Computer-assisted analysis of normal second trimester fetal heart rate patterns.

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Neonatal Monitoring

Background:

• Computer-assisted analysis of antenatal fetal heart rate (FHR) patterns is established.
• Reference ranges for third-trimester FHR are available.
• Second-trimester FHR reference values require further definition.

Purpose of the Study:

• To establish reference values for FHR patterns during the second trimester (20-29 weeks gestation).
• To assess changes in FHR variation and accelerations during early gestation.
• To determine the optimal recording duration for reliable FHR assessment.

Main Methods:

• One-hour FHR recordings were obtained from 77 women with uncomplicated pregnancies between 20 and 29 weeks gestation.
• Analysis included medium-term FHR variation, short-term FHR variation, and accelerations.
• Statistical analysis was performed to identify significant trends and correlations.

Main Results:

• Significant increases in medium-term FHR variation (r=0.48) and accelerations (r=0.34) were observed from 20 to 29 weeks.
• The lower limit of normal FHR variation increased from 18 msec at 20 weeks to 28 msec at 28 weeks.
• Short-term FHR variation also increased significantly (r=0.61), and decelerations were common (54%).

Conclusions:

• Fetal heart rate variation in the second trimester differs significantly from the third trimester.
• Established reference ranges for the third trimester are not directly applicable to the second trimester.
• Interpretation of second-trimester FHR records requires consideration of these developmental changes.