It used to be known as miscarriage, a term that’s rapidly losing its popularity. Sporadic, spontaneous pregnancy losses--random losses that appear to be occurring when there is no specific health problem--can be among an expectant couple’s worst fears. As doctors, we cannot remove the pain, but we hope that you can cope better if you understand why this might be happening.
In the first trimester of pregnancy, or less than 12 weeks from the last menstrual period, pregnancy losses are very common. But second trimester pregnancy losses--those occurring after 12 weeks of gestation and before 23 to 24 weeks of gestation--are much less common. It is thought that at least 60% to 70% of conceptions do not reach 23 to 24 weeks of gestation, when the fetus begins to have a chance to survive outside of the womb. Many, if not most, of these pregnancy losses may be unrecognized because they occur before the next menstrual period.
The most common reason for a single, sporadic pregnancy loss is fetal aneuploidy or abnormal fetal chromosomal content. These types of conceptions usually occur as the result of chromosomal abnormalities in the egg, the fertilizing sperm, or the resulting embryo. These abnormalities are typically random events, although the likelihood of chromosome abnormalities in the egg--and to a much lesser extent, the sperm--increases with parental age. Therefore, not only does the chance for a woman to have a baby born with a chromosome abnormality increase with age (greater chances of chromosome abnormality after age 35 and even greater after age 40), so too does her chance to suffer a pregnancy loss. Very few chromosomally abnormal conceptions result in the delivery of a live child, and when they do, the child is almost always affected by multiple medical problems as encountered in Down Syndrome. Most chromosomally abnormal conceptions result in early pregnancy loss.
Of course, early pregnancy loss is not always the result of chromosome abnormalities in the embryo. A wide range of other conditions may cause an early pregnancy loss. These may include anatomic problems in the female reproductive organs, hormonal problems, and a variety of others. Because chromosome abnormalities are so common, however, few practitioners will start medical testing to learn the cause of a single early pregnancy loss. Diagnostic testing is typically reserved for couples with more than one pregnancy loss, also known as recurrent pregnancy loss or recurrent miscarriage.
Unfortunately, experts may still disagree on what constitutes a diagnosis for recurrent pregnancy loss. Recurrent pregnancy loss may result from repeated but unrelated chromosomally abnormal conceptions. So, how many pregnancy losses must a woman have before she or her health care provider should suspect that something other than random fetal chromosome abnormalities may be occurring? This is an ongoing question. As doctors, we are concerned that if you have a diagnostic work-up too early, we may be over-testing. But we also do not want to miss possible treatable conditions to help you minimize the chance of another loss.
Some practitioners and medical societies suggest that a couple must have experienced at least three losses before they’re considered to suffer the clinical condition of recurrent pregnancy loss. Others believe that these losses must be consecutive. Many, including myself, feel the definition should include those who have experienced only two losses. This recommendation is tempered, however, if one or both of these losses is known to have had chromosome problems.
Unfortunately, the chromosome composition of tissue from a particular pregnancy loss is often unknown, because the tissue may not have been collected, testing may not have been performed, or the testing was uninformative. These problems can occur due to technical issues with the tissue chromosome analysis test. Researchers recently demonstrated in a large-scale study that the likelihood of finding a specific and often treatable reason for losses in a woman with two losses was the same as that for women with three or more losses. In addition, the final diagnoses for both sets of women had a fairly similar distribution. This argues that women with two unexplained early pregnancy losses should be considered candidates for a full diagnostic work-up to help her get the treatment she needs.
In my future blogs, I plan to talk more about the tests needed in diagnostic work-ups for women with recurrent pregnancy loss and also pregnancy loss after assisted reproduction, such as in vitro fertilization (IVF).
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