Nonstress test 'not good enough anymore': Doppler US key to evaluation of IUGR fetus.(Obstetrics)

BIG SKY, MONT. -- A negative nonstress test in a growth-restricted fetus can no longer be considered reassuring in an era when high-quality Doppler ultrasound is readily available, Dr. Arthur S. Maslow said at a meeting on ob.gyn., gynecologic oncology, and reproductive endocrinology.

"You can't rely on a nonstress test to help you decide if the fetus is sick or not. Nonstress testing is the last thing to go. That's not good enough anymore," said Dr. Maslow, director of maternal-fetal medicine at the Geisinger Health System, Danville, Pa., which sponsored the conference.

The key concept to bear in mind when reading the report of an ultrasound evaluation of a growth-restricted fetus is that the ultrasonographer, when insonating a blood vessel, is looking at downstream resistance, he explained during the meeting.

Abnormalities identified on the venous side of the circulatory system define fetal myocardial dysfunction. In contrast, abnormalities on the arterial side define the extent of blood flow redistribution favoring the heart and brain at the expense of the rest of the body.

Blood flow redistribution is a process that takes place gradually. When a fetus senses it's receiving less oxygen, it dilates the ductus venosus to shunt the best-oxygenated blood to the heart and brain.

Meanwhile, the fetus radically shuts off blood flow below the diaphragm. The kidneys receive less oxygenated blood; in response they produce less urine and the amniotic fluid index decreases. The body gets smaller for its age. An asymmetric growth pattern develops. Dr. Maslow explained.

In a structured Doppler ultrasound examination of a growth-restricted fetus, the first vessel scrutinized is the descending thoracic aorta. Normally, diastolic flow is evident.