the first trimester will necessitate an additional ultrasound
visit, an extra cost and may be time-wasting .
It is likely that for the first trimester anatomic survey, the unique features
of first trimester anatomy may be misdiagnosed as a fetal anomaly .
Until second trimester, some normal fetal structures (e.g. the cerebellar
vermis) are not fully formed and a reassurance to rule out abnormalities
in these structures in the first trimester is difficult .
In the same light, detecting fetal anomalies in the third trimester
is technically more challenging due to fetal growth, poor imaging with static
and decreased quantities of amniotic fluid . Also,
depending on the fetal position, examination of the fetal face, sacrum and
extremities may not be possible . Scans performed
beyond 22 weeks gestation may limit the ability to seek pregnancy termination.
A limitation for this study was that, we only focused on the ACR-AIUM-ACOG
practice guidelines as the only measure of appropriateness. The practice guidelines
for the performance of obstetric ultrasound differ from one organization to
This study shows that a large number of practitioners who request
for obstetric scans do not state the clinical history/indication
of the patients on the request forms. This may affect the quality
of service rendered and
in effect will affect clinical decisions and management of patients.
There is a need to continuously remind practitioners of the importance
completing request forms for investigations as this may be the
only means of communication between the clinician and the imaging
to all ultrasound examinations, sufficient clinical details are
required to ensure the right examination is performed. Also, most
of the practitioners´ requests
were appropriate for the scan indication. Though this finding is
laudable, as far as the patient´s health is concerned, the authors
suggest that there should be continuous medical education on the
importance of appropriate
indication for obstetric ultrasound. An understanding of the various
indications for first, second and third trimester ultrasound is
important to ensure
that ultrasound is used only when it is appropriate.
What is known about this topic
- Adequate and relevant history must be provided when making an obstetric ultrasound scan request;
- The type of examination done and examination findings must conform to standard guidelines.
What this study adds
- We found that a large number of obstetric practitioners
did not provide clinical history/indication on request
- Most of the indications for the obstetric scans were
appropriate indicative of adherence of practitioners
to international practice guidelines when making their
The authors declare no competing interests.
Emmanuel Kobina Mesi Edzie, Klenam Dzefi-Tettey and Philip Narteh
Gorleku made substantial contribution to the conception, design,
acquisition of data, writing and editing the final draft of the
paper. Edmund Kwakye
Brakohiapa, Benard Ohene Botwe and Adu Tutu Amankwa were involved
in data analysis, literature searches, writing and editing the
final draft of the
paper. Ewurama Andam Idun, Henry Kusodzi and Abdul Raman Asemah
were involved in data collection, analysis and interpretation
of data, literature searches,
writing and editing the final draft of the paper. All the authors
read and approved the final manuscript.
We are grateful to the staff of the ultrasound department of CCTH for helping with the data acquisition.
Tables and figures
Table 1: demographic characteristics
Table 2: appropriateness of scan requests from practitioners
Table 3: scan indications for the various trimesters
Table 4: inappropriate indications for scan by trimester
Figure 1: proportion of
request forms with/without history/indication in the various trimesters
Figure 2: appropriateness of clinical indications in the various trimesters compared with ACR-AIUM-ACOG guidelines
- Kim ET, Singh Kavita, Moran Allisyn, Armbruster Deborah, Kozuki Naoko. Obstetric ultrasound use in low and middle income countries: a narrative review. Reprod Health. 2018 Jul 20;15(1):129. PubMed | Google Scholar
- Herbst MK, Tafti Dawood, Shanahan MM. Obstetric Ultrasound. 2017. [Updated 2020 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Google Scholar
- Committee on Practice Bulletins-Obstetrics and the American Institute of Ultrasound in Medicine. Practice bulletin no. 175: ultrasound in pregnancy. Obstet Gynecol. 2016 Dec;128(6):e241-e256. PubMed | Google Scholar
- Salomon LJ, Alfirevic Zarko, Raine-Fenning Nicholas, Timor-Tritsch I, Seshadri S. ISUOG practice guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound in Obstetrics & Gynecology. 2013 Jan;41(1):102-13. PubMed | Google Scholar
- Crino J, Finberg HJ, Frieden F, Kuller J, Odibo A, Robichaux A et al. AIUM practice guideline for the performance of obstetric ultrasound examinations. J Ultrasound Med. 2013 Jun;32(6):1083-101. PubMed | Google Scholar
- American College of Radiology. ACR-ACOG-AIUM practice guideline for the performance of obstetrical ultrasound. American College of Radiology website. 2007. Accessed 25 September 2020.
- Papp Zoltàn, Fekete Tibor. The evolving role of ultrasound in obstetrics/gynecology practice. Int J Gynaecol Obstet. 2003 Sep;82(3):339-46. PubMed | Google Scholar
- Haruna Umar, Dandeebo Gordon, Galaa SZ. Improving Access and Utilization of Maternal Healthcare Services through Focused Antenatal Care in Rural Ghana: A Qualitative Study. Advances in Public Health. 2019 Jul 1;2019. Google Scholar
- ACOG Committee on Obstetric Practice. ACOG Committee Opinion. Number 299, September 2004 (replaces no. 158, September 1995). Guidelines for diagnostic imaging during pregnancy. Obstet Gynecol. 2004 Sep;104(3):647-51. PubMed | Google Scholar
- Fagerli TA, Mogren Ingrid, Adolfsson Annsofie, Edvardsson Kristina, ┼hman Annika, Holmlund Sophia et al. Midwives´ and obstetricians´ views on appropriate obstetric sonography in Norway. Sex Reprod Healthc. 2018 Jun;16:1-5. PubMed | Google Scholar
- Gammeltoft Tine, Nguyen HT. The commodification of obstetric ultrasound scanning in Hanoi, Viet Nam. Reprod Health Matters. 2007 May;15(29):163-71. PubMed | Google Scholar
- Haar GT. Ultrasonic imaging: safety considerations. Interface focus. 2011 Aug 6;1(4):686-97. PubMed | Google Scholar
- Abramowicz JS. Benefits and risks of ultrasound in pregnancy. Semin Perinatol. 2013 Oct;37(5):295-300. PubMed | Google Scholar
- Edzie EKM, Dzefi-Tettey Klenam, Gorleku PN, Idun EA, Osei Benard, Cudjoe Obed et al. Application of information and communication technology in radiological practices: a cross-sectional study among radiologists in Ghana. J Glob Health Rep. 2020;4:e2020046. Google Scholar
- Hlinomazova Zuzana, Hrazdira Ivo. ALARA-Principle and safety problems of diagnostic ultrasound. Scripta Medica (BRNO). 2005; 78(6):341-6. Google Scholar
- AIUM-ACR-ACOG-SMFM-SRU Practice Parameter for the Performance of Standard Diagnostic Obstetric Ultrasound Examinations. J Ultrasound Med. 2018 Nov;37(11):E13-E24 Epub 2018 Oct 11. Google Scholar
- American Institute of Ultrasound in Medicine. AIUM practice guideline for the performance of obstetric ultrasound examinations. J Ultrasound Med. 2010 Jan;29(1):157-66. PubMed | Google Scholar
- Depasquale Ruben, Crockford MP. Are radiology Request forms adequately filled in? An audit assessing local practice. Malta Medical J. 2005;17(4):36-38. Google Scholar
- Irurhe NK, Sulayymon FA, Olowoyeye OA, Adeyomoye AAO. Compliance Rate of Adequate Filling of Radiology Request Forms in a Lagos University Teaching Hospital. World J. Medical Sci. 2012;7(1):10-12. Google Scholar
- Martins Rute, Raimundo Pedro, Alves Pedro, Monteiro Rodrigo, Silva LD, Gomes André et al. Appropriateness of Radiology Test Requests by an Emergency Department: A Retrospective Study. Acta Méd. Port. 2020 Jan 3;33(1):7-14. PubMed | Google Scholar
- Carraro Paolo, Plebani Mario. Errors in a stat laboratory: types and frequencies 10 years later. Clin. Chem. 2007 Jul;53(7):1338-42. PubMed | Google Scholar
- Olayemi Edeghonghon, Asiamah-Broni Rebecca. Evaluation of request forms submitted to the haematology laboratory in a Ghanaian tertiary hospital. Pan Afr Med J. 2011;8:33. PubMed | Google Scholar
- Zemlin AE, Nutt Louise, Burgess LJ, Eiman Fredeline, Erasmus RT. Potential for medical error: incorrectly completed request forms for thyroid function tests limit pathologists' advice to clinicians. S Afr Med. J. 2009 Sep;99(9):668-71. PubMed | Google Scholar
- Oyedeji OA, Ogbenna AA, Iwuala SO. An audit of request forms submitted in a multidisciplinary diagnostic center in Lagos. Pan Afr Med J. 2015 Apr 29;20:423. PubMed | Google Scholar
- Committee on Obstetric Practice, the American Institute of Ultrasound in Medicine, and the Society for Maternal-Fetal Medicine. Committee Opinion No 700: Methods for Estimating the Due Date. Obstet Gynecol. 2017 May;129(5):e150-e154. PubMed | Google Scholar
- Reddy UM, Abuhamad AZ, Levine Deborah, Saade GR. Fetal Imaging Workshop Invited Participants. Fetal imaging: executive summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Institute of Ultrasound in Medicine, American College of Obstetricians and Gynecologists, American College of Radiology, Society for Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging workshop. Obstet Gynecol. 2014 May;33(5):745-57. PubMed | Google Scholar
- Callen PW. Ultrasonography in obstetrics and gynecology. 5th Philadelphia: Saunders Elsevier. 2008.
- Harper LM, Wood SL, Jenkins SM, Owen John, Biggio JR. The Performance of First-Trimester Anatomy Scan: A Decision Analysis. Am J Perinatol. 2016 Aug;33(10):957-65. PubMed | Google Scholar
- Syngelaki Argyro, Chelemen Teodora, Dagklis Themistoklis, Allan Lindsey, Nicolaides KH. Challenges in the diagnosis of fetal non?chromosomal abnormalities at 11-13 weeks. Prenat Diagn. 2011 Jan;31(1):90-102. PubMed | Google Scholar
- Hildebrand Eric, Selbing Anders, Blomberg Marie. Comparison of first and second trimester ultrasound screening for fetal anomalies in the southeast region of Sweden. Acta Obstet Gynecol Scand. 2010 Nov;89(11):1412-9. PubMed | Google Scholar
- Luck CA. Value of routine ultrasound scanning at 19 weeks: a four year study of 8849 deliveries. BMJ. 1992 Jun 6;304(6840):1474-8. PubMed | Google Scholar
- Levi Salvator, Schaaps JP, De Havay P, Coulon R, Defoort P. End result of routine ultrasound screening for congenital anomalies: the Belgian multicenter study 1984-92. Ultrasound Obstet Gynecol. 1995 Jun;5(6):366-71. PubMed | Google Scholar
- Woodward PJ. Obstetrics. 2nd Salt Lake City, Utah: Amirsys; Diagnostic imaging. 2011.
- Manegold Gwendolin, Tercanli Sevgi, Struben Hendrik, Huang Dorothy, Kang Anjeung. Is a routine ultrasound in the third trimester justified? Additional fetal anomalies diagnosed after two previous unremarkable ultrasound examinations. Ultraschall Med. 2011 Aug;32(4):381-6. PubMed | Google Scholar
- Ficara A, Syngelaki Argyro, Hammami A, Akolekar Ranjit, Nicolaides KH. Value of routine ultrasound examination at 35-37 weeks' gestation in diagnosis of fetal abnormalities. Ultrasound Obstet Gynecol. 2020 Jan;55(1):75-80. PubMed | Google Scholar