Terrified four years ago that she might be suffering her third miscarriage, Deborah S. Gregory testified yesterday, she ignored Cecil B. Jacobson's advice and scheduled an appointment with her regular gynecologist.

After her doctor performed a pelvic exam, he gave Gregory and her husband the bad news. Gregory, testifying in the first day of Jacobson's trial, said her doctor told her that not only was she not pregnant, but she also had probably never been pregnant.

"I had gained weight and I was wearing maternity clothes," said Gregory, her voice broken by sobs. "It was just a total shock -- not only were we being told we weren't pregnant, but we'd been lied to by someone we trusted."

Appearing in federal court in Alexandria, Gregory was the first witness in what is expected to be a two-week trial against Jacobson, 55, a former Fairfax County fertility specialist who has been charged with fraud and perjury in a case that has gained national attention because of the disturbing allegations.

Jacobson has been accused of two primary fraud schemes -- telling women they were pregnant when they were not and informing patients that he had an anonymous sperm donor program when he supposedly used his own semen to impregnate about 70 patients.

Addressing a jury of eight women and four men, Assistant U.S. Attorney Randy I. Bellows said in his opening statement that Jacobson's "deceitful, cunning and above all else cruel betrayal of trust" was motivated largely by greed.

Bellows noted that the Utah native was considered a leader in genetics in the 1970s, when he became the first U.S. doctor to perform amniocentesis, a procedure now widely used to detect some birth defects. When Jacobson opened his Reproduction Genetics Center in Vienna in 1976, amniocentesis was his "bread and butter," Bellows said. But as more hospitals and clinics began to offer the procedure, "the defendant's amnio practice began to dry up," he said.

Although Jacobson performed amniocentesis on as many as 600 patients a year during the peak of his practice, that number fell to 200 a year by the mid-1980s, Bellows explained. Jacobson's income also dropped, falling from $475,000 in 1982 to $300,000 four years later, the prosecutor said.

Trying to make up the difference, Jacobson opened a supposed fertility practice and began to dupe patients into believing they were pregnant so that he could charge them for more office visits, Bellows told the jury.

James R. Tate, one of Jacobson's attorneys, flatly rejected the government's version of his client's practice, promising the jury, "We're going to prove to you that Dr. Jacobson's treatment worked."

Tate explained that much of Jacobson's practice was born out of a belief that expensive modern treatments could be supplanted by "natural medicine." Where other doctors relied on biopsies and other procedures that invaded the woman's body, Jacobson believed that pregnancy was best achieved by keeping the woman's temperature charts and using natural hormones to regulate ovulation, Tate said.

Tate also said Jacobson had every reason to be proud of his record, having given fertility and insemination treatments to about 1,000 patients, of whom more than 300 had babies.

Jacobson's attorneys conceded that he used his own sperm to inseminate some patients, in part because donors failed to show up at his clinic at scheduled times.

On the stand for about three hours, Gregory retraced her treatment under Jacobson in detail, recounting how she had spent $6,000 and had been told three times that she was pregnant.

The Fairfax Hospital employee said that she and her husband were ecstatic when Jacobson first informed her that she was pregnant.

"It was around Christmas when we told our family and friends, and I started a diary for the child, writing about how excited we were," Gregory said.

A few weeks later, according to Gregory, Jacobson concluded that the fetus had died, probably because of the cold virus she had contracted, and that the tissue had been reabsorbed into her system.

"I knew his credentials, so I didn't question him," Gregory said. " . . . . I was blaming myself that I had been working too hard."