The length of time it takes for a couple to achieve a pregnancy may have a direct impact on the outcome of the pregnancy, such as miscarriage, stillbirth, or multiple pregnancy. That's the finding of a study from Sweden1 based on a review of earlier research.
But in an e-mail interview, study researcher Anna Axmon, PhD, stressed that this study "was an epidemiological one. This means that the results presented are only applicable to groups of women, i.e., as a group, women with extrauterine pregnancies have longer TTPs [time to pregnancy] than does the group of women who give birth to singleton live [infants]."
Thus, no conclusions can be drawn from this study about individual women, she pointed out. For instance, when analyzing individual cases in the study, there were women who experienced a miscarriage after becoming pregnant relatively quickly and there were women were took much longer to become pregnant and had a healthy baby, Axmon explained.
Still, Axmon and Lars Hagmar, MD, in the division of Occupational and Environmental Medicine and Psychiatric Epidemiology at University Hospital in Lund, Sweden, wanted to explore the association between the length of time it took women, as a group, to become pregnant and certain pregnancy outcomes that had not been assessed in earlier research.
"Previous studies have found that pregnancies ending in miscarriage took longer to achieve than those ending in live birth," they wrote. "The aim of the present study was to further explore a possible association between TTP and the risk of preterm delivery, as well as different pregnancy outcomes such as miscarriage, stillbirth, multiple birth, and extrauterine pregnancies."
Hunting for a Correlation
To make their determinations, the two researchers reviewed the results of three previous studies that involved more than 5,000 women.
The three studies focused individually on three separate groups of women. Each was sent questionnaires asking them about the length of time it took for them to become pregnant and the outcomes of their pregnancies. Women who underwent fertility treatment were excluded from the studies "because infertility treatment in itself can be a risk factor for adverse pregnancy outcome," Axmon and Hagmar wrote.
To ensure there were no other factors that might influence pregnancy outcome in the study, information on each woman's age, use of oral contraceptives before trying to get pregnant, and smoking habits, among other data, were also collected in the studies.
Time to Pregnancy Had Varying Effects
After analyzing data from all three studies, Axmon and Hagmar found that compared to pregnancies ending in the birth of one healthy baby, pregnancies that ended in miscarriage had taken longer to achieve, on average. There were no differences in the length of time it took to achieve pregnancy between those that ended in a single live birth and those ending in stillbirth. In addition, those that had a pregnancy outside of the uterus, such as an ectopic pregnancy, had reported it took longer to achieve the pregnancy compared to other women, the researchers learned.
In terms of the number of infants conceived, multiple births were linked with shorter lengths of time to become pregnant compared to women who became pregnant with one infant.
Among women who became pregnant with one infant, those who delivered preterm babies also had reported longer lengths of time attempting pregnancy, on average.
None of the potential factors that could have otherwise affected pregnancy outcomes, such as older age or smoking habit, had any influence on the results in these studies, the two researchers reported. When they did, their influence was only marginal.
While many of these women were forced to recall pregnancies that happened up to 30 years previously, the results were generally similar even among women who had to recall pregnancies that occurred only five to ten years earlier, Axmon and Hagmar noted.
Some Plausible Reasons
"It is not surprising" that women who experience miscarriage generally report longer amounts of time in attempting pregnancy, since miscarriage may be related to reproductive dysfunction in either the man or woman attempting pregnancy.
Extrauterine pregnancies may take longer to achieve because women with such pregnancies have been known to have lower levels of progesterone, according to the two researchers,2 and progesterone plays a role in transporting the embryo to the uterus.3
Why multiple pregnancies took shorter lengths of time to achieve than those with one infant isn't known. "The biology behind reproduction is very complicated," Axmon explained.
While previous research found associations between the length of time it takes to achieve pregnancy and its outcome, these earlier studies only looked at single live births, twin births, and miscarriages, Axmon and Hagmar pointed out.
"Studies comparing the TTP for pregnancies ending in live [single] birth to that of extrauterine pregnancies and pregnancies ending in stillbirth have, to the best of our knowledge, never previously been performed," the two researchers wrote.
"Hopefully, studies as the one we performed will help clarify different mechanisms for reproductive outcomes," Axmon added.
1. Axmon A, Hagmar L. Time to pregnancy and pregnancy outcome. Fertil Steril 2005 Oct;84(4):966-74.
2. Dumps P, Meisser A, Pons D et al. Accuracy of single measurements of pregnancy-associated plasma protein-A, human chorionic gonadotropin and progesterone in the diagnosis of early pregnancy failure. Eur J Obstet Gynecol Reprod Biol 2002 Jan 10;100(2):174-80.
3. Stewart DR, Overstreet JW, Nakajima ST, Lasley BL. Enhanced ovarian steroid secretion before implantation in early human pregnancy. J Clin Endocrinol Metab 1993 Jun;76(6):1470-6.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
