A slow embryo heart rate could mean that mothers who have undergone in vitro fertilization are at increased risk for miscarriage, according to a report in the journal Fertility and Sterility.

Somewhere between 10 and 25 percent of women who undergo in vitro fertilization suffer miscarriages, and slow embryonic heart rates have been known to be a sign of trouble. However, “The boundary between slow and normal embryonic heart rates has not been well established in the infertile population,” study co-author Dr. Zev Rosenwaks, of Weill Medical College of Cornell University, New York, and colleagues write.

The study featured 95 women with miscarriage in the first trimester and 555 without miscarriage. Aside from this difference, the two groups were similar. Transvaginal ultrasound was performed between 1 and 2 months into the pregnancy.

Slower embryonic heart rates were seen in the miscarriage group, the report indicates. Consistent with prior research, women with miscarriage were significantly older than those without miscarriage.

“This study was carried out to see if embryonic heart rate could be an added marker for potential viability…or, conversely, for potential miscarriage,” Rosenwaks told Reuters Health.

The author noted that a fetal heart rate higher than 130 beats per minute at approximately 7 weeks was associated with a 92 percent chance of carrying the pregnancy to term.

A heart rate of 160 was associated with an even greater chance of carrying the pregnancy to term-98 percent.

SOURCE: Fertility and Sterility, June 2009.