NEW YORK -- Fetal surveillance in high-risk pregnancies should be based on the specific underlying pathophysiologic threat, Dr. Anthony M. Vintzileos said at an obstetrics symposium sponsored by Columbia University and New York Presbyterian Hospital.
"There is no one test that predicts everything, so we must look at the fetus as any doctor looks at a patient: We try to identify the pathophysiologic process that puts them at risk, then figure out what type of testing they deserve," said Dr. Vintzileos, professor and acting chair of the department of obstetrics, gynecology, and reproductive sciences at Robert Wood Johnson Medical School, New Brunswick, N.J.
Each of the seven pathophysiologic processes leading to fetal asphyxia or death should be considered separately, and the available evidence used to decide on the best test, as follows:
* Decreased uteroplacental blood flow. Pregnancies at risk include those complicated by maternal chronic hypertension, pregnancy-induced hypertension (PIH)-preeclampsia, collagen/renal/vascular disease, and idiopathic fetal growth restriction.
Here, the best (level I) evidence backs Doppler assessment, while other tests for decreased uteroplacental blood flow that are supported by level I or level II evidence include estimated fetal weight by ultrasound, amniotic fluid assessments, nonstress tests (NSTs), and fetal biophysical profiles (FBPs). Doppler appears to be the most useful in gestations with fetal growth restriction less than 34 weeks, Dr. Vintzileos said.
Doppler velocimetry of the uterine artery gives clinical information about maternal blood flow to the uterus, Doppler of the umbilical artery shows the degree of placental resistance, and middle cerebral artery Doppler can demonstrate fetal compensation or adaptation.
Venous circulation evaluation via Doppler is used to test for fetal cardiac dysfunction, which is usually seen in the final stages of fetal compromise, he noted.
In three separate metaanalyses conducted in the mid-1990's comprising a total of 26 randomized controlled clinical trials and more than 18,000 patients, umbilical artery velocimetry, when combined with FBPs, reduced the fetal death rate in high risk pregnancies (fetal growth restriction and/or hypertension) by more than 40% and the perinatal mortality rate by more than 30%.
One study suggested that Doppler combined with fetal heart rate monitoring was highly predictive of outcome (J. Reprod. Med. 41[2]:112-18, 1996).
* Decreased gas exchange. Most of these cases, which represent placental transport problems, are associated with postdates or occasionally with fetal growth restriction.
Level II evidence supports use of crown-rump length in the first trimester, which provides accurate dating and reduces the postdate risk to just 5%, in contrast to the 10%-15% rate with last menstrual period. Other tests backed by level II evidence include estimated fetal weight by ultrasound, amniotic fluid assessments, NSTs. and FBPs.
No test is reliable after 42 weeks, however, and Doppler is not useful at all for assessing gas exchange, he said.
* Metabolic (fetal hyperglycemia/hyperinsulinemia). Since nearly all antepartum surveillance studies have reported good outcomes in pregnancies of women with well-controlled diabetes, maternal blood sugar measurements are probably the best measures of fetal condition in diabetic pregnancies.
Indeed, data suggest that neither Doppler velocimetry nor FBPs are reliable predictors of outcome in diabetic pregnancies without vascular compromise, as the results will vary with maternal blood glucose (Am. J. Obstet. Gynecol. 168[2]:645-52, 1993).
* Fetal sepsis. Premature rupture of membranes (PROM), preterm labor, maternal fever, and intraamniotic fluid infection all increase the risk for fetal sepsis, for which level II evidence supports the use of amniocentesis/amniotic fluid assessment, NSTs, and FBPs.
In a study of 146 women with PROM, Dr. Vintzileos and his colleagues reported a decrease in the overall infection rate by one-third among those in whom daily FBPs were done, compared with historical controls (Am. J. Obstet. Gynecol. 157[2]: 236-40, 1987).
However, daily NSTs fared about the same as did daily FBPs in a randomized controlled trial of 135 PROM patients. Cost effectiveness concerns led to the authors' conclusion that daily NSTs (with backup FBPs if nonresponsive) might be a better approach for gestations of greater than 28 weeks, while daily FBPs were the preferred test for those of 28 weeks or less (Am. J. Obstet. Gynecol. 181[6]: 1495-99, 1999).
* Fetal anemia. Conditions such as erythroblastosis fetalis, fetomaternal hemorrhage, and parvovirus B19 infection are all risk factors for fetal anemia.
While level II data still support the use of serial amniocentesis and cordocentesis, today's standard approach is more likely to include ultrasound assessment of late signs such as placental thickness, polyhydramnios, and increasing abdominal circumference, and earlier signs such as fetal liver length and increase in the peak velocity of systolic blood flow in the middle cerebral artery (MCA-PSV), he said.
Among 200 fetuses at risk for hemolytic anemia due to red-cell alloimmunization, all of those with anemia had enlarged livers (64 of 69 were at or above the 95th percentile), while the MCA-PSV was at or above the 95th percentile in 15 of 19 in whom it was measured. Overall, fetal liver length appeared more sensitive for mild anemia and MCA-PSV for moderate to severe anemia (Am. J. Obstet. Gynecol. 184[6]: 1251-55, 2001).
MCA-PSV does not appear to be very reliable after 35 weeks, however (BJOG 109[7]: 746-52, 2002).
* Fetal heart failure. Monitoring is indicated in cases of fetal arrhythmia, nonimmune hydrops, placental chorangioma, and aneurysm of Galen's vein. Level II and III evidence support the use of M-mode echocardiography to diagnose arrhythmias, and continuous fetal heart rate monitoring to determine the amount of time spent in sinus rhythm.
Data also back the use of Doppler to assess venous circulation, ultrasound to rule out hydrops, NST in cases of hydrops with no arrhythmia, and FBPs in all cases of hydrops, Dr. Vintzileos said.
* Umbilical cord accident. Five entities--umbilical cord entanglement with monoamniotic twins, velamentous cord insertion, funic presentation, oligohydramnios, and a noncoiled cord--are responsible for almost all cases. Level II evidence suggests that color Doppler should be used to verify the diagnosis, and frequent NSTs used to monitor the fetus, he advised.
During 1995-2001 at Robert Wood Johnson, there were just two deaths among 462 fetuses of mothers with type 1 diabetes, and only one each among 3,654 postdates and 6,665 with preterm PROM or preterm labor.
No deaths occurred among 1.821 fetuses with growth retardation, 120 with red cell alloimmunization (12 with hydrops), 32 with nonimmune hydrops, or 12 with tachycardia/bradycardia-arrhythmia, he reported.
BY MIRIAM E. TUCKER
Senior Writer
COPYRIGHT 2004 International Medical News Group
COPYRIGHT 2004 Gale Group
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