NIH Public Access Author Manuscript Clin Obstet Gynecol
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NIH Public Access Author Manuscript Clin Obstet Gynecol. Author manuscript; available in PMC 2013 June 17. NIH-PA Author ManuscriptPublished NIH-PA Author Manuscript in final edited NIH-PA Author Manuscript form as: Clin Obstet Gynecol. 2012 September ; 55(3): 722–730. doi:10.1097/GRF.0b013e318253b318. Antepartum Evaluation of the Fetus and Fetal Well Being ERICA O'NEILL, MD and JOHN THORP, MD Department of Obstetrics and Gynecology, University of North Carolina, Chapel Hill, North Carolina Abstract Despite widespread use of many methods of antenatal testing, limited evidence exists to demonstrate effectiveness at improving perinatal outcomes. An exception is the use of Doppler ultrasound in monitoring high-risk pregnancies thought to be at risk of placental insufficiency. Otherwise, obstetricians should proceed with caution and approach the initiation of a testing protocol by obtaining an informed consent. When confronted with an abnormal test, clinicians should evaluate with a second antenatal test and consider administering betamethasone, performing amniocentesis to assess lung maturity, and/or repeating testing to minimize the chance of iatrogenic prematurity in case of a healthy fetus. Keywords antenatal testing; fetal well-being; fetal movement counting; nonstress test; fetal lung maturity; Doppler ultrasound Introduction The primary goal of antenatal evaluation is to identify fetuses at risk for intrauterine injury and death so that intervention and timely delivery can prevent progression to stillbirth. Ideally, antenatal tests would decrease fetal death without putting large numbers of healthy fetuses at risk for premature delivery and the associated morbidity and mortality. Despite widespread use of many tests, limited evidence exists to demonstrate effectiveness at improving perinatal outcomes with application of these tests. Certainly, there is a definite need to find a reliable test of fetal well-being. The National Center for Health Statistics defines perinatal mortality rate (PMR) as the number of late fetal deaths (28-wk gestation or more) plus early neonatal deaths (infants 0 to 6 d of age) per 1000 live births plus fetal deaths. In the United States, stillbirths account for more than 55% of the perinatal mortality1 and could potentially be prevented with an effective form of fetal testing. Unfortunately, many barriers need to be overcome in the development of a reliable assessment of fetal well-being. First, the basis of fetal testing rests on the hypothesis that a compromised fetus undergoes a series of detectable physiological changes such as the redistribution of blood flow or decreasing unnecessary movements. However, in the third trimester, normal fetuses spend 25% of their time in a quiet sleep state. During the normal © 2012, Lippincott Williams & Wilkins Correspondence: Erica O'Neill, MD, Department of Obstetrics and Gynecology, University of North Carolina, 101 Manning Drive, 3031 Old Clinic Building, Campus Box #7570, Chapel Hill, NC. [email protected]. The authors declare that they have nothing to disclose. O'NEILL and THORP Page 2 sleep state the fetal heart rate variability is reduced, and there may be infrequent breathing movements.2 Tests performed while a fetus is in a resting state may be incorrectly classified NIH-PA Author Manuscript NIH-PA Author Manuscriptas an NIH-PA Author Manuscript abnormal test. Therefore, when using tests to evaluate fetal condition, clinicians need to appreciate whether a fetus is simply in a temporary quiet sleep state or neurologically compromised. Second, which pregnancies may benefit from testing is unclear. Observational studies show an increased PMR in high-risk pregnancies, with a 10-fold difference in perinatal mortality between high-risk and low-risk groups (70/1000 vs. 7/1000).3 Yet the overall prevalence of these high-risk conditions is low and 30% to 50% of perinatal deaths actually occur in low- risk patients. Therefore if a sensitive and specific test existed, all women would benefit from some form of fetal testing. Targeting only high-risk women would still be inadequate. Third, the prevalence of an abnormal condition has the greatest impact on the predictive capability of an antepartum test. Although stillbirths are devastating, they are unlikely even among high-risk women and very rare among low-risk women. In many cases an abnormal test may be more likely to indicate a false positive (healthy fetus), instead of a true positive (compromised fetus).2 Even in the case of high-risk pregnancies with a prevalence of 70/1000, a test that is 99% sensitive and specific only has a positive predictive value of 88%. Finally, to be successful at preventing death, an antepartum test needs to identify a compromised fetus in enough advanced time for an intervention to be successful. No known method of assessment can predict sudden events, such as a cord accident or placental abruption, which are frequent causes of fetal death. It is important for the clinician to keep these limitations in mind when evaluating the merits of an antenatal test of fetal well-being. Maternal Assessment of Fetal Activity Fetal movement counting is an evaluation method which pregnant women quantify the fetal movements they feel. In theory, decreased movement alerts the mother of a deteriorating fetal condition. She can then bring this to the attention of health care providers who can evaluate further and intervene as needed to prevent fetal death. Because it can be performed each day, or multiple times daily, it has advantages over other fetal tests that cannot practically be performed this frequently. Women who report decreased fetal movement have an incidence of stillbirth that is 60 times higher than women without this complaint.2 Although decreased fetal movement commonly precedes fetal death, it does not necessarily indicate fetal death is imminent. Many factors other than worsening fetal condition can influence the perception of movement, including maternal activity, position, obesity, medications, gestational age, placental location, and amniotic fluid volume. Fetal movement also varies normally over the course of the day, 2 peaking between 9PM and 1 AM when maternal glucose levels are falling. The most commonly recommended counting technique is the count-to-ten method where the woman is instructed each day to count and record the time she feels the 10th fetal movement. Studies use a variety of definitions of the “alarm,” the time when a woman should seek evaluation immediately if she has not felt 10 kicks. What constitutes a clinically important change in the maternal perception of fetal movement is unknown, although most experts currently recommend that women seek care after 2 hours. A later alarm has a low sensitivity to identify compromised fetuses, whereas an earlier alarm generates an unacceptably high false-positive rate (Table 1).4 Our inability to define an appropriate alarm for women is undermining fetal movement counting as a means to reduce adverse perinatal outcomes. Clin Obstet Gynecol. Author manuscript; available in PMC 2013 June 17. O'NEILL and THORP Page 3 A prospective study of fetal movement counting in low-risk women noted a fetal mortality rate of 8.7/1000 during a 7-month control period, which then decreased significantly to 5 NIH-PA Author Manuscript NIH-PA Author Manuscript2.1/1000 NIH-PA Author Manuscript during the study time period. Patients used the count-to-ten approach with a 2- hour alarm, and the number of antepartum tests performed to assess decreased fetal activity increased 13% during the study period. However, given that this was not a randomized trial it is impossible to identify the exact factor that contributed to the difference seen. This improvement could be due to some unmeasured difference in the 2 populations and not necessarily due to the fetal movement counting intervention. The only randomized controlled trial evaluating formal fetal movement counting enrolled over 68,000 low-risk women and did not show a benefit.6 The antepartum death rate was equal in both groups, 2.9/1000 in the intervention group versus 2.7/1000 in the control group.7 There were several problems with this study, including that the compliance for reporting decreased fetal movement was only 46% and that 9% of the control participants received formal fetal movement counting charts. These problems could have accounted for the lower than expected rate of fetal deaths in the control group and led to an internal bias that reduced the difference seen between the intervention and control groups.6 No randomized controlled trials have been performed looking at fetal movement counting specifically in high-risk women. Not enough evidence is available to recommend or condemn formal fetal movement counting in either low-risk or high-risk women. The indirect evidence of the ability of formal fetal movement counting to identify fetuses at risk of intrauterine death was not translated into reduced perinatal mortality.6 The lack of high-quality randomized trials makes it difficult to draw definitive conclusions. Nonstress Test (NST) The cardiotocograph (CTG) is a continuous record of the fetal heart rate obtained by an ultrasound transducer placed on the mother's abdomen, with a second transducer placed over the uterine fundus to record uterine activity simultaneously. Components of the fetal heart rate that are assessed include baseline rate, variability, accelerations, and decelerations as well as the relationship between fetal heart rate and the timing of uterine