Maternal serum testing at 1516 weeks

1. Triple screen (a-fetoprotein, human chorionic gonadotropin [hCG], estriol). In women under age 35 years, screening for fetal Down syndrome is accomplished with a triple screen. Maternal serum alpha-fetoprotein is elevated in 20-25% of all cases of Down syndrome, and it is elevated in fetal neural tube deficits. Levels of hCG are higher in Down syndrome and levels of unconjugated estriol are lower in Down syndrome.

2. If levels are abnormal, an ultrasound examination is performed and genetic amniocentesis is offered. The triple screen identifies 60% of Down syndrome cases. Low levels of all three serum analytes identifies 60-75% of all cases of fetal trisomy 18.

B. At 15-18 weeks, genetic amniocentesis should be offered to patients >35 years old, and it should be offered if a birth defect has occurred in the mother, father, or in previous offspring.

C. Screening ultrasound. Ultrasound measurement of crown-rump length at 7 to 14 weeks is the most accurate technique for estimation of gestational age; it is accurate within three to five days.

D. At 24-28 weeks, a one-hour Glucola (blood glucose measurement 1 hour after 50-gm oral glucose) is obtained to screen for gestational diabetes. Those with a particular risk (eg, previous gestational diabetes or fetal macrosomia), require earlier testing. If the 1 hour test result is greater than 140 mg/dL, a 3-hour glucose tolerance test is necessary.

E. Second trimester education. Discomforts include backache, round ligament pain, constipation, and indigestion.

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