Joffe, M., & Li, Z. (1994). Association of time to pregnancy and the outcome of pregnancy. Fertility and Sterility, 62(1), 71-75. https://doi.org/10.1016/s0015-0282(16)56818-6
Joffe M, Li Z. Association of time to pregnancy and the outcome of pregnancy. Fertil Steril. 1994;62(1):71-75. doi:10.1016/s0015-0282(16)56818-6
Joffe, Michael, and Zhimin Li. "Association of time to pregnancy and the outcome of pregnancy." Fertility and Sterility, vol. 62, no. 1, 1994, pp. 71-75.
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Institute of Statistical Science, Academia Sinica, Taipei, Taiwan02jv2qv86
Pregnancies that end in miscarriage tend to take longer to conceive
In a British birth cohort of first pregnancies, women who miscarried tended to take 23% longer to conceive than women with live births. Conception tended to take 15% longer before a preterm delivery than before other live births. The study covered 3,132 live births and 248 miscarriages, adjusted for age, smoking and education.
Key Findings
Miscarriage was associated with a time to pregnancy that tended to be 23% longer, risk ratio 0.814 (95% CI 0.703, 0.942), after adjustment.
Preterm delivery (37 weeks or less) was associated with a time to pregnancy that tended to be 15% longer, risk ratio 0.871 (95% CI 0.763, 0.993).
Low birth weight (2,500 grams or less) showed no statistically significant association after adjustment; its chi-square value of 2.75 fell below the 3.84 entry criterion.
Of first pregnancies ending in miscarriage, 30.65% had taken more than 12 months to conceive, compared with 21.97% of live births (unadjusted).
Censoring at 12 months strengthened the effects slightly: 29% longer for miscarriage and 18% longer for preterm delivery.
Interpretation
The study compared time to pregnancy across outcomes in a British cohort that represents the national population. The authors found that stopping the clock at 12 months gave very similar results, slightly stronger. They conclude that higher-risk pregnancies following treatment for infertility do not explain the findings. All data were self-reported, and the authors note that miscarriage may be reported poorly, which would likely understate the link. The analysis covered first pregnancies up to age 33.
RRM Context
The authors consider a shared continuum of early pregnancy loss plausible. Restorative reproductive medicine seeks the cause of slow conception. In this cohort, delay was associated with miscarriage and preterm delivery.
Our editorial summary of this paper, not the article's abstract.
Abstract
Objective
To examine the relationship of subfertility with miscarriage, low birth weight, and preterm delivery.
Design
Comparison of time to pregnancy distributions between pregnancies that had different outcomes. Three comparisons were made: (a) miscarriages with live births; within live births, (b) low birth weight infant (up to 2,500 grams) or not low birth weight; (c) preterm birth (37 weeks or less) or not preterm. Cox regression was used to adjust for covariates.
Population
All first pregnancies were analyzed from the National Child Development Study, a large survey of young adults aged 33 years, which is nationally representative of the British-born population.
Main Outcome Measures
The distribution of the time taken to conceive (time to pregnancy), miscarriage, birth weight, and preterm delivery.
Results
Pregnancies that ended in miscarriage tended to take 23% longer to conceive, after adjustment for the other variables. Pregnancies that resulted in preterm delivery tended to take 15% longer to conceive. There was no statistically significant association with low birth weight.
Conclusions
Delay in time to conception is a risk factor for poor obstetric outcome, irrespective of medical intervention.
