With funding from the USA's National Institutes of Health, researchers at Boston University, Massachusetts, and Beijing Medical University in China studied a population of 518 healthy, nulliparous and newly married women who intended to conceive. The women were all textile workers in Anhui, China, and aged between 20 and 34 years. None smoked or drank alcohol, although 65 percent were exposed passively to cigarette smoke.

Upon stopping contraception, the women kept daily records of vaginal bleeding and provided daily first-morning urine specimens for 12 months or until a pregnancy was clinically confirmed, whichever came first. The urine samples were assayed for human chorionic gonadotropin (hCG), to detect early pregnancy loss (EPL). EPL was defined as clinically unrecognized pregnancy loss detected only by this highly specific and sensitive assay.

Explaining the rationale for their study, the researchers write: "Per-cycle conception rates, rates of early pregnancy loss (EPL), and time to clinical pregnancy are of fundamental importance to understanding the reproductive process."

Rates of conception and loss

Their main findings, reported in detail in the latest issue of the journal Fertility and Sterility, were as follows:

* The conception rate per cycle was 40 percent over the first 12 months.

* Approximately 50 percent of all the women studied became clinically pregnant during the first two cycles, and > 90 percent during the first six cycles.

* Of the total of 618 detected conceptions, 7.9 percent ended in clinical spontaneous abortion (defined as pregnancy loss after a clinical pregnancy that had been < 28 weeks' gestation), and 24.6 percent in EPL.

* EPL was detected in 14 percent of all the cycles without clinical pregnancy.

* EPL in the preceding cycle was associated with increased odds of conception (odds ratio 2.6), clinical pregnancy (odds ratio 2.0) and EPL (odds ratio 2.4) in the next cycle.

* EPL in the preceding cycle was not associated with clinical spontaneous abortion, low birth weight, or preterm birth in the next cycle.

Discussing the findings, the researchers write: "We found that the overall per cycle conception rate was 40 percent over the first 12 months. The rate of clinical pregnancy was 30 percent. Approximately one-third of all the conceptions detected by urinary hCG assay failed to survive to delivery. More than two-thirds of these losses occurred before the pregnancy had been clinically recognized."

EPL a positive indicator?

They say the result extend our understanding of conception and EPL, especially the finding that EPL appears to raise the chances of conception, clinical pregnancy and EPL in the subsequent cycles. "Our data lend support to a previous notion that EPL is apparently a positive indicator that the stages of reproduction leading to implantation are intact."

The researchers say the reliance on the efficacy of urinary testing for hCG means that the true rate of EPL may be higher than found in the study. They also point out that the women studied were young and nulliparous, and advise caution before generalizing the findings to other populations.

Source: Fertility and Sterility 2003; 79: 577-84, 10 March 2003