Analysis of serum human chorionic gonadotrophin levels in normal singleton, multiple and abnormal pregnancies

Some researchers claim that first trimester beta-human chorionic gonadotrophin (beta HCG) levels have a constant doubling time; others suggest doubling time increases as pregnancy progresses. This study was designed to settle the debate by analysing a large series of serial serum beta HCG determinations from 143 pregnant women whose day of ovulation was precisely determined. Regression analysis was used to evaluate linear and quadratic models for the relationship of HCG with time in normal pregnancies. Doubling times were calculated for three time periods: 10-20 days post-ovulation (period 1); 21-30 days post-ovulation (period 2); greater than 30 days post-ovulation (period 3). Analysis of variance was used to compare the mean doubling time by time period and type of pregnancy (single, multiple, spontaneous abortion and ectopic). The analysis showed that a quadratic model best described the pattern of HCG rise in early normal pregnancy. Furthermore, for normal pregnancies, the mean doubling time increased significantly with advancing gestational age between time periods 1 and 2 and between periods 2 and 3. The mean doubling time was the same for single and multiple pregnancies. The doubling time was prolonged with ectopic pregnancy in period 1; and for aborters reaching ultrasound at 8 weeks, the doubling time was normal in period 1 but prolonged in period 2. Careful observation of the doubling time may aid clinicians in the detection of abnormal pregnancies.