Genetics and Immunology Reproductive Genetics
RRM Academy Synopsis
Miscarriage risk was 23.7% after one earlier loss and 12.3% with none
A 1964 Montreal study of pregnancy histories from mothers seen at a hospital genetics unit found that a miscarriage ended 23.7 out of 100 pregnancies after an earlier miscarriage, against 12.3 out of 100 with none. In the sample, 14.7 out of 100 recognized pregnancies ended in miscarriage.
Key Findings
- Of 6835 pregnancies, 1003 ended in spontaneous abortion, a frequency of 14.7 per cent (plus or minus 0.4) of all pregnancies, with the proband child omitted from each family.
- Pregnancies in women with no earlier abortion carried a 12.3 per cent risk of aborting, which differed significantly (P < .001) from the risk in women with a previous abortion.
- The risk of aborting was 23.7 per cent after one previous abortion, 26.2 per cent after two and 32.2 per cent after three; the authors could not test this rise.
- After an earlier abortion, risk appeared to hover near 24 per cent at all maternal ages (P > .60); with none, it appeared to rise with age (P < .05).
- About 7 per cent of pregnancies at ages under 20 occurred in women who had aborted before, against 43 per cent of pregnancies at ages over 40.
Interpretation
Researchers interviewed mothers whose children were seen at a Montreal genetics unit between 1952 and 1962 and analyzed their pregnancy histories, a retrospective interview series. Every woman had at least one live birth, and only recognized pregnancies were counted. The authors note that women who had only abortions are missing from the sample. The reported risks are averages across women. The authors reported no large increase in risk as earlier losses accumulated. Parental age and birth order were closely linked, so the authors left their separate effects undecided.
RRM Context
Restorative reproductive medicine treats a history of pregnancy loss as a reason to look for the cause. This 1964 dataset puts the average risk of the next pregnancy ending in miscarriage at 23.7 out of 100 after one loss. Later cause-based evaluation of recurrent pregnancy loss can be read against that baseline.
Abstract
SPONTANEOUS ABORTION is one of the most common and least understood pathological processes. Because it is so difficult to obtain reliable information about abortion, even the basic facts about its frequency, familial distribution, and relation to parity and parental age are largely unknown or disputable. Such information is needed to provide a basis for advising women with several abortions about their chances of successfully completing another pregnancy, to evaluate measures for the prevention of abortion, as well as to provide clues to the etiology of the condition. Reproductive histories taken by personal interview with a random series of women would probably be the best available data for estimating spontaneous abortion statistics. These would include very early terminations of pregnancy, recognized as spontaneous abortions by the women concerned but not receiving medical attention, which are under-represented in series of consecutive hospital admissions or in consecutive cases from private obstetrical practice. They would allow estimation of abortion risks in women with given numbers of previous abortions and at given ages. Some reservations must be held about the validity of self-diagnosis of early abortion, but this source of error should not affect comparisons within the sample.
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Topics
Keywords
Abortion, Induced, Abortion, Spontaneous, Female, Genetics, Medical, Humans, Pregnancy, Reproductive History, Risk, Statistics As Topic, ABORTION, GENETICS, HUMAN, PREGNANCY, STATISTICS
