Ultrasound markers useful in determining early pregnancy viability: don't rely on [beta]-HCG levels.
"Transvaginal ultrasound is the single most important diagnostic modality we have for early pregnancy failure," she said at the meeting, sponsored by the University of California, San Francisco.
Many clinicians determine whether [beta]-HCG levels have doubled within 48 hours, a sign of normal pregnancy, but sometimes they rely on this sign too far into the pregnancy, according to Dr. Autry of the university.
[beta]-HCG doubling occurs only in the first 6 weeks of gestation, at which point a pregnancy should be visible on ultrasound, and sonography can be used for diagnosis.
"This is an incredible source of mismanagement of the algorithm for diagnosis of abnormal first-trimester pregnancy. Once you confirm [by ultrasound] that the pregnancy is in the uterus, there is no place for [beta]-HCG," she said.
Ultrasound detects growth abnormalities better than serial [beta]-HCG measurements and is superior for dating, Dr. Autry said.
By 42 days' gestation a 2- to 3-mm gestational sac should be visible in the uterus on ultrasound. The mean sac diameter increases by 1 mm/day in a normal pregnancy. To estimate gestational age in days, add 30 to the mean sac diameter. By the time the sac is 10 mm in diameter, you should see the double decidual sac sign--the gestational sac with inner and outer echogenicity.
At 5 weeks' gestation, the first intrachorionic structure becomes visible, a 6- to 8-mm yolk sac. During the 6th week, cardiac activity should be apparent when the fetal pole is 5 mm.
In normal pregnancies, crown-rump lengths increase by 1 mm/day, and the days of gestational age can be estimated by adding the crown-rump length plus 42, Dr. Autry said.
"These are your landmarks. They're rules of thumb, but they're great" to remember, she said.
Any of the following three signs on transvaginal ultrasound indicate a nonviable pregnancy: no yolk sac in a 10-mm gestational sac, no embryonic pole in a 20-mm gestational sac, or no cardiac activity with a crown-rump length of 5 mm.
Those are the easy-to-remember numbers that Dr. Autry said she uses.
Obstetric textbooks suggest a range of sac sizes for the first two signs: no yolk sac in a 6- to 13-mm gestational sac or no embryonic pole in a 16- to 25-mm gestational sac.
Even if those signs of nonviability are absent, prognosis for a normal pregnancy is poor if there's a large yolk sac (>5 mm), a slow embryonic heart rate, or subchorionic hemorrhage, among other signs. Miscarriages ultimately occur in about 85% of embryos that have a slow heart rate.
Color flow Doppler imaging increases the sensitivity and specificity of transvaginal ultrasound for diagnosing an early viable pregnancy by showing increased blood flow around the pregnancy, whether it's intra- or extrauterine.
Transabdominal ultrasound should be reserved for confirmed cases of intrauterine pregnancy or for living ectopic pregnancy with heartbeats, Dr. Autry said.
Progesterone levels rarely are helpful but may be useful in a few cases for diagnosing with confidence the nonviability of an early pregnancy.
A progesterone level that is less than 5 ng/mL indicates either an ectopic pregnancy or a nonviable intrauterine pregnancy but cannot distinguish between the two.
San Francisco Bureau
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|Publication:||OB GYN News|
|Date:||Aug 15, 2003|
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