Protocols for the Use of Ultrasound in Pregnancy

Protocols for the use of Ultrasound in Pregnancy

Title: The Use of Ultrasound in Pregnancy

Ownership: Leeds Teaching Hospitals NHS Trust

Publication Date: September 2012

Review date: Published November 2007, Reviewed November 2009: Reviewed May 2010: September 2012

1.0 Aims and Objectives

To ensure appropriate use of ultrasound scans in pregnancy

To ensure that all staff working within Maternity Services are aware of the indications for the use of ultrasound in pregnancy. These guidelines are particularly aimed at junior doctors and midwives in an attemptto ensure that the majority of decisions made to perform ultrasound scans are evidence based and to make best use of a limited resource.

2.0 Background

All women who book for delivery within LTHT should be offered:

• a dating scan (at 11-14 weeks)
• a nuchal translucency scan as part of screening for Down’s syndrome (usually carried out at time of dating scan)
• afetal anomaly scan (at 18-20 weeks)

There are clear protocols within the Radiology Department relating to these scans which should be followed.

In low risk groups these two scans should suffice, however, there are clearly some women who warrant further scans during their pregnancy either because of their past obstetric history or because of complications arising during their current pregnancy. In the past we have been fairly generous about who we scan and how often we scan. This has resulted in a big increase in the workload for the sonographers mainly within our own outpatient areas i.e. in the Fetal Assessment Units and Antenatal Clinics at both LGI and SJUH. Unfortunately, because our capacity to scan is not limitless we cannot sustain the current volume of work going through these areas. We therefore need to ensure that we only request an ultrasound examination only if there is a real clinical indication.

3.0 Management

The indications for requesting an ultrasound scan other than the routine dating and anomaly scans are shown in table 1. All fetal assessment requests should be made on the specific request form (see appendix 1) and the referral and indication documented in the handheld or hospital notes. If there are reasons for requesting a fetal assessment not listed on the form, they should be discussed in person with the sonographers in fetal assessment.

Women having scans should be reviewed afterwards in the antenatal clinic or in antenatal day-care and a plan of care made which should include the need for follow up scans.

For details of fetal surveillance in pregnancy complicated by diabetes see Guidelines Diabetes in pregnancy

Table 1: Indications for Additional Scans in Pregnancy

3.1 Suspected Small for Gestational Age Fetus

Women may be suspected as having a small for gestational age fetus based on:

• a fundal height (SFH) measurement of 4cm or more below expected for gestational age
• a first measurement of SFH below the 10th centile plotted on a customised growth chart
• static growth on either a customised growth chart or a plot of serial SFH measurements
• reduced growth velocity of serial measurements of SFH, ideally plotted on a customised chart

Women should be referred for an ultrasound scan to assess fetal biometry and liquor volume within 48 hours although an individual plan of care should be made taking into account gestation, any additional risk factors and the pattern of fetal movements. If there is concern about reduced fetal movementsor there are no available appointments within 48 hours, the case should be discussed with a senior obstetrician (ST5 or above)and a plan of care made. This particularly applies to weekends/bank holidays.

Appendix 1 summarises the management following an initial scan for suspected SGA.

If fetal biometry is normal (growth above 10th centile; normal liquor volume) and in keeping with other growth scans, follow up can revert to her planned antenatal care

Re-referral of appropriately grown babies is NOT necessary unless the SFH drops further below its current centile when serial measurements are plotted on a chart i.e. a slowing of the growth velocity.

If the baby is confirmed to be small for gestational age, umbilical artery Doppler studies should be carried out as part of the assessment of fetal wellbeing. Maternal size, ethnicity and past obstetric history should be taken into consideration when making a diagnosis of SGA and ideally customised charts of SFH and fetal weight should be used. The guidance below should be followed for further follow up.

3.2 Confirmed Small for Gestational Age Fetus

Babies who are confirmed to be on or below the 10th centile for gestational age will require further ultrasound follow up.This may be as a result of a planned growth scan indicated on past history or maternal disease, or a scan for suspected small for gestational age (see section 3.1). Once the gestation reaches 37 weeks, consideration should be given to timing of delivery.

Similarly where there is clear evidence of decreased growth velocity (failure to follow centile over 4 week period, even if above 10th centile) follow up will be required.

If the umbilical artery Doppler’s are normal then a repeat growth scan should be arranged in two weeks.

If the liquor volume is reduced i.e. AFI less than 5cm, then a repeat scan should be arranged for one week to reassess liquor volume and umbilical artery Doppler.

If theDoppler’s are non-reassuring (raised PI; absent or reversed end-diastolic flow), further assessment of the fetal circulation and wellbeing is indicated, as a minimum to include a full biophysical profile. Referral to the fetal medicine team should be made, on the same day or the woman should be reviewed by a Consultant Obstetrician. They will arrange further follow up as appropriate.

Women with SGA babies should be reviewed by an experienced obstetrician (ST3 or above) and a plan of care made and documented in the handheld records. A fetal heart rate recording (CTG) is not a substitution for ultrasound assessment as they are of no predictive value in isolation.

3.3 Previous Small for Gestational Age

Women with a past obstetric history of small for gestational age babies will need more ultrasound surveillance than low risk women. It can be difficult to distinguish between a baby that was constitutionally small and one that was growth restricted (FGR) and the mothers height, weight, ethnicity and parity should be taken into account. If a customised growth chart is available, this should be used. Where not in use, the frequency of scans will depend on the clinical history.

If the history is consistent with FGR (poor growth velocity, abnormal Doppler’s, early delivery because of poor growth, reduced liquor volume) then growth scans should be started at 24 weeks gestation and should be repeated on a four weekly basis thereafter. If there is evidence of FGR in the current pregnancy and the frequency of scans may need to be adjusted on an individual basis

Women with a previous baby born below the 10th centile for gestational age but no other features suggestive of FGR in that pregnancy, should have growth scans at 28 and 34 weeks to assess fetal growth velocity. If these are normal, no further scans are required.

3.4 Suspected Large for Gestational Age Fetus

Women who are clinically large for gestational age i.e. with a fundal height of 5cm or more above the expected for gestational age should be referred for an ultrasound scan to measure fetal biometry and liquor volume within one week. If a customised growth chart is in use, referral should be made if there is a significant increase in the growth velocity with the measurements exceeding the 95th centile. If the initial measurement is above the 95th centile but the growth velocity is normal, another scan is not required.

If the abdominal circumference is above the 95th centile for gestational age then a glucose tolerance test (GTT) should be arranged as per the current antenatal guidelines.

A previous baby that is above the 95th centile for gestation is NOT an indication for growth scans in the third trimester.

3.4.1Confirmed Large for Gestational Age Fetus

Once a baby has been confirmed as being LGA there is little to be gained from repeated ultrasound scans. The exception to this would obviously be in diabetic pregnancies. Thus follow up scans are not necessary for women with LGA babies.

3.4.2 Polyhydramnios

If the amniotic fluid volume (AFI) is above the 95th centile for gestational age then maternal blood should be sent to microbiology to screen for toxoplasmosis, cytomegalovirus and parvovirus and a GTT should be arranged. Women should be reviewed in their own ANC with the results of these investigations and care discussed with the consultant obstetrician in that clinic.Further scans should not be necessary for women with hydramnios in the absence of other pathology.

3.5 Oligohydramnios

In the presence of an appropriately grown baby with normal Doppler’s and with no history of ruptured membranes, if the AFI is 5cm or less a repeat scan to assess growth and liquor volume should be arranged within 2-4 weeks and the woman reviewed by a senior obstetrician (ST5 or above). If the liquor volume remains stable no further scans should be needed.If the woman is term then consideration should be given to induction of labour.

3.6 Previous antenatal stillbirth

Women with a history of in-utero death need ultrasound follow up on clinical grounds (e.g. if baby was FGR) but also to allay maternal and obstetric anxiety. The frequency of these scans should be decided upon by the Consultant and couple concerned however, as a general rule once a month should suffice.

3.7 Maternal factors affecting ability to monitor growth by SFH

3.7.1 Raised maternal BMI

Obese women are a particularly difficult problem in terms of fetal surveillance. It is very difficult to accurately assess uterine size clinically and can be equally difficult to obtain accurate fetal measurements with ultrasound. However, in view of the poor sensitivity of clinical assessment and lack of validity of customised growth charts, obese women (BMI over 35kg/m2) should have a growth scan at 28 & 34 weeks gestation to exclude FGR (for further information see guidelines Obese Pregnant Women (BMI 30 kg/m2 or above)

Women with a low BMI do not require any specific arrangements for ultrasound surveillance other than those dictated by their history or the presence of medical/obstetric complications.

3.7.2 Fibroids

If the uterus is significantly enlarged by fibroids, it can be difficult to assess fetal growth clinically and fundal height measurements may be an unreliable method of measuring fetal growth. The decision to offer serial scans should be individualised taking into account the number, size and position of the fibroids. Scans should be considered if fibroids are around 10cm or more or if there are at least 3 moderate fibroids (5cm or more). Growth scan at 28 & 34 weeks gestation are adequate although a later scan may be required to assess obstruction if the fibroids are in the cervical region.

3.8 Substance Abuse

Women who attend the Substance misuse clinic should have growth scans arranged for 28 & 34 weeks gestation because of the association of drug use with fetal growth restriction. The risk is obviously dependent on the type of drug being used and this guidance should be individualised.

3.9 Antepartum Haemorrhage

Women presenting with a history of antepartum haemorrhage should have an ultrasound scan within 24hrs of the onset of bleeding when ever possible (this may not be possible at weekends).

A single episode of APH, in the absence of placenta praevia or FGR, does not require further ultrasound assessment. If the APH becomes recurrent there is a risk of fetal growth restriction and serial scans should be performed. The frequency of the scans will depend on the severity of the situation but is usuallly every 2 weeks.

3.10 Malpresentation

Where there is a query about fetal lie, then women can be seen in the antenatal day care unit where a scan will be done to assess presentation.

3.11 Assisted Conception

Due to an association with FGR, women who have had IVF or ICSI should have two growth scans in the third trimester, one at 28 and one at 34 weeks gestation. This would not normally be required following ovulation induction(for more information see guidelines Singleton pregnancies conceived by Assisted Reproductive technologies (ART)

3.12 Previous Shoulder Dystocia

Women who last delivery was complicated by shoulder dystocia defined as needing suprapubic pressure and/or internal manoeuvres to deliver the baby may require a growth scan at 36 weeks to inform decisions about mode and timing of delivery. However, it should be remembered that for a large baby the accuracy is poor (said to be +/- as much as 20%). The results should be plotted on a customised growth chart and the woman reviewed by a senior obstetrician (ST5 or above).

4.0 Evidence base

Obstetric Protocols. Department of Radiology 2007

RCOG Guideline 31; The Investigation and Management of the Small for Gestational Age Fetus. RCOG 2002

5.0 Provenance:

Author: Colette Sparey; Consultant Feto-maternal medicine

Published: March 2012

Review date: March 2015

Person responsible for review:Colette Sparey:

Previous versions:

Objective: To ensure appropriate use of ultrasound in pregnancy

Target patient group: all women booked to deliver within LTHT

Target Professional groups: All staff working in the Leeds Teaching Hospitals Trust, Maternity Service

Accompanying Guidance

Previous versions of the protocol have been available in the obstetric department in paper form.

Obstetric Protocols, Department of Radiology

Summary of the consultation process:

This guideline was written by Colette Sparey (Consultant Obstetrician). Drafts were circulated to the following groups and changes made based on comments received:-

Head of Midwifery

Consultant Obstetricians

Team Leaders for Obstetric Ultrasound, Antenatal Clinics, Fetal Assessment Units, Community and Delivery suite.

Radiologists

6.0 Monitoring Compliance

Audits will be carried out in accordance with the maternity services audit plan.

Audit criteria include:

• Compliance with indications for ultrasound in pregnancy
• Frequency of ultrasound scans

Audit results will be presented at the Women’s Services Clinical Governance and Audit meeting and an action plan developed as necessary. A lead will be appointed for monitoring of the action plan, including re-audit, and the status of the action plan reported to the Women’s Services Clinical Governance and Risk management Forum (WSCG&RMF) quarterly. Audit results will be included in the Maternity quarterly risk management report and any resulting changes disseminated via the Maternity Services Forum, Team Leaders Forum, Supervisors Forum.

Appendix 1: Management following scan for suspected SGA

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