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Pregnancy Care Guidelines

51 Diagnostic testing

The suitability of diagnostic tests is determined by gestational stage. The tests are invasive and have previously been associated with a 1% increased risk of miscarriage. However, recent studies suggest the additional risk is not significant (Akolekar et al 2015; Wulff et al 2016) and is related to the skill and experience of the person carrying out the test (Bakker et al 2016).

Diagnostic tests are based on chromosomal analysis of cells collected using:

  • chorionic villus sampling (tissue from the villi of the chorion [part of the placenta]): testing takes place any time after 11 weeks pregnancy or
  • amniocentesis (to sample fetal skin cells in the amniotic fluid): testing takes place after 15 weeks pregnancy.

51.1 Timing of diagnostic tests

There is high quality evidence from a Cochrane review (Alfirevic et al 2003) and a subsequent randomised trial (n=3,775) (Philip et al 2004) that amniocentesis before 15 weeks pregnancy increases the risk of miscarriage and procedure-related indicated terminations and the incidence of talipes equinovarus compared to chorionic villus sampling at that time. Transabdominal chorionic villus sampling is the method of choice for diagnosis of fetal chromosomal anomalies before 14 weeks pregnancy (Philip et al 2004).

Some women may not have the option of chorionic villus sampling (eg if it is not feasible for the test to be conducted before 14 weeks pregnancy or due to placental positioning) and others may choose to wait for amniocentesis after 15 weeks gestation.

Recommendation

  • Grade B
  • 54

If a woman chooses to have a diagnostic test for chromosomal anomaly, base the choice of test on gestational age (chorionic villus sampling before 14 weeks pregnancy and amniocentesis after 15 weeks) and the woman’s/couple’s preferences. 

Approved by NHMRC in December 2011; expires December 2016

51.2 Discussing diagnostic tests

So that women can give informed consent to diagnostic testing, it is important to explain:

  • the chromosomal anomalies that may be diagnosed
  • the available tests, the gestational stage at which they should be undertaken, the process of the procedure and the risks involved
  • the possibility that the procedure may not be successful or the result may not accurately reflect the fetal status
  • the possibility of other fetal anomalies that are not identified by the test
  • the timeframe for receiving results and making further decisions if necessary
  • options to consider if a chromosomal anomaly is identified (eg continuation of the pregnancy or termination where this is permitted under jurisdictional legislation), the need for additional care if the pregnancy continues (eg specialist management of the pregnancy and the baby) and options for adoption or alternative care arrangements
  • the health and developmental outcomes for children diagnosed with this condition and the potential long-term considerations for the woman and her family
  • the impact on a woman and her family of a false negative or false positive result (eg anxiety among women receiving false positives may remain (Green et al 2004))
  • costs involved and how they are to be met.

51.3 Discussing diagnostic test results

When a woman has a diagnostic test and fetal chromosomal anomaly is detected, follow-up with an appropriate health professional should occur at the earliest opportunity. Appropriate health professionals include obstetricians, midwives experienced in genetic counselling, genetic counsellors and clinical geneticists.

Careful consideration should be given to the way diagnostic test results are conveyed and experienced interpreters should be used when this is necessary to enable effective communication. It is very important that there is no negative commentary on the condition diagnosed and that women do not feel pressured into any course of action. Accurate information about the chromosomal condition should be given and women offered information about relevant support organisations (see Section 53.1).

Women receiving a diagnosis of fetal chromosomal anomaly may be unable to absorb information for some time and follow-up support may require several consultations. Counselling should be sensitive to the nature of decisions to be taken, should respect individual decisions and allow time to reach decisions (NSW Health 2007). Appropriate follow-up when an anomaly is detected may require referral to genetic counselling services, other professional services or support networks.

If a woman has a normal diagnostic test result, she should be advised of the residual probability of having a baby with a chromosomal anomaly as the diagnostic tests have a sensitivity of less than 100%.

Recommendation

  • Consensus-based
  • LI

Offer rapid access to appropriate counselling and ongoing support by trained health professionals to women who receive a diagnosis of fetal chromosomal anomaly. 

Approved by NHMRC in December 2011; expires December 2016

Recommendation

  • Practice point
  • EEE

Refer women with a high-probability screening test result but negative diagnostic test for further specialist assessment because of the increased likelihood of other fetal anomalies. 

Approved by NHMRC in December 2011; expires December 2016

References

  • Akolekar R, Beta J, Picciarelli G et al (2015) Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound Obstet Gynecol 45(1): 16-26.
  • Alfirevic Z, Sundberg K, Brigham S (2003) Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Database of Systematic Reviews DOI: 10.1002/14651858.CD003252.
  • Bakker M, Birnie E, Robles de Medina P et al (2016) Total pregnancy loss after chorionic villus sampling and amniocentesis - A cohort study. Ultrasound Obstet Gynecol.
  • Green JM, Hewison J, Bekker H et al (2004) Psychosocial aspects of genetic screening of pregnant women and newborns: A systematic review. Health Technol Assess 8(33): iii, ix–x, 1–109.
  • NSW Health (2007) Prenatal Testing/Screening for Down Syndrome & Other Chromosomal Abnormalities. PD2007_067. Sydney: NSW Health.
  • Philip J, Silver RK, Wilson RD et al (2004) Late first-trimester invasive prenatal diagnosis: results of an international randomized trial. Obstet Gynecol 103(6): 1164–73.
  • Wulff CB, Gerds TA, Rode L et al (2016) Risk of fetal loss associated with invasive testing following combined first-trimester screening for Down syndrome: a national cohort of 147,987 singleton pregnancies. Ultrasound Obstet Gynecol 47(1): 38-44.
Last updated: 
20 November 2018