Ultrasound Pregnancy

Guidelines for ultrasound in pregnancy

Compiled by Dr Rajat Ray

Routine ultrasound examination has become an established part of antenatal care.

The guidelines for use of ultrasonography in pregnancy has been formulated by Ministry of Health & Family Welfare,Govt of India.The salient features are described below.


Maternal & neonatal morbidity and mortality are the two most important health indicators for a country. To ensure appropriate maternal and neonatal health, it is important that the quality of antenatal care is optimized based on current knowledge and available resources. Ultrasonography (USG) isnow an established tool in the clinical management of pregnancy. It is beneficial in detection of congenital malformations, multiple pregnancies, placentaprevia and for confirmation of period of gestation. Theprevalenceofcongenital anomalies ranges from 2% to 4% of all births, but they account for 20-25% of all perinatal deaths and an even higher percentage of perinatal morbidity. Diagnosis of malformations by routine USG providesearly informationand helps in making timely decisions during pregnancy for termination, appropriate treatment at birth and prompt transfer to units specialized in the care of the newborn. Thereby reducing perinatal mortality and morbidity.In the event of concurrent epidemic of infections, the effect of Chicken pox,Dengue,Zika virus etc can also be looked for. Certain conditions such as ectopic pregnancy, multiple gestations, and placenta previa which may lead to potential life threatening complicationscan be identified earlier and appropriately managed with the help of USG. Accurate gestational dating from ultrasound can assist in the management of abnormal foetal growth in pregnancies, which is a leading cause of perinatal morbidity & mortality in both developed and developing countries. Crane et al in a meta-analysis of four randomized controlled trials of routine versus selective ultrasound scanning in pregnancy found a reduction in perinatal mortality in the routine screening group. Trials with high detection rates of diagnosis of congenital anomalies showed an increased rate of elective abortions and therefore reduced the number of perinatal deaths. A Cochrane reviewof 11 randomized controlled trials including 37,505 women for outcome after routine early pregnancy ultrasound (before 24 weeks)versus selective ultrasound hadrevealed that, ultrasound in early pregnancy significantly increased detection of foetal abnormalities before 24 weeks of gestation. Routine ultrasoundalso increased the detection rateof multiple pregnancies and improved gestational dating which resulted in fewer inductions for post maturity.

Number of Ultrasound in Pregnancy:

After reviewing the literature and considering available resources and feasibility, it has been decided that one obstetric ultrasound should be done during pregnancy between 18 and 19 weeks of pregnancy as part of routine Ante Natal Care (ANC)package. Additional ultrasound examinations can be done if clinically indicated

Timing of obstetricultrasound:

If a single scan is to be performed in pregnancy, ideally it should be done between 18 to 22 weeks of gestation. Routine USG in first trimester has not been able toprovide any benefit in low risk pregnancies, except for the diagnosis of ectopic pregnancy. Clinically indicated ultrasound in the presence of risk factors or clinical suspicion based on history and physical examination, can correctly diagnose ectopic pregnancy in 80 to 100% of cases.If the USG is done before 18 weeks, many anomalies will be missed. USG between 18 and22 weeks provides some information about multiple aspects of pregnancy.It presents an opportunity to diagnose congenital anomalies and/or to detect soft markers of aneuploidy and to identify maternal pelvic pathology. Besides, it can confirm the number of fetuses present, the gestational age and the location of the placenta. To allow for intervention after USG, if any anomaly is detected, an adequate period between gestational age forUSG and the upper limit of gestational age at which MTPis permissible isrequired. Therefore the upper limit of gestational age for routine scan in second trimester varies from country to country depending on their MTP law .The law in our country permits MTP up to 20 weeks only; hencea single routine obstetric ultrasound should be performed between 18and19 weeks. In the last two decades, the infant death rate from congenital anomalies has decreased by 50% in infants born after 24 weeks. This is probably partially related to early diagnosis of congenital anomalies leading to either pregnancy termination or better neonatal care. Second trimester diagnosis of congenital anomalies also provides the opportunity for foetaltherapy. Second trimester Ultrasound Examination can diagnose up to 94.4% twin pregnancies if done before 19-20 weeks. The occurrence of twins, undiagnosed at delivery is extremely rare when women have received a second trimester ultrasound. The likelihood of 11 10 unnecessary induction for post date pregnancy and intrauterine growth restriction also decreases significantly by second trimester USG. However, it may be desirable for an ultrasound to be done earlier if there is some high risk factor. If the woman comes for the first time after 20 weeks,the USG should be done for clinical indications only. The woman should be counseled before conducting ultrasound about the purpose of USG and after theultrasound about the prognosis of foetal anomaly, if any anomaly is detected and options available. No prior preparation of the woman is required for the ultrasound examination. As far as possible, the day of ultrasound should coincide with ANC examination day and fixed days for USG should be avoided,as this may lead to multiple visits by the pregnant women.

Purpose/ indication for USG

  1. To detect chromosomal abnormalities, foetal structural defects and other abnormalities.
  2. Estimation of gestational age which results in reduction of post term pregnancies
  3. To detect number of foetuses and their chorionicity.
  4. Evaluation of placental position and abnormalities
  5. Assessment of cervical canal and diameter of internal Os to detect incompetent Os.

Components of the routine obstetric ultrasound scan

The following systems are examined to assess for any congenital anomalies and screen for high risk pregnancy.

  • foetal number, multiple gestations - chorionicity, amnionicity, comparison of foetal sizes, estimation of amniotic fluid volume (increased, decreased, or normal) in each gestational sac
  • Qualitative or semi quantitative estimate of amniotic fluid
  • Placental location, appearance, and relationship to the internal cervical Os
  • Umbilical cord - number of vessels in the cord, and placental cord insertion site
  • Measurements: Bi-parietal diameter, head circumference, abdominal circumference, and femoral diaphysis length.
  • foetal anatomic survey:
    • Head, face, and neck
    • Lateral cerebral ventricles, Choroid plexus, Midline falx, Cavum septi pellucidi, Cerebellum, Cistern magna,
    • Upper lip
    • Chest : Shape/ Size of chest & Lungs
    • Heart : Four-chamber view, Left ventricular outflow tract, Right ventricular outflow tract
    • Abdomen : Stomach (visualization, size, and sites), Kidneys, Urinary bladder,
    • Umbilical cord insertion site into the foetal abdomen
    • Spine : Cervical, thoracic, lumbar, and sacral spine
    • Extremities : Legs and arms
    • Maternal anatomy : Evaluation of the uterus, adnexal structures, and cervix should be performed when appropriate.

Consent forms and Reporting formats

  1. A written informed consent of the woman undergoing obstetric USG has to be taken in Form F as per PC & PNDT Act and Rules.
  2. All women should receive a clear explanation of the purposes of ultrasound scanning, the information that may be discovered, and the degree of certainty about the information. The implications of finding a FOETAL abnormality should be discussed with PW. Government health facility providing USG services will maintain a register showing, in serial order, the names and addresses of the women subjected to USG,the names of their spouses and the date on which they first reported for USG.

  3. Reporting Format
  4. The USG report has to be entered in the Form F for the purpose of PC-PNDT Act and Rules For ensuring quality and completeness of reporting during the obstetric USG an additional form (Annexure-2) should be filled in at all government facilities which are implementing the use of USG program. If any component of the ultrasound examination listed in the guideline is not visualized adequately, it should be documented in the report and serial scans suggested

  5. Record Keeping
  6. All the records, forms and reports required to be maintained under the PC& PNDT Act and the rules have to be preserved for a period 2 years or for such period as may be prescribed from time to time. Therefore all scans should be carefully documented and archived for at least 2 years. The use of hard copy for routine normal scans has major cost implications. However, when abnormalities are found, or when specific structures are seen which may appear suspicious, hard copy is recommended.


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