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
Kinderwunsch